Investigation of safety for accelerator driven system; Investigation for abnormal event and safety analysis for accident event

Sugawara, Takanori  ; Nishihara, Kenji  ; Tsujimoto, Kazufumi ; Kurata, Yuji; Oigawa, Hiroyuki 

It is supposed that the Accelerator Driven System (ADS) is safer than other critical systems such as Fast Reactors since the ADS is driven by the external neutron source in the subcritical state. In this study, the investigation to confirm the possibility of Core Disruptive Accident (CDA) for the ADS was performed by Level 1 PSA and detailed safety analyses. Abnormal events for the ADS were sorted by Level 1 PSA and calculation cases for the safety analysis were discussed. Based on these results, safety analyses for Unprotected Transient Over Power (UTOP) and Unprotected Loss of Flow (ULOF) were carried out. These results showed that there were hardly possibilities of CDA for the ADS. In the beyond design basis accidents (UTOP and ULOF), it was considered that the creep rupture of the clad tube would happen. However, the frequency of the accidents was exceedingly small. It was concluded that the ADS had very little possibility of CDA or the re-criticality accident.