Fukushima Unit 2 Spent Fuel Removal Plan May Drastically Change

TEPCO previously announced their plan for removing spent fuel from unit 2 at Fukushima Daiichi. This involved removing the roof and walls of the refueling floor level. The refueling floor is heavily contaminated from the meltdown at that unit. Unit 2 has historically been the largest contributor to airborne radiation escaping the plant. So much so that TEPCO installed a HEPA filter system on the blow out panel opening.

Part of the reason for this plan to remove the walls and roof is the need to remove the original fuel handling machine. There has been an assumption that the radiation levels inside were too high to allow maintenance work and that the fuel handling machine was too contaminated to work on.

This plan to remove the walls and roof comes with considerable risk. The building materials contain a significant amount of radioactive materials. Earlier demolition work at units 1 and 3 showed that this kind of demolition work is problematic, with a high probability of releasing radioactive dust to the environment. So much so that work at unit 1 to remove the remains of the refueling floor has taken years with limited progress. Dust suppression tactics are in use at unit 1, yet the work has still be slow.

In the most recent roadmap report, a new plan has emerged for dealing with unit 2. This new plan wouldn’t involve removing the roof and walls. It would instead attempt to repair the existing fuel handling machine then use a new type of rig to remove spent fuel casks from the refueling floor via the air lock platform recently installed on unit 2. The new plan described in the far right column.

In the report TEPCO describes that the existing fuel handling machine (FHM) could potentially be used rather than the need to replace the entire system. Machine translation below:

“Unit 2 reactor building pool fuel extraction at the appropriate time “debris removal
Plan from the two proposals for the “Pool fuel extraction specialization” and “Proposal for
.
 At the outset, we examined the restoration (decomposition, decontamination, repair, etc.) of the existing tencle and FHM
On the operating floor (hereinafter, operational flow).
In November 2015, it was difficult to recover existing tencle FHM
Determined that the body needed.
 In the operational survey conducted from November 2018 to February 2019, 2011 to 2012
The tendency that the dose is reduced when compared with the results of the survey was confirmed.
(Reported on February 28, 2019 at the team meeting Secretariat)
 Based on the results of the above survey, the shielding and other appropriate The prospect that can be carried out if it is a limited work within.”

This does not describe in detail how they would repair the fuel handling machine but it is being considered as a possible approach.

The text of the right side column describing this new side access approach, machine translated:

In addition to the method of dismantling the upper part of the reactor Building (plan A), the program

We will examine two proposals of the method (plan B) to access from the south without dismantling the upper part as much as possible.

The pool Fuel Extraction Specialization Plan |

Plan B (upper operational Flow)
Fuel extraction Base
Fuel handling Equipment

Crane
Open the south side of the operating
Access from the side of the operating

Set up a structure
• Pipe in the reactor building

Can work in a state of
• Do not dismantle the upper building,
If workers ‘ exposure is suppressed

Assumed.

• Do not dismantle the upper building, so there is no rainwater inflow.
• The main construction yard is a reactor building.
⻄ In other construction to become the south Side Easy to share a side yard.

 

The benefits of this new plan are obvious. The challenges will be limiting workers exposure doses while they conduct work on the refueling floor. Decontamination work on the refueling floor has been underway over the last year using remote controlled equipment and robots. Some of the work to repair the fuel handling machine could be assisted by robots but will require extensive hands on work to complete. A rig in use at unit 3 allows workers to remove fuel from the spent fuel pool into transit casks remotely. A similar modification to the existing fuel handling machine could potentially allow remote fuel removal at unit 2. TEPCO has not expressed this as an official plan yet, but the potential is obvious.

A solid date to begin the next phase of the spent fuel removal, where they must decide if they will remove the walls and roof or not, has yet to be set.

Unit 2’s side air lock below:

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