Volume 09 / Number 1 & 2 / July 2009 Potential Impacts of ...

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Potential Impacts of RBHT Results on LOCA Evaluation Models

by Steve Bajorek, USNRC

he effect of spacer grids on reflood heat transfer has been observed in several test series (FLECHT-SEASET, FLECHT, FEBA). Important effects which were found included convective

enhancement downstream of the grid, droplet breakup and grid rewet. The NRC has sponsored tests at the

Penn State Rod Bundle Heat Transfer Test (RBHT) Facility to investigate reflood heat transfer and other LOCA processes. The NRC has recently begun to evaluate the data and incorporate the findings into analysis codes.

(Continued on page 2)

Recent RELAP5 User Problems

ince the User Problem feature of the NRC web site is not yet back in operation, a summary of user problems since the last newsletter is

provided below. If you encounter a problem with RELAP5 or one of the associated NRC codes, please report it to [email protected].

Since the last newsletter was published, four user problems submitted earlier have been resolved. Three new user problems were submitted and two of those are resolved. The section below informs users on the problems that have been submitted and, if resolved, discusses the manner of resolution.

(Continued on page 3)

NRC Notes by Chris Murray, USNRC

RACE Version 5.0 Patch 01 is now being widely used within the agency, by CAMP members and by agency contractors. Indicative of the

increasing use of TRACE is the significant number of code user trouble reports that have been filed (see TRACE User Problems on page 4). At this stage of the code life cycle the frequency of trouble reports is still increasing due to the more extensive code usage. This is an expected occurrence. As these trouble reports are

resolved the frequency of trouble reports is expected to eventually decrease as the more common problems are resolved and the code matures. (Continued on page 3)

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S p o n s o r e d b y t h e U . S . N u c l e a r R e g u l a t o r y C o m m i s s i o n

Thermal-Hydraulic Code News

Committed to the support of the

T/H Codes User Community

Contents:

• Potential Impacts of RBHT Results on LOCA Evaluation Models

• Recent RELAP5 User Problems • NRC Notes • Spring 2009 CAMP Meeting • TRACE User Problems Web Sites: http://www.nrccodes.com http://www.nrcrelap5.com

Volume 09 / Number 1 & 2 / July 2009

Thermal-Hydraulic Codes News July 2009

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Potential Impacts of RBHT Results on LOCA Evaluation Models … continued from page 1 The Rod Bundle Heat Transfer (RBHT) Facility is designed to conduct systematic separate-effects tests under well-controlled conditions in order to generate fundamental rod bundle heat and mass transfer data from single phase steam cooling tests, low flow boiling tests, and dispersed flow film boiling heat transfer tests. The facility is capable of operating in both forced and variable reflood modes covering a wide range of flow and heat transfer conditions at pressure from 0.13 to 0.42 MPa. The RBHT facility is designed to simulate a full-length portion of a Pressurized Water Reactor (PWR) fuel assembly. The facility consists of a 7x7-rod bundle with 45 electrically heated rods, mixing vane grids, and over 500 instrument channels for measuring temperature, differential and absolute pressure, steam and liquid flow rates, power, etc. The figure below shows the RBHT facility which has extensive instrumentation and windows for viewing and recording the details of the reflood process.

Spacer grid effects include local convective enhancement downstream of spacer grids that is due to disruption in the boundary layer. This “entrance length effect” increases the heat transfer coefficient as the boundary layer reforms. Droplet breakup increases the interfacial area of the droplet field. Rapid evaporation decreases the steam temperature, which increases the rod to fluid heat flux. The conventional “theory” has been that the primary mechanism for droplet breakup (and the resulting downstream increase in evaporation) is due to drops interacting with a dry grid. That is, sharp obstructions shear the incoming droplet into two or more smaller droplets.

The figure below shows the differing droplet formation processes for dry and wet grids. Dry grid (shown on the left) drop sizes were found to be small. The drop formation occurs by breakup at sharp interfaces, and may not persist except far from the quench front, or if the inlet velocity (VIN) is small. In the case of a wet grid (on the right), drop sizes increase as the quench front approaches a grid. Drop formation may be due to entrainment from film on the grid. For VIN>1.0 in/s, most grids show quick rewet.

RBHT data from a recently completed test series is now being evaluated and used in code assessment. RBHT reflood test data show grid rewet to occur everywhere in the bundle when VIN>3 in/sec and on two or more grids ahead of the quench front for low flooding rates. Drop sizes downstream of a wet grid are larger than those produced by a dry spacer grid, indicating that the mechanism for drop formation changes.


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RELAP5 User Problems…from page 1

No. 2008-14 (7/22/2008) Code Versions Affected: RELAP5 3.3 A domestic user found that the Moody choking model was giving strange results; the flow rate periodically dropped to zero and then back to a finite value. The Ransom-Trapp and Henry-Fauske choking models did not exhibit this unphysical behavior. The zero flow occurred when subcooled liquid was upstream of the choking junction, such as might happen when the accumulators empty. In this situation the Moody model failed to converge The model was changed to use an enthalpy based on saturation conditions rather than one based on subcooled liquid conditions. This change is consistent with the derivation of the Moody model, which assumes saturated stagnation conditions. The fix was implemented in 3.3id. This problem is Resolved. No. 2008-18 (10/17/2008) Code Versions Affected: RELAP5 3.3hh A CAMP user found an indexing error in the ipump subroutine and supplied the fix. This indexing error only affected the ipump edit and not any of the pump calculations. The fix was implemented in 3.3ic. This problem is Resolved. No. 2008-22 (12/3/2008) Code Versions Affected: RELAP5 3.3 A domestic user discovered that RELAP5 failed when running a helium pebble bed reactor (PBR) problem. The code failed with water property errors at the triple point. The resolution was to use the g = 2 option on the 120 card to signify a pure noncondensable problem. This option does not use the water property tables and only solves the noncondensable vapor energy, and vapor mass conservation equations. This problem is Resolved. No. 2008-24 (12/4/2008) Code Versions Affected: RELAP5 3.3hi A CAMP user was modeling the ROSA condensation induced water hammer experiment and discovered that 3.3gl ran but 3.3hi failed in the initialization phase. The resolution was to use larger time steps and let the code set the maximum time step based on the Courant limit. This problem is Resolved. No. 2009-01 (2/5/2009) Code Versions Affected: RELAP5 3.3

A CAMP user reported that the turbine component has an error for the constant efficiency stage group. The user supplied a fix for the problem. The fix was implemented in 3.3ic. This problem is in Resolved. No. 2009-02 (5/4/2009) Code Versions Affected: RELAP5 3.3 A domestic user reported that with a top offtake break attached to a horizontal volume, the Ransom-Trapp choking model had periods of no flow for up to 15 seconds even through there was a 1000 psi pressure drop across the break. The Henry-Fauske choking model did not exhibit this unphysical behavior. For the Ransom-Trapp choking model, the user needs to insert an intermediate vertical volume between the break and the horizontal volume because of an irresoluble conflict between the RT choking and offtake models. This problem is Resolved. No. 2009-03 (5/5/2009) Code Versions Affected: RELAP5 3.3 A CAMP user did a comparison of the critical flow model in 3.3 with the critical flow model in 3.2. Very different results were obtained. This problem is in Work. NRC Notes…from page 1 A fairly extensive assessment of the TRACE Patch01 version was conducted that uncovered a number of code issues. Many of these have been resolved and the updates will be included in the next Patch version. The Version 5.0 Patch01 Addendum to the Assessment Report is available on the www.nrccodes.com web site. The NRC is also planning on releasing a Patch04 version of RELAP5/MOD3.3. The patch version will include the fixes that were developed to address code trouble reports that have been resolved over the past few years. We note that Dr. Mirela Gavrilas, Chief of the Safety Margins and Systems Analysis Branch, has accepted a rotation assignment as Chief of the Steam Generator Tube Integrity and Chemical Engineering Branch in NRR. Steve Frankl is the Acting Branch Chief during the six month rotation period. The dates and location have been set for the Fall 2009 and Spring 2010 CAMP Meetings. The Fall CAMP Meeting will be held in Williamsburg, Virginia from November 4 through November 6, 2009. The Spring


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2010 Meeting is scheduled to be held from June 9 through 12 at the Royal Institute of Technology in Stockholm, Sweden hosted by Prof. Tomasz Kozlowski. More information on the upcoming meetings will be posted on the TH codes web sites in the near future. If you have questions or would like additional information, please contact me at [email protected] or 301-251-7513.

Spring 2009 CAMP Meeting

he Spring 2009 CAMP Meeting was held from June 17 through 19 at the Technische Universität München (TUM), Lehrstuhl für Nukleartechnik in

Munich, Germany hosted by Professor Rafael Macian-Juan. After welcoming remarks by Professor Macian-Juan, Chris Hoxie (USNRC) gave a presentation on the Status of NRC Code Development.

