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Source: Asahi Shimbun
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, the highest since the triple core meltdown in March 2011, Tokyo Electric Power Co. Holdings Inc. said.
At 530 sieverts, a person could die from even brief exposure, highlighting the difficulties ahead as the government and Tepco grope their way toward dismantling all three reactors crippled by the March 2011 disaster.
An official of the National Institute of Radiological Sciences said medical professionals have never considered dealing with this level of radiation in their work.
Tepco also announced that, based on its analysis of images taken by a remote-controlled camera, that there is a 2-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.
- "Highest radiation reaching since 3/11 detected at Fukushima", Japan Times, February 3, 2017 .
Based on image analysis, a two-meter hole has been found in the metal grate under a pressure vessel in reactor No. 2’s containment vessels at the Fukushima No. 1 nuclear power plant. Image: Tokyo Electric Power Company
Fumiya Tanabe, an expert on nuclear safety who analyzed the 1979 Three Mile Island nuclear accident in the United States, said the findings show that both the preparation for and the actual decommissioning process at the plant will likely prove much more difficult than expected.
- "Radiation Level in Fukushima Reactor could kill within a minute", Asahi Shimbun, February 3, 2017.
It is clear to us now that the radiation level in the containment vessel of the crippled Reactor 2 is much higher than experts had believed.
The danger of Reactor 2 reminds me of the story of the potential collapse of Reactor 4 after the March 11, 2011, earthquake. That reactor contained 14,000 times the radiation of the Hiroshima bomb.
The danger of Reactor 2 begs us to ask many new questions:
- What is the probability of next strong earthquake?
- What is the earthquake resistance of the building that houses the reactor?
- How do we find the location of the irradiated cores in the pressure vessels?
- If it collapsed, what is appropriate evacuation distance?
- What is the the damage to ocean marine life?
- What are the potential risks to children and people on the West Coast of North America, who may be affected by the flow of much stronger contaminated water into ocean from Fukushima?
I am very pleased that Dr. Shuzo Takemoto — professor of the Department of Geophysics, Graduate School of Science, Kyoto University — responded to my concerns. I share his perspective below.
– Akio Matsumura
Potential Global Catastrophe of the Reactor No.2 at Fukushima Daiichi
by Professor Shuzo Takemoto
On July 28, 2016, the Tokyo Electric Power Company (Tepco, the utility that operates the reactors) published the images of the F1 Unit 2 reactor screened by muon particles coming from the universe — similar to an X-Ray. They showed the shadow of materials equivalent to 180 – 210 tons at the lower part of the pressure vessel. Consequently, Tepco concluded “Most of the nuclear fuels are estimated to remain in the vessel.”
Muon imaging setup for Fukushima Daiichi Unit 2. FMT-2 is installed inside a concrete radiation shield in front of the reactor building. Typical muon scattering angles are a few degrees.
It can hardly be said that the Fukushima accident is heading toward a solution. The problem of Unit 2, where a large volume of nuclear fuels remain, is particularly crucial. Reactor Unit 2 started its commercial operation in July 1974. It held out severe circumstances of high temperature and high pressure emanating from the March 11, 2011, accident without being destroyed. However, years long use of the pressure vessel must have brought about its weakening due to irradiation. If it should encounter a big earth tremor, it will be destroyed and scatter the remaining nuclear fuel and its debris, making the Tokyo metropolitan area uninhabitable. The Tokyo Olympics in 2020 will then be utterly out of the question.
The number of nuclear fuel rods in the cooling pool are as follows; Unit 1: 392, Unit 2: 615, Unit 3: 566. In ordinary times, these fuel rods can continue to be cooled if electricity is secured to pump water. We are filled with anxiety when we think of a power failure and of a strong earthquake befalling them, and of their consequences.
The earthquake of November 22, 2016, off the coast of the Fukushima Prefecture (magnitude 7.4) and the earthquake of December 28, 2016, in the Northern part of the Ibaragi Prefecture (magnitude 6.3) are situated in the aftershock area of the 2011 earthquake off the Pacific coast of Tōhoku. In this area, we must foresee a number of magnitude 7 class earthquakes. Consequently, we cannot exclude the possibility of intensity 6 and intensity 7 earthquakes befalling the Fukushima Daiichi. What is most dreaded is what could happen to the Unit 2 whose pressure vessel contain a large volume of nuclear fuel debris.
This pressure vessel has endured the sudden change of temperature and pressure in the accident of March 2011, but in light of its possible weakening due to irradiation, it could be seriously damaged if a new big earth tremor occurs nearby.