Development and validation of a numeric tool for partially degraded core quenching under low injection rates

Abstract

Quenching of reactor core has been studied numerically with the help of several numeric tools reported in literature. These tools have been developed to simulate core quenching under design basis conditions. Hence, most of these tools make use of classical homogeneous equilibrium model of two phase flow which are reported to perform better under high pressure conditions with relatively small temperature gradients. System codes such as RELAP5 make use of two fluid model. Such system codes can simulate core quenching under design basis injection rates (1 g/s per unit length of single fuel pin) prescribed under Emergency Operating Procedures (EOPs). However, because of possibilities of flow path breakage under Severe Accident conditions, the injection rate reaching the core is expected to be lesser than the typical injection rate used for Severe Accident Management Guidelines (SAMG). A numeric tool ‘Program for Degraded Reactor Core Reflood’ (PDRCR) has been developed to simulate quenching of partially degraded reactor core under low injection flow rates. PDRCR has specific modules to tackle issues such as water packing, high temperature gradients in the fuel and simulation of parallel flow paths to account for flow re-distribution in partially ballooned fuel pin condition. This paper presents validation results for PDRCR. The predictions of PDRCR for SEFLEX and DRCRE test facilities and comparison with the experimental results are presented. The predictions of PDRCR are found to be better than RELAP5 for low injection flow conditions.