Dr. Hoxie provided the following e-mail contact information for the CAMP Program and the various NRC codes. • CAMP Program: [email protected] • RELAP5: [email protected] • TRACE: [email protected] • SNAP: [email protected] • PARCS: [email protected] Access to information on all of the NRC codes provided through the CAMP agreement can be obtained from the www.nrccodes.com web site, including bug reports, code fixes, and current code documentation. There is also a new “Code Forums” discussion group to post questions and answers about code usage. The NRC will continue to support RELAP5 as needed in the future and RELAP5 will be part of new CAMP agreements. Recent RELAP5 activity at the NRC

involves only bug fixes. There is no significant new code development on RELAP5 at this time. RELAP5 is used at the NRC for operating reactor calculations in support of power uprates and in a supporting role in licensing the AP1000, ESBWR, US-EPR and US-APWR. The Patch04 version of RELAP5 will be released in 2009. The release date will be determined by the severity of outstanding error reports and by the rate of new error reports. Users were encouraged to report any errors encountered while using the code. The status of PARCS development was then reviewed and the following status of activities was reported: • PARCS Source Code F90 Conversion (Complete) • TRACE Point Kinetics from PARCS (Complete) • Extension of Analytic Nodal Method (Complete) • Multi-Cycle Depletion Capability (Ongoing) • Microscopic Depletion Capability (Ongoing) • Implicit Code Coupling (Ongoing) • TRACE/PARCS Stability Restart Deck Generator

(Complete) • BWR Pin Power Reconstruction (Complete) It was noted that the term “complete” does not mean it is in the current TRACE/PARCS code version. It means it is in PARCS 3.0 and will be in a future version of TRACE/PARCS.

The F90 conversion of PARCS source code implemented NRC/TRACE code modernization guidelines. The converted code was compiled and tested for different compilers and operating systems. It was tested with the TRACE Regression System and with SNAP Regression Testing. TRACE point kinetics can now be generated using PARCS steady state options. The kinetics can be 3D, with power-weighted core average parameter feedback, adjoint-weighted cross section change as reactivity

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excluding the control rod reactivity component, or without feedback (user input reactivity). The implicit TRACE/PARCS coupling is in the stage of algorithm testing with Matlab. Steps include construction of the components of the matrix, the use of a simplified single phase 1-D fluid/heat transfer model for preliminary assessment, and constructing and performing test problems. Once algorithm testing is complete, TRACE testing and implementation can begin. Dr. Hoxie also discussed the BWR stability analyzer in SNAP which includes interactive input for control rod perturbations.

SNAP 1.0 has recently been released. The current focus of SNAP development is on usability improvements and model documentation features. SNAP is now very useful for RELAP5 to TRACE conversion. Current and near-term activities include a new model notebook report generator in an open document format (ODF), attribute level ownership and reviewer data, master integrator support, the addition of a user interface to AptPlot for axial plotting (available in AptPlot version 6.2.5), job stream plug-in/runtime improvements, and an engineering template plug-in. The new electronic model notebook is ODF based, and replaces the HTML based notebook. It can open directly in MS Word or OpenOffice. It includes model summary data, validation report results, hyperlinks across connections, embedded attribute level documentation, generated plots for select data, optional classification markings and optional ownership/reviewer data. The Master Integrator allows users to import subsystems from one model into another model. It automatically reconnects components to an integrated subsystem when reimported. Users can also build standalone composite-component models such as steam generators,

pumps, etc. Exportable subsystems can be created, and these subsystems can be integrated into a full plant model. The Master Integrator supports concurrent development of subsystem models and provides a foundation for development of a component library. It is currently being worked on for RELAP5. A job stream plug-in provides a user interface for graphically constructing a sequence of runs. Applications can define any number of input and output files. The plug-in accepts file based inputs from either local or document management systems, and plug-in based inputs generated from other SNAP plug-ins. There currently is a working prototype with a parametric set of runs, conditional execution logic and post processing. Runtime improvements include the implementation of a grid computing framework (Globus). An independent plug-in was used to create input templates to constrain modifications to one or more source models. The source model is queried for available shared numerics. These variables are then available to create 2D views that serve as template forms. Changes to the model are limited to data exposed by shared numerics in the source model. The Template Plug-in generates cases by setting the numerics in the source model and then exporting the model. It will interact with the Job Stream plug-in to produce sets of parametric runs. Current TRACE uses in licensing support include: • ESBWR design certification • EPR design certification • APWR design certification • AP1000 COL • ABWR COL • Operating reactor power uprates • Generic safety issue (GSI) support

A Peer Review of TRACE 5.0 has been completed. The report is available in public ADAMS at www.nrc.gov


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(accession number ML090760541). Results of the Peer Review were presented to the NRC ACRS. An effort is underway to address individual comments from the peer review. Applicability of TRACE will be expanded in the future by addition of assessment manual sections on: • B&W design reactors • BWR Transients and Stability • PWR Transients • Additional BWR and PWR LOCA assessment • Anything needed for new reactor designs supported

by TRACE TRACE is the future of NRC safety systems analysis. The NRC is committed to TRACE. TRACE will have all capabilities of RELAP5. TRACE has superior capabilities and accuracy for most applications compared to RELAP5. The USNRC would like CAMP members to focus their assessments on TRACE. However, RELAP5 will be maintained for legacy purposes and is included in the CAMP agreements. Joe Staudenmeier then made a presentation on "TRACE Code Development Status" co-authored by Chris Murray (USNRC). Dr. Staudenmeier provided a roadmap that described TRACE code development status. The NRC intends to follow the RELAP5 system of releasing periodic numbered patch releases starting with V5.0 Patch Release 01 that was released internally on October 17, 2008. The present TRACE focus is on resolving bugs, addressing peer review comments, and making V5.0 robust. The plan is to release V5.0 Patch Release 02 sometime this Fall.

Statistics regarding TRACE trouble reports are indicative of the increasing use of TRACE both within the agency and by CAMP and User Group members. There are currently 459 total trouble reports in our tracking system. Status of these reports is as follows: 102 trouble reports are resolved, but not yet closed out; 267 trouble reports

are closed out; 90 trouble reports are still open (many are probably resolved/closed; we just haven’t confirmed it yet). Of the 145 trouble reports opened since January 1, 2007 (mostly these reflect known problems in the V5.0 code base), 61 have a resolution but are still waiting to be applied in an official code version, 54 have been closed out and 30 are still considered open. Since the last CAMP meeting 20 new trouble reports were submitted and 18 trouble reports have been resolved and/or closed out. Eighty two new developmental code versions were created in that same timeframe. The current developmental version of TRACE is V5.170. In the Fall 2008 CAMP meeting, the changes that went into TRACE up to V5.141 were presented. In this meeting, Dr. Staudenmeier described the changes that have gone into TRACE for V5.150 to V5.170. The following article on TRACE User Problems has descriptions of the changes since they resulted from fixes to reported problems. A number of items that TRACE users should be aware of were described by Dr. Staudenmeier. One item concerns the TRACE fuel thermal conductivity model which does not account for burnup or gadolinium. Both reduce thermal conductivity and increased stored energy in the fuel. Also, the current TRACE flashing is nonmechanistic and gives large heat-transfer coefficients to decrease liquid superheat. Nucleation delay requires a mechanistic model. A mechanistic model was developed for TRACE but was never activated. Activation of the model shows a nucleation delay. The model will be activated in a future version of TRACE. Users should be aware that TRACE has a new choked flow solver. The old solver first bounds the velocity and then converges. The new solver uses a Singular Value Decomposition (SVD) and a linear extrapolation to approximate the next velocity. The SVD-based method converges more reliably and with fewer iterations, resulting in a small change in code runtime. Recently, the CONTAN component has been debugged and assessed. The assessment shows results comparable to CONTAIN and MELCOR. Deficiencies identified for future improvement include the need for film based wall and interfacial heat transfer and improved coupling to TRACE through signal variables and trips. Short term goals for TRACE development include: • Direct VESSEL-to-VESSEL connections • Vessel choking • Implement the new choked flow solver


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• Mechanistic flashing • Updated/improved correlations and transitions • Make the IAPWS tables the default EOS algorithm • Integrate latest updates to IAPWS model from

RELAP5 • Integrate PARCS 3.0 • More geometric input • Mechanistic CONTAN models for sprays and films

on walls and improved CONTAN/TRACE communication (signal variables, trips)

• Homogeneous multiplier of loss coefficients • Reynolds number-dependent loss coefficients • RELAP5 cladding rupture model • Implicit numerics • Complete the transition to the TPR-format dump file Long term TRACE development goals include: • Code uncertainty methods • Implicit TRACE/PARCS coupling • Parallel processing • Droplet field and grid models • Enthalpy form of energy equation for TRACE based

containment modeling. • Interfacial area transport equation • Dissolved gas field • Higher-order solute tracking methods • Improved subcooled boiling model • Improved models for phase separation at TEE’s Additional presentations included: • Dan Prelewicz, ISL, USA “RELAP5 Status and User

Problems” • Badreddine Belhouachi, Imperial College, UK, “Rod

Bundle Study Using RELAP5 Coupled to MABEL”

• Nader Ben Said, Westinghouse Electric, Germany,

“Modeling of Self-Controlled Valves in RELAP5”

• A. Petruzzi, University of Pisa, “Modeling of CANDU

Darlington NGS with the RELAP5 Code” • Andrej Prošek, Jozef Stefan Institute, Slovenia

“Animated RELAP5 Calculations for Krško NPP” • Dong Gu Kang, KINS, Korea, “Improvement of

RELAP5/MOD3.3 Reflood Model Based on the Assessment against FLECHT-SEASET Tests”

• Jordi Freixa-Terradas, PSI, Switzerland “TRACE and

RELAP5 Thermal-Hydraulic Analysis on Boron Dilution Tests at the PKL Facility”

• Tomasz Kozlowski, Royal Institute of Technology,

Sweden, “BWR Analysis with RELAP5/PARCS and TRACE/PARCS”

