Comparison of FIREBIRD III and CATHENA Code Simulations of a 100 Percent Reactor Outlet Header Break

Abstract

The objective of this study was to compare the predictions of a homogeneous thermalhydraulic code (FIREBIRD-III MOD1) with an advanced two-fluid code (CATHENA) for a postulated CAW LOCA scenario, a 100% ROH break with pumps running. A CATHENA model was generated to resemble, as closely as possible, the existing FIREBIRD-III MOD1 model for the CANDU-600 reactor. Simulations were performed with each of the codes to 200 seconds using H2O as coolant in the primary heat transport system, as H2O will dominate after emergency core coolant injection following the short blowdown phase. FIREBIRD and CATHENA simulation results are compared, with emphasis placed on how the two codes model thermalhydraulic non-equilibrium effects associated with cold water injection into steam. There are differences in predicted refill of the broken (non-critical) core pass, due to the treatment of cold injection water mixing in the inlet header with hot fluid from the steam generator. For the critical core pass, the agreement in the refill predictions between the two codes is very good.