Keywords: boiling water reactors, BWR stability, transient behaviour, time domain simulation, validation, coupled codes, TH/, NK, reactor simulation, RELAP5/, PARCS, thermal hydraulics, neutron kinetics, nuclear reactors, nuclear energy, nuclear power, uncertainties, modelling, unstable conditions, core–plant interaction, local perturbations, plant stability tests
Predicting actual reactor conditions: why time–domain simulation is necessary for BWR stability
Despite two decades of development and successful use of coupled thermal–hydraulics/neutron–kinetics (TH/NK) codes for the analysis of design basis accidents, the application of coupled codes to BWR stability transients remains a formidable challenge. While the issues in physical models and numerical methods can be identified, quantified and managed through special developments and separate–effect tests, other aspects (e.g. coupling, modelling assumptions) can only be addressed through benchmarking on full plant stability tests. However, often incomplete information causes uncertainties, whose significance on the modelling and simulation must be evaluated. The objective of this paper is to define validation data needs that allow prediction of the transient behaviour should an unstable condition occur. It is shown that the confidence in exploiting advantageous features of the coupled TH/NK system codes in dealing with core–plant interaction, transient effects and local perturbations can only be evaluated with well–characterised, well–documented plant stability tests and stability events.