Evaluation of a freeze-tolerant decay heat removal system redundancy for fluoride salt-cooled high-temperature reactors (FHR)

Abstract

Typical FHRs use a direct reactor auxiliary cooling system (DRACS) for decay heat removal under a variety of accident scenarios where active normal shutdown cooling is unavailable. Response surface method has been used for evaluating the reliability of the passive system. In this paper, a loss of heat sink (LOHS) accident sequence is evaluated using the response surface methodology. Response surfaces on maximum core outlet temperature and DRACS freezing time has been presented for evaluating the effects of friction loss, heat transfer coefficients and partial and full blockages of the DRACS. The present study shows that for one DRACS failure situations, the system is unconditional safe. But, for two DRACSs failure situations, there is probability that peak core outlet temperature (PCOT) will not exceed the allowable temperature. During the LOHS accident, the DRACS would not freeze within 3.33 days. This study will provide an insight for investigating DRACS redundancy and functional failure.