Enhancing Tehran Research Reactor safety through a Second Shutdown System: A probabilistic safety assessment

One of the conceivable safety features for enhancing safety of a research reactor such as the Tehran Research Reactor (TRR) is a Second Shutdown System (SSS). One innovative SSS is designed with considering the TRR requirements and limitations such as safety, operational problems, neutronic and aging problems. The SSS of TRR is a reliable, independent and diverse shutdown system which can actuate and shut down the reactor following the First Shutdown System (FSS) failure. In the present study, the effect of this new option on upgrading the reactor safety is studied with performing level 1 of Probabilistic Safety Assessment (PSA) using the SAPHIRE code based on the selected initiating events. PSA is increasingly being used as a part of the decision making process to assess the level of safety of nuclear reactors. Considering only internal events in this analysis, it is seen that with the existence of the SSS the failure rate of reactor shutdown system decreases at least to 3.20E-04 of its previous value. The core damage frequency conservatively turns out to decrease at least by the half of the value previously reported to be 8.37E-06/y. In order to enhance the TRR, reactor personnel and other public safety, equipping TRR with a SSS is a rational plan. To avoid accidents which can cause mass environmental damage and human loss is the prime advantage of equipping TRR with this engineered safety feature.