• Sergio Gallardo, University of Valencia, Spain

“OECD/NEA ROSA Project Test 3.2 Simulation with TRACE5”

• Marc Thieme, Westinghouse Electric, Germany, “3D

Thermal Hydraulic TRACE BWR Plant Model using Measurement Data”

• Christoph Hartman, Westinghouse Electric,

Germany, “Cross Section Generation with Lattice Code SCALE6/TRITON for Use in the Coupled Code System”

• César Queral, University of Madrid, Spain,

“Validation of TRACE Model of Almaraz NPP”

• Oddbjörn Sandervåg, Swedish Radiation Safety

Authority, “Swedish Camp Activities” • Byung Gil Huh, KINS, Korea, “Best-Estimate

Calculation with Uncertainty Evaluation in KINS”


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• M. Frings, Westinghouse Electric, Germany, “Investigations of Counter-Current Flow Models In Nodalized Safety Analysis Codes”

• C.H. Ban, Korea Nuclear Fuel Co., “Sensitivity of

Fuel Gap Conductance” • Rafael Miro-Herrero, Polytechnic University of

Valencia, Spain, “Implementation of Control Rod Movement and Boron Injection Options by Using Control Variables in RELAP5/PARCS v2.7”

• Sergio Chiva-Vincent, Polytechnic University of

Valencia, Spain, “Analysis with TRACE of ROSA TEST 1.2: 3D Modeling in the Reactor Vessel and in the Cold Legs”

• Rafael Macian-Juan, Technical University Munich,

Germany, “Uncertainty and Sensitivity Analysis in the Neutronic Parameters Generators over the Coupled Thermal-hydraulic-neutronic Nuclear Power Plant Simulation”

Highlights of the meeting included an evening at Weihenstephan that included an elegant dinner. The meeting also included a tour of the Nuclear Engineering Department at TUM.

The Fall 2009 CAMP Meeting will be held in Williamsburg, Virginia from November 4 to 6, 2009, while the Spring 2010 Meeting will be held from June 9 through 11 at the Royal Institute of Technology in Stockholm, Sweden.

TRACE User Problems by Jay Spore, ISL

his is a report on TRACE user problems and resolutions. Open Trouble Reports identified in the previous Newsletters with no new progress are not

discussed, but can be found in the TRACE Trouble Report system (TRACEZilla) on the TRACE website (www.nrccodes.com). For the time period between January 1, 2009 and June 30, 2009, 15 new Trouble Reports were submitted to TRACEzilla. One hundred Trouble Reports were either resolved or closed during this same time period. As of June 30, 2009, there are 462 Trouble Reports in the TRACE bug reporting system and 75 of those Trouble Reports are open, with the remaining resolved or closed. A resolved Trouble Report indicates that the Trouble Report has been addressed with an update that is pending. A closed Trouble Report indicates that it has either been addressed by re-running the test problem(s) of interest with a current version of TRACE or has been closed by the incorporation of a pending update into the NRC development version of TRACE. An update pending implies that it has been tested and documented and reviewed and submitted to the NRC, but has not been included into the NRC developmental version of TRACE. Inclusion of a pending update into the NRC developmental version of TRACE typically requires additional review and testing by the NRC staff. The most current developmental version of TRACE is version 5.170 as of June 30, 2009. Updates included into version 5.170 can be found on the NRC TRACE

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development web site. New Trouble Reports Still Open The following Trouble Reports are new (i.e., opened during the time period January 1, 2009 to June 30, 2009 and still open. Trouble Report 453 – SJC Trip. A user reported that TRACE SJC does not have trip capability and that a RELAP5 Time Dependent Junction, with trip capability was converted to a TRACE PUMP SJC. In order to simulate the trip behavior for this flow path, the user added a VALVE upstream of the TRACE SJC component and requested that TRACE SJC include trip capability. The trip status is available as a signal variable, so it should be possible with the appropriate control block model to simulate the desired tripped flow rate in a PUMP SJC component. In addition, it is bad modeling practice to connect a VALVE to a PUMP SJC component (See Trouble Report 392). Therefore, the recommended approach to address this problem until a fix has been developed is to use appropriate control block models that include the trip status, rather than a VALVE connected to a PUMP SJC. Including trip capability for a PUMP SJC would be a user convenience that will be considered for a future TRACE update. This Trouble Report is still open. Open Trouble Reports with Recent Activity The following Trouble reports are still open, but some recent activity has been reported for the Trouble Report during the time period from January 1, 2009 to June 30, 2009. Trouble Report 44 – More FIST level tracking problems. A user reported that the TRACE FIST model failed when level tracking was turned on for the VESSEL component. Initial investigation of this problem with version 5.150 indicated a TRACE failure due to errors in the level tracking logic. Failure occurred very early in the calculation. Version 5.150 + Fx3DLevTrak update ran further, but failed due to conflicts with the separator model and the 3D level tracking logic. Update Fx3DLevTrak was modified to address these conflicts and the FIST calculation with 5.151 plus the modified Fx3DLevTrak update ran to ~400 seconds into the transient before failure. The modified Fx3DLevTrak documentation and testing was updated and re-submitted for inclusion into TRACE. The failure at ~400 seconds into this transient is still under investigation. When level tracking is turned off in the VESSEL component, this calculation completes with version 5.150 and 5.150 + Fx3DLevTrak. If the level tracking model is turned on only in the CHAN component, then

this calculation completes with version 5.150 + Fx3DLevTrak. This Trouble Report is still open. Trouble Report 100 – Transition boiling value too low to cause return to nucleate boiling. Semiscale test LH-2 was run with version 5.157. It was necessary to include the FxFlapper update into version 5.157 in order for TRACE to run. The FxFlapper update is currently pending. Version 5.157 + FxFlapper does not predict a dryout for this test. The void fraction in level 12 of the CHAN component in this model hung around 70% when the fuel rods should have been drying out. There were a number of input errors that version 5.157 detected in this original input model, that also had to be correct. Since version 5.157 + FxFlapper didn't dry out, it cannot be determined that re-wet will be calculated. The flow during this time period is mostly co-current and low on the order of 30 kg/m**2-s, which implies that the critical quality correlations do not apply. The normal qchf table in TRACE should be transitioning to pool boiling critical heat flux as the mass flux approaches zero. Experimental data for this test indicates a significant heat-up after dry-out and then re-wet in the top of the fuel assembly. In order to predict dryout, TRACE needs to predict a slightly higher void fraction in the top of the CHAN. This Trouble Report is still open. Trouble Report 108 – Poor mesh convergence on transient unpowered conduction. For a relatively thick slab HS (i.e., ~1 m), with a sudden drop in the inside surface fluid temperature, accurate heat flux predictions at the inside surface with uniform noding requires on the order of 100 radial nodes. However, for non-uniform noding with relatively small nodes at or near the inside surface, accurate results can be obtained with less radial nodes. Longer term plans are for a higher order conduction solution for the TRACE HS component. This Trouble Report is still open. Trouble Reports Closed The following Trouble Reports have been closed with updates included into the NRC developmental version of TRACE or have been closed by rerunning the test problems of interest with the most current version of TRACE and/or by modifying TRACE documentation to address the issue during the time period from January 1, 2009 to June 30, 2009. Trouble Report 10 – Error in backup logic for kinetics. Reactor power/reactivity backup logic was re-written to make it easier to understand and maintain. Update FxPowBackup was included into version 5.167 and closes out this Trouble Report.


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Trouble Report 19 – useRod notification? The code presently does not write the value of the namelist variable userod to the output file. Update Fix1 included into version 5.162 closes out this Trouble Report. Trouble Report 46 – Browns Ferry restart failure. Because of the changes in input processing for CHAN and POWER components, the TRAC-B format steady-state input file no longer ran with TRACE. A number of newer Browns Ferry input decks in TRACE format are available and currently used for Browns Ferry steady-state and transient analysis. This Trouble Report is closed. Trouble Report 52 – Array bounds error for Susquehanna input model. The TRAC-BWR Free Format input deck was run with version 5.157. There were a number of input errors in the input deck, which earlier versions of TRACE had not detected. With the user input fixed, the modified input model ran OK with version 5.157. This closes this Trouble Report. Trouble Report 54 – FIST restart problem. Restart with TRACE version 3.450 failed for a FIST test problem. Version 5.170 identified a number of input errors that version 3.450 did not detect. With these input errors corrected the steady-state and restart for this test problem ran with version 5.170. This closes this Trouble Report. Trouble Report 59 – Error in sum N control block. With version 3.1070 and default SI units used, the Sum N control block was failing. Version 5.170 detected a number of input errors that version 3.1070 did not detect. After these input errors were corrected, the test problems that demonstrated this problem ran without failure with version 5.170. This closes this Trouble Report. Trouble Report 69 – HTSTR input consistency checking. With version 3.1113 the MB2 input problem results in HTSTR input error detection, but fails with an array bounds error. An existing HTSTR test problem in the MasterList sub-directory was modified to detect the HS to fluid component connectivity errors. This test problem with input errors was run with version 5.157 and TRACE detected input errors, wrote appropriate messages, and stopped before the array bounds error. This closes this Trouble Report.

