The radiation level in the containment vessel of reactor 2 at the crippled Fukushima No. 1 power plant has reached a maximum of 530 sieverts per hour—enough to kill anybody within a few minutes—and is the highest since the triple core meltdown after the March 2011 tsunami.
The readings, described as “unimaginable,” are now so high that they will even destroy unmanned robots after just two hours of operation.
According to a statement from the Tokyo Electric Power Co. Holdings Inc. (Tepco), the radiation reading was taken near the entrance to the reactor core. This means that at least some of the melted fuel has escaped its surrounding pressure vessel.
530 sieverts is strong enough to kill a person with only the briefest exposure. Previously, the highest reading taken was 73 sieverts per hour at the reactor.
An official of the National Institute of Radiological Sciences said medical professionals have never considered dealing with this level of radiation in their work.
According to the institute, 4 sieverts of radiation exposure would kill 1 in 2 people. Experts say 1,000 millisieverts, or 1 sievert, could lead to infertility, loss of hair, and cataracts, while exposure to doses above 100 millisieverts increases the risk of cancer.
Tepco also announced that, based on its analysis of images taken by a remote-controlled camera, there is a two meter hole in the metal grating under the pressure vessel in the reactor’s primary containment vessel. It also thinks part of the grating is warped.
The hole could have been caused when the fuel escaped the pressure vessel after the mega-quake and massive tsunami triggered a station blackout that crippled the plant’s ability to cool the reactors.
The reading means that it is becoming increasingly difficult to carry out repairs and to decommission the plant. The company said it planned to deploy a remote-controlled robot to check conditions inside the containment vessel, but it will have to plan the operation carefully because the robot will only have two hours of operational life before the radiation kills it.
Photos released by Tepco clearly showed the two meter hole on the infrastructure, along with black deposits which are presumed to be melted fuel.