Further analysis on Identification of Thermalhydraulic Phenomena for PWR Transient Analysis and Simulation

In the domain of reactor transient simulation, the identification of thermalhydraulic phenomena (THP) plays a major role. The system codes should model all influent THP and should be validated against integral effect tests (IET) and separate effect tests (SET) which cover all influent THP. The uncertainty quantification should cover every model related to an influent THP. A list of 116 THPs synthesizes more than 30 years of OECD and IAEA activities conducted by many world high-level safety analysis experts. It covers all water-cooled reactors and DBA analyses. A new tentative method to identify THP was proposed based on two sources of information, the observed parameter evolutions in transients (depressurization, voiding, refill, heating,..) and the set of balance equations with source and sink terms for convection, diffusion, interfacial transfers, wall transfers. The analysis is made at system, component, and basic process levels. This paper compares the two approaches for the particular case of GEN-2 PWRs. No major contradiction is found. Both methods identified phenomena at system, component, and process level. The 116 list intends to cover system code validation needs and better identified phenomena that require ‘special models’. The use of equations identified many more local process THPs, which may help identifying validation needs and ranking phenomena in a scaling analysis. The comparison confirms a potential synergy and complementarity between the two approaches and suggests further efforts to combine them and complement them in a new international collaborative context. This analysis reports on-going discussions between members of the FONESYS network of system code developers.