Officials insist that the situation is under control, but environmentalists and scientists are saying the fission event show the situation at the quake rocked, tsunami hit plant are anything but. They have also noted that chain reactions could be occurring in other of the plant’s hobbled reactors.
A fission event involves the splitting of atoms, which, in the case of certain uranium isotopes, can lead to an uncontrolled chain reaction and emission of radiation.
According to Bellona physicist and executive director, Nils Bøhmer, and Dr Komei Hosokawa, head of the Department of Environmental and Social Research at Japan’s Kyoto Seika University, Xenon-133 and Xenon 135 gas were detected in reactor No 2’s secondary containment.
The presence of these gasses indicated fresh nuclear fission taking place in the hot debris of the melted fuel rods at the bottom of the container, said Hosokawa and Bøhmer.
“This clear indication that a nuclear chain reaction is going on in one the reactors is a very bad sign. TEPCO had said that the situation would be stable within nine months after the accident,” said Bøhmer.
“Any on-going uncontrolled chain-reaction is not an indication of a stable rector, and we could face a much longer period of instability until the reactors are safe,” he said.
A TEPCO official has confirmed a so-called “partial re-criticality” incident in reactor No 2, said Hosokawa in the information he forwarded to Bellona. Hosokawa said the term “partial re-criticality was “a new vague word for [TEPCO’s} spin practice.”
Other radioactive gasses detected at the reactor, said Hosokawa, included Xenon-131m and Krypton-85, which are likely remnants of the chain reactions that occurred immediately after the earthquake and tsunami.
Will the fission event effect cold shutdown?
TEPCO had hoped to bring the wrecked reactors at Fukushima Daiichi to cold shutdown by the end of this year, meaning that the temperatures in their cores would be sustained at 100 degrees Celsius. Evidence of a new chain reaction may impact the shutdown date.
Japanese nuclear authorities, however, say the chain reactions will not affect the projected shut-own schedule. Currently the temperature at the hot zones of the reactors is been sustained at below 100 degrees Celsius by seawater constantly being pumped in.
Hosokawa, however, strongly disagreed, citing the apparent present condition of the nuclear fuel in reactor No 2, if not others.
“TEPCO so far claimed that the melted-down uranium had formed an oval shape with a cooled-down crust. Their roadmap for the “cold shutdown, if ever, is based on this condition,” said Hosokawa. “Now that they propose a quite
different view regarding the condition of nuclear fuel, the roadmap vision [for shutdown] cannot be intact.”
Independent reports on Fukushima unsettling
The news the fresh chain reaction follows a recent report in the Atmospheric Chemistry and Physics journal, arguing that radiation fallout after the Fukushima catastrophe could be underestimated by as much as 80 per cent.
The report claims the registered contamination with caesium-137 depicts only about 19 per cent of the radioactive debris, which actually fell on Japanese territory. The rest was dissolved in the Pacific. It is believed that only two per cent of cesium from Fukushima will reach foreign coasts.
A similar report by the Norwegian Institute for Air Research released last week posited that releases of caesium-137 from the plant after the initial disaster was underestimated by half, and that fallout has reached some 40 percent of Chernobyl.
TEPCO in July admitted four months after the fact that reactor Nos 1,2 and 3 had experienced full fuel melts in the first several hours after Fukushima Daiichi was hit by a massive 9.0 magnitude earthquake and tsunami on March 11, knocking out its primary, back-up and battery cooling systems.
Bringing the chain reactions under control
TEPCO began spraying boric acid on reactor No 2, where the new chain reaction is taking place, at 2:48 a.m. Japan time to prevent accidental chain reactions, according to a statement sent to Bellona from Hosokawa.
Junichi Matsumoto, a general manager at TEPCO told reporters on Monday that, “Given the signs, it’s certain that fission is occurring,” Bloomberg news agency reported.
Matsumoto added that there has been no large-scale criticality and no increase in radiation – something corroborated by Hosokawa’s statements.
It is possible there are similar reactions occurring in reactor Nos 1 and No. 3 reactors, the other cores damaged at the station, Matsumoto told reporters.
“Melted fuel in the No. 2 reactor may have undergone a sustained process of nuclear fission or re-criticality,” Tetsuo Ito, the head of Kinki University’s Atomic Energy Research Institute, told Bloomberg.
“The nuclear fission should be containable by injecting boron into the reactor to absorb neutrons,” he said.
The Fukushima accident, the worst atomic disaster since Chernobyl in 1986, was responsible for the biggest discharge of radioactive material into the ocean in history, according to a study from a French nuclear safety institute.
TEPCO and NISA have declined to comment all three studies as of Wednesday.
Chain reactions possible in other reactors
“We are evaluating whether there are many reactions or not or whether its stopped,” Matsumoto said. The incident won’t affect its schedule of bringing the plant under control by the end of this year,’ Matsumoto told reporters..
Should fissioning have occurred the injection of boron will have stopped it, Tadashi Narabayashi, a former reactor safety researcher at Toshiba Corp. and now a nuclear engineering professor at Hokkaido University told The Deccan Herald news site.
What the reactors have weathered
Fukushima’s reactor Nos 1, 2 and 3, experienced hydrogen pressure explosions due to the fuel melts that occurred during the first days of the crisis. The explosions of the reactor buildings are credited with damaging reactor containment vessels.
Four of the plants six reactors sustained major damage, as well as possible damage to a spent nuclear fuel storage pool. It was several weeks before TEPCO was able to restore independent cooling to the reactor. Prior to that, the only resort was to inundate the reactors with sea water dropped from helicopters and fired from water cannons, leaving the plant to deal with thousands of tons of radioactive water and leaks.
The radioactive caesium that flowed into the sea from the plant was 30 times the amount estimated by TEPCO, according to the Institute for Radiological Protection and Nuclear Safety, which is funded by the French government.
The oceanic study estimates 27,000 terabecquerels of radioactive cesium 137 leaked into the sea from the plant.