Trouble Report 73 –TRAC-BWR input processing is incomplete. Debug input for TRAC-BWR Free Format was not getting converted to TRACE input models. However, testing with current versions of TRACE indicate that the TRAC-BWR CHECKOUT card input was getting converted to NSEND in TRACE. This closes this Trouble Report. Trouble Report 96 –Accumulator depressurization with no out flow. With version 4.000 an accumulator in a Semiscale model was depressurizing below the system pressure even though the accumulator check valve was closed. This input model was run with version 5.170 and the accumulator pressure did not go below the system pressure. This closes this Trouble Report. Trouble Report 101 – Insufficient error checking for Heat Structure Input. With version 4.000, input model included an input error that cell 0 of a pipe was connected to a HS and no input error was detected. This test problem was run with version 5.151 and it detected the input errors and wrote appropriate messages and stopped. This Trouble Report is closed. Trouble Report 111 – Need description of NVTB1 for Valve Type 8. A non-zero input for NVTB1, should be an input error for valve type 8 (i.e., TRAC-B Motor Valve). Version 5.170 with NVTB1 = 1 and valve type 8 detected this input error. The current User’s Guide VALVE component input description clearly indicates that NVTB1 must be input as 0 for valve type 8. This closes this Trouble Report. Trouble Report 131 – Total reactor power form CHANs did not match the input total reactor power in the POWER component. For a BWR plant deck, the CHAN power and POWER component total reactor power did not match. The test problems identified with this Trouble Report with version 5.170 and the total reactor power is now consistent between the power going to the CHAN component and the expected total reactor POWER supplied by the POWER component. This closes this Trouble Report. Trouble Report 134 – Moderator heating capability apparently inactive in power component. For version 4.044 running the HB Robinson plant model, the direct moderator heating option for the POWER component was not working. This test problem was run


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with versions 5.0P1 and 5.170 and direct moderator heating is now working correctly. This closes this Trouble Report. Trouble Report 165 – Level tracking bug. The JetpLtrak test problem in the Regression test problem set was failing due to a level tracking bug, associated with incorrect level tracking parameters getting passed from the JCELL of a TEE into the side of the TEE. The FxSideJLevTrak update fixes this logic error and was included into version 5.164, closing this Trouble Report. With the FxSideJLevTrak update the JetpLtrak test problems runs without failure. Trouble Report 178 – General Table Types 5-9 are incorrectly documented. Current General Table TRACE documentation and coding for version 5.170 was reviewed and found to be consistent. Earlier versions of the General Table documentation were in error. This closes this Trouble Report. Trouble Report 186 – Axial power peaking factor is not the same on the last major edit as it is on other edits. SCTF input with eleven core hydro cells and eleven core HS levels and 17 POWER axial levels had inconsistent axial power peaking with fine mesh turned on. This test problem was run with version 5.170 and the axial power peaking edits were consistent at all times. This closes this Trouble Report. Trouble Report 188 – Radiation heat flux term in output and xtv appears not to be working correctly. For THTF assessment calculations radiation heat flux edits indicated that the radiation heat transfer model turned on correctly, but was not turned off as the core refills. Earlier versions of TRACE included an initialization error for the radiation heat fluxes, such that they did not get initialized back to zero, when the radiation heat transfer model turned off after being on for some period of time. The THTF assessment calculation was rerun with version 5.170 and radiation heat fluxes went to zero when the radiation heat transfer model turned off. This closes this Trouble Report. Trouble Report 221 Radiation enclosure is effectively being shut-off. A user reported that radiation heat transfer was zero for the Regression test problem RadEncCylinder. Earlier versions of the RADENC model required that a fluid cell be connected to the HS surface in order for a heat transfer regime to be determined. The heat transfer regime was used as a flag to determine when the radiation heat transfer model should be turned on. This

test problem does not include any fluid cells between the HS surfaces. An update was added to TRACE to detect this modeling situation so that standalone radiation heat transfer calculations could be run with just HTSTR and RADENC components and no fluid components. For version 5.170 it was verified that radiation heat transfer fluxes were calculated for the RadEncCylinder test problem and were consistent with hand calculations for cylindrical geometry. Comments in the RadEncCylinder test problem were found to be in error and were modified and the input model with modified comments was submitted along with the FxChanEng update. The FxChanEng update is pending. This Trouble Report is closed. Trouble Report 222 – Non condensable gases are being disabled with non-water fluids. This issue was resolved with update Fix4 that was included into version 5.163. This Trouble Report is closed. Trouble Report 223 – Pre-Input processing bug. This pre-input processing bug was associated with fluid eos input such as “air”, which includes the character ‘i,’ which was incorrectly assumed to be an interpolation directive for array input processling. This issue was resolved with the Fix4 update that was included into version 5.163. This Trouble Report is closed. Trouble Report 224 – Pump Component: Inability to control pump speed with control blocks. A user indicated that for PUMP Type 1, with the trip off and NPMPSD not equal to zero, the NPMPSD signal was not used to control the impeller speed. The case was run with version 5.170 PUMP Type 1 with the trip off with NPMPSD equal to zero and not equal to zero. Calculated PUMP behavior was consistent with TRACE User’s Guide descriptions. This Trouble Report is closed. Trouble Report 227 – Input model is failing without any input error messages. A user reported that the input model used to investigate break flow with a 3D VESSEL was failing without any error messages with version 4.052 beta. Stack over flow was identified as the problem. Using version 4.160 with changes to the TRACE data architecture for the VESSEL component eliminated the stack over flow problem. After the stack overflow problem was fixed, input errors were detected by TRACE and this input model ran OK. This closes this Trouble Report. Trouble Report 232 – NPIPES option not behaving appropriately for PIPEs.


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Choked flow mass flow rate did not change when NPIPES was changed from 1 to 2. This test problem was run with version 5.170 and the choked flow mass flow rate increased by a factor of 2, when NPIPES was changed from 1 to 2. This closes the Trouble Report. Trouble Report 253 – Running MIT Pressurizer Test Inflow-Outflow with level tracking on results in code failure because it cannot reduce the time step any further. For version 4.220 the MIT pressurizer test simulation failed with level tracking turned on. This problem was resolved with update FxSideJLevTrack that went into version 5.164. The MIT Inflow-Outflow test problems with level tracking turned on and off was run with version 5.170 and calculations ran to completion without failure. This closes this Trouble Report. Trouble Report 284 – TRACE ESBWR GDLB transient dies in wetwell. TRACE verison 5.0RC2 ESBWR GDLB transients continue to die due to convergence problems where the SRV lines exit into the wetwell. This test problem was run with version 5.141 without failure. This resolves this Trouble Report. Trouble Report 291 – SCTF fails with steam tables. An SCTF assessment test problem fails with steam tables, but runs with TRAC-P EOS fits. This test problem runs with version 5.141. This resolves this Trouble Report. Trouble Report 307 – CCTF Run 58 fails on "cannot reduce time step" with V5.0RC2. CCTF, Run 58 fails at ~52 seconds into the heat-up phase of the transient with version 5.0RC2. Version 5.141 ran this test problem out to 100 seconds without failure, then started running at very small time step sizes (i.e., 0.0001 seconds) and died at ~105 seconds. It was determined that the problem was that the cold leg TEEs that did not have a flow loss coefficient between the primary side and secondary side of the TEE. Including a K loss of 1.0 between the primary and secondary sides of the cold leg TEEs resulted in an input model that ran to completion without failure for version 5.141. This resolves this Trouble Report. Trouble Report 324 – Elevation versus GRAV input leads to different results. A simple test problem was made to mimic VESSEL, PIPE, SJC PIPE models with known inconsistencies in the elevations around the loops. With GRAV input, spin-up was calculated. Spin-up is steady-state flow due to inconsistencies in the elevation changes around the loop.

With elevation input, no spin up was calculated. The difference in results was traced to different methods used to resolve inconsistent gravs within TRACE. With the FxElevJun update, TRACE inconsistent elevations are flagged as fatal input errors. Without this change TRACE would convert the elevation input to GRAVs and GRAVs out of bounds (i.e., larger than 1.0 or smaller than –1.0) resulted in a warning and the calculation continued. When the loops in the original model are closed the results are the same independent of whether GRAVs are used or elevation input. This closes this Trouble Report. Trouble Report 328 – Ordering of MROD array input for CHAN component. There was confusion about the algorithm for converting MROD-1D vector input into a MROD-2D array. The TRACE logic for converting the 1D vector input for the MROD-1D array into a 2D array for the fuel rods in a BWR fuel assembly goes as: MROD(i, j) = MROD-1D(i + (j-1) * nRows) Where i is the column index and j is row index. The TRACE documentation, coding, and SNAP are all consistent with this algorithm. This Trouble Report is closed. Trouble Report 347 – TRACE supporting SNAP R5 to TRACE. A number of problems were identified in terms of the conversion of RELAP5 input models into TRACE input model via SNAP. See the detailed Trouble Report documentation in TRACEzilla. All of these problems were resolved in TRACE version 5.0P1 and this Trouble Report is closed. Trouble Report 380 – Level Tracking Model apparent error. A significant mass error was observed during debugging of the BWRMassErrTest and the mass error was traced to failure of the level tracking model with version 5.020. With version 5.141, most of the mass error was resolved. With 5.141 + FxSideJLevTrack the mass error for this problem and several other test problems with level tracking was essentially eliminated. The FxSideJLevTrack update went into version 5.164. This Trouble Report is closed. Trouble Report 381 – Singularity with Non-Condensable Gas Mass Continuity for EPR model. A TRACE EPR calculation resulted in a non-condensable gas partial pressure of 2,600 Mpa. This is expected behavior when the singularity in the linearized non-condensable gas mass continuity equation is


