Replacement of Secondary Heat Transport System Components In the Experimental Fast Reactor JOYO

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川原 啓孝 ; 川原 啓孝 ; 市毛 聡 ; 礒崎 和則 ; 仲井 悟

Kawahara, Hirotaka; Kawahara, Hirotaka; Ichige, Satoshi; Isozaki, Kazunori; Nakai, Satoru

高速実験炉「常陽」で進めているMK-III計画では、熱出力がMK-II炉心の100MWtから140MWtに増大する。冷却系除熱能力を高めるための冷却系改造工事で、IHX、主冷却器(DHX)の交換と制御系の改造を行った。ナトリウム系への不純物混入防止のため、シールバッグの使用、系統内カバーガス中の窒素濃度管理、カバーガス低圧力制御を行った。ナトリウム中で長期間使用したフェライト系低合金鋼の健全性、新旧配管溶接部の健全性を材料試験により確認した。

A recently completed major upgrade of the JOYO experimental sodium-cooled fast reactor, to the MK-III design, increased its irradiation capability approximately four times. 0ne major change was a 40% increase in thermal power to 140 MWt, which necessitated the replacement of the heat exchangers. Each of the two coolant loops includes an intermediate heat exchanger (IHX) and sodium pump in the primary system, and two dump heat exchangers (DHXs) and a pump in the secondary system. The heat transfer area of the finned tubes in each (air-cooled) DHX was doubled, compared to the old design, to achieve a 35 MWt rating, Major challenges in the replacement of secondary components, such as piping and DHX, were control of impurity ingress into the sodium system, and integrity assurance of the welding. Damage to existing components and systems was avoided during cutting and welding operations by taking measures to Prevent ingress of air into the sodium systems. The measures included use of seal b