2011年4月13日11時41分
福島第一原発の廃炉や敷地の除染などには「数十年から１００年かかる可能性がある」――。英科学誌ネイチャーは、１１日付電子版で、米スリーマイル島（ＴＭＩ）原子力発電所事故を経験した専門家らの見方を掲載した。
記事によると、福島第一原発の建設の一部を請け負った東芝による「１０年程度」という廃炉計画について、ＴＭＩ処理の経験者は「福島第一原発でははるかに時間がかかるだろう」と述べている。原子炉が安定しておらず、さらに放射性物質が大量に放出される可能性も残っているからだ。
ＴＭＩを経験した別の技術者は、福島第一原発で採用されている沸騰水型炉（ＢＷＲ）は「配管や弁などが密集している」と指摘。ＴＭＩより作業が難しくなる可能性を示唆した。
また記事では、旧ソ連・チェルノブイリ原発では事故から約８０年後に当たる２０６５年まで除染が行われる予定、と言及している。（ワシントン＝勝田敏彦）
福島原発の廃炉作業に最長１００年…英科学誌
【ワシントン＝山田哲朗】英科学誌ネイチャー（電子版）の最新版は、東京電力福島第一原子力発電所の廃炉作業に数十～百年かかるとの見方を紹介する記事を掲載した。
同誌は、１９８６年に国際的な尺度でレベル７の大事故を起こしたチェルノブイリ原発では、放射性物質の汚染除去などの作業が、２０６５年まで続く見通しだと指摘。東芝などが作った１０年計画の廃炉工程表に言及し、実現性に疑問を投げかけている。
５７年に火災事故を起こした英セラフィールド核施設では一時、作業を中断したため、放射線量が下がり、計画を練る余裕ができた。同施設の元幹部は同誌に「封印し、百年がかりで」と提言している。
米スリーマイル島原発の撤去・除染作業にかかわった専門家は、炉ごとにクレーンを備えた建物を作り、炉内作業用ロボットを用意するなどで、準備だけで数か月はかかるとしている。
（2011年4月13日18時04分 読売新聞）
福島原発の廃炉、汚染除去に百年 英科学誌が見解紹介
英科学誌ネイチャーは１３日までに、東京電力福島第１原発の廃炉や周辺の土地の汚染対策が終わるまでには、今後数十年、場合によっては１００年を要するとの専門家の見解をまとめた記事（電子版）を発表した。
記事は１９７９年に米国で発生したスリーマイルアイランド（ＴＭＩ）原発事故処理に加わった複数の専門家の見解に基づき、損傷しているとみられる燃料を含めた炉内の放射性物質の除去に長期間を要する上、原子炉の冷却が進んで中の状況を調べられるようになるまでも長い時間が必要になると指摘。
沸騰水型原子炉の特徴として、多数の配管や弁などが複雑に配置されていること、使用済み燃料を運び出すためのクレーンなどが爆発で破損していることなどによって、福島第１原発の廃炉は「ＴＭＩよりはるかに困難な作業になる」との意見も紹介。
ＴＭＩよりもはるかに大量の汚染水の処理が必要になることからも、８６年に原子炉が爆発し、最終的な対策の除染の終了が２０６５年までかかるとされている旧ソ連の「チェルノブイリ原発と同様の除染対策が必要になるだろう」と指摘した。
2011/04/13 21:31 【共同通信】
Fukushima set for epic clean-up
Latest data suggest a Chernobyl-like effort will be needed.
As the immediate threat from Fukushima Daiichi's damaged nuclear reactors recedes, engineers and scientists are facing up to a clean-up process that could last for many decades, or even a century.
Experts on previous nuclear accidents say that the sheer quantity of nuclear material that needs to be removed from the site, together with the extent of the damage, makes Fukushima a unique challenge. The plant's damaged reactors are home to just under 1,000 tonnes of nuclear fuel and thousands of tonnes of radioactive water (see graphic).
Last week, the Toshiba Corporation floated a rough proposal to clean up the site in a decade. But veterans of clean-up operations at sites such as Three Mile Island in Pennsylvania say that it will probably take much longer. The removal of the radioactive material will require a carefully planned and technologically sophisticated programme, made all the more challenging by the devastation left after partial core meltdowns and explosions.
No clean-up can begin until the reactors are stabilized. Radiation around the plant is beginning to wane, but the threat of further releases has not yet passed. On 7 and 11 April, severe aftershocks struck nearby, raising fears that the three crippled reactors could be damaged further. The Tokyo Electric Power Company (TEPCO), which manages the plant, says that no additional damage has been detected.
