How to Clean Up Hundreds of Tons of Melted Nuclear Fuel

In more than 6 years they have not been able to really find yet the melted fuel, despite their beautiful PR stunt last week, and now they talk about which techniques to use to remove it. Maybe they should better find it first before talking about how to remove it, that is if most of it has not been already vented and projected into our skies.

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How to Clean Up Hundreds of Tons of Melted Nuclear Fuel

More than six years after three nuclear reactors melted down in Japan, the country is homing in on the lost fuel inside one of them. Japan’s biggest utility and owner of the wrecked Fukushima Dai-Ichi plant, Tokyo Electric Power Co. Holdings Inc., last week released images that for the first time showed what’s likely melted fuel inside the No. 3 reactor.

If confirmed, the nation will have to devise a way to remove the highly radioactive material, a mixture of melted nuclear fuel and reactor debris known as corium. The cleanup process that may last 40 years and cost 8 trillion yen ($72 billion) will require technology not yet invented.

Here are a few ways the removal could be done, including the government’s preferred approach by taking it out the side:

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Special tools and techniques will have to be developed to undertake such a task that has never been attempted before anywhere in the world,” said Dale Klein, an adviser to Tepco, as the utility is known, and a former chairman of the U.S. Nuclear Regulatory Commission. “Once Tepco has identified the characteristics of this material, then they can develop a plan to remove this material in a safe manner.”

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The search for the fuel has left a trail of dead experimental robots specifically designed to find and photograph the estimated combined 600 metric tons of fuel and debris in the three melted reactors. While the No. 3 reactor was the last unit to be probed, its the first to produce a strong indication of where the fuel came to rest. The removal process is slated to begin in 2021.

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Long-handled devices guided by a television monitor system were developed to remove fuel core debris at Three Mile Island in the U.S. after its 1979 meltdown. The so-called defueling process took from 1985 to 1990 and involved removing the partially melted fuel core from inside the pressure vessel of the No. 2 reactor, which remained intact. Fukushima offers a more complex challenge since three reactors suffered total meltdowns, with melted fuel rupturing pressure vessels and falling to the bottom of the units.

No such effort is being made at Chernobyl, where a concrete sarcophagus was used to entomb the wrecked plant that melted down in 1986.

Technology research and development should focus on removing fuel through the side, the Nuclear Damage Compensation & Decommissioning Facilitation Corp., Tepco’s top government shareholder, said Monday. That method is safer for workers than flooding the reactor, which would also require the management of radioactive water.

Japan will decide how it will remove the fuel by September, Industry Minister Hiroshige Seko said after the discovery last week, according to national broadcaster NHK.

https://www.bloomberg.com/news/articles/2017-07-31/how-japan-could-remove-melted-nuclear-fuel-it-hunted-for-6-years

 

31 july 2017 fuel removal technique

New proposal suggests removing Fukushima plant’s melted nuclear fuel from side

A method to remove melted nuclear fuel debris on the bottom of the containment vessels of Fukushima No. 1 Nuclear Power Plant’s first, second and third reactors from the side was proposed by the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) on July 31.

Hajimu Yamana, head of the NDF, which is tasked with considering how to remove fuel debris from the reactors, for the first time explained the organization’s specific method proposal to the heads of local governments at a countermeasures for the decommissioning and handling of the contaminated water council meeting held in Iwaki, Fukushima Prefecture.

The method would focus on prioritizing the removal of debris from the bottom of the vessels from the side, using robotic arms and other remote devices while flushing water over the debris.

However, ways to block radiation and countermeasures against the scattering of airborne radioactive dust still remain unsolved. The central government and Tokyo Electric Power Co. (TEPCO) plan to finalize their policy to remove the debris and amend the decommission schedule in September.

In all three of the reactors, contaminated water has collected at the bottom of the containment vessels. The NDF had previously considered a “flooding method” that would fill the containment vessels completely with water to block radiation from leaking. However, measures to repair the containment vessels and prevent leakage of the radioactive water would be difficult, so the plan was put aside for having “too many issues.”

https://mainichi.jp/english/articles/20170801/p2a/00m/0na/014000c

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