NRAD Reactor Benchmark Update

International Conference on Nuclear CriticalityEdinburgh, Scotland

September 19-22, 2011

Benchmark Evaluation of the NRAD Reactor LEU Core Startup Measurements

John D. BessThomas L. MaddockMargaret A. MarshallIdaho National Laboratory

This paper was prepared at Idaho National Laboratory for the U.S. Department of Energy under Contract Number (DE-AC07-05ID14517)

Neutron Radiography (NRAD) Reactor 250 kW TRIGA Mark II Conversion-type Located at INL

Former PRNC 2-MW reactor 60 U(30/20)ErZrH rods

Formerly HEU FLIP fuel 12 graphite reflectors 3 control rods 2 neutron radiography

beam lines Empty positions for in-

core experimentation Part of Hot Fuels

Examination Facility (HFEF)

2

NG

HIJ

LNK

M

A

B

C

D

E

F

1 2 3 4 5 6

Linear channel

Safety channel 2

Log channelSafety channel 1

Northbeamtube

Eastbeamtube

North beam aperture

East beamaperture

Standard fuel element

Control rodNeutron source (AmBe)

Fuel cluster assembly

Graphitereflectorassembly

Empty grid location

Irradiation positions10-GA50002-04-3

NW NE

SW SE

TRIGA Fuel Conversion

3

NominalDesign Data

HEU(FLIP) Fuel

LEU (30/20)

FuelNumber of Fuel Rods 60 60

Fuel Type UErZrH UErZrH

Uranium Enrichment % 70 19.75

Uranium Density wt-% 8.42 30

Erbium wt-% 1.48 0.90

Zirconium Rod OD, mm 5.715 5.715

Fuel Meat OD, mm 34.823 34.823

Fuel Meat L, mm 381 381

Clad Thickness, mm 0.508 0.508

Clad Material 304 SS 304 SS

Core Configuration OperationalNumber of Fuel Elements 60

Total Mass (g) 2506.5 ± 3.4Uranium Mass (g) 749.9 ± 2.7

235U Mass (g) 148.0 ± 0.6235U Enrichment (%) 19.74 ± 0.02

U Mass Content (wt.%) 29.92 ± 0.09H/Zr Ratio 1.58 ± 0.01

Er Content (wt.%) 0.90 ± 0.02C Content (wt.%) 0.30 ± 0.02

Fuel Element Length (mm) 380.2 ± 0.4Fuel Element Diameter (mm) 34.805 ± 0.003

Cladding Inner Diameter (mm) 34.894 ± 0.005Fuel-Clad Difference (mm) 0.089 ± 0.005

NRAD LEU TRIGA Start-Up Tests March 9 – June 7, 2010 Fuel loading approach

to critical Initial critical

56 fuel rods Rod worths, ER, SDM

Operational core 60 fuel rods Critical, rod worths, ER,

SDM

4

Calorimetric power calibrations 100, 200, 250 kW

Full power operation ER

Graphite reflector movements

Dry tube worth Radiography beam

characterization performed after start-up tests were completed

Current Benchmark Status 60-fuel-rod critical

configuration completed

Available in March 2011 edition of IRPhEP Handbook

http://irphep.inl.gov/ [email protected] To also be available

in 2011 edition of ICSBEP HandbookUseful for storage,

handling, and transportation of UZrH

5

Experiment Evaluation – Uncertainties Extensive Effort

Characterize All Geometries and Compositionso Drawingso Mass Spectrometry

Primary Uncertainties Fuel Parameters

o 234U Contento 236U Contento Er Contento Hf Content

Steel Claddingo Mn Content

6

Water Saturation of Graphite BlocksLargest Single

Uncertainty±0.0021 ∆k (1σ)±$0.28

Total Experimental Uncertainty±0.0027 ∆k (1σ)±$0.36

Effect of Graphite Water Saturation

7

Experiment Evaluation – Biases Simplifications were

neededUnderstand worth

and sensitivity of various components

Develop easier to use benchmark model

Speed up calculation time

Most simplifications caused minor changes in keff

8

Noticeable biasesSimplification of fuel

rod end fittingsRemoval of steel

impuritiesUse of average fuel

compositionReplace control rod

guide tubes with H2OReplace beam line

structure with void Total Bias+0.0012 ± 0.0009 ∆k+$0.16 ± 0.12

Calculated Spectral Data (MCNP5)

