Multi-physics framework for whole-core analysis of transient fuel performance after load following in a pressurised water reactor

Abstract

The increasing deployment of renewable energy sources and greater electrification of demand is requiring more frequent use of load following in pressurised water reactors (PWRs) . A limiting aspect with respect to load following is the thermo-mechanical behaviour of the fuel. Hence a greater use of best-estimate multi-physics tools that can more accurately capture such behaviour during load following manoeuvres – in particular, extended reduced power operation (ERPO) – has become important in recent years. To this end, we have developed a coupled, whole-core analysis framework and demonstrated it with a new generic PWR model. The demonstration is for uncontrolled RCCA bank withdrawal at power (URWAP) faults following a period of ERPO, since such scenarios are often limiting with respect to fuel integrity. The coupled, whole-core analysis framework that was developed consists of the PARCS neutronics code, the RELAP and CTF thermal–hydraulics codes, the ENIGMA fuel performance code, and the NEXUS platform for whole-core fuel performance. The generic PWR model constructed is for a 1240 MWe plant with a modern core design (maximum assembly burnup of 51.0 GWd/tHM, cycle length of 16 months, and an average fuel residence time of 2.3 cycles per assembly). Previous work in the literature on URWAP faults has focused on coupled neutronics and thermal–hydraulics analysis, with fuel performance assessment and the effects of load following neglected. These shortcomings are therefore addressed here. From a fuel performance perspective no fuel was predicted to fail due to pellet-clad interaction (PCI). Of the remaining failure indicators, margin to clad yield stress was most limiting, although no failure was predicted in all cases under the scenarios considered.