A study of the probabilistic risk assessment to the dry storage system of spent nuclear fuel

Abstract

Due to the large power supply in the energy market since 1960s, the nuclear power planets have been consistently constructed throughout the world in order to maintain and supply sufficient fundamental power generation. Up to now, most of the planets have been operated to a point where the spent fuel pool has reached its design capacity volume. To prevent the plant from shutdown due to the spent fuel pool exceeding the design capacity, the dry cask storage can provides a solution for both the spent fuel pool capacity and the mid-term storage method for the spent fuel bundles at nuclear power planet. Currently, the dry cask storage system and relevant operating procedures have also gradually been deployed and consistently developed in order to facilitate the dry storage for the spent fuel bundles. In other words, spent fuel bundles dry storage and its safety has become an important issue and will directly affect the smooth operation of the plants once the spent fuel pool reaches its design capacity. Plants in the United States, Nuclear Regulatory Commission, the Office of Nuclear Material Safety and Safeguards (NMSS), the Office of Nuclear Regulatory Research (RES) and Spent Fuel Project Office (NMSS) have jointly developed a pilot methodology for probabilistic risk assessments. Adopting quantitative and qualitative evaluating methods to the subject BWR plants based on the handling, transfer and storage three phases. Obtaining the annual risk for one cask in terms of the individual probability of a prompt fatality within 1.6 km and a latent cancer fatality within 16 km can provide useful risk information for the subject BWR plant. This pilot study used NUREG-1864 [1],“A Pilot Probabilistic Risk Assessment of a Dry Cask Storage System at a Nuclear Power Planet”, related generic data and built prototype models for risk assessments in Taiwan Nuclear Power Plants. This pilot study investigated the handling, transfer and storage three phases to establish its risk evaluating methodologies, which includes initialing events, failure probabilities for canister and cask under mechanical loads and proceeded risk assessment for all three phases using quantitative fault tree analysis. The results of this study can be as a reference for future more detailed developments of the dry cask storage system risk assessments at Taiwan Nuclear Power Plants.