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combined with the two-phase flow mass and energy conservation equations. Updates FxWaterPacker, FxRhog, and FxMassChecker were all included into version 5.090 and closed this problem. Trouble Report 406 – Sensivity of results due to time step size version 5.090. North Anna hot leg results for version 5.090 oscillated if DTMAX was larger than 0.01 seconds. These oscillations were traced to changes in the 3D momentum flux terms and associated with the NOSETS = -1 option. The FxDvDv update, which removed the NOSETS = -1 option from TRACE and made fixes to the 3D cross-flow momentum flux terms was included into version 5.100 and closed this Trouble Report. Trouble Report 418 – Material property functional fit input problem in English unit decks. The material property functional fits when the TRACE input file is in English units was converted to SI units twice. The FxMatUnits update went into version 5.166 and closed this Trouble Report. Trouble Report 419 – Divide by zero when normalizing cpowr array. Divide by zero was encountered in the NormalizeCPowr routine for an input model that included heat structures with different axial nodalizations. The problem was traced to user input of NZPWTB = 0, which should have resulted in an input error. The update FxMatUnits includes input checking to catch NZPWTB = 0 and to catch the division by zero in the NormalizeCPowr if the HS total volume is zero. The FxMatUnits update went into version 5.166 and closes this Trouble Report. Trouble Report 424 – TRACE Version 5.110 failed for Seabrook LBLOCA calculation. A user reported that with TRACE Version 5.110, the Seabrook LBLOCA calculation failed with can not reduce time step size below user input for DTMIN. The FxTsatLogic resolved this Trouble Report and was included in version 5.151 of TRACE, which closes this Trouble Report. Trouble Report 430 - Error in noncondensable gas (NCG) mass in a PIPE component. For a 1/5th scale accumulator test, significant mass error was observed for the TRACE simulation. Investigation of this model indicated that mass error was due to the lower limit for steam partial pressure in the TRACE steam tables being 1 Pa, which corresponds to a sublimation temperature of ~200 K. The FxTsatLL update went into version 5.154 and closes this Trouble Report.

Trouble Report 432 - V5006opt dies on non-convergence when 1-D level tracking is activated. Turning on level tracking for a pressurizer, accumulators, and steam generators for the EPR steady-state model resulted in improved steady-state predictions. However, the LBLOCA failed with level tracking turned on when the pressurizer emptied. The LBLOCA model runs with level tracking turned off. This Trouble Report was closed with update FxSideJLevTrack, which went into version 5.164. Trouble Report 433 – Browns Ferry LBLOCA drywell pressure too large because of level tracking conflict with side junction. During 5.141 assessment calculations for the Browns Ferry LBLOCA, TRACE calculated a peak drywell pressure of ~19 bars, which is unreasonably high. The problem was traced to a conflict in the level tracking model and the side junction model. With level tracking turned off in the drywell the peak drywell pressure is predicted to be ~3.3 bars, which is consistent with the Version 5.0 result of ~3.5 bars. Update FxSideJLevTrack closes this Trouble Report, since it was included into version 5.164. Trouble Report 436 – Small break modeling guidelines. During assessment of version 5.0P1 it was determined that the BWR SBLOCA assessment calculation gave significantly different results between versions 5.0 and 5.0P1. Changes to the momentum flux solution around side junctions at TEE primary to secondary sides that went into version 5.0P1 were determined to be the root cause. New small break modeling guidelines were developed and when followed with versions 5.0 and 5.0P1 gave essentially the same results for the BWR SBLOCA. In addition, update fxechoke5162 which went into version 5.168 resulted in fixing logic errors in the choked flow model in TRACE that allowed the new SB modeling guidelines to predict critical flow rates consistent with version 5.0 using the old modeling guidelines. This closes this Trouble Report. Trouble Report 439 – Input processing for heat structure coupled to CONTAN compartment. A user attempted to associate more than one CONTAN compartment to a single TRACE heat structure component. Although the input was accepted without an input error, TRACE 5.141 input processing does not support this capability. The FxCont update addresses this issue and modifies TRACE input processing for the heat structure component so that more than one CONTAN compartment can be associated with a single TRACE heat structure component. The FxCont update


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was included into version 5.157 and closes this Trouble Report. Trouble Report 440 – CONTAN component and heat structures. A user provided input decks for a simple CONTAN model that produced significantly different results when the compartment heat structures were simulated with a TRACE heat structure or with a CONTAN heat structure. Investigation of this problem indicated that a TRACE heat structure level tracking logic error resulted in no heat transfer to the CONTAN compartment. This Trouble Report is closed with the FxCont update that went into version 5.157. Trouble Report 442 – aRatioP in EdgeLoc undefined. A user reported that when running test problem CCTF_ColdLeg on a 64-bit LINUX operating system with the NAG compiler, the code failed with an undefined for aRatioP in the EdgeLoc data structure. Update FxaRatioP resolves this problem and was included into TRACE version 5.152, which closes this Trouble Report. Trouble Report 443 – Packer Failed. A user reported that a TRACE restart ran, but water packer messages were written independent of the size of DTMAX. The TRACE executable is v5.141_epr_opt.exe. TRACE version 5.0p1 on 32-bit Windows XP OS with CVF compiler using optimized or debug compiler ran this test problem without failure. However, the water packer/stretch message was written for nstep = 0 for a stretch in a cold leg PIPE. This behavior is typical for a LBLOCA restart when the first time step is relatively large. If the namelist input for DTSTRT is changed from –1.0 to 0.0001 seconds, then the water packer/stretch message for nstep = 0 does not appear. DTSTRT = -1.0 implies that the time step size for the first time step for the restart will be obtained from the restart file. With DTSTR = 0.0001, the water stretch in the code is not calculated to occur. However, water packer messages are generated later in the calculation. This closes this Trouble Report. Trouble Report 449 – CONTAN Heat Transfer Coefficient (HTC) Oscillates. A user indicated that the TRACE CONTAN model of the CVTR test facility resulted in oscillations in the CONTAN calculated HTCs. The HTC oscillations were traced to large oscillations in the mass flow rates through the CONTAN compartments. The large oscillations in the mass flow rates are due to the relatively large flow area and small flow resistance associated with the passive junctions in this model. The CONTAN component hydrodynamic solution numerical method is explicit, which is adequate for a typical CONTAN model for a

BWR containment. A typical CONTAN model involves relatively large compartment volumes connected by junctions with relatively small flow areas and reasonable flow resistances. For this CVTR model the test tank was simulated with 3 CONTAN compartments, with flow areas for the passive junctions connecting these compartments on the same order of magnitude as the compartment average flow area. A model of this type will result in numerical oscillations with the CONTAN component explicit hydrodynamic solution method. For this test facility, the 3 CONTAN compartments could be lumped together into a single CONTAN compartment and the oscillations in HTCs will not occur. A longer term solution would be to replace the CONTAN explicit numerical method with a more implicit numerical method. A short term solution for this problem is including some relaxation into the calculated HTC for CONTAN components. The same relaxation logic for TRACE HS HTC was included into the CONTAN HTC calculation with the FxCont update that went into version 5.157. This eliminated the oscillations in the calculated HTC for the 3 CONTAN compartment model, although oscillations in the passive junction mass flow rates continued. For this test problem the user noted that TRACE CONTAN compartment vapor temperatures were significantly above the test results. The experimental data indicated that the total inflow energy specified in TRACE was larger than indicated by measurements. When the energy inflow was modified to be consistent with the experimental data, results were consistent with observations. This Trouble Report is closed. Trouble Report 454 – Single phase vapor heat transfer coefficient (HTC) in error when noncondensable gas (NCG) content is significant in a fluid cell. A developer reported that the derivative of the steam density given a change in vapor temperature was used in the TRACE HTC calculations for the themal expansion coefficient. It should have been the derivative of the vapor density given a change in vapor temperature. The derivative of the steam density given a change in vapor temperature will approach zero as the steam partial pressure approaches zero. For fluid cells with single phase vapor with mostly NCG, the natural circulation heat transfer will be significantly under-predicted. For example, this will significantly impact the heat transfer to the gas space in an accumulator model. The FxNatCirc update was included into version 5.155 and closes this Trouble Report. Trouble Report 455 – Level tracking in version 5.141 contains logic errors. A user indicated that US-APWS full height ½ scale accumulator tests results were not as expected when ilev was input as 0, -1, and 1. Rerun of the test problems with version 5.154, which includes a number of


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fixes for level tracking logic in TRAC, gave results that are consistent with expectations for ilev input as 0, -1, and 1. This closes this Trouble Report. Trouble Report 456 – 5.154 compile fails for MAC compiler. A user reported that version 5.154 failed during compile on a MAC. The problem was traced to source lines longer than 130 characters. Updated FxDEgDT addresses these issues and was included into version 5.161. This closes this Trouble Report. Trouble Report 457 – Property errors in calls to routine HTIF. A developer reported that incorrect derivatives were passed as vapor and liquid phase specific heats to the interfacial heat transfer routine HTIF. Update FxDEgDT addresses these issues and was included into version 5.161. This closes this Trouble Report. Trouble Reports Resolved with Updates Pending The following Trouble Reports have been resolved with updates pending during the time period from January 1, 2009 to June 30, 2009. Trouble Report 4 – Reflood initialization logic not consistent within TRACE. The initialization logic for user input for DTXHT and DZNHT was different in TRACE depending upon whether the heat structure (HS) was input as a HTSTR component, a ROD/SLAB, or a spawned HS. The user input for DTXHT is no longer used in TRACE. The TRACE axial temperature gradient at which new fine mesh nodes are added or deleted is based on the local heat transfer regime and is defined in the User’s Guide Chapter 2 HTSTR component description. Update FxDZNHT sets the default for HS paths through input to be 0.001 m. This update is pending and resolves this Trouble Report. Trouble Report 28 – Junction problem in Prizer. Coding for PRIZER models assume JUN1 is at the top of the pressurizer and JUN2 is at the bottom of the pressurizer, but there is no input checking to verify that the user conforms to this geometry. The FxPRIZER update adds input checking logic to ensure that this assumed geometry is used for the PRIZER component. This update is currently pending and resolves this Trouble Report. Trouble Report 31 – Vontrol block 'time' not correct for BFSS.inp.

