Benchmark based on NUPEC PWR Sub-channel Bundle Tests

OECD Nuclear Energy Agency (NEA), Penn State University (PSU), Japan Nuclear Safety Organisation (JNES) and US Nuclear Regulatory Commission (US NRC)

Definition of the Benchmark

An approach, similar to the OECD/NRC BFBT benchmark, is adopted by dividing the PSBT benchmark activity in Phases. Each Phase consists of several Exercises. It is desirable also to plan the benchmark specification to accept as many potential numerical approaches as possible.

The NUPEC PSBT benchmark will consist of two Phases, with each Phase consisting of three Exercises. The Phase I is the Void distribution benchmark, and Phase II is the DNB benchmark. The participants can choose either of the following two Phases and any of the Exercises within the Phases to take part and contribute. The preliminary indications show that a sufficient number of participants will attempt both Phases with different numerical approaches.

In addition to the measured experimental data and the relevant boundary conditions, the detailed geometrical data of mock-up assemblies, spacers and the test loop will be included as far as possible in the specification in order to allow a wide range of numerical modelling. Below is the definition of the corresponding Exercises of the two Phases:

Phase I: Void Distribution Benchmark

Exercise I-1: Steady-State Single Sub-channel Benchmark

The goal of this exercise is to benchmark the subchannel, meso- and microscopic numerical approaches. The experimental data includes CT scan measurements of the subchannel averaged void fraction in four subchannel types: typical central, central with a guide tube, side, and corner. In addition, graphical images of the void distribution within the typical central subchannels and central subchannel with guide tube are available. The test cases are selected at PWR rated conditions. Different types of single subchannel test assemblies are used to investigate the effect of geometry on phenomenon in concern.

Exercise I-2: Steady-State Bundle Benchmark

This exercise is designed for benchmarking meso-scopic numerical approaches. The experimental data includes X-ray densitometer measurements of void fraction (chordal averaged over the four central subchannels) at three axial elevations along the bundle length and graphical images of the bundle void distribution. The test cases for this exercise are chosen at PWR rated conditions and deviations of quality from the rated conditions.

Exercise I-3: Transient Bundle Benchmark

NUPEC PSBT database includes simulation of four representative transients of PWRs; power increase, flow reduction, depressurization, and temperature increase. All four transients are selected as benchmark cases. The experimental data includes time histories of X-ray densitometer measurements of void fraction (chordal averaged over the four central subchannels) at three axial elevations along the bundle length for four transient scenarios: power increase; flow reduction; depressurization; and temperature increase. Exercise 3 of Phase I is designed for benchmarking subchannel numerical approaches.

Exercise I-4: Pressure Drop Benchmark

This exercise is designed for performing code-to-code comparisons concerning axial pressure drop. Although no empirical data is available, code results will be compared with relevant graphical data.

Phase II: DNB Benchmark

Exercise II-1: Steady-State Fluid Temperature Benchmark

Exercise 1 of Phase II is designed to assess the thermal-hydraulic codes' capabilities of predicting the exit coolant temperature. The experimental data includes measurements of the subchannel-averaged fluid outlet temperatures.

Exercise II-2: Steady-State DNB Benchmark

The goal of Exercise 2 of Phase II is to assess the thermal-hydraulic codes' capabilities of correct prediction of DNB along rod bundles. The experimental data includes the power at which DNB occurs and the corresponding locations in the bundle.

Exercise II-3: Transient DNB Benchmark

Exercise 3 of Phase II is designed to enhance the currently underway development of truly mechanistic models for DNB prediction during the four postulated transients in PWRs. The experimental data includes the time histories of the boundary conditions and the detected DNB time for four transient scenarios: power increase; flow reduction; depressurization; and temperature increase.

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Last reviewed: 23 March 2016

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