Web-based post-processor for RELAP5: a development based ...

166 Int. J. Nuclear Energy Science and Technology, Vol. 7, No. 2, 2012

Copyright © 2012 Inderscience Enterprises Ltd.

Web-based post-processor for RELAP5: a development based on LabVIEW

L.A. Macedo*, W.M. Torres, G. Sabundjian, D.A. Andrade and A. Belchior Jr. Nuclear Engineering Center – CEN, Nuclear and Energy Research Institute, IPEN – CNEN/SP, Av. Prof. Lineu Prestes, 2242 Cidade Universitária, CEP 05508-000 São Paulo, Brazil Email: [email protected] Email: [email protected] Email: [email protected] Email: [email protected] Email: [email protected] *Corresponding author

Abstract: This work presents the development of a LabVIEW web-based post-processor for the RELAP5 output. A RELAP5 model was developed for the thermal-hydraulics experimental facility, called Natural Circulation Circuit. A visual basic for application program (Xtrip) was developed to transform binary data file from RELAP5 in an ASCII file. This new output file can be displayed in user-friendly Graphical User Interfaces (GUIs) of the post-processor. Temperatures are showed in a XY plot as a function of time. Other parameters can be selected and displayed in the same way. Void fractions, levels, and also the temperatures are displayed in colour-coded scales on other GUIs. This post-processor allows an easier visual understanding of the thermal hydraulics circuit behaviour for calculated and experimental results. One of the main features of this post-processor is the possibility of information interchange, and distance teaching, via the web. In future work, this post-processor will be coupled to RELAP5 for simultaneous calculation and graphical display.

Keywords: post-processor; RELAP5; LabVIEW; graphical user interface; advanced computing; nuclear reactors; nuclear power; simulations; world wide web.

Reference to this paper should be made as follows: Macedo, L.A., Torres, W.M., Sabundjian, G., Andrade, D.A. and Belchior Jr., A. (2012) ‘Web-based post-processor for RELAP5: a development based on LabVIEW’, Int. J. Nuclear Energy Science and Technology, Vol. 7, No. 2, pp.166–178.

Biographical notes: L.A. Macedo is Senior Researcher of the Nuclear Engineering Center at the Nuclear and Energy Research Institute (IPEN/CNEN – SP). He is Mechanical Engineer from the Engineering School of the Mackenzie University (1984), MSc from the São Paulo University (2001) and PhD from the São Paulo University (2008). He has been working in the experimental area with two-phase flow in the presence of the non-condensable gases and is RELAP5 and LabVIEW user.

W.M. Torres holds a BE Mechanical (1979) from the Guaratingueta Engineering College (FEG-UNESP), MSc (1982) from the Rio de Janeiro Federal University (UFRJ) and PhD (2008) from the São Paulo University. He

Web-based post-processor for RELAP5 167

is Senior Researcher of the Nuclear Engineering Center at the Nuclear and Energy Research Institute (IPEN/CNEN – SP) and is a Researcher in the area of thermal hydraulics, heat transfer and nuclear engineering.

G. Sabundjian is Senior Researcher of the Nuclear Engineering Center at Nuclear and Energy Research Institute (IPEN/CNENSP). She is a Physicist from Catholic University (1978), MSc (1982) and PhD (1999) from São Paulo University. The main activities are concerned with Safety Analysis. She has worked with a group that is responsible for at least some activities, which are: transients and accidents simulation in Nuclear Power Plants, and study of the natural circulation phenomena. Since 2000 she has been collaborating with IPEN graduate programme.

D.A. Andrade is Senior Researcher of the Nuclear Engineering Center at the Nuclear and Energy Research Institute (IPEN/CNEN – SP) in the area of thermal hydraulics, heat transfer, computational fluid dynamics and nuclear engineering. He is a Mechanical Engineer from the Federal University of Uberlândia, 1983 (UFU-Uberlândia-MG); MSc from the Technological Institute of Aeronautics, 1987 (ITA-São José dos Campos, SP) and PhD from the São Paulo University, 1999 (São Paulo).

A. Belchior Jr. is Researcher of the Nuclear Engineering Center at the Nuclear and Energy Research Institute (IPEN/CNEN – SP) in the area of thermal hydraulics, heat transfer, computational fluid dynamics, nuclear engineering and safety analysis. He is a Physicist from the São Paulo University, 1987 (São Paulo); MSc from the São Paulo University, 1992 (São Paulo).

