Another failed mission?

 March 22, 2017

Robot can’t find melted fuel at No. 1 reactor of Fukushima plant

http://www.asahi.com/ajw/articles/AJ201703220046.html

THE ASAHI SHIMBUN

Tokyo Electric Power Co. (TEPCO) extended the mission of a survey robot after it failed to locate melted nuclear fuel at the No. 1 reactor of the Fukushima No. 1 nuclear power plant.

The robot on March 20 was sent into the reactor’s containment vessel, where the melted fuel is believed to have landed at the bottom, but pipes blocked its view, TEPCO said March 21.

The utility lengthened the period of research from four days to five days until March 22 to check other areas with high probabilities of melted fuel.

According to estimates, some of the melted nuclear fuel may have fallen into a cylinder-shaped structure that supports the pressure vessel, flowed out from the structure through a door for workers, and then spread at the bottom of the containment vessel.

The bottom of the containment vessel is covered with accumulated cooling water.

The survey on March 20 took place in an area about 1 meter from the door. The robot’s measurement device, equipped with a camera and a dosimeter, was hung from a stage for workers and lowered into the water below.

Although the pipes blocked the view of the conditions at the bottom of the containment vessel, the camera took pictures of what appears to be sand piling up on the pipes.

The radiation level around the area in the water was 6.3 sieverts per hour.

“Judging from the radiation level, there is a high possibility that what is piling up on the pipes is not nuclear fuel,” a TEPCO official said.

March 22, 2017

Robot probe of No.1 reactor to continue until Wed.

https://www3.nhk.or.jp/nhkworld/en/news/20170321_33/

The operator of the crippled Fukushima Daiichi nuclear power plant says a robotic survey of fuel debris at the No. 1 reactor is being hampered by plumbing and other structures. The utility says it will extend the probe by one day, until Wednesday.

So far engineers have detected strong radiation of about 11 sieverts per hour in the water inside the containment vessel.

Tokyo Electric Power Company on Saturday started sending a remote-controlled robot into the reactor's containment vessel to look at the state of debris -- a mixture of melted fuel and reactor parts. The robot is equipped with a camera and a dosimeter.

The melted fuel is believed to still be at the bottom of the vessel, where about 2 meters of contaminated water accumulates.

TEPCO released the results of the ongoing survey on Tuesday. It said the robot moved to a location believed to be just above the debris and lowered the camera and dosimeter into the accumulated water.

The dosimeter detected radiation of 6 sieverts per hour one meter from the bottom. But piping prevented the device from reaching deeper, and it has yet to confirm the debris.

TEPCO also said the robot recorded about 11 sieverts of radiation per hour about 30 centimeters from the vessel's bottom at another location. Officials believe the radiation may be coming from contaminated fragments that fell to the bottom, as they expected no debris there.

Through the extended probe, TEPCO hopes to collect more data on conditions inside the vessel.