Control block time is not correct for TRAC-BWR free format input for Browns Ferry steady-state input model. The update FxTBSV21 which is currently pending resolves this Trouble Report. Trouble Report 32 – Mixture enthalpy signal variable formulation is based on static enthalpy Signal variable mixture enthalpy formulation is based on static enthalpy (i.e., slip ratio = 1.0) and most users may be expecting flow enthalpy. The FxFlowEnthalpy update modifies the signal variable mixture enthalpy formulation to use flow quality when vapor velocity times liquid velocity is greater than or equal to 10-6 m/s. Flow enthalpy is not defined or well behaved for zero mass flux or for counter-current flows, so when vapor velocity times liquid velocity is less than 10-6 m/s, then static enthalpy is calculated. Note this is a cell-center signal variable and actual enthalpy transport is at the cell edges. The FxFlowEnthalpy update resolves this Trouble Report and is currently pending. Trouble Report 33 – Programming guideline violation in WireCbOut. In subroutine WireCbOut, the code uses pointers as means of overwriting the memory location that is pointed to. The WriteCbOut function converts TRAC-BWR control block logic into the TRACE required logic to control component actions. The FxTBSV21 fix re-writes the WireCbOut logic so that pointers in component variable length tables are not modified directly, but TRACE consistent logic is established to allow TRACE component actions consistent with the original TRAC-BWR input. This update is pending and resolves this Trouble Report. Trouble Report 39 – Axial power shape problems. Problems with NZPWZ < 2 were identified for the POWER component for early versions of TRACE. When NZPWZ is input as < 2, then the number of points in the axial power shape is determined based on the HTSTR powered by the POWER component (i.e., NZPWZ is redefined to be NZHTSTR or NZHTSTR + 1, when NZPWZ is input as < 2). The FxNZPWZ update makes this logic consistent within TRACE and updates the User Guide documentation to be consistent with this update. The FxNZPWZ update is pending and resolves this Trouble Report. Trouble Report 43 – Level Model Turned on for CHAN component in a BWR Model Fails with Time Step Size Can Not Reduce to Less Than DTMIN. A user reported that when the level model was turned on for the CHAN component in a TRACE model for the FIST test facility, TRACE failed. A number of level tracking logic errors were resolved with the Fx3DlevTrak


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update which is currently pending. This update resolves this Trouble Report. Trouble Report 45 – Negative power at CHAN inlet. For a given test problem NZPWZ = 2 for the POWER component input resulted in negative power at the CHAN inlet node. The original test problem was not available. Several test problems were run with version 5.157 + FxNZPWZ with NZPWZ and axial power profiles calculated by TRACE were correct. Update FxNZPWZ is pending and resolves this Trouble Report. Trouble Report 48 – Time step diagnostic edits not available in TRACE. Logic for user input for TSDLS, TSDUS, TSDLT, and TSDUT for time step diagnostic edits was not in TRACE. Logic to include time step diagnostic edits was included into the FxHGAM update. The FxHGAM update is pending and resolves this Trouble Report. Trouble Report 72 – Oscillations with point kinetics with reactivity feedback model. TRACE calculated reactor power oscillations after simulation of a simple over-pressurization transient. Reactor power was expected to return to a new steady-state value. When time step size was reduced the expected behavior was observed. The instability was traced to explicit calculation of reactivity feedback. The FxReact update adds time step control logic to ensure that explicit reactivity feedback does not result in instability. This update was included into version 5.153, resolving this Trouble Report. Trouble Report 88 – CHAN Component Not Working with Water Rod as First Rod Group. TRACE requires that the first rod group for each CHAN component must be a full length powered fuel rod. This was not clear from the current User Guide Documentation, so the documentation was updated to resolve this Trouble Report. The updated documentation was included into the FxPumpInpChk update that is currently pending. This resolves this Trouble Report. Trouble Report 115 – RPKF Input fails when the power component has multiple heat structures with supplemental rods. The input description for the RPKF supplement rod , rod-to-rod peaking was confusing and misleading. The FxPowerRst update includes documentation changes that attempt to improve the input requirements description for the RPKF array. This update is pending and resolves this Trouble Report.

Trouble Report 116 – Input processing failure when rpowri = 0.0 TRACE input processing redefined reactor power of 0.0 to be 10-10 W. If RPOWRI = 0.0 and the time zero point in a reactor power table had 0.0 power, then an input error would occur, since RPOWRI had been redefined to be 10-10 W, which is not consistent with the time zero point in the reactor power table. The FxRPOWRI update eliminates the re-definition of zero reactor power to 10-10 W. The original intent of this coding was to guard against division by zero during any power normalization calculations. With the FxRPOWRI update any divisions in TRACE are not allowed to divide by zero, but rather by a lower limit of 10-10 W. This update is pending and resolves this Trouble Report. Trouble Report 130 – Control blocks with duplicate IDCB numbers. There was no input checking for duplicate control block ids for a TRACE input model. The FxDupCN includes logic to test for duplicate control block ids. This update is pending and resolves this Trouble Report. Trouble Report 152 – Stated restrictions on HTSTR and RADENC comp. numbering is incorrect. TRACE input descriptions for RADENC and HTSTR indicate that component numbers should not be larger than 999. A user found that no input error occurred if a RADENC or HTSTR component number was > 999. The potential problem avoided by having NUMs <= 999 was associated with spawned components. Spawned component numbers are set internally by TRACE, when the component is spawned. TRACE spawned component numbers searches for un-used component numbers starting at 1000 * gnum + 1 and larger, where gnum is the component number of the parent component. If gnum is allowed to be larger than 999, then spawned component numbers will be larger than 1000000. Output edits logic may fail if component numbers are larger than 106 (i.e., more than 6 digits). The FxZSGRID update includes modifications to the spawned component number selection logic so that even when the parent component is > 999, the spawned component number is never larger than 999999. This implies that an upper limit to the total number of parent and spawned components in a given TRACE input model of 999999. We currently do not envision TRACE models with more than 106 components, but if necessary this logic can easily be modified to allow for more than 999999 components in a given TRACE input model. The FxZSGRID update is pending and resolves this Trouble Report. Trouble Report 168 – 3D level tracking problems with ESBWR.


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Two ESBWR models failed with level tracking turned on in the 3D VESSELs. The TRAC-BWR free format input models for these two test problems failed with input errors for version 5.170. With TRACE ASCII input models for the ESBWR version 5.170 failed at ~30 seconds into the steady-state calculation with apparent errors in the 3D level tracking logic. Version 5.170 + Fx3DlevTrak ran the ESBWR input without failure with level tracking turned on. The Fx3DlevTrak update is pending and resolves this Trouble Report. Trouble Report 169 – Duplicate Component Numbers. Input decks with duplicate component numbers gave input errors that were confusing and not related to duplicate component numbers. The FxDupCN update moves the input checking for duplicate component numbers to occur earlier in the input processing before misleading input errors occur and stops the input processing if duplicate component numbers are found. The FxDupCN update is pending and resolves this Trouble Report. Trouble Report 175 – Memory bounds error in ReTprCntlBk on restart. TPR restart was failing when the NTCB for the restart was smaller than the NTCB in the TPR restart/dump file. In general for restarts, even when control blocks and/or signal variables are replaced by including the control block/signal variable input in the ASCII input restart file the total number of control blocks and signal variables input in the ASCII input file must be at least as large as the number of control blocks and signal variables in the restart/dump file. For signal variables there is re-allocation logic that increases the value for NTSV if necessary so that all of the restart signal variables can be processed from the restart/dump file. However, there was no re-allocation logic for control blocks if NTCB was input to be too small relative to the total number of control blocks on the restart/dump file. The FxRstCB update adds re-allocation logic for the control blocks so, if necessary, the control block arrays can be re-allocated so that all of the control blocks on the restart file are processed. This update is pending and resolves this Trouble Report. Note this update also resolves a problem with changing the input for TRACBOUT across restarts. Trouble Report 196 – No input checking between nfci and nfcil. When NFCI = 1, then the fuel-clad interaction model is turned on and NFCIL is the number of interations per time between the conduction solution and the fuel-clad interaction model. There was no input checking to verify that NFCIL > 0, when NFCI = 1. The FxNFCIL update adds consistency checking between the NFCI and

