A government advisory body has compiled a draft blueprint for recovering nuclear fuel debris from the No. 1 to 3 reactors that melted down at Tokyo Electric Power Company Holdings Inc.’s Fukushima No. 1 power plant, it has been learned.
According to the draft from the Nuclear Damage Compensation and Decommissioning Facilitation Corporation, the recovery project will prioritize collection of debris that has piled up at the bottom of the reactors, installing a robot arm into the reactor containment vessels from the side and controlling it remotely as its main operation.
The aim is to start the project in 2021. All the decommissioning work is expected to be completed sometime from 30 to 40 years after the disaster occurred.
The draft was presented Monday at an expert panel meeting held by the Economy, Trade and Industry Ministry in Iwaki, Fukushima Prefecture, to discuss ways to decommission reactors and get rid of contaminated water. The government will decide sometime in September, based on the blueprint, on a means to remove debris from each reactor.
Fuel penetrated pressure vessels that contain reactor cores, causing debris to form at different levels on the bottom of the containment vessels of the Nos. 1 to 3 reactors.
It was decided to recover the fuel from the side because that will allow work to retrieve fuel from spent pools located in the upper part of the reactor buildings to be conducted at the same time. If recovery was attempted from above, the robot arm would have to reach down to the bottom of the containment vessels, about 30 meters away. The distance would be only about 10 meters if the arm is installed from the side, making it easier to work on the project. The draft deems it feasible to recover debris from the side to get things started.
Details will be discussed in the future, but the draft suggests making use of holes in the containment vessels’ wall or boring new ones, from which the robot arm can be installed to be operated remotely.
■ Fuel debris
A substance created when atomic fuel such as uranium reaches high heat, begins to melt with metal fuel cladding and the material of the reactor’s structure, and then consolidates. The shape, hardness and content of debris vary depending on how it was formed, so it can resemble rocks, pebbles or sand. When recovering it, care must be taken not to trigger recriticality.