Key to dismantling nuclear reactors: Waste disposal

Near Chubu Electric Power Co.’s buildings for nuclear reactor Nos. 1 and 2, work is underway to dismantle such equipment as transformers.

A decision was made in March to decommission all five aging nuclear reactors in the nation, including the Nos. 1 and 2 reactors at Kansai Electric Power Co.'s Mihama plant in Fukui Prefecture. The time has come for many of Japan's nuclear plants to be decommissioned.

Using the ongoing dismantling of the Nos. 1 and 2 reactors at Chubu Electric Power Co.'s Hamaoka plant as a starting point, Eiji Noyori reports on the circumstances and challenges surrounding the reactor decommissioning process, which lasts nearly 30 years.

When I visited the Hamaoka nuclear power plant last month, I saw red and white tape stretched across transformers and other parts of the Nos. 1 and 2 reactors, indicating plans for them to be taken apart. There were only traces left of tanks that had once held such material as chemicals and crude oil.

Since 2009, decommissioning work has included processing nonradioactive building material surrounding structures such as those that house reactors and turbines.

Starting this fiscal year, preparations have been under way to dismantle equipment inside buildings such as turbines and condensers. They will then be removed from the buildings over an approximately 15-year period.

Work to dismantle the reactor body is scheduled to begin in fiscal 2023, with the decommissioning process planned for completion in fiscal 2036.

Reducing radioactivity

At this point, a particularly vital procedure is reducing low-level radioactive waste (See below). The surfaces of reactor components, for example, are tainted with radioactive material.

Components that were originally not radioactive were also contaminated after being exposed to neutrons.

Reducing radioactive levels and the amounts of such low-level radioactive material would make them easier to handle and open up the possibility of reusing them.

"It's possible to greatly reduce radioactive levels and amounts of waste through a number of methods, including stripping their surfaces of radioactive substances and decontaminating them using chemicals," said Yoshihiro Ichikawa, decommissioning supervisor at the Hamaoka plant.

Initial projections indicated about 14,000 tons of low-level radioactive waste around the nuclear plant, which the clean-up process is aiming to reduce to about 4,000 tons. Radioactive amounts found on parts such as the plumbing can also feasibly be brought down to about one-hundredth of their original levels.

Tough questions

But the biggest challenge ahead is deciding on a disposal site for low-level radioactive waste.

Reactor decommissioning is already under way at Japan Atomic Power Co.'s Ibaraki Prefecture-based Tokai plant, where low-level radioactive material has already been generated.

The waste would ideally be buried underground at the site, but the prefecture has yet to approve such plans. At the Hamaoka plant, a decision was made to store radioactive material on-site until a disposal site is found.

Dismantling a single reactor generates roughly 2,700 tons to 12,700 tons of low-level radioactive waste, according to projections by The Federation of Electric Power Companies of Japan. Continuing to decommission aging reactors means a growing mountain of waste with nowhere to go.

Tackling public opinion

"Low-level radioactive waste generated from dismantling reactors has remarkably fewer risks compared to high-level radioactive waste produced from reprocessing spent nuclear fuel," said Nagoya University Prof.

Tetsuo Iguchi of the Department of Quantum Engineering. "Residents must be given careful explanations to deepen their understanding of the disposal process. Training is also urgently needed to address the shortages of specialists involved in developing technology and other matters for reactor decommissioning."

Low-level radioactive waste

Generated from decommissioning work. Broken down into three levels, from the relatively high L1 that includes reactor core shrouds to such parts as pressure vessels at L2 and finally the relatively low L3. The higher the level, the tougher the storage container needs to be and the deeper underground it needs to be stored.

Decommissioned material lower than L3 aren't required to be treated as radioactive waste. Proper preparation opens up options for these components to be reused.

For example, metal produced from dismantling the Tokai nuclear power plant is being used for benches and concrete blocks.

Regulations for L1 material, for example with regards to their storage period, are still undecided - a study panel from the Nuclear Regulation Authority is aiming to work out standard criteria sometime this year.Speech

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