1 Introduction

Advanced computing plays an important role in the design, licensing and operation of nuclear power plants. Modern nuclear reactor systems operate at a complex level. Human reasoning and simple theoretical models are unable to provide the level of understanding required of complex system response to perturbation. Over the last 30 years there has been a great deal of effort devoted to the power utilities, such as those of the US Nuclear Regulatory Commission (NRC) and of foreign organisations, to improve advanced computational tools for simulating system-wide reactor thermalhydraulics behaviour during transient scenarios. Particularly, advanced codes are used to analyse loss of coolant accidents (LOCAs) and transients for light-water nuclear reactors. Lessons learned from simulations performed with these computer codes help to form the basis for decisions concerning the design, operation, and safety of the plant (US Nuclear Regulatory Commission, 2011). RELAP5 (US Nuclear Regulatory Commission, 2001), TRACE (US Nuclear Regulatory Commission, 2010), RETRAN (Computer Simulation & Analysis, 2001), CATHARE (Cathare, 2011) and MARS (Jeong et al., 1999) are the main thermo-hydraulics and accident analysis codes.

Advances in computer technology have made it possible for these codes to run on a personal computer. One of the limiting factors for using of these codes is the complex structure of input/output (I/O code structure). The development of friendly Graphical User Interfaces (GUIs) improves the interpretation of the advanced code results (Kim and Uddin, 2007).

168 L.A. Macedo et al.

Snider et al. (1995) developed the first RELAP5 GUI called Nuclear Plant Analyser (NPA). Later on, other interfaces have been built. Symbolic Nuclear Analysis Package (SNAP) was developed by Eltawila (1996). SNAP supports the RELAP5 and TRACE. An interactive tool, called GUITHARE, was developed by Geffraye et al. (2006) for CATHARE output results. GUITHARE, when used as a pre-processing tool, is a helpful interface to create an input file, which can be imported, edited and modified. A SNAP was also developed for RELAP5 at Krsko nuclear power plant with the aim to help result analysis (Prosek and Mavko, 2011).

Another simulator was successfully created by Yang et al. (2009) for advanced boiling water reactors (ABWRs) to help the design, operation and safety of this plant. It was based on two-separate RELAP5-3D synchronised modules in a platform, called 3-Key Master.

Jeong et al. (2002) developed a severe accident management advisory system with the training simulator, SAMAT, which is an available information source for severe accidents. SAMAT information was reorganised and was provided to the management staff with the objective to reduce uncertainties. This system includes a graphical display for the plant, showing indicators of the equipment status, and the expected plant behavior using the severe accident training simulator.

Another simulator (Diaz and Garrido, 2004) is being used for training of nuclear power plant operators in a safe way. It is based on a complex architecture of simulation models where modern object-oriented methodologies have been applied.

This work presents the development of a Web-Based Post-Processor (WBPP) using LabVIEW (Laboratory Virtual Instrument Engineering Workbench) to display the RELAP5 output. WBPP contributes to the development of new technologies applied to nuclear reactors, especially in thermal-hydraulics safety analyses. This post-processor allows an easier visual understanding of the thermal-hydraulics behaviour of experimental facilities using graphical display interfaces. A numerical model employing RELAP5 was created for the simulation of the thermal-hydraulics experimental facility, called Natural Circulation Circuit (NCC). WBPP can also be used to show experimental results from NCC. The methodology used here is general, and can be easily applied to other analysis codes.

This work also presents a description of the experimental facility and its numerical model, methodology and tools.

2 The NCC experimental facility

NCC is an experimental facility installed at the Nuclear Engineering Center (CEN) of Nuclear and Energy Research Institute (IPEN). It was built to provide thermal-hydraulics data and information for the natural circulation phenomena involved under single and two-phase flow (Torres et al., 2009).

It is a rectangular circuit that is 2600-mm high and 850-mm wide and made of borosilicate glass tubes of 38.1-mm inner diameter and thickness of 4.42 mm. It has a heated section, also in glass tube of 76.2 mm of inner diameter and a length of 880 mm. There are two stainless steel cladding Ni-Cr alloy U-form electric heaters (H1 and H2), connected in parallel to a 220 VAC electric power supply. H1 operates at maximum power (4.4 kW) without adjustment, while the electric power output of H2 can be adjusted in the range from 0 to 100% (0 to 4.4 kW). The heaters have external diameter


of 8.5 mm and the total length is 1200 mm (each). The cooled section consists of a heat exchanger, also in glass, with two internal coils where the cooling water flows. Tap water is pumped from a 2 m3 tank to the heat exchanger. The cooling flow rate is measured by two rotameters. The circuit has an expansion tank opened to atmosphere in order to accommodate the fluid density changes due to the temperature and void fraction changes. This tank is connected to the circuit through a flexible tube at its lower region in order to prevent steam entrance. Approximately 12 litres of demineralised water are used to fill the circuit.

