New submersion method added as option to aid Fukushima debris cleanup

A state-backed body helping with the scrapping of the Fukushima Daiichi nuclear power plant, which suffered core meltdowns in 2011, added as an option a new submersion method for removing radioactive fuel debris that would wholly encase a reactor building in a water-filled, tank-like structure, the body said Monday.

The method, expected to reduce the risk of leakage of radioactive waste, was outlined in the 2022 edition of the technical strategic plan for decommissioning the crippled plant by the Nuclear Damage Compensation and Decommissioning Facilitation Corp. The technique could be applied to the No. 3 reactor of the power plant operated by Tokyo Electric Power Company Holdings Inc.

In the aftermath of the March 2011 Great East Japan Earthquake and tsunami, nuclear fuel cooling processes failed at the Fukushima plant's Nos. 1 to 3 reactors, causing the fuel to melt and resolidify into radioactive debris mixed with concrete, metal and other materials present in the reactors.

The removal of melted reactor fuel is one of the largest challenges in the decades-long cleanup work and is crucial for the plan to complete the decommissioning sometime between 2041 and 2051.

Some 880 tons of radioactive waste material is estimated to have been created by the nuclear meltdowns across the three reactors.

The new submersion method involves building a strong, pressure-resistant structure, such as a ship's hull or a plane's body, completely encapsulating the reactor, including underground. The structure could then be filled with water, and removal work would take place from the top.

However, implementation of the method carries its own problems as the massive amount of water used in submersion would also become contaminated and could be hazardous in the event of a leak or an earthquake.

"The notion of using water to contain radiation sounds very attractive," an NDF official said. "But we are not fully convinced of the feasibility of the technology, and thorough consideration is necessary."

Another "dry method" involving extracting the material without filling the reactor with water is also under consideration, as are the respective costs and technical challenges associated with each.

TEPCO is expected to narrow down potential methods in time for its planned commencement of the debris cleanup for the No. 3 reactor in the early 2030s.

Cleanup at the No. 2 reactor, delayed after being originally slated to start last month, is now set to begin in the second half of fiscal 2023 using the dry method.

In the latest plan, the NDF said it will also provide technical support to TEPCO, which plans to discharge treated water from the nuclear plant into the ocean from spring 2023, aiming to share accurate information and foster understanding among other countries concerned about the release.

© Kyodo News