Application of Probabilistic Safety Assessment to Rokkasho Reprocessing Plant, (I)

The Occurrence Frequency of Loss of Hydrogen Scavenging Function in Plutonium Solution Vessel

Abstract

In the application of the probabilistic safety assessment (PSA) to a reprocessing plant, target accidents for the assessment should be identified first. The HAZOP method developed for a chemical plant was used to identify abnormal candidate events systematically and comprehensively. Among the many abnormal events thus identified, several typical accidents with high latent consequences were selected for the target accidents of PSA. Among them the PSA for complete loss of scavenging air to prevent explosion of radiolyzed hydrogen in the reservoir of concentrated PuNO₃ solution is taken up. Its occurrence frequency, uncertainty of the frequency and also relative risk-importance of each apparatus and operator's action composing its prevention were evaluated using the method originally developed for the PSA of a nuclear power plant. The frequency was calculated as 8×10^-6/yr. The results showed that the design of the scavenging system of the Rokkasho plant is adequate to prevent the accumulation of hydrogen. In addition, it was shown that even the present results with somewhat large uncertainties could be applied for practical use of risk-informed management of the reprocessing plant due to its low latent consequence compared to a nuclear power plant.