11 Sieverts/hour but no melted fuel yet

March 22, 2017

Robot probe finds lethal radiation levels in water near bottom of Fukushima reactor 1 vessel

JIJI

http://www.japantimes.co.jp/news/2017/03/22/national/robot-probe-finds-lethal-11-sieverts-water-near-bottom-fukushima-reactor-1-vessel/#.WNInmGdFeos

A radiation level of 11 sieverts per hour has been detected in tainted water inside a reactor containment vessel at the Fukushima No. 1 nuclear power plant, Tokyo Electric Power Company Holdings Inc. said Tuesday.

The reading was measured in a survey using a robot on Sunday at a point about 30 cm from the bottom of the containment vessel of reactor 1.

The reading is the highest radiation level detected in water inside the containment vessel. If exposed to this level of radiation, a person would likely die in about 40 minutes.

The survey showed the accumulation of sandy substances at the bottom of the vessel, but Tepco said it does not believe they are melted nuclear fuel.

Nuclear fuel melted from the reactor’s pressure vessel is believed to have accumulated in contaminated water at the bottom of the containment vessel. No such debris has been found so far.

Reactors 1, 2 and 3 at the plant suffered meltdowns in March 2011 after it was hit by a massive earthquake and tsunami.

On Monday, a radiation level of 6.3 sieverts per hour was detected in water at a point about 1 meter from the bottom of the containment vessel, where Tepco had seen possible fuel debris.

Sandy substances and something that resembled melted fuel were found there but Tepco said it was not fuel debris.

A radiation level of 1.5 sieverts per hour was monitored on Saturday in water at another point 1 meter above the bottom of the containment vessel.

Tepco decided to extend the survey by one day through Wednesday to look for melted fuel.