Damaged Japan nuclear reactor may still be active

Nuclear fission by-products have been detected at one of the reactors at the Fukushima Daiichi nuclear power plant, the government said Wednesday, raising the possibility that some parts of the melted core may still be active.

The Nuclear and Industrial Safety Agency said that small amounts of Xenon-133 and 135, both by-products of nuclear fission, were detected in a survey of the reactor. Neither substance poses a risk to public health. Xenon-133 has a short half-life of five days, and Xenon-135 just nine hours, an agency spokesman said.

Any nuclear reaction would likely be taking place on a localised basis, the spokesman said. A return of nuclear fission would be a setback for plant operator Tokyo Electric Power Co., which hopes to bring the reactors to a safe condition known as cold shutdown by the end of the year.

But agency officials said that it was too soon to say whether the finding represented a major concern. They said there have been no abnormalities detected in the temperature or pressure of the reactor, which has recently cooled down sharply.

“Judging from the amount of xenon detected, any reaction happening in the reactor seems very small scale,” said Tetsuo Sawada, assistant professor of reactor engineering at the Tokyo Institute of Technology. “It doesn’t look like something you have to worry about too much, but we need more information, especially on the scale of the possible reaction,” he said.

Tepco began injecting boric acid, which serves to stop a nuclear reaction, into the reactor early Wednesday morning.

“It is possible that free neutrons still remain inside the reactor, causing a nuclear reaction,” said Satoru Tanaka, a professor of nuclear engineering at Tokyo University. He said this suggests a further meltdown of the fuel itself is not taking place.

Xenon was found when air inside the reactor was taken out for filtering, as part of an effort to reduce radioactive emissions from the plant. The initiative was undertaken only for the reactor No. 2. The agency said that Xenon might well be detected in the air inside the reactors No. 1 and 3.

The three reactors are widely believed to have suffered a core meltdown in the wake of the March 11 earthquake and tsunami, resulting in substantial damage to the reactors including the containment structure.

Officials said that nuclear fission could have been continuing undetected, albeit on a very limited scale. “We do not deny any possibility, including that of localised criticality inside the reactor,” said agency spokesman Yoshinori Moriyama.

Criticality refers to a sustained nuclear chain reaction, which can release a large amount of energy.

Moriyama said that he doesn’t expect any change to the timetable as a result of the latest discovery.

“What is important is to keep monitoring any signs of fissile reaction and maintain an ability to deal with it,” he said.

The discovery coincides with the first authorised restart of a nuclear reactor since the March 11 disaster.

Kyushu Electric Power Co. said that its Genkai No. 4 reactor, which automatically shut down after a fault on October 4, was restarted Tuesday evening and would begin generating electricity Wednesday afternoon. -By Mitsuru Obe and Shawn Schroter

Nuclear fission by-products have been detected at one of the reactors at the Fukushima Daiichi nuclear power plant, the government said Wednesday, raising the possibility that some parts of the melted core may still be active.

The Nuclear and Industrial Safety Agency said that small amounts of Xenon-133 and 135, both by-products of nuclear fission, were detected in a survey of the reactor. Neither substance poses a risk to public health. Xenon-133 has a short half-life of five days, and Xenon-135 just nine hours, an agency spokesman said.

Any nuclear reaction would likely be taking place on a localised basis, the spokesman said. A return of nuclear fission would be a setback for plant operator Tokyo Electric Power Co., which hopes to bring the reactors to a safe condition known as cold shutdown by the end of the year.

But agency officials said that it was too soon to say whether the finding represented a major concern. They said there have been no abnormalities detected in the temperature or pressure of the reactor, which has recently cooled down sharply.

“Judging from the amount of xenon detected, any reaction happening in the reactor seems very small scale,” said Tetsuo Sawada, assistant professor of reactor engineering at the Tokyo Institute of Technology. “It doesn’t look like something you have to worry about too much, but we need more information, especially on the scale of the possible reaction,” he said.

Tepco began injecting boric acid, which serves to stop a nuclear reaction, into the reactor early Wednesday morning.

“It is possible that free neutrons still remain inside the reactor, causing a nuclear reaction,” said Satoru Tanaka, a professor of nuclear engineering at Tokyo University. He said this suggests a further meltdown of the fuel itself is not taking place.

Xenon was found when air inside the reactor was taken out for filtering, as part of an effort to reduce radioactive emissions from the plant. The initiative was undertaken only for the reactor No. 2. The agency said that Xenon might well be detected in the air inside the reactors No. 1 and 3.

The three reactors are widely believed to have suffered a core meltdown in the wake of the March 11 earthquake and tsunami, resulting in substantial damage to the reactors including the containment structure.

Officials said that nuclear fission could have been continuing undetected, albeit on a very limited scale. “We do not deny any possibility, including that of localised criticality inside the reactor,” said agency spokesman Yoshinori Moriyama.

Criticality refers to a sustained nuclear chain reaction, which can release a large amount of energy.

Moriyama said that he doesn’t expect any change to the timetable as a result of the latest discovery.

“What is important is to keep monitoring any signs of fissile reaction and maintain an ability to deal with it,” he said.

The discovery coincides with the first authorised restart of a nuclear reactor since the March 11 disaster.

Kyushu Electric Power Co. said that its Genkai No. 4 reactor, which automatically shut down after a fault on October 4, was restarted Tuesday evening and would begin generating electricity Wednesday afternoon. -By Mitsuru Obe and Shawn Schroter

http://online.wsj.com/article/SB10001424052970204394804577012782638556906.html

 

Category: Japan