Pressurized water reactor - pressurized water reactor

Japanese: 加圧水型軽水炉 - かあつすいがたけいすいろ

A power reactor in which the pressure inside the reactor core (pressure vessel), which contains fuel that generates heat from nuclear fission reactions, is increased to 157 atmospheres by a pressurizer to prevent the cooling water from boiling. The primary cooling water is heated to 320°C in the reactor core, and the heat is transferred to the secondary cooling water by a steam generator outside the reactor. It is then pumped back into the pressure vessel. The secondary cooling water turns into steam to turn the power generating turbine, is cooled in the condenser and turned back into water, and is sent back to the steam generator. In Japan, seawater is used to cool the condenser. In Europe and the United States, lake water or river water is used. In a 1 million kW class nuclear reactor, about 5 tons of primary cooling water passes through the core every hour. If a small hole is developed in the fuel rod, it becomes contaminated with fission products. Even if the fuel rod is not damaged, impurities in the water can become radioactive. The secondary cooling water does not become radioactive unless the steam generator is damaged. The fact that radioactive materials can be contained within the primary system is an advantage in terms of safety. There is no need to shield the turbine building as with boiling water reactors. A standard reactor has four steam generators inside the containment vessel, with approximately 3,400 inverted U-shaped heat transfer tubes through which the primary cooling water passes. They are prone to corrosion and cracking due to heat and vibration. Tubes with holes are plugged and not used, but if the number of tubes increases, the steam generator must be replaced. This system has been adopted by electric power companies in Kansai, Shikoku, Kyushu, and Hokkaido.

(Koshi Atsumi, Asahi Shimbun reporter / 2008)

Source : "Chiezo" published by Asahi Shimbun Publications Co., Ltd. About Chiezo

Japanese:

核分裂反応で熱を発する燃料を収めた炉心(圧力容器内)を加圧器によって157気圧に高め、冷却水が沸騰しないようにした発電炉。一次冷却水は炉心で320℃になり、炉外にある蒸気発生器で二次冷却水に熱を伝える。そのあとポンプで圧力容器に戻される。二次冷却水は蒸気になって発電タービンを回し、復水器で冷やされて水に戻り、また蒸気発生器に送られる。復水器を冷やすために日本では海水が使われる。欧米では湖水か河川水。100万kW級の原子炉では、毎時約5tの一次冷却水が炉心を通る。燃料棒に小さな穴が開いたりすると核分裂生成物で汚染される。燃料棒破損がなくても、水中の不純物が放射能を帯びることがある。二次冷却水は、蒸気発生器に破損がない限り放射能をもつことはない。放射性物質を一次系に閉じ込められることが、安全面で長所となっている。沸騰水型炉のようにタービン建屋を遮蔽(しゃへい)する必要もない。蒸気発生器は標準的な炉では4台が格納容器内にあり、内部に一次冷却水が通る逆U字形の伝熱細管は約3400本。熱や振動により腐食、ひび割れが起きやすい。穴が開いた細管は栓をして不使用とするが、その数が増えると、蒸気発生器を交換しなくてはならない。関西、四国、九州、北海道の各電力会社が採用。

(渥美好司朝日新聞記者／ 2008年)

出典　(株)朝日新聞出版発行「知恵蔵」知恵蔵について　情報

<<: Pressurized water reactor - pressurized water reactor

>>: Compressed thoracotomy - KAATSUKAIKYOU