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Biotechnology

The long goodbye for Japan's aging nuclear reactors

The country is about to get deeply familiar with the arduous task of decommissioning

Work to decommission two reactors, seen here at the left, at Kansai Electric Power's Mihama nuclear plant is underway.

TOKYO Japan's nuclear power infrastructure is not getting any younger. Many reactors have either passed the 40-year threshold the country's nuclear watchdog deems the limit for safety, or will soon get there. This means numerous decommissioning projects lie ahead, and the task is a lot more complicated than simply pulling the plug.

The Nuclear Regulation Authority in April approved the decommissioning of five reactors at four nuclear plants. All of the units are more than 40 years old, and scrapping them will take nearly as long -- around 30 years, from start to finish.

What does decommissioning involve? And why does the process take so much time?

TAKE IT SLOW Japan was forced to rethink nuclear safety after Tokyo Electric Power Co.'s Fukushima Dai-ichi plant was wiped out by the 2011 earthquake and tsunami. As a general principle, the NRA decided it would not approve the operation of reactors that have been in service for more than 40 years. Since, naturally, old equipment is more prone to problems, this should at least reduce the risk of serious accidents.

The Fukushima Dai-ichi plant had come onstream in 1971.

The NRA is willing to grant 20-year extensions, if a plant passes an examination. But the cost of safety upgrades is likely to make retirement a more appealing option.

Utilities made that calculation in applying to decommission the five reactors: Japan Atomic Power's Tsuruga Unit 1, in the western prefecture of Fukui; Kansai Electric Power's Mihama Units 1 and 2, also in Fukui; Chugoku Electric Power's Shimane Unit 1, in the western prefecture of Shimane; and Kyushu Electric Power's Genkai Unit 1, in the southwestern prefecture of Saga.

The NRA approved their requests on April 19 -- the first such approval since the new 40-year rule took effect.

All of the reactors in question entered service in the period from 1970 through 1975.

The utilities cannot simply set about dismantling the reactors, though. To varying degrees, the equipment has become contaminated with radioactive materials over the years. So the work must progress slowly, to minimize the risk of exposure.

In a way, decommissioning a reactor is a waiting game. Radioactivity, or a material's power to emit radiation, gradually weakens over time. Cobalt-60, which is produced in nuclear plants, loses half its radioactivity in about five years. After 10 years, its potency is cut by another half, to just a quarter of the original level.

The longer one waits, the lower the risk.

Even then, you still need a place to put all the waste -- and this is a real problem.

"EMOTIONAL RESISTANCE" The five reactors are expected to leave behind 27,000 tons of radioactive waste. Japan has decided to bury it, with the depth depending on the level of radioactivity. The all-important disposal location, however, has yet to be determined.

This is not a new issue. Chubu Electric Power started decommissioning work on its Hamaoka Units 1 and 2 in Shizuoka Prefecture, just southwest of Tokyo, back in 2009. Dismantling of the peripheral equipment started in 2016. For the time being, the waste is being kept on-site in a temporary storage facility.

Right now, the only viable candidate for permanent disposal is Japan Atomic Power's Tokai plant in Ibaraki Prefecture, north of the capital. Dismantling work has been underway there since 2001.

The company and the NRA are discussing the possibility of opening a disposal site on the grounds measuring 80 meters wide and 100 meters long. If permission from the authorities is granted, radioactive waste would be placed in iron or plastic containers -- depending on the type -- and lowered into a 4-meter hole at the disposal site.

"The technology necessary for decommissioning reactors is emerging," said Akitsugu Nomura, deputy head of the NRA's decommissioning project promotion office. "However, actual burial requires the understanding of local residents."

There is also the question of what to do with debris that is not hazardous.

Radioactive waste accounts for just 1-4% of the total produced by decommissioning a reactor. In the U.S. and Europe, some of the leftovers are reused, say, as tile or weights for construction. Japan, too, created a system in 2005 for reusing some of the material. But so far only a fraction has been used, in such things as benches for nuclear plants.

"There is considerable emotional resistance [among the public] to anything that came from a nuclear power plant," said Susumu Shibuya, director of the Radioactive Waste Management and Nuclear Facility Decommissioning Technology Center.

Excluding those already set for decommissioning, there are 42 nuclear reactors in Japan. By the 2020s, more than half will have reached the 40-year operational threshold. So the government and power industry are going to have to reach some conclusions on various challenges, including final disposal locations.

Kicking the can down the road will no longer be an option.

Keyword: Nuclear waste

Radioactive waste is broken down into three categories -- L3, L2 and L1 -- based on the level of contamination. The means of disposal depends on the level.

L3 waste, which is the least contaminated, can be buried in holes several meters deep, like the one at the Tokai plant. L2 waste, meanwhile, should be placed in concrete-walled holes at depths of about 10 meters.

L1 waste, which consists of equipment from inside the reactor itself and has the highest level of contamination, should be buried for 100,000 years at a depth of at least 70 meters.

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