Enlargement of the Assessment Database for Advanced Computer Codes in relation to the VVER Technology: Benchmark on LB-LOCA Transient in PSB-VVER Facility

The OECD/NEA PSB-VVER project provided unique and useful experimental data from the large-scale PSB-VVER test facility for code validation. This facility represents the scaled down layout of the Russian designed PWR reactors, namely VVER-1000. Five experiments were executed in the project, dealing mainly with the loss of coolant scenarios (small, intermediate, large break loss of coolant accident); a primary to secondary leak and a parametric study (natural circulation test) aimed at the characterization of the VVER system at reduced mass inventory conditions. The comparative analysis described in the paper deals with the analytical exercise on the large break loss of coolant accident experiment (Test 5). Four participants from three different institutions were involved in the benchmark and applied their own analytical models, set up for four different thermal-hydraulic system codes. The benchmark demonstrated that almost all performed post-tests appeared qualified against fixed criteria. Few mismatches between the results and acceptability thresholds are discussed and understood. The analysis involves the relevant features of the input models developed, the steady state conditions and the results of the simulations. The results submitted by the participants are discussed in the paper considering the resulting sequence of main events, the qualitative comparison of selected time trends, the analysis of the relevant thermal-hydraulic aspects and, finally, by the application of the Fast Fourier Transform based method.