Risk analysis in molten salt reactors (MSR)

In this study, reliability assessment was performed for molten salt reactors using probabilistic risk analysis method. Fuel salt drain system, heat removal system and off-gas systems were shown schematically and reliability values were calculated. Component reliabilities used in calculations were obtained from components with similar structures and functions in commercially used reactor types. Reliabilities were calculated by performing fault tree analysis for each system. Reliability value for fuel salt drain system was found as 0.9487. Reliability for heat removal system was found as 0.8731. Reliability for off-gas system was obtained as 0.7833. Reliabilities for containment systems of reactor were obtained from similar armor barriers in literature and were found as 0.9999 for primary containment barrier, 0.9999 for secondary containment barrier and 0.999999 for reactor building, respectively. When the reliability values obtained for all systems are compared with the reliability values of the safety systems in boiling water reactors, it is seen that the reliability values calculated for the fuel salt drain system, primary containment barrier, secondary containment barrier and reactor building are close to the boiling water reactor safety system values and at reasonable values. It is seen that the reliability values calculated for the heat removal system and off-gas system are lower than the safety system values of boiling water reactors. An event tree analysis was performed for the pump accident and fission product release initial events. The success rate against pump accident was found to be 0.9999. The success rate against fission product release was obtained as 0.9999. It was seen that the safety system designs for molten salt reactors should be improved. It is seen that the protection of the reactor in case of an accident is provided by successively added systems in accordance with the defense in depth principle.