Improved safety measures at Japan Nuclear Fuel Ltd.'s spent nuclear fuel reprocessing plant in Rokkasho, Aomori Prefecture, on Wednesday gained official approval from the Nuclear Regulation Authority. This plant is the centerpiece of the nuclear fuel cycle and pivotal to the nation's energy policy. In this article, The Yomiuri Shimbun explores the fuel cycle, the reprocessing flow and some issues yet to be resolved.
Japan, which has a dearth of its own fossil fuel resources such as oil, must use energy efficiently. This reality was behind the adoption of a policy to use new nuclear fuel made from spent fuel at the nation's nuclear power plants. This process is called the nuclear fuel cycle. Japan began considering the potential for this cycle in the 1950s, around the same time as the nation was introducing a nuclear power generation policy.
Spent nuclear fuel contains uranium and plutonium, which can be reused as nuclear fuel. Chemical treatment and extraction of this uranium and plutonium is called reprocessing.
The government is promoting the use of uranium-plutonium mixed oxide (MOX) fuel, which is made by reprocessing, for pluthermal power generation at commercial nuclear reactors. In 2009, the No. 3 reactor at Kyushu Electric Power Co.'s Genkai nuclear power plant in Saga Prefecture became the first to use MOX fuel. A total of four reactors in Japan have used MOX fuel since the March 2011 nuclear accident at Tokyo Electric Power Company Holdings, Inc.'s Fukushima No. 1 nuclear power plant.
Nevertheless, Japan does not have an operational facility for reprocessing nuclear fuel and processing it into new fuel. Consequently, spent nuclear fuel has been shipped to nations including France and MOX fuel production entrusted to them.
The government also wanted to introduce a next-generation reactor called a fast-breeder reactor as part of the nuclear fuel cycle. Theoretically, generating power by using MOX fuel in this reactor should have produced at least as much fuel as it consumed.
However, the Japan Atomic Energy Agency's Monju prototype fast-breeder reactor in Fukui Prefecture was plagued by problems, and in 2016 the government decided the reactor would be decommissioned. Since then, research and development of such a reactor has slowed to a trickle.
-- Reprocessing stage
Several key operations take place at a reprocessing plant.
First, spent fuel from nuclear plants across Japan is cooled in pools of water and the amount of radioactivity coming off the fuel is lowered to less than 1% of its original level. Next, the fuel rods, which are about three meters long, are sheared into pieces several centimeters long while still in their external metal casing. These metal chips are separated from the uranium and plutonium while being dissolved in nitric acid.
The uranium and plutonium are then separated and purified. Finally, they are denitrated and end up as powdered uranium-plutonium MOX and uranium oxide.
MOX fuel could be produced in Japan if JNFL's fuel plant starts operation after passing the nuclear watchdog's screening process. Uranium oxide will be stored at the reprocessing plant.
The remaining liquid waste cannot be reused and is solidified by being mixed with melted glass. Eventually, this highly radioactive waste will be disposed of underground at a depth of at least 300 meters.
France, Russia and Britain operate reprocessing plants to produce fuel for commercial nuclear power plants, according to the Japan Atomic Industrial Forum, Inc. China plans to construct such a plant. The United States, which had spearheaded development of reprocessing technologies since the 1950s, halted reprocessing operations for commercial nuclear plant fuel in the latter half of the 1970s.
-- Safety steps
JNFL's reprocessing plant has six main buildings to handle radioactive materials and each deals with one step of the process. These buildings are linked on the 390-hectare site by about 1,300 kilometers of pipes. Safety precautions are needed against a criticality accident in which nuclear fission reactions spiral out of control, and also against fires and other emergencies.
According to JNFL, conceivable accidents at the reprocessing plant include a situation in which radioactive effluent boils, and steam containing radioactive substances leaks outside the building. To prepare for such an eventuality, the company will install special equipment that collects this vapor.
Steps to cope with natural disasters have also been carefully considered. The maximum strength of an earthquake expected to strike the plant was revised, and measures to cope with tornadoes and volcanic eruptions are also being implemented.
The Nuclear Regulation Authority screened about 80 items after the company applied for safety checks in 2014. The watchdog will check at least 10,000 pieces of equipment in its future checks of the plant.
Previous accidents at the plant include repeated leaks from the fuel storage pool, and the glass melter broke down during a trial run. Construction of the plant began in 1993, and its completion date has been pushed back 24 times. The construction cost was initially estimated at 760 billion yen, but this has blown out to 2.9 trillion yen.
-- Disposal site undecided
About 16,000 tons of spent fuel is stored at nuclear power plants across Japan. This amounts to at least 70% of the overall storage capacity at these plants. Power utilities are seeking ways to alleviate this problem, such as by boosting the capacity of these storage pools.
When operating at full speed, the reprocessing plant could handle up to 800 tons of spent nuclear fuel each year. The plant is scheduled to operate for 40 years, so it is calculated to be able to reprocess all the stored spent fuel.
However, what to do with the seven tons of plutonium that would be produced annually remains a thorny problem. The four reactors that have conducted pluthermal power generation can consume only a combined 2.3 tons per year. As of the end of 2018, Japan had about 45.7 tons of plutonium, which had been reprocessed overseas. This stockpile was stored in Japan and abroad.
Plutonium is strictly managed around the world because it can be used to make nuclear weapons. In 2018, Japan and the United States automatically extended a bilateral agreement on rules covering the storage and supply of nuclear substances, which allowed Japan to continue using plutonium for peaceful purposes. Despite this, the Japanese government has indicated it plans to reduce this stockpile due to concerns that holding so much plutonium could spark suspicions overseas that Japan might seek to possess nuclear weapons.
Plenty of other problems remain. A final disposal site for highly radioactive waste has yet to be finalized. Aomori Prefecture is one candidate site. However, as the nuclear fuel cycle remains bogged down, the prefecture fears it could gradually end up becoming the chosen site by default.
The government has hammered out a policy to reduce coal-fired thermal power as part of its efforts to combat global warming. In this regard, the necessity of natural energy sources and nuclear power will only increase in the years ahead.
Hiroshi Miyano, head of the Atomic Energy Society of Japan's committee studying the decommissioning of the Fukushima No. 1 nuclear plant's reactors, said, "The government should show more leadership than it has done so far to promote the restart of Japan's nuclear plants."
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