Fukushima Unit 2 Spent Fuel Pool Inspection

TEPCO announced an upcoming inspection of unit 2’s spent fuel pool.
The work will be done using an underwater ROV type robot. Due to the high radiation levels on the refueling floor, remote operated equipment will be used to place and retrieve the ROV.

The ROV unit

What they will be investigating:
(1) Fuel and fuel rack top • Check for interference and deformation at the top of the fuel rack
(2) Caskpit • Bottom interference, cask pit beam deformation
(3) Control rod • Confirmation of control rod fall, control rod hanger deformation
(4) Pool gate • Deformation of pool gate, check bolt condition to suppress pool gate
(5) Skimmer, surge tank inlet • Deformation of the movable weir at the entrance, check the outside of the stop screw of the movable weir

Diagram of the spent fuel pool

Key on right, translated:
1. Fuel, fuel rack
(□represents a rack that does not contain fuel)
2. Caskpit
3. Control rod, control rod hanger
4. Pool Gate
5. Skimmer tank inlet

 

How the ROV will be used:

Installation of survey equipment
Using remote unmanned heavy machinery, the survey equipment is transported and installed as follows.
 South side: Equipment for transporting underwater ROV, underwater lighting
 Northeast side: Underwater lighting
 After installing the survey equipment, the underwater ROV is released to SFP and the investigation is started.

Unit 2 has no working lighting system and lacks the direct sunlight of the more damaged units, this requires the additional lighting not used at other units.

 

Preparation and training have been ongoing at the robot research facility in Minamisoma.

This inspection should provide important data that will be used to refine the plans for spent fuel removal. TEPCO has already presented a fuel removal plan that involves a remote operated design. The high radiation levels on the refueling floor have prevented human entry into that area.

Original report in Japanese
https://www4.tepco.co.jp/decommission/information/committee/roadmap_progress/pdf/2020/d200430_07-j.pdf

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