Fukushima Daiichi NPS Prompt Report 2015

Robots, which change shape to squeeze through tight spaces, captured images showing conditions and important data on temperature and radiation dose

FUKUSHIMA, Japan, April 17-A pair of unique, shape-shifting robots that can alter form to squeeze through tight spaces have obtained information on conditions inside one of the Fukushima reactors that is critical to the nuclear cleanup, the Tokyo Electric Power Co. has reported.

The eventual goal of the cleanup is removal of nuclear fuel that had once sat at the center of the reactor's interior steel pressure vessel but is believed to have fallen to the bottom of the reactor, and likely onto the floor of the primary containment vessel (PCV), when it melted down during the March 2011 accident. A clear understanding of the location and condition of that fuel is essential to the development of a plan to remove it.

Robots are being used because the space remains too hazardous for workers to enter safely. Because it contains tight spaces and unknown obstacles caused by damage during the accident, the robots had to be specially designed to be able to change shape as they moved around inside. They were sent onto the deck above the bottom of the steel pressure vessel, which is encased by the PCV, a thick concrete shell.

Both robots successfully obtained and sent back data from the Unit 1 PCV. Although the first robot eventually became blocked after collecting data from 14 out of 18 points, a second robot was sent into the reactor and is also returning valuable information. It is expected to continue its exploration this week, with sensors that can record temperature and radiation dose, and cameras that can send back images.

Radiation, Temperature Found Lower than Expected

Results so far indicate that the radiation dose was about 4.7 to 9.7Sv/h, less than a tenth of what was expected. That means the second robot can stay inside for about two to three days, rather than about 10 hours as originally planned. The first robot, after becoming stuck, will be left inside the reactor. Temperatures were found to be even lower than normal room temperature, indicating the effectiveness of cooling systems.

The robots also determined that there are no obstacles around the opening that leads to the bottom of the PCV - an area of especially thick concrete known as the "pedestal area." Because that is an area where fuel is likely to be found, it is the critical route for the next investigation, and confirming that it is obstacle-free should enable that investigation to proceed.

The robots also found that there was no significant damage to such components as pipes and the pedestal wall.

Continuing Exploration

The robots began their exploration on April 10, and after the data was captured from the first robot, its tethering cables were deliberately severed on April 13 in accordance with contingency plans, to prevent the second robot from becoming entangled. The second robot entered the reactor on April 15, collecting data at all 11 points it was assigned to cover on a clockwise circuit of the reactor.

The robots were developed by Hitachi-GE Nuclear Energy, Ltd., in conjunction with the International Research Institute for Nuclear Decommissioning IRID. Both robots were designed to withstand the severe radiation conditions inside the reactor, and to be able to shift their shape from a slim I-shape (to pass through a 10 cm-diameter pipe) to a C-shape (to crawl around on the grating inside the PCV).

Fukushima Daiichi Plant Chief Akira Ono said, "We appreciate the efforts of IRID and the manufacturers and workers involved. It is a great step forward towards decommissioning that we could earn necessary data for the next investigation at the bottom of the PCV."

To See Videos and Images

Videos of the investigation may be obtained at TEPCO's Facebook page at: https://www.facebook.com/OfficialTEPCOen

Other images of the robot's activity may be viewed on TEPCO's website at http://photo.tepco.co.jp/en/date/2015/201504-e.html.

Detailed materials of the investigation is obtained at http://www.tepco.co.jp/en/nu/fukushima-np/handouts/index-e.html

About TEPCO

Tokyo Electric Power Company, Inc. (TEPCO) is Japan's largest power company, supplying energy to the greater Kanto area, including Japan's two most populous cities, Tokyo and Yokohama. Its 34,000 employees are committed to providing safe, reliable power to its 29.0 million customers, diversifying energy resources to ensure sustainability, and contributing to economic growth while fully meeting its responsibilities after the Fukushima Daiichi accident.
TEPCO Website: http://www.tepco.co.jp/en/index-e.html
TEPCO Facebook page: https://www.facebook.com/OfficialTEPCOen
TEPCO Twitter page: https://twitter.com/TEPCO_English