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2011-03-24

〔★★★★★ 原発NEWS〕 海水注入 炉内残留の塩分で燃料棒被覆破壊の恐れ   2・3号機ではそれぞれ45トンの推定も

  ニューヨーク・タイムズによると、世界の「フクシマ型」原発(炉)の専門家グループが、炉内への海水の注入に対して懸念を表明していることを、日本の政府当局者が明らかにした。

 日本の当局は、注入した海水について、「海水の一部は海に戻っている」という表現で報告しているが、これは海水に混じった塩の一部が炉内に残留していることを意味する。

 残留した塩の一部は炉の底に沈殿すると見られるが、ミネアル分を多く含んだ地域の湯沸しがひび割れを起こしやすいように、燃料棒のジルクコウム被覆を破壊する恐れが出ている。

 米国の専門家によると、「1号機」には5万7千ポンド(25.85トン)、2号機、3号機ではそれぞれ9万9千ポンド(44・91トン)の塩が貯まっているとみられる。 
 ⇒ http://www.nytimes.com/2011/03/24/world/asia/24nuclear.html?partner=rss&emc=rss

 Richard T. Lahey Jr., who was General Electric’s chief of safety research for boiling-water reactors when the company installed them at the Fukushima Daiichi plant, said that as seawater was pumped into the reactors and boiled away, it left more and more salt behind.

 He estimates that 57,000 pounds of salt have accumulated in Reactor No. 1 and 99,000 pounds apiece in Reactors No. 2 and 3, which are larger.

 The big question is how much of that salt is still mixed with water and how much now forms a crust on the uranium fuel rods.

 Crusts insulate the rods from the water and allow them to heat up. If the crusts are thick enough, they can block water from circulating between the fuel rods. As the rods heat up, their zirconium cladding can rupture, which releases gaseous radioactive iodine inside, and may even cause the uranium to melt and release much more radioactive material.

 Some of the salt might be settling to the bottom of the reactor vessel rather than sticking to the fuel rods. But just as a heating element repeatedly used to warm tea in a mug tends to become encrusted in cities where the tap water is rich with minerals, boiling seawater is likely to leave salt mainly on the fuel rods.

 The Japanese have reported that some of the seawater used for cooling has returned to the ocean, suggesting that some of the salt may have flowed out again. But clearly a significant amount remains.

 A Japanese nuclear safety regulator said on Wednesday that plans were under way to fix a piece of equipment that would allow freshwater instead of seawater to be pumped in.

 He said that an informal international group of experts on boiling-water reactors was increasingly worried about salt accumulation and was inclined to recommend that the Japanese try to flood each reactor vessel’s containment building with cold water in an effort to prevent the uranium from melting down. That approach might make it harder to release steam from the reactors as part of the “feed-and-bleed” process that was being used to cool them, but that was a risk worth taking, he said.

Posted by 大沼安史 at 12:37 午後 |

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