NFCIL input for TRACE. This update resolves this Trouble Report and is currently pending. Trouble Report 228 – 1-D level tracking with noncondensable gas (NC). Level tracking problems were identified with the PCCS drain tanks in a 2-VESSEL ESBWR model. This problem was run with version 5.170 + FxTBSV21 out to ~0.6 seconds where it died with a problem with low steam partial pressure in containment fluid cells. The TRAC-P EOS fits do not do well for partial steam pressures approaching 0.0. However, the TRAC-BWR free format input does not include an input option to use the TRACE steam tables. The TRAC-BWR free format input was used to generate a TPR restart file and then the SNAP Model Editor was used to read the TPR file and create a TRACE ASCII input file. This input contained some input errors that were corrected. With the input errors corrected version 5.170 + FxTBSV21 + Fx3DlevTrak was able to run this test problem without failure. Updates FxTBSV21 and Fx3DlevTrak are pending. Update FxTBSV21 includes logic to ignore consistency checks for view factor input if the radiation heat transfer model is turned off and update Fx3DlevTrak includes fixes for the 3D level tracking logic. The converted input did not have consistent view factors and for this test calculation radiation heat transfer did not come on, so it was easier to turn off radiation heat transfer, rather than fix the view factor input. This resolves this Trouble Report. Problems identified with SNAP were transmitted to the SNAP development team. Trouble Report 238 – Unable to convert the old ROD component (TRAC-P) into the new TRACE "heat structure" and "power" components using the newhsinput file. Converting ROD component input to HTSTR component input was an option available in TRACE before the SNAP model editor was developed. With the SNAP code these input models can be read directly into SNAP, which can then be used to generate a TRACE ASCII input file with the appropriate HTSTR and POWER component input. The RmNewHSInp update removes the newhsinput logic from TRACE, since it is no longer maintained or recommended to be used. SNAP is the recommended approach for converting this input. This update is pending and resolves this Trouble Report. Trouble Report 239 – When the NAMELIST option INLAB=3 is used, the produced inlab input file doesn’t work properly when run with TRACE. The inlab = 3 input option is an old TRAC-P capability to generate an input deck that includes comments with input variables identified. However, this capability is no longer maintained in TRACE and is no longer recommended. The SNAP Moder Editor can be used to


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generate a comment labeled TRACE ASCII input file. The RmInlab update is pending and resolves this Trouble Report, by removing the inlab logic from TRACE. Trouble Report 276 – Can't use multiple fluids when new Steam Table water is one of the fluids. For version 4.240 a user was unable to run multiple fluid calculations if one of the fluids was input as ‘sth2o’. The user identified a bug in pre-input processing that was not handling ‘sth2o’ or ‘STH2o” correctly. The fix proposed by the user was included in the FxMultFluid update. This update is pending and resolves this Trouble Report. Trouble Report 298 – PUMP Table Was Not Evaluated A user reported that the PUMP table was not used during a TRACE steady-state calculation. It was determined that although the PUMP table input was provided, the input for IPMPSV was zero. This indicated that there was no signal variable or control block output to be used to evaluate the PUMP table. Update FxPumpInpChk adds input error checking logic to ensure that IPMPSV is non-zero if needed to evaluate a PUMP table. This update resolves this Trouble Report and is currently pending. Trouble Report 302 – TRACE MCPR Calculation May Be in Error for Non-Uniform Axial Power Profiles. The original TRACE MCPR calculation logic assumed that the minimum CPR would always occur at the exit of the heated section of the CHAN component. However, for non-uniform and transient conditions, the minimum CPR may occur at a lower elevation. The FxMCPR update is pending and resolves this Trouble Report. This update changes the MCPR logic so that all axial levels are searched for the minimum CPR. During testing, a problem occurred with the rod-to-rod peaking factor used in the MCPR calculation. Specifically, the CPOWR input is used to estimate the rod-to-rod peaking factor when more than one rod group is used in a given CHAN component. However, for the special case of one CHAN component with one rod group, the CPOWR input was not normalized and the user had input a value for CPOWR(1) of 0.01666667. This resulted in a relatively large RFACTOR in the critical quality calculation. The FxMCPR update also ensures that CPOWR is always normalized to one, so that a reasonable rod-to-rod peaking factor is available. Trouble Report 303 – NoFat Logic No Longer Needed. A developer indicated that the NoFat logic had originally been developed to address numerical problems with the TRAC-P code. The original NoFat implementation had been relaxed when the BWR models were included in TRAC. It appears that TRACE does not exhibit the numerical problems associated with large area ratios

that were observed with TRAC-P. The RmNoFat update resolves this Trouble Report and removes the noFat logic from TRACE. Some user warnings concerning large area ratios are still in TRACE. The RmNoFat update is pending. Trouble Report 308 – Long running time for PANDA test problem. A user reported relatively long running time for PANDA test simulations with version 5.0RC2. It took ~7000 cpu hours to run the first 20 seconds of a 5000 second transient. TRACE convergence problems were traced to the 3D VESSEL components used to simulate the PCCs pools. During this transient there is sub-cooled boiling on the outside of the PCCS tubes. The sub-cooling boiling mass transfer rate is treated as an explicit source in TRACE. This explicit coupling is believed to be causing the convergence problems that require relatively small time step sizes. If the fluid volume of the PCCS pool cells is increased then cpu time required to run the first 20 seconds of the transient reduces by an order of magnitude. With the original noding, version 5.141 took ~1600 cpus to run the first 20 seconds of this transient. The HSupgrade update makes the sub-cooled boiling model more implicit and it is anticipated that it will reduce the cpu costs. This Trouble Report is currently resolved with the 5.141 results. However, this test problem will be re-run with the HSupgrade update to determine if run time results improve as expected. Trouble Report 311 – TRACE ROD/SLAB conversion to HTSTR gives duplication of components. Conversion of ROD/SLAB component input into HTSTR using the TRACE newhsinput capability resulted in duplicate component numbers. The newhsinput capability is no longer maintained in TRACE, because this capability is available in SNAP. The update RmNewHSInp removes the newhsinput logic from TRACE and is currently pending and resolves this Trouble Report. Trouble Report 335 – TRACE / PARCS Restart Edits with TPR. A user indicated that for a TRACE/PARCS coupled calculation, PARCS was not writing a TPR restart dump, when TRACE wrote a TPR dump. The user indicated the fix required to solve this issue. The fix was included into the RmRst update, which is currently pending and resolves this issue. Trouble Report 349 – Problem with units for side junction angle. Internal TRACE logic assumed that side junction angles were always in units of degrees. TRACE input processing assumes that user input angles units are


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radians for SI units and degrees for English units and assumed that internally TRACE expected radians. The FxAngleUnits update which went into version 5.159 changed the TRACE input logic for side junction angles to always be in degrees and no conversion is made so that user input is consistent with the TRACE internal model for side junction angles. This closes this Trouble Report. Trouble Report 361 – Error message when valve table is entered and shouldn't be. A user attempted to use over-riding trip input with VALVE Type 9 and TRACE failed while trying to read VTB2 input, but no input error was written that indicated that NVTB2 must be 0 for Valve Type 9. The FxCVOverRide update adds input checking to catch input errors when NVTB1 or NVTB2 are non-zero, but must be 0. In addition, it adds over-riding trip capability to VALVE Type 9 and updates documentation to ensure that users are aware of which VALVE types support over-riding trip capability. This update is pending and resolves this Trouble Report. Trouble Report 363 – Input Error Checking for Negative Flow Loss Factors. A user reported that a TRACE calculation stopped without any error message. Negative flow loss factors in the range of –1020 < FRIC < 0 are flagged as an input error. FRIC < –1020 are used to turn on an old TRAC-P phase separation model. This old phase separation model is not recommended, however FRIC < –1020 are not considered an input error at this time. The specific problem encounter by the user occurred when NFRIC1 was input as 1 and the user input a negative reverse flow loss factor in the range of –1020 < FRIC < 0. A logic error in the input checking resulted in the calculation stopping with input errors, but no error message was written. The FxNegFricInpChk update resolves this Trouble Report and is pending. Trouble Report 369 – Problem with SETS/Timestep control. A user reported that results were significantly different for a VESSEL model representing a hot assembly depending up on DTMAX. Differences in results were traced to the explicit sub-cooled boiling term. The HSupgrade makes the subcooled boiling term more implicit, which addresses this problem. The FxHGAM update includes some relaxation logic in the temperature (tld) at which boiling begins, which is a parameter in the sub-cooled boiling model. In addition, the FxHGAM update implements time step control based on maximum allowed change in tld for each time step. With the FxHGAM update new namelist user input of MAXTLDCA allows the user to input the maximum allowed change in tld each time step (default is 5 K). Both of these updates