Fifteen 1.5-mm K type (Chromel-Alumel) ungrounded thermocouples are assembled along the circuit to measure the fluid and the ambient temperatures. TEFLON™ sleeves were made to install these thermocouples between the glass tubes. Metallic connections with ‘O rings’ also are used to install the thermocouples along the circuit. Three K type thermocouples with exposed junction are attached on the glass tube wall at the circuit hot leg to estimate the heat losses to the ambient.

Two differential pressure sensors, P1 and P2, are used to measure the relative pressure at the heated section outlet and at the expansion tank inlet, respectively. Electric signals from the instruments are sent to a Data Acquisition System assembled with National Instruments components and programming on LabVIEW. Figures 1 and 2 show, respectively, a schematic drawing and a NCC photo.

Figure 1 NCC schematic draw


Figure 2 NCC photo

3 The NCC RELAP5 model

A RELAP5 nodalisation model, shown in Figure 3, was developed using PIPE and BRANCH components to represent the experimental facility. A good agreement was observed between the experimental data and the output RELAP5 for single and two-phase natural circulation flow (Sabundjian et al., 2010). At initial conditions, except for BRANCH 210 which was filled with air, all other volumes were filled with water, at the


upper region of the expansion tank. Heat losses to the ambient also were considered. This model was able to predict single and two-phase flow conditions. The analysis revealed that the two-phase flow oscillations starts for high void fraction in the upper region of the hot leg. Other initial conditions for simulation were – 8.030 W, 0.03 kg/s, 25°C and 19°C for the heating power, cooling water mass flow rate, water and ambient temperatures, respectively. Table 1 shows the RELAP5 nodalisation and NCC components.

Figure 3 NCC nodalisation


Table 1 RELAP5 nodalisation and NCC components

NCC Component Component Number Component Type

Heater 100 PIPE

Heater – outlet 110 SNGLJUN

Hot leg 120 PIPE

Hot leg – outlet 130 SNGLJUN

Heat exchanger primary 140 PIPE

Heat exchanger primary – outlet 150 SNGLJUN

Cold leg 160 PIPE

Cold leg 170 BRANCH

Cold leg 175 BRANCH

Surge line 180 PIPE

Expansion tank 185 BRANCH



Heat exchanger secondary 220 PIPE

Heat exchanger secondary – inlet 230 TMDPVOL

Heat exchanger secondary – inlet 240 TMDPJUN

Heat exchanger secondary – outlet 250 SNGLJUN

Heat exchanger secondary – outlet 260 TMDPVOL

Containment -environment 500 TMDPVOL

4 Methodology and tools

4.1 Visual basic for application (VBA) program – Xtrip program

The RELAP5 output data, a binary file, are stored in the restart-plot file. It contains all calculated parameters such as pressures, temperatures, void fractions, mass flow rates, etc. The Xtrip is a macro of the Excel Visual Basic program for Application (Belchior Jr. et al., 2011). Xtrip can read the binary restart-plot file and export it to an Excel spreadsheet in ASCII format, which is read by WBPP. Xtrip can also make data unit conversions as well as to export them to other graphical spreadsheet programs.

The following calculated parameters were used in the WBPP: time t (s), ambient temperature Tamb, and water temperatures T11 to T22, all in (°C), mass flow rate (kg/s), expansion tank level (m), void fractions (0 to 100%) and the volume levels (m). Figure 4 shows the Xtrip program front panel for temperatures. Other parameters such as pressure, void fraction, level, and flow rate can be selected using the same front panel.


Figure 4 Xtrip program front panel

4.2 The LabVIEW WBPP

NCC transient simulation produces a large amount of data that are stored in the restart-plot file. The understanding of the transient behaviour through restart-plot file is very difficult and graphical plots can be very helpful. The WBPP was then designed to provide graphical displays of these results so that users can easily follow and visualise the transient behaviour. This post-processor consists of three friendly web-based GUIs that can be accessed to display a wide range of data. Each GUI has two alarms, one for the case of onset boiling temperature at the heater outlet region and the other to indicate the end of the presentation.

