Development of probabilistic design method for annular fuel. Development of BORNFREE-CEPTAR code

The increase of linear power and burn-up during the reactor operation is considered as one of measures for the utility of fast reactor in future, and then the application of annular fuels is under consideration. In order to make a design for thus annular fuels, annular fuel design code 'CEPTAR' has been developed in Japan Atomic Energy Agency (JAEA). In addition, probabilistic fuel design code 'BORNFREE' has been also developed for the reasonable fuel design with safety and the quantitative evaluation of design margin. In this study, aiming at the development of probabilistic design method, we developed BORNFREE-CEPTAR code to develop the reasonable design method for annular fuels. As the results of probability evaluation of fuel melting at the transient at the initial power increase, by using the probabilistic annular fuel design code 'BORNFREE-CEPTAR', the melting probability for annular fuels was estimated to be approximately two figures lower than that for solid fuels, and the remarkable decrease of melting probability, which was caused by the fuel restructuring effect, was seen in the estimation results for solid fuels, on the other hand, the results for annular fuels indicated that this effect was comparably small. In addition, the permissive linear power for annular fuels tended to enhance from that for solid fuels with the increase of initial central-hole diameter under the similar fuel melting probability condition. This indicated the possibility of higher linear power operation for high-density annular fuels than low-density solid fuels. (author)