Thirty Years’ Experience in RELAP5 Applications at GRNSPG & NINE

The application of RELAP5 at GRNSPG & NINE (Nuclear Research Group of San Piero a Grado–Nuclear and Industrial Engineering) started more than 30 years ago during which several versions of the code have been applied for the analysis of a very large variety of scenarios occurring in facilities and nuclear installations. The present paper has two goals: (1) to summarize the results and main outcomes achieved through the application of RELAP5 to international projects and benchmarks in which GRNSPG & NINE was involved and (2) to qualify the system’s thermal-hydraulic code calculations through the systematic application of a set of developed procedures. Among the analyses performed, this paper will provide insights into the code results and, whenever possible, into the comparison with the reference/experimental data of scenarios measured in (1) integral test facilities: PSB-VVER, ATLAS, PKL, LOBI, LOFT, SPES, PACTEL; (2) separate effect test facilities: BFBT, Neptun, PANDA; (3) research reactors: Experimental Breeder Reactor (EBR); and (4) nuclear power plants: Atucha-II [pressurized heavy water reactor (PHWR)-Konvoi], VVER-1000, Darlington (CANDU). In relation to the methodology developed for qualifying a system thermal-hydraulic code calculation, this paper provides a short description and spot results of the systematic application to the cases mentioned above in respect to some of the following steps: (1) demonstration of the geometrical fidelity; (2) demonstration of the steady-state achievement; (3) qualification at the on-transient level, which implies the characterization of (a) phenomenological windows and (b) relevant thermal-hydraulic aspects; and (4) quantitative analysis to evaluate the accuracy of the code calculation using the fast Fourier transform based method. Finally, the main outcomes of the analyses summarized in this paper are the characterization of the level of assessment of RELAP5 and the demonstration of existence of a robust procedure to qualify system thermal-hydraulic code calculations