LabVIEW was used to develop the post-processor. It is a platform based on the graphical programming in G language, which uses icons instead of command lines to create applications. Its programming is based on dataflow, bringing advantages for scientific and engineering applications, especially in data acquisition systems. Icons are added in a block diagram to make specific functions and results are displayed and controlled through front panel. Many laboratories, experimental facilities, and industries use LabVIEW for control and data acquisition systems (National Instruments, 2011).

WBPP was developed on LabVIEW plataform due to easier programming language and its specific libraries to read different kind of input files (binary and ASCII).

RELAP5 results can be shared online with researchers through WBPP via the World Wide Web. WBPP can be a useful tool for teamwork when there is a need to share results online, allowing interaction among researchers through many geographically distant regions (Kim et al., 2006). It is important to emphasise that as a web-based application, researchers do not need to have LabVIEW software installed on their personal computers in order to use WBPP. Schematic remote panels for web-casting are shown in Figure 5.

Figure 6 shows the WBPP block diagram. ASCII file from Xtrip is read (Figure 6A), concatenated as a string and written step by step by a programming structure FOR LOOP


(Figure 6B). After that, it is converted to a defined dimension array (Figure 6C) and separated in selected variables (Figure 6D). Results will be displayed in XY plots and in colour-coded scale interfaces representing the NCC.

Figure 5 Schematic remote panels

Figure 6 WBPP block diagram

5 Results

WBPP results are presented in the Sections 5.1 and 5.2 for the developed GUIs.


5.1 GUI – NCC XY plots

Figure 7 presents the GUI – NCC front panel for parameters presentation in XY plots, where the temperatures are showed as a function of time for 2 s steps. The presentation speed can be modified using a front panel numerical control (A). The 2D table (B) shows the parameter values being displayed row by row, while the ambient temperature is presented in (C). Other XY plots for inlet and outlet temperatures of heated section and heat exchanger, mass flow rate and expansion tank level can be displayed selecting the corresponding tabs (D, E, F and G) on the front panel. Presentation time is showed in (H).

Figure 7 GUI – NCC XY plots

Results presented in XY plots provide information about parameter behaviour and trends such as – increase, decrease, oscillations, stability, etc. It is easier to understand the temperature behaviour by observing the XY plots instead of data tables. Figure 7 shows the characteristic temperature behaviours for single (smooth) and two-phase (oscillatory) natural circulation flows, which cannot be observed in the data tables. When specific parameter values are desired, data tables are very useful.

5.2 GUI – NCC Colour-Coded Scale: temperatures, void fractions and levels

Colour-Coded Scale interfaces are used frequently in the control tables of process industries including nuclear power plants and research reactors. They provide a fast visualisation of the parameter behaviour, are useful for data interpretation, and in a decision process. Colour-Coded Scales can also be used to show the calculated code parameters for each nodalisation node. Temperatures, void fractions, and levels are displayed in colour-coded scales as a function of time on a graphical interface representing the NCC.


Figure 8 shows the colour-coded scale interface for temperatures and void fractions corresponding to 3200 s of simulation. It is possible to observe the occurrence of high temperatures (saturation) at the hot leg and high void fractions at the upper region of hot leg. Heated section outlet temperature is shown through the indicator (A). There also are two control buttons to accelerate and stop the data presentation. Similar interfaces for temperatures and levels are shown in Figure 9, where the low water levels at the upper region of hot leg can be observed.

Figure 8 GUI – NCC Colour-Coded Scale – temperatures and void fractions

Figure 9 GUI – NCC Colour-Coded Scale – temperatures and levels


6 Conclusions

This work presents the development of a LabVIEW web-based post-processor using the output results of the best-estimate nuclear system analysis code, RELAP5, to be used for graphical user interfaces and webcasting. The output results were obtained by numerical simulations of the Natural Circulation Circuit located at the Nuclear Engineering Center of IPEN using RELAP5. Three user-friendly web-based GUIs were developed with LabVIEW. They allow an easier visual understanding of the thermal-hydraulics behaviour of the NCC for calculated and experimental results. Since the output data are in ASCII, the methodology used is general, and can be easily applied to other advanced codes, experimental facilities, or nuclear power plants. Simulation results can also be shared with researchers through WBPP via the World Wide Web, allowing interaction among research institutions of geographically distant regions.

In future work, the WBPP will be coupled with the RELAP5 code for simultaneous calculation and graphical display. Studies are in developing to concatenate at the same time the output RELAP5 with LabVIEW input file. This tool could serve as a model of data presentation for use by other experimental facilities.

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Web-based post-processor for RELAP5: a development based ...

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