Modelling an Unprotected Loss-of-Flow Accident in Research Reactors using the Eureka-2/Rr Code


The main purpose of reactor safety is not to permit any release of radioactivity from the reactor core to the environment. To ensure reactor safety, the reactor must have sufficient margins during normal operation as well as in all possible accidental events, such as reactivity-induced accidents (RIAs), loss-of-coolant accidents (LOCAs), loss-of-flow accidents (LOFAs), etc. This study focuses on LOFA analysis of research reactors with the aim of investigating the impact of an unprotected LOFA on reactor safety. Two different research reactors, one a rod-type reactor with a cylindrical flow channel and another a plate-type reactor with rectangular flow channels, are taken as references for modelling LOFAs in coupled point kinetics, neutronics and thermal hydraulics code EUREKA-2/RR. Initially, LOFAs under protected conditions were simulated for both reactors. Major parameters such as fuel cladding temperature and bulk coolant temperature are evaluated to investigate whether these parameters exceed their safety limit or if any nucleate boiling occurs in the bulk coolant. For a protected LOFA, these parameters are found to remain within their design limit, and the reactor is sufficiently safe. In the case of an unprotected LOFA, although the Training Research and Isotope Production, General Atomics (TRIGA) reactor was found to be safe from the viewpoint of nucleate boiling not occuring in the bulk coolant, both reactors were found to be unsafe because the maximum cladding temperatures for both reactors are above the melting point in the course of an unprotected LOFA.


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