Robot enters Fukushima Daiichi unit 1 containment vessel

UPDATED A shape-changing robot began surveying conditions within the primary containment vessel of the damaged unit 1 of the Fukushima Daiichi plant on 10 April. However, the robot stopped working before completing its mission.

UPDATED - This article has been updated to include details of the failure of the robot during the surveillance of the PCV on 10 April.

A shape-changing robot began surveying conditions within the primary containment vessel (PCV) of the damaged unit 1 of the Fukushima Daiichi plant on 10 April. However, the robot stopped working before completing its mission.

The robot begins its inspection of the first floor of the containment vessel (Image: IRID)

The robot has been developed by the International Research Institute for Nuclear Decommissioning (IRID) and Hitachi-GE Nuclear Energy to investigate hard-to-access areas of the plant. It consists of three segments: the robot's main body and two compact crawlers. The robot can assume a long, straight shape for passing through narrow spaces, such as pipes. Alternatively, it can rotate its crawlers by 90 degrees in relation to its central body to assume a U-shape, with the crawlers providing better stability when travelling over flat surfaces.

The robot is 9cm in height. Depending on the position of its crawlers, it is 25cm to 64cm in length and between 6.5cm and 27cm in width. Weighing 7.5kg, the robot is operated via a 40m cable.

Following several weeks of test runs, Tokyo Electric Power Company (Tepco) announced today that the robot had travelled through a 10cm-diameter pipe to reach the inside of the unit's PVC. Although various robots have already been used in the investigation and clean-up of other parts of unit 1, as well as the other units at the plant, this marks the first time that a robot has entered any of the damaged units' PCVs.

After entering unit 1's PCV, the robot was lowered by cable onto the grating on the first floor outside the pedestal (the structure which supports the reactor containment vessel). Here it was to assume a U-shape. It was then to measure radiation and temperature levels, as well as photograph the interior of the vessel.

Tepco planned to deploy the robot today to survey half of the first floor of the PCV and then again on 13 April to survey the other half.

However, Tepco said that after taking measurements at 14 out of 18 planned points, the robot stopped working. It said the inspection planned for 13 April had been postponed while the cause of the robot's failure was investigated.

According to a report by the Kyodo news agency, Tepco intends to use the robot to explore the water-filled lower portion of the containment vessel, where the molten fuel is believed to have collected. However, it says the current robot is not waterproof. A waterproof version will reportedly be developed by the end of March 2016.

Researched and written
by World Nuclear News