9

Model Detailed SimpleCross Section Library ENDF/B-VII.0 ENDF/B-VII.0

keff 1.00805 1.00925±σk 0.00007 0.00007

Neutron Leakage (%) 0.03 2.21

Fission Fraction,by Energy (%)

Thermal(<0.625 eV) 80.38 80.52Intermediate 16.60 16.47

Fast(>100 keV) 3.02 3.01

Fission Fraction,by Isotope (%)

234U 0.015 0.015235U 98.727 98.732236U 0.009 0.009238U 1.249 1.244

Average Number of Neutrons Produced

per Fission2.444 2.444

Energy of AverageNeutron Lethargy

Causing Fission (eV)0.27218 0.26859

Simplified Benchmark Model

10

10-GA50002-145-9Dimensions in cm

65.72251

16.51

Beamfilter tube

Graphitereflector

block

Fuelrod

23.095

19.92

108.73751

1.905

5.08

Fuelmidplane CL

Water

Fullywithdrawncontrol rod

Fullyinserted

control rod

38.1

0.123825

S2

S1

R

Fuel rod

Shim 1 control rod

Shim 2 control rod

Regulating control rod

Graphite reflector block

S1

S2

R

10-GA50002-145-6

Dimensions in cm

Water

13.97

13.97

D 90

Northbeamtube

(void)

East beamtube (void)

Criticality Calculation Results – 60 RodsExperiment keff + Simplification Bias = Benchmark keff

1.0000 + 0.0012 = 1.0012 ± 0.0029 (±$0.39)

AnalysisCode Neutron Library

Calculated Bias Worth ($)keff ± σ

MCNP5

ENDF/B-VII.0 1.00925 ± 0.00007 0.80 1.08JEFF-3.1 1.00719 ± 0.00007 0.60 0.80

JENDL-3.3 1.00633 ± 0.00007 0.51 0.69ENDF/B-VI.8 1.00458 ± 0.00007 0.34 0.45

KENO-VI

ENDF/B-VII.0(238-group) 1.00874 ± 0.00007 0.75 1.01

ENDF/B-VII.0(continuous energy) 1.00450 ± 0.00008 0.33 0.44

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Reactor Physics Calculation Results – 60 Rods

Worth Measurement Experimental ($) DetailedModel ($)

SimpleModel ($)

Graphite Block C1 -0.41 ± 0.07 -0.37 ± 0.01 -0.37 ± 0.01Graphite Block D1 -0.43 ± 0.07 -0.37 ± 0.01 -0.40 ± 0.01Graphite Block F4 -0.45 ± 0.07 -0.29 ± 0.01 -0.31 ± 0.01Graphite Block A5 -0.16 ± 0.07 -0.13 ± 0.01 -0.14 ± 0.01Excess Reactivity 1.13 ± 0.07 1.23 ± 0.02 1.20 ± 0.02Shutdown Margin -6.86 ± 0.32 -7.20 ± 0.10 -7.22 ± 0.10

Shim Rod 1 -2.70 ± 0.17 -2.68 ± 0.04 -2.67 ± 0.04Shim Rod 2 -2.77 ± 0.21 -2.39 ± 0.03 -2.37 ± 0.03

Reg Rod -2.43 ± 0.11 -2.49 ± 0.04 -2.49 ± 0.04Experiment Dry Tube -0.06 ± 0.01 -0.03 ± 0.01 -0.05 ± 0.01

12

Criticality Calculation Results – 56 RodsExperiment keff + Simplification Bias = Benchmark keff

1.0000 + 0.0013 = 1.0013 ± TBD

AnalysisCode Neutron Library

Calculated Bias Worth ($)keff ± σ

MCNP5ENDF/B-VII.0 1.00793 ± 0.00007 0.66 0.89ENDF/B-VI.8 1.00328 ± 0.00007 0.20 0.27

KENO-VI

ENDF/B-VII.0(238-group) 1.00756 ± 0.00007 0.63 0.84

ENDF/B-VII.0(continuous energy) 1.00337 ± 0.00008 0.19 0.26

13

Reactor Physics Calculation Results – 56 Rods

Worth Measurement Experimental ($) DetailedModel ($)

SimpleModel ($)

Excess Reactivity 0.37 ± 0.02 0.40 ± 0.01 0.45 ± 0.01Shutdown Margin -7.60 ± 0.29 -8.93 ± 0.12 -8.90 ± 0.12

