Application of Hazard and Operability Technique to Level 1 Probabilistic Safety Assessment of Thai Research Reactor-1/Modification 1: Internal Events and Human Errors

摘要

The pilot Probabilistic Safety Assessment (PSA) of Thai Research Reactor-1/Modification 1 (TRR-1/M1) was implemented to fulfill the new Thai Ministrial Regulation on Periodic Safety Review (PSR). The paper's objective is to conduct the level 1 PSA of TRR-1/M1 for internal events and human errors. Considering the graded approach, Hazard and Operability (HAZOP) and Human-Hazard and Operability (Human-HAZOP) analyses which require moderate details were selected to assess hazardous events and eventually determine Initiating Events (IEs). Fault Tree Analysis (FTA), Event Tree Analysis (ETA), and Bayesian updating were used to calculate Core Damage Frequencies (CDFs). The assessment showed that HAZOP analysis is suitable for an uncomplicated research reactor like TRR-1/M1 since it does not require lengthy calculation time and detailed failure data. Human-HAZOP analysis revealed inherent-operational errors that were ignored in TRR-1/M1, especially the situation that valves V-3 and V-4 were kept open in order to quicken reactor startup operation. IE1: Loss of Coolant Accident (LOCA), IE2: Insertion of excess reactivity, and IE3: Failure of equipment in fuel handling process were identified as the main IEs. The largest CDF of IE3 (4.36E-02 1/yr) implies that it is the main risk issue of TRR-1/M1 to which operators should pay more attention during the operation.