Application of Probabilistic Safety Assessment to Rokkasho Reprocessing Plant, (II)
The Occurrence Frequency of Boiling Accident of Highly Active Liquid Waste

Abstract

  A probabilistic safety assessment (PSA) is made on the boiling accident of a highly active liquid waste tank, which may result in significant consequences, in accordance with the procedure for PSA developed for nuclear power plants. Obtained as results are the frequency of boiling accident of a certain tank of 2.0×10⁻⁸/y (frequency of boiling accident of any tank of 4.1×10⁻⁸/y), its error factor of approx. 6, and information on the relative risk importance based on the FV index and RAW for various components, systems and activities of personnel and on the sensitivity of key parameters. Furthermore, the effect of the time required for repairing failed instruments on the frequency of accident, how to deal with the common cause of failure of the duplicated dynamic components, one of which is at least in operation, and conservative exposure dose in the event of an accident are examined. The database for the Rokkasho reprocessing plant has not been established yet, but the PSA results utilizing available failure rate databases of existing nuclear power plants and reprocessing plants in Japan and abroad can be used effectively to optimize operations and maintenance, if they are interpreted properly and some uncertainties are taken into account.