Nuclear fuel debris to be collected from 2021

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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.

Plan to tunnel under the reactor buildings to remove melted fuel

Buried in technical reports was this interesting plan. Researchers have developed a method to tunnel under the reactor buildings to remove melted fuel.

The plan itself bases itself in existing concepts for sealed underground tunnel systems similar to the BART train system in the US or the Channel in the UK. Japan has a similar tunnel system used for rail lines that run between the main island of Honshu and Hokkaido.

TEPCO has attempted to continue presenting a narrative that the melted fuel remained in the reactor vessels or at least remained in the containment vessels, making it more straightforward to remove. This new plan assumes fuel to have melted deeply down into the reactor building basement concrete or potentially through the ground below.

The plan doesn’t clarify how much human entry to the underground base unit would be allowed or required. Seeing broader planning for potential scenarios would seem a wise move after early work found unexpected surprises causing designers to go back and rework plans. For such a plan to be under development means there is some thought among the decommissioning research teams that a worst case scenario could exist. These would include further inspections inside the containment structures and horizontal drilling below the reactor buildings to obtain soil samples.

The divergence between the work of the parties that have to actually plan the decommissioning work vs. the parties that have a stake in comforting public relations is quite clear. The very notion of such a plan raises questions about the true nature of the meltdowns.

A complex system of drilling equipment, debris retrieval, and nuclear waste casks would be included in the system. Additional inspection work will be required to determine if this new method will be needed.

The same report also includes the controversial sarcophagus plan.