A 26 March report from the US Nuclear Regulatory Commission (NRC), leaked to The New York Times, says that massive explosions at the plant in March scattered fuel from the reactors' spent-fuel pools around the site. NRC officials also believe that a portion of the uranium fuel inside the unit 2 reactor may have escaped its stainless steel containment vessel and fallen onto the concrete floor below, although the Japanese government has yet to confirm this. In addition, the document indicates that water is not circulating properly through the cores of the damaged reactors, so it will be necessary to continue to flood them, says Richard Lahey, an emeritus professor of nuclear engineering at Rensselaer Polytechnic Institute in Troy, New York.
This strategy creates its own problems. The reactors' cooling systems are normally a closed circuit. Flooding the cores means that water contaminated with radioisotopes will continue to spill out into the environment. TEPCO has already reported highly radioactive water in buildings and trenches around the site.
Dealing with the water will be a pressing priority for any clean-up operation, according to Jack DeVine, an independent nuclear consultant who spent six years dismantling the unit 2 reactor at Three Mile Island after it partially melted down in 1979. The accident left thousands of tonnes of water laced with radioactive caesium-137 swilling around in the reactor's basement. Over the course of months, the US team built a system that could suck the water out and pass it through radiation-resistant zeolite filters. The zeolite removed the caesium and other radioisotopes, leaving almost pristine water, which was eventually evaporated at a facility on the site. A similar system could work at Fukushima, says DeVine, although the constant leakage from the damaged cores means that any clean-up is a race against time. More than 10,000 tonnes of low-level radioactive water has already had to be dumped from storage tanks into the Pacific Ocean to make way for more-radioactive cooling water (see page 145).
Cleaning up the reactors themselves presents an even greater challenge. Debris and high radiation levels are making it impossible to conduct proper surveys of the damage. In the near term, robots will need to explore the reactor buildings and map the radiation inside, says Red Whittaker, a robotics expert at Carnegie Mellon University in Pittsburgh, Pennsylvania, who has developed systems for other nuclear accidents.
It could be years before anyone can look inside the cores themselves. At Three Mile Island, engineers had to wait three years before radiation levels had fallen sufficiently to allow them to lower a camera through a control rod drive shaft into the heart of the reactor. At Fukushima, it could take longer still. The boiling water reactor (BWR) design used there is sealed with a solid stainless-steel cap that can only be removed by a heavy, fuel-loading crane located above the reactor. Explosions at three of the units with fuel in their cores mean that "their cranes are clearly toast", says DeVine. Plant operators will have to find another way in.
The reactor's design also presents other problems. "The BWR is just a rat's nest of tight spaces, pipes and valves," says DeVine. To effectively remove the fuel, DeVine thinks that one or more new buildings with dedicated cranes must be built around each reactor. "It's not something that will be up in a month or two," he says. Whittaker adds that robots and humans will need to share the work in a methodical, coordinated way. "The nature of these operations is that they are patient and persistent," he says.
Indeed, the effort required seems likely to be more akin to the clean-up strategy at Chernobyl in the Ukraine than that of Three Mile Island. Engineers at Chernobyl are beginning to lay the foundations for a massive €1-billion (US$1.4-billion) enclosure, complete with automated cranes, that will eventually lift apart the sarcophagus of steel and concrete hastily thrown up around the stricken unit 4 reactor in the months after it exploded in 1986. The new building, which is intended to last a century, was agreed in principle in 2001, but will not be completed until at least 2015. Clean-up of the site is scheduled to last until 2065 — almost 80 years after the accident.
TEPCO almost certainly cannot afford a clean-up on this scale. "I think that, ultimately, the government is going to have to pay for it," says Robert Alvarez at the Institute for Policy Studies in Washington DC, who oversaw clean-up of former US nuclear weapons plants during the administration of President Bill Clinton. The government already seems to be mulling whether to take over the utility, shares in which have plunged since the accident.
Given the complexity of the task ahead, some think it may be better to abandon Fukushima entirely — at least for the time being. "My bet would be: you seal it and wait a hundred years," says Alan Johnson, a retired reactor physicist who was head of Britain's Sellafield nuclear processing site in the late 1980s.
Sellafield, once known as Windscale, was in 1957 the site of the United Kingdom's worst nuclear accident, when a reactor's graphite core caught fire. Final decommissioning of the reactor is still at least 20 years away, but the hiatus has allowed radioactive materials to decay and given engineers time to develop the best clean-up strategies possible. "What's the rush in doing it quicker?" asks Johnson.
But natural disasters are rare in England. Given the threat of major earthquakes, tsunamis and typhoons that could strike Japan in the decades to come, DeVine has his doubts about applying the same strategy. "Bottling it up and leaving it seems to me to be a really bad choice," he says.
