A study of safety core design on beam transient for accelerator driven system

Beam transient is the inherent transient on accelerator driven system, and safety analyses on beam transient are performed in the present study. The safety of the core is evaluated by the cladding temperature and the stress state on a cladding from the aspects of short term and long term. Beam shape change and beam incident position change are analyzed. As the result of safety analyses, the rapid increase of the load for a cladding is seen especially in beam incident position change, and the original core design does not fulfill the criteria specified in the present study. The safety core design is investigated in response to the results of safety analyses. The modification of the fuel composition is adopted as the core design approach, and safety analyses are performed for the designed cores. By the introduction of various fuel compositions, the cladding temperature is reduced by about 110degC at most on the normal beam state, and the load for a cladding is relieved to a great degree on the transient conditions. The core design with the modification of the fuel composition is found to be able to satisfy all the criteria. However, the requirements for an accelerator specification are increased, and further development is needed in the accelerator to assure the safety of the core only by the modification of core design. (author)