Verification of a CATHENA integrated Point Lepreau plant model for safety analysis

This paper presents an assessment of a CATHENA integrated plant model, which was created by linking together several existing stand-alone and very detailed CATHENA representations of different Point Lepreau systems. The CATHENA code was coupled with LEPCON, a FORTRAN 77 emulation of the Overall Plant Controller, Reactor Regulating System and a large number of analogue controllers. The stand-alone idealizations represent the most relevant Point Lepreau systems such as the Primary Heat Transport, the Pressure and Inventory Control, the Emergency Core Cooling, and the Steam and Feedwater systems. The tests performed to validate the model include steady state calculations at different power levels and several transient simulations. The model was also compared with results from a CATHENA simpler model with a single average channel per pass and the NUCIRC code at 85% power and 102% full power. Although several transient cases were simulated with the integrated model, this paper presents the results from two of those: 1) a failed open LRV and 2) a power maneuver which comprised a power reduction from 103% to 60% F.P., followed by a power increase to 103% F.P. The comparison of the steady state results at 85% full power that are predicted with the model with plant data, the other CATHENA model and the NUCIRC code shows excellent agreement. The comparison of the results at 102% full power with the NUCIRC code shows some disagreement in the PHTS pressures. The outlet header pressure values obtained with CATHENA are closer to the PHTS pressure set point at full power. The discrepancy is due to the higher flow resistance for two-phase flow used in the NUCIRC plant model. The comparison with the results with the CATHENA single average channel model showed very good agreement. The conclusion from the transient simulations is that the model produced correct results. This conclusion can be extended to the current emulation of the Overall Plant Controller and the analogue controllers included in LEPCON to emulate the PlC system, BPC and BLC, and also the ECC system and its associated logic. The overall conclusion indicates that the coupling between the CATHENA representation and LEPCON lead to simulation results that are consistent with the expected behaviour. (author)