New robot to locate melted fuel in No.2 reactor

September 6, 2016

Robot to probe nuke fuel debris in Fukushima No. 2 reactor

http://www.asahi.com/ajw/articles/AJ201609060001.html

By TAKASHI SUGIMOTO/ Staff Writer

A robot will be sent into the No. 2 reactor containment vessel at the crippled Fukushima No. 1 nuclear power plant to locate the melted fuel inside and assess its spread ahead of future retrieval.

Tokyo Electric Power Co. announced on Aug. 25 that it would undertake the difficult operation early next year at the soonest.

Under consideration for the work is a scorpion-shaped robot developed by Toshiba Corp., whose slender body allows it to pass through narrow openings. It is designed to raise its rear camera toward the front to capture images when it has arrived at a planned survey location.

The robot will crawl through an entrance into the No. 2 reactor containment vessel and travel along a rail to go deeper into its interior and confirm the state of the melted fuel inside and other conditions.

TEPCO and other parties are planning to draw on the survey results to decide on the fuel retrieval method as early as fiscal 2018 and set out on the actual retrieval process, expected to pose extreme difficulties, in 2021.

The initial plan would have sent the “scorpion" into the No. 2 reactor last summer, but radiation levels around the entrance were so high that cleanup work had to be done to reduce them for workers who would be sending the scorpion in.

Remote operations to remove a steel plate that blocked the entrance also turned out to be a time-consuming process.

If the operation to send the robot proceeds as planned, its use will still be a year and a half behind schedule.

Robots of a similar kind were sent last year into the No. 1 reactor and were partially successful in capturing images inside the containment vessel. However, the survey has had rough going, as the robots failed to spot any fuel.

TEPCO and the government are planning to draw on the robot survey results and other information to make a decision in fiscal 2018 on the melted fuel retrieval method for the No. 1, No. 2 or No. 3 reactors.

They are hoping to use the “submersion method,” which would involve filling the containment vessel with water to reduce worker radiation doses, during the retrieval work to be started in 2021. However, water is leaking from holes in the containment vessels, and the holes have yet to be located.

TEPCO and other parties have begun weighing alternative retrieval methods that do not involve filling the containment vessels with water.