resolve this Trouble Report. With version 5.157 the test problem obtains consistent steady-state results with DTMAX < 0.045 seconds. Version 5.157 + Hsupgrade + FxHGAM predicts consistent steady-state results with DTMAX <= 0.05 seconds. If DTMAX is increased to 0.1 seconds oscillations about the correct steady-state value appear. However, it should be noted that version 5.157 does not oscillate about the correct steady-state solution. The tld relaxation logic is required to ensure that the oscillations about the correct steady-state solution. Trouble Report 373 – SJC Valve Connection to Vessel. A user reported that a SJC VALVE cannot be connected between a VESSEL component and 1D fluid component. It was determined that there was an error in the boundary logic for a SJC VALVE connected to a 3D VESSEL. The FxVlveVss update resolves this Trouble Report. This update is pending. Trouble Report 392 – Flow Rates Incorrect for PUMP SJC Type 11. A user reported that the flow rate through a PUMP SJC Type 11 was not calculated correctly by TRACE. The error was found to be associated with the water packing logic which assumed that the momentum equation was solved for the PUMP SJC. However, for PUMP SJC Types 10/11, the momentum equation is replaced with the user specified flow rate. The FxPump11 update is pending and resolves this Trouble Report. In addition, it adds input checking to warn users about the bad modeling practice of a FILL or PUMP SJC Types 10 or 11 next to a VALVE component. A VALVE closed next to a FILL or PUMP SJC Types 10 or 11 with non-zero flow will result in an unbounded pressure solution. Trouble Report 401 – TPR write failure on 64-bit LINUX operating system. TPR write failures occurred on 64-bit LINUX OS with Lahey, NAG, and Intel compilers. Changes to the TRACE cPibAccess.c and cPbiAccess.h were developed that allow TPR read/writes to work on both 32-bit Windows XP OS and 64-bin LINUX OS. These changes were incorporated into the RmRst update, which is pending. This update resolves this Trouble Report. Trouble Report 412 – Void Fraction Distribution in First Level of 3 Ring Drywell VESSEL is in Error. A user reported that the void fraction in the first level of a VESSEL component simulating the PUMA test facility drywell is in error. Specifically, the void fraction in ring 1, level 1 after 20 seconds into the transient was < 20% and the void fraction in rings 2 and 3 was > 90%. The anticipated solution is the same void fraction in rings 1 through 3 in level 1 of the drywell VESSEL component. This Trouble Report was resolved with the Fx3DlevTrak


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update, which is pending. This update implements the 1D horizontal stratified flow model into the 3D VESSEL level tracking model. Note that this model only comes on when the level tracking model is turned on in the VESSEL component. Trouble Report 423 – Removal of the ROD/SLAB to HTSTR input conversion logic from TRACE TRACE includes the capability to read heat structure input for ROD/SLAB and write a new input file that includes HTSTR input. However, this capability is available in SNAP. The RmNewHSInp update removes this unnecessary coding. The RmInlab update removes the inlab logic, which writes a labeled input deck as input is processed by TRACE. Again this capability is available from SNAP. The RmNewHSInp and RmInlab updates resolve this Trouble Report. Trouble Report 425 – Large eMass and massE. A relatively large mass error was calculated for the Calvert Cliffs SBLOCA calculation with version 5.171. The Choke1D-3D update which is pending resolves this Trouble Report. Trouble Report 427 - UPTF 21-271 fails with Version 5.141 During the assessment of the Patch Release version of TRACE (i.e., 5.141), UPTF test 21-271 failed with pressure increasing without bounds in a fluid cell at the top of the downcomer. The problem was traced to instability in the 3D momentum flux terms. Update Fx3DmomFlux resolves this Trouble Report and is pending. Trouble Report 431 - Supplemental rod appears to be affecting hydraulics. Results for an EPR model are affected by which heat structure includes supplemental rods. Supplement rods should have no impact on the hydraulic solution. For Version 5.141 it was found that no significant impact occurred when supplemental rods where included in the EPR model. However, during testing it was determined that an input error could go undetected and affect the hydraulic solution. The NHSCA array in the VESSEL component input identifies the reflood heat structure in the core region of the VESSEL component. The ordering of the heat structures in this NHSCA array determines which horizontal plane cell index will be associated with these structures. If the NHSCA array index is not consistent with the reflood heat structure input, then logic errors will occur in the data transfer between the reflood heat structures and wall drag model for the core region of the VESSEL component. The quench front location is used in the core region of the VESSEL component to determine if the fuel rods are

wetted or not. The FxVessRefld update is pending and adds logic to indicate an input error if the NHSCA array input is not consistent with reflood heat structure input. This Trouble Report is resolved with update FxVessRefld. See this Trouble Report for examples of how to make sure that NHSCA and reflood HS input are consistent. Trouble Report 437 – Non-physical void profile in core for EPR SBLOCA calculation. While running EPR SBLOCA calculations it was noticed that a non-physical axial void profile developed in the core. The flow regime number predicted in the region where the void profile appeared to be incorrect was output as 8.0, which indicates that the flow regime is reflood heat transfer. The Fx1Drefld update resolves this behavior and is currently pending. Trouble Report 441 – V5.0P1 crashes on a MATH DOMAIN error when simulating the ADS test facility. A user reported that for ADS test 240 TRACE version 5.0 crashed with a math domain error when the BREAK inlet boundary conditions are two phase and all of the ADS valves are open. This Trouble Report is resolved with the Fx3DmomFlux update, which is pending. Trouble Report 444 – Divide by zero in Off-Take Model. A user reported that Version 5.141 failed for test BETHSY 6.2TC with a divide by zero. The problem was identified as a divide by zero in the off-take model when the upstream void fraction approached 1.0. Update FxOffTake resolves this problem. Update FxOffTake is currently pending. Trouble Report 446 – V5.0p1 crashes during the calculation phase (at the first time step). A user reported that TRACE V5.0p1 fails during the first time step for several experimental facility models. An array bounds error was found that was caused by a logic error in the boundary condition logic for a VALVE component, when the VALVE cell edge (i.e., IVPS) was located at NCELLS + 1. This is an acceptable input model if the VALVE NCELLS + 1 cell edge is connected to a BREAK component. However, an error in the VALVE component boundary condition logic resulted in the code attempting to obtain the volume average flow area from the neighboring component for the other end of the VALVE component. If the other end of the VALVE component is connected to a VESSEL component, then an array bounds error occurs. The FxVlveVss update resolves this Trouble Report. The FxVlveVss update is currently pending. Until this update has been included into TRACE, the problem can be avoided by moving the cell edge for the VALVE from NCELLS + 1 to NCELLS.


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Trouble Report 447 – Power component gives different results for internal and external reactivity steps. A user was getting different reactor power results, when the expectation was that the results should be the same when specifying programmed reactivity via table and a control block signal. Logic errors were found in the POWER component when reactivity was coming from a signal variable, control block, or general table. Fixes to resolve this logic error were included into the SAPower update which is pending. This resolves this Trouble Report. Trouble Report 448 – ICHANS intent is incorrect in routine DetermineFirstChan. A user reported a coding error in the routine DetermineFirstChan routine. ICHANS was used before it was defined. The FxMCPR update resolves this Trouble Report. The FxMCPR update is currently pending. Fixing this error on a 32-bit Windows XP OS with CVF compiler had no impact upon the results. However, a different platform or different compiler may result in code failure or a logic error without this update. Trouble Report 451 – Errors were encountered in the Channel component when British units were selected. However, SI system works OK. A user reported that a SNAP .med file containing a CHAN component which exported ASCII input in SI units ran, while the same .med file which exported ASCII input in English units failed. The initial failure was in the view factor calculation, which indicated that the water rod and fuel rods were overlapping. The problem was determined to be associated with the XLOC and YLOC CHAN input, which had not been converted to English units by SNAP. This SNAP problem was communicated to the SNAP development team. After the XLOC and YLOC input were manually converted to English units, additional units problems occurred in the TRACE logic. Specifically, several CHAN arrays were converted from English units to SI units when they were already in SI units. The FxChanEng update resolves this Trouble Report for TRACE and is currently pending. The FxChanEng update includes modifications to the CHAN User Guide Input description to ensure that units for the CHAN input are identified. Trouble Report 458 – CONTAN component is not handling subcooled water injected into BWR drywell correctly. A user reported that for a BWR LBLOCA calculation subcooled water draining from the break into the drywell was not resulting in condensation in the drywell. Update FxCONTANBreak fixes logic errors in the CONTAN FlashSpray routine that resolves this problem. The update FxCONTANBreak is pending and resolves this

Trouble Report. Trouble Report 459 – Math error for restart with multi-power distribution and hot rod. A user identified a math error in TRACE for the St Luice 1 LBLOCA restart. The TRACE model included multi-power distributions for the POWER component and a hot rod. An error in restart logic for the POWER component was resolves with the FxPowerRst update. This update is pending and resolves this Trouble Report. Trouble Report 460 – 648 CHAN input model fails with NSOLVER = 1. A user reported that an ESBWR model with 648 CHAN components in the input failed when NSOLVER was set to 1. Update FxLargeModel removes the array size checker for the SUPERLU solver option which is no longer needed. This update is pending and resolves this Trouble Report. Trouble Report 461 – Property table error. During a restart with version 5.170 for a PWR LBLOCA calculation a user reported an error in the properties table search. It appeared that during a search for a converged solution, TRACE attempted to determine the liquid phase properties at a pressure smaller than the critical pressure, but at a temperature larger than the critical temperature. The FxIAPWS update was developed to keep liquid temperatures below the critical temperature, when pressures are smaller than the critical pressure. In addition, it was found that the TRACE calculation resulted in a number of time step backups due to velocity reversals in the 3D VESSEL component during the time period after core recovery, when velocities in the 3D VESSEL were relatively small and void fractions were approaching zero. The fxlock5152 update had been implemented into version 5.170 to address a similar problem in 1D fluid components. The fxlock5152 fix logic was included into the FxIAPWS update and appeared to significantly reduce the number of velocity reversal time step backups in the 3D VESSEL during the time period when velocities were relatively low and void fractions were approaching zero. The FxIAPWS update is pending and resolves this Trouble Report. Trouble Report 462 – Property table error. Resolved because it is a duplicate of Trouble Report 461.

Volume 09 / Number 1 & 2 / July 2009 Potential Impacts of ...

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