There are no prospects that spent mixed-oxide (MOX) fuel, made by reprocessing spent nuclear material, can be further reprocessed and reused for nuclear power generation in accordance with the Japanese government's energy policy. Storing such fuel for a long period has thus raised safety concerns.
Shikoku Electric Power Co. showed work to replace and store MOX fuel in the No. 3 reactor building at its Ikata Nuclear Power Plant to media outlets on Jan. 14.
It was the first time that the company has removed spent MOX fuel since it began to use MOX fuel -- produced by extracting plutonium and other reusable nuclear materials from spent nuclear fuel and mixing them with uranium -- for commercial power generation at the plant.
An employee operated a crane to extract MOX fuel rods, each of which is about 4.1 meters long and weighs some 700 kilograms, from the reactor core and transfer them into a storage pool one by one inside the reactor building.
According to the company, work to extract spent nuclear fuel rods began on the evening of Jan. 13, and will have removed 16 rods by Jan. 16. In early March five new rods will be inserted into the core. The firm will keep cooling down spent MOX fuel in the pool for more than 10 years.
However, the Nuclear Regulation Authority (NRA) has expressed concerns that the storage of spent MOX fuel in the pool over such a long period is highly dangerous. In case of a power blackout, the temperature of the water in the pool could not be maintained at a certain level and it would become unable to cool the fuel just as was the case with the Fukushima nuclear crisis.
"From the viewpoint of safety, it's undesirable that a large number of such rods are preserved," said NRA Chairman Toyoshi Fuketa.
Furthermore, spent MOX fuel generates heat about three to five times that generated by ordinary used nuclear fuel. In case of trouble with a cooling system, such MOX fuel would be far more dangerous than conventional spent nuclear material.
Nevertheless, an employee of an electric power company confessed that the firm "has no leeway to think about what it should do after cooling down spent MOX fuel."
Pools holding spent fuel at nuclear power plants are almost full, and utilities operating atomic power stations are struggling to find places to store the material.
The Federation of Electric Power Companies of Japan (FEPC) intends to use MOX fuel in 16 to 18 nuclear reactors across the country. Tokyo Electric Power Company Holdings Inc. (TEPCO) and Chubu Electric Power Co. had planned to use MOX fuel in the No. 3 reactor at the Kashiwazaki-Kariwa Nuclear Power Plant in Niigata Prefecture, and the No. 4 unit at the Hamaoka Nuclear Power Plant in Shizuoka Prefecture, respectively.
However, such fuel is being used at only four reactors -- Ikata's No. 3 reactor, the No. 3 and 4 reactors at Kansai Electric Power Co.'s Takahama plant in Fukui Prefecture and the No. 3 unit at Kyushu Electric Power Co.'s Genkai complex in Saga Prefecture.
If MOX fuel is used at more reactors, the amount of spent material will keep increasing. However, utilities are dealing with the problem by shifting fuel whose heat generation volume has declined to facilities where the spent fuel is air-cooled.
The government is aiming to reprocess spent MOX fuel to reuse it in an effort to "effectively utilize resources." If spent nuclear fuel including MOX fuel were to be disposed of as radioactive waste, the government's atomic power policy based on the assumption that spent nuclear fuel should be reused would waver.
Japan and France are the only countries in the world that are still working on the extraction of reusable nuclear materials from spent MOX fuel. Japan's Agency for Natural Resources and Energy will have allocated a total of 1.4 billion yen from state budgets in fiscal 2019 and 2020 for basic research on reuse of spent MOX fuel, and will earmark more funds through fiscal 2024.
However, it remains to be seen how far such technology can be developed in the foreseeable future.
"There have been no research achievements enabling the commercial use of the technology," said an official of the Japan Atomic Energy Agency.
Even if the technology to reuse spent MOX fuel is developed, there is a possibility that sufficient funds will not be secured to put it into commercial use unless idled nuclear power stations are restarted steadily because massive amounts of money are needed just for reprocessing spent nuclear fuel. Many atomic power stations remain offline because safety regulatory standards for such facilities have been stiffened following the outbreak of the Fukushima nuclear crisis in March 2011.
An official of the Agency for Natural Resources and Energy said the reprocessing and reuse of spent MOX fuel is not a priority.
"There is approximately 19,000 metric tons of ordinary spent nuclear fuel that hasn't been reprocessed in Japan, and priority is placed on reprocessing such material into MOX fuel. The volume of spent MOX fuel is extremely small, and we're not working fast enough to consider how to reuse such fuel," said the official.
(Japanese original by Yuichi Nakagawa and Ryoko Kijima, Matsuyama Bureau, and Suzuko Araki, Riki Iwama and Yuka Saito, Science & Environment News Department)