Evaluation on Calculation Accuracy of the Sodium Void Reactivity for Low Void Effect Fast Reactor Cores with Experimental Analyses

Calculation accuracy of the sodium void reactivity for safety-enhanced fast reactor core concepts was evaluated with analyses of critical experiments. In these concepts, heterogeneous core configuration and sodium plenum replacement are adopted to reduce the sodium void reactivity to around zero. In the past, a variety of critical experiments for heterogeneous cores had been carried out in the ZPPR facility, some of which are compiled in the IRPhEP handbook. Further, several experiments for core with sodium plenum had been performed in the BFS-2 facility. Calculation analyses of above mentioned critical experiments have been performed by using the Japanese current reactor physics analytical system. These analyses clarified that accuracy for homogeneous and axially-heterogeneous cores was sufficient, though accuracy for the radially-heterogeneous core and/or core with sodium plenum was not satisfactory. In order to achieve satisfactory accuracy for various types of cores, investigation on several design methods was performed. (author)