Reactor Well Inspections Start At Fukushima Unit 1

TEPCO published preliminary photos July 18th showing the start of inspection work of the reactor well for unit 1. Two photos with brief explanations were distributed as a press handout. This showed the SUGV robot leaving the robot enclosure then entering the gap in the reactor well cover.

 

SUGV robot leaving the robot box from handout dated July 18, 2019. Photo – TEPCO

SUGV crawling under the dislodged concrete cover slab. Photo – TEPCO

A July 17th NHK report indicated work was going to start on the 17th or 18th.  The planned work will include use of a 3D camera and collecting radiation swipes. NHK did not clarify if the 3D camera would record spatial measurements, radiation gamma signatures or both. TEPCO’s reporting shows they will also be taking radiation readings through the process.

A July 11 report from TEPCO shows the work area on the refueling floor and the placement of a shielded robot box. Work took place to test the robot box and the on board camera ahead of the July 18 inspection work.

Shielded box for robot in the “yard” near the reactor buildings. Photo – TEPCO

Shielded box for robot being placed on the refueling floor. Photo – TEPCO

This photo provides a new view of unit 1’s refueling floor. Previously this area was covered with the collapsed roof panel, obscuring the reactor well and other details. In this new photo the dislodged reactor well concrete cover can be seen clearly. The area in the lower left of the photo is the tool pit.

Placement of robot box on refueling floor with ramp. Photo – TEPCO

View from the on board camera located in the robot box, looking across the tool pit divider cover.
Photo – TEPCO

Diagrams of the entrance location for the robots. Red area on left, purple area on right diagram show the area where the robots will attempt to travel under the reactor well cover slabs. This general location is the same area where the test run of the robot box took place. Diagrams found in the recent roadmap documents.

Diagrams above from the same TEPCO roadmap document. These show the estimated position of the concrete reactor well cover slabs based on earlier scope inspections of the area. Red box in the last diagram shows the robot entry point.

TEPCO plans to use two new robots to inspect down inside the unit 1 reactor well. SUGV will do the inspection work, FirstLook will do support work.

Robot transport box diagram showing robots, from TEPCO roadmap document.

Actual inspection work is scheduled to take place between July 20th and August 7th per TEPCO’s June roadmap report.

Radiation readings cited in the NHK report were from a 2017 of the area. 2.3 Sieverts/hr were found near the center of the reactor well.

Readings below were taken in 2017 at varying heights. The high reading at the center of the reactor well was expected. The high reading near the tool pit divider, where the robots will enter was unexpected.

The inspection work should provide new understanding of the damage inside the reactor well. This includes the actual location of the dislodged slabs, and interior radiation levels. It would be unlikely this work could identify damage to the containment cap due to the position of the slabs. Part of the inspection work includes the collection of radioactive debris swipes. Similar work at unit 2 identified fuel microparticles ejected from the reactor to the environment.

This work will also inform researchers what measures may be needed to safely remove spent fuel from the adjacent spent fuel pool. Steps will need to be taken to isolate and shield the reactor well so spent fuel removal can take place. Similar work at unit 3 has been completed to begin the removal of spent fuel. This required extensive efforts to reduce radiation exposure levels so remote equipment could be installed.

There should be more information forthcoming on this inspection work at unit 1 as work progresses.

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