Shim Rod 1 -2.78 ± 0.18 -2.98 ± 0.04 -3.02 ± 0.04Shim Rod 2 -2.74 ± 0.18 -2.51 ± 0.04 -2.55 ± 0.04

Reg Rod -2.45 ± 0.14 -2.62 ± 0.04 -2.67 ± 0.04

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Discussion of Current Efforts – I Benchmark

EvaluationWater saturation in

graphite blocko Large uncertaintyo Potential additional

biasModel simplification

o Small biaso Does not account for

large computational bias

o No change in core spectral characteristics

o Beam lines unaffected

15

Computational Bias of 1% Other TRIGAs with same

problemo Musashi Mark II (100 kW)

– MCNP+ENDF/B-Vo Slovenia Mark II (250 kW)

– MCNP+ENDF/B-VII Bias variation

o Quantity of fuelo Cross Section Datao Monte Carlo Code

Reactivity measurements are generally in good agreement

Discussion of Current Efforts – II Cause of Bias?

Cross section and/or code related

Fuel rods significant 235U and 238U

Small difference between JENDL-3.3 and ENDF/B-VII.0 datao JENDL thought to be “more

correct” 91Zr and ZrH S(α,β)

Bias identifiedo Slovenia TRIGA Mark IIo Fuel contains no Ero ICNC 2011 (Sept.)

ZrH S(α,β) calculated differently in JEFF-3.1 and ENDF/B-VII.0

16

Er KENO and MCNP keffvalues agree when Er is

removed Low-lying resonance

approximations in free-gas scattering kernels ?

Currently being investigated

Graphite (Cnat) (n,γ) larger in JENDL-3.3

than ENDF/B-VII.0 (n,γ) increased further

in JENDL-4.0 base on HTGR research

Conclusions Computational bias

exists for UZrH and UErZrH fuelsMCNP and KENOAll cross section data

libraries Reactivity

measurements and neutron spectraNo significant impact

on spectraWorths can be

reasonably calculated

17

Path ForwardImprove quality of

NRAD benchmark model

Investigate differences in codes and cross section data

Develop additional benchmarks to support verification and validation efforts

Future Work – IModel Improvements 234U, 236U, Hf content

in fuelo More accurate values

availableo Reduce uncertainty

– -$0.05o Negligible Bias

– -$0.01 ± 0.01Water Saturation

o Plan to weigh graphite blocks

o Reduce uncertaintyo Properly assess

absolute computational bias

18

Additions to Current Benchmark56-rod critical

configurationo Currently only 60-rod

critical configuration is benchmarked

Reactivity measurementso Shim rods, reg rod,

excess reactivity, shutdown margin, dry tube

Future Work – II NRAD Core Upgrade4 additional fuel rods4 graphite rods

MeasurementsCriticality with 62 and

64 fuel rodsReactivity worth

measurementsFlux wiresBeam line

characterizationEtc.

19

S2

S1

R

Graphite element

Fuel element

Shim 1 control rod

Shim 2 control rod

Regulating control rod

Graphite reflector block

S1

S2

R

11-GA50002-31-3

Dimensions in cm

Water

13.97

13.97

D 90

Northbeamtube

(void)

East beamtube (void)

Future Work – IIIComputational

MethodsContinue to

investigate ErInvestigate thermal

scattering S(α,β) cross sectionso Collaborative effort

20

Additional “To-Do” BenchmarksSNAP 10A/2 water

immersion experiments

Expand NRAD benchmark library

Invite other members of TRIGA community to benchmark their reactors

¿Questions?

21

References Bess, J. D., Maddock, T. L., Marshall, M. A., “Fresh Core Reload of the

Neutron Radiography (NRAD) Reactor with Uranium(20)-Erbium-Zirconium-Hydride Fuel,” INL/EXT-10-19486, Idaho National Laboratory (2010).

International Handbook of Evaluated Reactor Physics Benchmark Experiments, NEA/NSC/DOC(2006)1, OECD-NEA, Paris, France (2011).

Matsumoto, T., Hayakawa, N., “Benchmark Analysis of TRIGA Mark II Reactivity Experiment Using a Continuous Energy Monte Carlo Code MCNP,” J. Nucl. Sci. Tech., 37(12), 1082-1087 (2000).

Snoj, L., Žerovnik, G., Trkov, A., “Analysis of Cross Section Libraries on Zirconium Benchmarks,” Proc. ICNC 2011, Edinburgh, Scotland, September 19-22 (2011).

