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Cold shutdown reached at Fukushima?

Nuclear Monitor Issue: 
WISE Amsterdam

September 28, 2011 marked a milestone of sorts for the Fukushima Daiichi reactors: some six-and-a-half months after the onset of the accident, temperature levels at all of the reactors and fuel pools fell below the boiling point (100 degrees Celsius) for the first time since March 11. But there are some caveats to that statement. Meanwhile, hydrogen detected in a pipe will cause no explosion "in the immediate future". Plutonium has been found as far as 45 km from the plant.

The temperature at Unit 2 fell only to 99.4 degrees Celsius, and has been going up and down in recent days, so could quickly return to the boiling point. Moreover, while the reactor temperatures are measured at the bottom of the pressure vessel, it’s not clear that is where the hottest temperatures are. Since fuel melted and containments failed, allowing fuel to go below the pressure vessel, temperatures below the vessel where the molten fuel has collected may remain higher than the boiling point.

Meanwhile, the cooling system that has brought down temperatures is a jerry-rigged system nothing akin to the normal cooling systems found in reactors, and its long-term reliability is in serious question. This is especially so because the region continues to suffer earthquakes (a 5.6 earthquake struck the region on September 29), not to mention typhoons and other problems.

In other words, there remains some time before cold shutdown of the reactors can be proclaimed. And in the meantime, radiation releases continue, although they are reported to be a small fraction of earlier releases. They’re now on the order of one million becquerels/hour (as opposed to a trillion/hour a few months ago and thousands of times more than that in March). Although, a caveat to that too: Tepco has admitted that it doesn’t really know how much radiation is being emitted--it’s estimating.

On Oct 2, Tepco announced that it had estimated that the interruption for about 38 hours of water injection into the cores would prompt their nuclear fuels to melt again. Unless water injection is restarted about 18 hours after being stopped, a massive amount of radioactive substances would be released into the environment. In the estimate for the No. 1 to No. 3 reactors at the March disaster-ravaged Fukushima No. 1 nuclear power plant, TEPCO assumed that their pressure vessels would have no water to cool nuclear fuels when water

injection stops. The temperate of the nuclear fuels would rise by about 50 degrees Celsius every hour from 300 degrees at the time of the coolant loss and reach 2,200 degrees about 38 hours later, the power utility estimated. At that time, the nuclear fuel would start melting, and some would break through the pressure vessel to fall into the containment structure, according to the company.

A couple of reports have struck us recently. One widely reported is that Tepco seriously considering abandoning the Fukushima facility in mid-March when it reduced its on-site workforce to 50 people. Another, also widely reported, is that then-Prime Minister Kan was actively considering ordering an evacuation of Tokyo in mid-March as conditions deteriorated and foresaw a potential end to Japan as a functioning nation. It may go without saying that if Tepco actually had abandoned its efforts at the time, that’s exactly what would have happened.

On September 23,Tepco said that hydrogen has been detected in a pipe at the No. 1 reactor, but there is no possibility it will cause an explosion "in the immediate future". According to Tokyo Electric Power Co., hydrogen of at least 10,000 parts per million was detected at two spots in a pipe passing through the containment vessel on the reactor building's first floor. This concentration was higher than Tepco had anticipated. Although Tepco is not certain how much hydrogen is still inside the vessel, the utility believes it is possible the concentration of the highly flammable gas is higher than had been assumed.

In air and liquid, 10,000 ppm is equivalent to 1 percent. Air containing at least 4 percent hydrogen and 5 percent oxygen is at risk of causing explosion. Tepco has been injecting nitrogen into the containment vessel since April so it is assumed there is virtually no oxygen. As a result, the utility ruled out the possibility of an explosion "in the immediate future."

Japanese officials said they have found, for the first time, small amounts of plutonium from the damaged Fukushima nuclear power plant as far as 28 miles (45 kilometers) away. At a  October 2, Tokyo news conference, federal officials announced the first discovery plutonium outside the immediate vicinity of the power plant, as well as radioactive strontium in 45 spots as far as 50 miles (80km) from the reactors, The Wall Street Journal reported.

Meanwhile, Tepco is fighting to keep its pre-disaster emergency-response procedures a secret from politicians and the public, arguing they contain valuable trade information. In September the company angered members of a parliamentary committee when it handed over manuals outlining steps that its nuclear plant operators are meant to follow in the case of accidents. All but a few words of the texts were redacted with black ink.

The storm of controversy that followed – one newspaper columnist compared it to wartime censorship – seems not to have softened the company’s stance. Early October it asked Japan’s nuclear safety regulator, which had ordered it to resubmit the manuals without redaction, to allow it to keep much of the material secret. So far only the regulator, the Nuclear and Industrial Safety Agency (Nisa), has seen the originals, which run to thousands of pages. It has not passed them on to the lawmakers who originally requested them. 

Tepco has told Nisa that if the manuals are to be made public, 90 per cent of the content related to “severe accidents” such as that at Fukushima should be kept under black ink. “The manuals contain knowhow that we have built up over a long period of operation,” a company spokesman said. “There are also issues of national security.”

Largest trade union changes policy on nuclear power. The leadership of Rengo, Japan's largest trade union organization will rethink the body's energy policy in light of the Fukushima nuclear crisis, with a view to shifting from its stance of promoting nuclear power to one that aims for a society not reliant on atomic energy, according to Rengo sources on October 3. Since Rengo is the largest supporter of the ruling Democratic Party of Japan, the turnaround is expected to have an impact on the energy policy of the DPJ-led government. Rengo, which counts labor unions of power utilities among its members, has struggled to reconcile differences within the organization over nuclear energy policy. But its leadership has decided on the policy turnaround by taking into account the seriousness of damage brought by the Fukushima nuclear plant disaster, they said. In August 2010, Rengo decided for the first time to promote nuclear power generation and back construction of new nuclear power plants.
Japan Times, 5 October 2011

Sources: The Yomiuri Shimbun, 24 September 2011 /  NIRS Fukushima Update, 29 September 2011 / Jiji Press, 2 October 2011 /  UPI, 2 October 2011 / Financial Times (UK), 5 October 2011

Contact: Citizens' Nuclear Information Center (CNIC). Akebonobashi Co-op 2F-B, 8-5 Sumiyoshi-cho, Shinjuku-ku, Tokyo, 162-0065, Japan
Tel: +81-3-3357-3800