1 Mai 2017
After the end of WWII, Japan was persuaded by the Allies to embrace nuclear power -- partly as a way of expiating the horror of the Atomic Bomb explosions at Hiroshima and Nagasaki, but mainly as a way of achieving energy independence. To avoid the necessity of purchasing fuels off-island, the Japanese were urged to embrace the nuclear reprocessing option. By routinely extracting plutonium and unfissioned uranium from irradiated nuclear fuel, they were informed, new fuel could be fabricated by blending the recovered plutonium with the unfissioned uranium. This new plutonium-based fuel is called MOX – an acronym for Mixed Oxide fuel. As a result, Japan developed no plans for the long-term storage of irradiated nuclear fuel. Spent fuel was to be regarded as an energy resource rather than as nuclear waste. And as it happens, spent MOX fuel contains even larger amounts of highly toxic radioactive substances than spent uranium fuel from conventional reactors.
The Fugen advanced converter reactor started up in 1978. It was the first reactor in the world to use a full MOX fuel core. It had 772 MOX fuel assemblies, the most for any reactor anywhere. It has received the title of a historic landmark from the American Nuclear Society. The Fugen reactor boiled ordinary water as in standard boiling water reactor (BWR) but used heavy water as a moderator as in a CANDU reactor. The Fugen reactor was shut down permanently in 2005.
The Monju prototype fast breeder reactor (1994-2016) was designed to produce more plutonium as a byproduct than the plutonium it uses as a fuel. That’s why it’s called a “breeder”. But for this breeding process to work, the fuel has to be much more “enriched” in fissile material. It has to be nuclear-weapons-usable material,, capable of sustaining a nuclear chain reaction using “fast neutrons”, without the use of any moderator. That’s why it’s called a “fast” breeder. So, instead of using water as a.coolant (which inevitably slows down the fast neutrons) the Monju reactor uses liquid sodium (a liquid metal) as a coolant. Needless to say, the liquid sodium becomes highly radioactive, just as the primary coolant of any recator is highly radioactive.
The Monju reactor has been inoperative for most of the time since it was first built. It last operated in 2010, and last year it was decided top decommission it. The Japanese have no idea at present how to dispose of the spent fuel or the radioactiuve sodium from Monju. Radioactive sodium is yet another nuclear conundrum.
At Fukushima-Daiichi nuclear power plant, Unit 3 (one of the reactors that suffered a complete core meltdown) was fuelled with a heterogenous core of uranium oxide fuel and plutonium-based mixed oxide fuel (about 6 percent of the fuel was MOX). Unit 3 was the only one of the six reactiors at Fukushima-Daiichi that had MOX fuel in its core.
Japan Times, April 30, 2017
About 610 tons of spent nuclear fuel stored at seven of the 17 reactors in Japan that are set to be decommissioned have no fixed transfer destination, it was learned Sunday, threatening to hold up the decommissioning process.
If it remains undecided where to transfer the spent nuclear fuel, work to dismantle reactor buildings and other structures may not be carried out as planned.
The tally excludes the six reactors at Tokyo Electric Power Co. Holdings Inc.’s Fukushima No. 1 plant, which was heavily damaged by the March 2011 earthquake and tsunami.
The seven reactors are
1) the Japan Atomic Energy Agency’s Fugen advanced converter reactor,
2) the agency’s Monju prototype fast-breeder reactor,
3) Japan Atomic Power Co.’s reactor 1 at its Tsuruga plant,
4-5) reactors 1 and 2 of Kansai Electric Power Co.’s Mihama plant,
6) reactor 1 of Chugoku Electric Power Co.’s Shimane plant and
7) reactor 1 of Kyushu Electric Power Co.’s Genkai plant,
according to the companies and the agency.
The Fugen reactor has 70 tons of spent mixed-oxide, or MOX, fuel, a blend of uranium and plutonium recycled from spent nuclear fuel.
The agency has abandoned its plans to move the MOX fuel out of the reactor site in the current fiscal year to March 2018. It has considered consigning the reprocessing of the fuel overseas but a contract has not been signed yet.
The agency’s schedule to finish the decommissioning work by fiscal 2033 has remained unchanged, but an official admitted that the timetable will be affected if a decision on where to transfer the spent fuel is not made.
As for the trouble-prone Monju reactor, the agency has yet to submit a decommissioning program to authorities. How to deal with 22 tons of spent MOX fuel at the reactor is a major issue.
The Mihama No. 1 reactor has 75.7 tons of spent conventional nuclear fuel and 1.3 tons of spent MOX fuel, while the No. 2 reactor has 202 tons of spent nuclear fuel. Kansai Electric plans to take them out of Fukui Prefecture, which hosts the power plant, by fiscal 2035, but the transfer location has not yet been selected.
At the Tsuruga plant’s reactor 1, Japan Atomic Power plans to transfer 31.1 tons of the reactor’s 50-ton spent nuclear fuel to the fuel pool of reactor 2, with the rest to be transported by fiscal 2026 to a Japan Nuclear Fuel reprocessing plant under construction in the village of Rokkasho in Aomori Prefecture.
After being postponed more than 20 times, the completion of the reprocessing plant is currently slated for the first half of fiscal 2018 and the blueprint is undergoing screenings by the Nuclear Regulation Authority, a nuclear watchdog.
As nuclear fuel cannot be brought into the reprocessing plant until it starts operations after receiving all necessary regulatory approval, it is uncertain whether the Tsuruga reactor fuel can be transferred as planned.
Chugoku Electric aims to transfer 122.7 tons of spent nuclear fuel at its Shimane plant’s reactor 1 to the Rokkasho reprocessing plant by fiscal 2029.
Kyushu Electric hopes to take 97.2 tons of spent nuclear fuel at the Genkai reactor 1 out of its fuel pool by fiscal 2029, but the destination has not been fixed.
At three other nuclear plants with reactors set to be decommissioned, spent nuclear fuel is mostly planned to be moved out of the current pools to other pools within the same plant.
In the case of Tepco’s disaster-stricken Fukushima No. 1 plant, the site of the 2011 triple meltdown accident, where the 2,130 tons of spent nuclear fuel will be transferred to has yet to be decided.
Still, the decommissioning work for the six reactors there will not be affected in any significant way for the time being, as more urgent tasks, such as a survey of melted fuel, have been given higher priority, officials said.