Fast breeder reactor

Abbreviation: FBR. A nuclear reactor that uses the high-speed neutrons produced by nuclear fission without slowing them down, causing a nuclear reaction at the same time as the fission to breed nuclear fuel material. In FBRs that have been realized, uranium-plutonium mixed oxide fuel (MOX) is used as fuel, and energy is obtained from the nuclear fission reaction of ²³⁹ Pu by high-speed neutrons, and plutonium is breeding to an amount greater than that consumed by nuclear fission (breeding ratio > 1) through the neutron capture reaction of ²³⁸ U ²³⁸ U + n → ²³⁹ U and two beta decays ( ²³⁹ U → ²³⁹ Np → ²³⁹ Pu). Since no moderator is required, it has a compact structure, and molten sodium is used as a coolant. To prevent the sodium from coming into contact with air and being oxidized, argon is filled into the reactor vessel as an inert atmosphere. There are two types: a tank type in which the reactor core, sodium primary circulation pump, and heat exchanger are housed inside the reactor vessel, and a loop type in which the circulation pump and heat exchanger are connected by piping and placed outside the reactor vessel. The temperature at the reactor outlet is 500-550°C, higher than that of a light water reactor. Monju (Tsuruga, Fukui Prefecture), which is being developed by the Japan Atomic Energy Agency (formerly the Nuclear Cycle Development Institute), is a loop type prototype fast breeder reactor power plant with a thermal output of 710,000 kW and an electrical output of 280,000 kW. It reached criticality in April 1994, but operation has been suspended since due to a sodium leak accident (December 1995), and construction is underway to restart it. A total of 14 FBRs have been in operation around the world, but many are shut down due to sodium handling and other technical problems, or because they have reached the end of their design life. Well-known reactors include France's Superphenix demonstration reactor and the United States' Fermi 1 experimental reactor, but both have stopped operating and are in the process of being dismantled (decommissioned). The sodium will be processed first, but the reactor itself will not be dismantled or removed until radioactive decay has occurred several decades from now. In this situation, Russia is continuing with its FBR plans, due in part to the need to process plutonium from the dismantling of nuclear weapons, and is operating the prototype reactor BN-600. India is also building a 500 MW PFBR prototype reactor following the FBTR experimental reactor which began operation in 1985, and China is also building the experimental reactor CECR.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

略称FBR．核分裂で発生する高速中性子を減速せずにそのまま利用して，核分裂と同時に核反応を起こさせて核燃料物質を増殖させる原子炉．実現されているFBRでは，燃料として，ウラン・プルトニウム混合酸化物燃料(MOX)を用い，高速中性子による ²³⁹Pu の核分裂反応でエネルギーを得て，²³⁸U の中性子捕獲反応 ²³⁸U ＋ n→ ²³⁹U と2回のβ崩壊によって(²³⁹U→ ²³⁹Np→ ²³⁹Pu)，プルトニウムを核分裂により消費された量以上(増殖比 ＞ 1)に増殖する．減速材は不要であるからコンパクトな構造で，冷却材として溶融ナトリウムを使用する．ナトリウムが空気に触れて酸化されることを防ぐために，不活性雰囲気としてアルゴンが原子炉容器に充填される．炉心，ナトリウム一次循環ポンプ，熱交換器を原子炉容器におさめたタンク型と，循環ポンプ，熱交換器とを配管でつなぎ，原子炉容器の外におくループ型の2種類がある．炉出口温度は500～550 ℃ で，軽水炉より高い．日本原子力研究開発機構(旧核燃料サイクル開発機構)が開発を進めている「もんじゅ」(福井県敦賀市)はループ型で，熱出力71万kW，電気出力28万kW の高速増殖炉発電プラントの原型炉である．1994年4月に臨界に達したが，ナトリウム漏えい事故(1995年12月)のため，その後，運転を停止中で，再開に向けて工事が進められている．世界で合計14基のFBRが稼働したが，ナトリウムの取り扱いや，ほかの技術的な問題などから，あるいは設計寿命に達したことによって停止しているものが多い．フランスのスーパーフェニックス実証炉，アメリカのフェルミ1号実験炉などが有名であるが，両炉ともに運転を停止し，解体(デコミッショニング)の段階にある．ナトリウムの処理を先行するが，原子炉本体の解体撤去は放射能減衰を待って数十年後に行われる予定である．このような情勢のなかで，ロシアは核兵器解体によるプルトニウムの処理の必要性などから，FBRの計画が続行中で，原型炉BN-600を運転中である．インドも1985年に運転を開始したFBTR実験炉を受けて500 MW PFBR原型炉を建設中で，中国も実験炉CECRを建設中である．

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