Power flattening study of ultra-long cycle fast reactor using thorium fuel

Abstract

SUMMARY: This paper presents a design study of power shape flattening for an optimized ultra-long cycle fast reactor with a power rate of 1000MWe in order to mitigate the power peaking issue and improve the safety with a lower maximum neutron flux and reactivity swing. There are variations in the core designs by loading thorium fuel or zoning fuels in the blanket region and the bottom driver region of ultra-long cycle fast reactor with a power rate of 1000MWe. While it has lower breeding performance in a fast breeder reactor, thorium fuel is one of the promising fuel options for future reactors because of its abundance and its safety characteristics. It has been confirmed that the thorium fuels, when loaded into the center region of a reactor core, lower the power peaking factor from 1.64 to 1.25 after 20years and achieves a more flattened radial power distribution. This consequently reduces the maximum neutron flux and the speed of the active core moving from 3.0cm/year to 2.5cm/year on the average over the 60-year reactor operation. It has been successfully demonstrated that the three-zone core is the most optimized core, has the most flattened radial power shape, and is without any compromise in the nature of long cycle core, from the neutronics point of view, in terms of average discharge burnup and breeding ratio.