Melted Debris Detected

Tokyo Electric Power Company announced on Friday that it detected blocks, which was supposed to be melted nuclear fuels, under a broken nuclear reactor of First Fukushima Nuclear Power Plant. It was the first time for the power company to confirm debris of nuclear accident in the plant after the unprecedentedly severe accident in 2011. The findings can be hard evidence that the nuclear reactors were actually melted down, the fact which TEPCO denied right after the accident. The process for dismantlement of the plant is still unclear, anyway.

TEPCO has been examining the situation of broken reactors #1, #2 and #3, using special robot for exploring in the water in which the broken reactors were soaked. It was Reactor #3 where TEPCO found melted debris. In the water under the pressure vessel of the reactor, the robot detected melted debris hanging from the beneath of the vessel like icicles or accumulated like lava of volcano.

Reactor #3 has been supposed to have completely broken down and all the nuclear fuels were to be melted down. The findings endorsed that analysis. “It looked like something that were melted down from pressure vessel and solidified thereafter. We think it to be melted nuclear fuel mixed with other materials inside the pressure vessel,” told spokesperson of TEPCO in the press conference.

If the debris would be confirmed as melted nuclear fuels, it is the great progress for the dismantlement. Robot and camera are proved to have worked. Those devices will be useful in further investigation in other reactors. Information about the situation of Reactor #3 should be contributing to make a plan for containment of radiation and extracting the debris.

However, the situation now is far from total solution. It is still unclear what is the material that consists the debris, how much debris remaining or to what extent the pressure vessel or other structure in the building is damaged. Without those kinds of information, extraction of broken nuclear fuels cannot be started. TEPCO is planning to continue the research in the plant.

In the mid- and long-term plan for dismantlement, TEPCO and Government of Japan will make a plan of how to extract the debris by this summer. Actual extraction in one of the three broken reactors is supposed to start in 2021. Chairman of Nuclear Regulation Authority, Shun-ichi Tanaka, is skeptical so far about determining actual process for extracting debris. Collecting further information and disclosure of obtained facts will be the keys for the process.