Reactivity-Initiated-Accident Analysis without Scram of a Molten Salt Reactor

Abstract

Recently, a conceptual design of a small MSR, named FUJI-12 has been proposed. FUJI-12 operates with the same fuel salt as the Molten Salt Breeder Reactor (MSBR) designed by ORNL. The authors are interested in the MSR concept due to its high potential in the areas of safety, proliferation resistance, resource sustainability and waste reduction, all necessary requirements for the generation IV nuclear power systems. The authors believe that additional investigations are necessary for future study. From this point of view, the authors have analyzed various reactivity insertion accidents due to control rod malfunctions in FUJI-12. The MSR can be operated with a small excess reactivity. However, at the same time, the delayed neutron fraction is quite small due to the usage of U-233 as fissile material and the circulation of the fuel salt. Therefore, the reactivity insertion accident should be qualitatively evaluated. The reactor transients were analyzed without scram in order to evaluate the severity of such accidents against the safety. Although the total primary system design of FUJI-12 is not completed, and thus, the accident analyses include some crude assumptions, it can be expected that the reactivity insertion accident in FUJI-12 would not result in severe plant conditions.

KEYWORDS:

• molten salt reactor
• reactivity-initiated accident
• transient without scram
• reactor safety
• control rod malfunction
• reactivity coefficient
• safety analysis