A Conceptual design study of a small natural convection lead-bismuth cooled reactor without refueling for 30 years

30年間燃料無交換の自然循環鉛ビスマス冷却小型炉の概念設計検討

近澤 佳隆  ; 此村 守; 水野 朋保; 水戸 誠*; 丹治 幹雄*

Chikazawa, Yoshitaka; Konomura, Mamoru; Mizuno, Tomoyasu; Mito, Makoto*; Tanji, Mikio*

実用化戦略調査研究フェーズIIの一環として、分散電源を想定して、経済性、安全性などの要求条件を満たす鉛ビスマス冷却小型炉の概念設計を実施した。炉心設計では窒化物燃料、ダクトレス集合体を使用した炉心の採用により、30年以上の長寿命を達成した。プラント設計では、自然循環方式の採用や、原子炉容器内への蒸気発生器設置によりシステムを簡素化した。安全性の面では固有・受動的安全性によりATWS発生時に、高温整定し、炉心損傷防止する概念の可能性を追求した。経済性は都市部電源としては割高だが、燃料無交換壁地電源として有望なことが明らかになった。

Small fast reactors have a potential to be utilized as a power source applicable to diversified social needs and reduce capital risks. In remote sites such as Alaska and Hawaii, power sources without refueling whose capacities are lower than 50 MW-electric are required, because fuel transfer cost is expensive in such sites. In the case of power sources for developing countries, capacities are required in a range 50-300 MW-electric and proliferation resistance must be enhanced. A solution of a power plant without refueling is a fast reactor plant with a very long life core and proliferation resistance in such a plant is supposed to be tough. We have studied concepts of small fast reactor with various attractiveness such as economical competitiveness, reactor safety and very long lived core. In this study, a design concept of a small lead-bismuth cooled reactor, which pursues long operating cycle and inherent safety has been studied. The core is nitride fueled two regions homogeneous core cooled by natural circulated lead-bismuth eutectic. The burnup reactivity is kept 0.93 %dk/k and without refueling 30 years operation with 7.8 GWd/t average burnup. Since lead-bismuth eutectic is chemically inert in lead-bismuth-water contact, a simple tank type design with the steam generator in the reactor vessel is adopted eliminating an intermediate circuit system. The transient analysis shows the reactor has possible capability to keep the reactor system and fuel integrity in UTOP and ULOHS events. The target construction cost for remote sites is achieved by the first plant with 50 MW-electric capacity. The economical target of power sources for developing countries cities is also achieved in the condition of 150 MW electric power regarding series effect.