Jeraj, R., Ravnik, M., “TRIGA Mark II Reactor: U(20)-Zirconium Hydride Fuel Rods in Water with Graphite Reflector,” IEU-COMP-THERM-003, International Handbook of Evaluated Criticality Safety Benchmark Experiments, NEA/NSC/DOC(95)03, OECD-NEA, Paris, France (2010).

Shimakawa, S., Goto, M., Nakagawa, S., Tachibana, Y., “Impact of Capture Cross-Section of Carbon on Nuclear Design for HTGRs,” Proc. HTR 2010, Prague, Czech Republic, October 18-20 (2010).

22

Extra Slides

23

Summary of the Benchmark Process

24

Detailed Model Development

25

Fuel Clusters

26

10-GA50002-74-2

TopAssembly

BottomAssembly

Fuel Rods

10-GA50002-145-4

Dimensions in cm

3.8862

Top View

3.8862

10-GA50002-145-5Dimensions in cm

7.7089

8.10006

Fuel Rods

27

10-GA50002-145-1

Dimensions in cm

58.73751

1.27

38.02

0.079375

8.6868

1.27

8.68680.724535

Top end fitting (SS 304/304L)OD 3.4894 cm

Top axial reflector (graphite)OD 3.27914

Zirconium rodOD 0.5715

Bottom axial reflector (graphite)OD 3.27914

Void gap

U-Er-Zr-H fuelID 0.635, OD 3.4805

Molybdenum poison discOD 3.46964

Cladding (SS 304/304L)ID 3.4894, OD 3.591

Bottom end fitting (SS 304/304L)OD 3.4894

25.875 + 0.000- 0.031

23.125 (REF)

0.180 MIN.

1.370 I.D. (REF)

Top fuel fitting

Bottom fuel fitting

Molybdenum poison disc

Fuel pellets (3)

Zirconium rod

1.414 DIA.NOM. (REF)

Dimensions in inches10-GA50002-76

Cladding

+ 0.003- 0.000

Upperfuel

reflector

Lowerfuel

reflector

Control Rods

28

10-GA50002-145-2

Dimensions in cm

59.436

1.9685

38.1

1.5874

17.78

B C absorberOD 3.014984

Bottom end fitting (Al 6061)OD 3.03276

Top end fitting (Al 6061)OD 3.03276

Void

Cladding (Al 6061)ID 3.03276

OD 3.175

1-1/4" O.D. x 0.028" wallL 23.4Al alloy tube

Boron carbideD 1.187

15.0

23.4023.25

24.00REF

Dimensions in inches10-GA50002-90

Void

Spacer1.187 O. D.0.5 D thruL 0.5

+ 0.000- 0.005

0.750.625

0.1875

0.060+0.000-0.0041/16 DIA

THRU

D 1.194

0.125

+ 0.000- 0.030

2.5

0.5

1.25

0.625

1.194 D0.40 D

1/2-13 UNC-2A

5/8 flats

0.125

0.18750.060

Detail of bottom fitting

1/16 x 1/16 groove

Detail of top fitting

1-1/8" O.D. x 0.035" wall L 6.5Al alloy tube

0.5

+ 0.000- 0.004

Guide Tube

29

Graphite Reflectors

30

10-GA50002-145-3

Dimensions in cm

65.72251

7.366

7.366

0.9525 cm x 45° chamfer

Top View

2.900square

Dimensions in inches

25.875± 0.125

HandleW0170-0089-DE (REF)

Graphite elementreactor grade

Dowel pin0.645 DIA x 1-1/2 LG

Alum 2011-T3, 2 REQD

Tie rod5/8 x 7-7/8 LG

ALUM 2011-T3

AdapterALUM 2011-T3

Hex nut5/8-11 UNC-2B THD

ALUM 2011-T3

D 1.968

10-GA50002-05-1

+ 0.000- 0.030

+ 0.000- 0.100

AdapterW0170-0090-DD (REF)

Screw, HEX SOC HD5/8-11 UNC-2A x 2 LG

ALUM 2011-T32 REQD

0.375 ± 0.030 x 45° ± 5°Chamfer TYP

5/8-11 UNC-2A THDBoth ends

0.656 DIA DRILLx 0.875 ± 0.060 DP

2 places

+ 0.005- 0.002

Photograph of NRAD Tank

31