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<<   作成日時 : 2011/03/18 20:02   >>

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 燃料棒冷却との苦闘は数週間つづく
 水曜日にワシントンでは第4号炉の脅威を強調したが、日本の当局は再利用プルトニウムを含んだMOX燃料を搭載した第3号炉がより大きな脅威であると考えて、軍によるヘリコプターと特殊な放水車による放水を実施した。
 西欧の核技術者は大気へのMOXの放出がウラン燃料棒の分散より危険な放射性プリューム(プルトニウム放射能雲)を産生するだろうと言う。3号炉の圧力が急激に低下したことを当局は発表しており既に破裂した可能性がある。1時間に約250ミリシーベルトの放射能が上空100フィートで検出された。これは米国での警察官・消防士・救急隊員に対する生涯被曝量基準に等しい。
 オバマ大統領は、放射線管理専門の軍事部隊を含めた追加の支援を菅総理に説明したと言い、国防総省は9人のアセスメントチームがまもなく到着する予定だと公表した。米軍は破損した原発の情報を集めている。Global Hawk drone が現場上空を飛行し、U-2偵察機は、日本政府が地震と津波への対応計画を手助けするために画像を提供した。
 木曜早朝に、日本軍は合計約8,000ガロンの海水をヘリコプターから3号炉に投下した。日本政府は1日50トン(約12,000ガロン)が冷却には必要だとしている。午後には、放水トラックを使用する計画である。
(NYT)
画像

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日本の原子力発電所で重大事故が起きる可能性にMOX燃料の使用が与える影響
エドウィン・S・ライマン (PhD) 核管理研究所(NCI)科学部長 1999年10月
http://kakujoho.net/mox/mox99Lyman.html

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With Quest to Cool Fuel Rods Stumbling, U.S. Sees ‘Weeks’ of Struggle
http://www.nytimes.com/2011/03/18/world/asia/18nuclear.html

By NORIMITSU ONISHI, DAVID E. SANGER and MATTHEW L. WALD
Published: March 17, 2011

TOKYO ― Amid widening alarm in the United States and elsewhere about Japan’s nuclear crisis, military fire trucks began spraying cooling water on spent fuel rods at the country’s stricken nuclear power station late Thursday after earlier efforts to cool the rods failed, Japanese officials said.

The United States’ top nuclear official followed up his bleak appraisal of the grave situation at the plant the day before with a caution that it would “take some time, possibly weeks,” to resolve.

The developments came as the authorities reached for ever more desperate and unconventional methods to cool damaged reactors, deploying helicopters and water cannons in a race to prevent perilous overheating in the spent rods of the No. 3 reactor.

Moments before the military trucks began spraying, police officers in water cannon trucks were forced back by high levels of radiation in the same area. The police had been trying to get within 50 yards of the reactor, one of six at the plant.

The five specially fitted military trucks sprayed water for about an hour, but the full impact of the tactic was not immediately clear.

The Japanese efforts focused on a different part of the Fukushima Daiichi Nuclear Power Station, 140 miles northeast of here, from the reactor ― No. 4 ― depicted in Washington on Wednesday as presenting a far bleaker threat than the Japanese government had offered.

The decision to focus on the No. 3 reactor appeared to suggest that Japanese officials believe it is a greater threat, since it is the only one at the site loaded with a mixed fuel known as mox, for mixed oxide, which includes reclaimed plutonium.

Western nuclear engineers have said that the release of mox into the atmosphere would produce a more dangerous radioactive plume than the dispersal of uranium fuel rods at the site. The Japanese authorities also expressed concern on Wednesday that the pressure in the No. 3 reactor had plunged and that either gauges were malfunctioning or a rupture had already occurred.

After the military’s effort to cool the spent fuel atop the reactor with fire trucks, Hidehiko Nishiyama, deputy director-general of the Nuclear and Industrial Safety Agency, said it was too early to assess the success of the attempt.

Mr. Nishiyama also said that radiation of about 250 millisievert an hour had been detected 100 feet above the plant. In the United States the limit for police officers, firefighters and other emergency workers engaged in life-saving activity as a once-in-a-lifetime exposure is equal to being exposed to 250 millisieverts for a full hour. The radiation figures provided by the Japanese Self-Defense Force may provide an indication of why a helicopter turned back on Wednesday from an attempt to dump cold water on a storage pool at the plant.

A White House statement late Wednesday said that President Obama had “briefed Prime Minister Kan on the additional support being provided by the U.S., including specialized military assets with expertise in nuclear response and consequence management.”

On Thursday a Pentagon spokesman, Col. David Lapan, said the military expertise made available to the Japanese included a nine-person assessment team that has or will shortly arrive there to work with the Japanese military and government.

The team members, Colonel Lapan said, will then recommend whether additional American military forces are needed to assist in the effort.

The American military is also gathering information on the damaged nuclear power plant. Officials said that a Global Hawk drone was flying missions over the reactor. In addition, U-2 spy planes were providing images to help the Japanese government map out its response to the quake and tsunami.

Earlier Thursday Japanese military forces tried to dump seawater from a helicopter on Reactor No. 3, making four passes and dropping a total of about 8,000 gallons as a plume of white smoke billowed. The Japanese government said that the reactor typically needs 50 tons of water, or about 12,000 gallons, a day to keep from overheating.

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