Nuclear fuel has melted in three reactors at Japan’s Fukushima Daiichi nuclear power plant and fallen to the lower sections of their container vessels, raising the specter of overheated material compromising a container and causing a massive radiation release
, the Atomic Energy Society of Japan said in a report released on Friday (see GSN
, April 15).
The group played down the possibility of a container breach, though, noting that only a small amount of fuel had melted so far and affected material had assumed a granulated structure and remained relatively cool, Kyodo News reported. The six-reactor plant was crippled by the 9.0-magnitude earthquake and devastating tsunami that hit Japan on March 11; the confirmed death toll from the events now exceeds 12,000 people.
The melted fuel was thought to have dispersed uniformly across the lower portions of the containers of reactors No. 1, No. 2 and No. 3, making the material highly unlikely to resume the fission process in a “recriticality,” according to the organization, which said fuel rods in all three reactors had been harmed. Fuel in the No. 1 and No. 2 reactors has made contact with air, while the No. 3 reactor’s rods have remained underwater, the group said.
Bringing the fuel under control could take between two and three months if restoration work moved forward as expected, said Takashi Sawada, the group’s deputy chairman. The organization based its assessment on information provided by the Japanese Nuclear and Industrial Safety Agency and by Tokyo Electric Power, the plant’s operator.
Plant personnel pressed ahead in efforts to prevent additional radioactive material from escaping the site, deploying steel barriers around a No. 2 reactor pipeline and proceeding with the insertion of nitrogen gas into the No. 1 reactor to prevent additional hydrogen blasts. Pressure in the No. 1 reactor has fallen to a certain degree, pointing to the possible escape of air, but radiation in the area has remained largely unchanged.
Tokyo Electric Power indicated it could drop sandbags filled with zeolite into the nearby ocean as soon as Friday to help curb the spread of radioactive contaminants (Kyodo News I, April 15). Silt fencing was deployed in front of screening at the No. 3 and No. 4 reactors for containing radioactive water, the International Atomic Energy Agency said on Thursday (International Atomic Energy Agency release, April 15).
Workers earlier this week transferred roughly 660 tons of radiation-tainted water out of an underground passage, but fluid flooding the area reached its original depth by Friday morning, Kyodo News quoted the atomic safety agency as saying. Contaminated water has hindered efforts to restore cooling mechanisms needed to help prevent additional radioactive material from escaping the site.
A nuclear waste treatment area intended to receive the water was still undergoing inspection for possible weak points in pipelines.”‘I’m hoping that work to stop water leaks at the (facility) is finished as soon as possible to start channeling the water there,” said Industry Minister Banri Kaieda said on Friday (Kyodo News I).
Fresh water continued to be transferred into reactors No. 1, No. 2 and No. 3, the U.N. nuclear watchdog said. Conditions remained consistent at the No. 5 and No. 6 reactors (International Atomic Energy Agency release).
Soil samples taken at the facility between March 31 and April 4 contained small amounts of plutonium, Kyodo News reported on Friday. The finding marked the third detection of plutonium traces at the site (Kyodo News I).
Radioactive iodine and cesium levels might increased dozens of times over in groundwater close to the No. 1 and No. 2 reactors between April 6 and 13 (Kyodo News II, April 15). Strontium also turned up in soil close to the facility for the first time, the Sydney Morning Herald reported on Friday.
Tokyo Electric Power was still developing a longer-term strategy for stabilizing plant conditions, company president Masataka Shimizu said (Danielle Demetriou, Sydney Morning Herald, April 15).
Specialists with Toshiba, one supplier of plant components, said conditions could be brought under control “in several months,” Norio Sasaki, the firm’s chief executive, said on Thursday. A plan developed by the company calls for the removal of fuel from reactor containers to start after five years and for decontamination to take place over another five years, the New York Times reported on Thursday.
Hitachi, which has developed a separate plan to decommission the facility, said Toshiba’s proposal was too hopeful and suggested the fuel removal process alone could take a decade to complete.
The status of the nuclear fuel at the site would affect the speed of dismantlement, said Tetsuo Matsumoto, a nuclear engineering professor with Tokyo City University. “Will it still be shaped like rods? Or will it have melted and collapsed into a big mass?” the expert asked. “It could be 10 years or it could be 30. You just won’t know until you open up the reactor” (Hiroko Tabuchi, New York Times, April 14).
Tokyo Electric Power on Wednesday said the deterioration of spent fuel stored in the No. 4 reactor’s cooling pond appeared confined, the Asahi Shimbun reported. Fuel in the reactor was only partly compromised, the company indicated (Asahi Shimbun I, April 15).
The Japanese government on Friday indicated a smaller quantity of radioactive contaminants had been poured into the ocean in a controlled dump of low-level radioactive water than previously suspected, Kyodo News reported. Tokyo Electric Power suggested the 10,393 tons of water jettisoned between April 4 and 10 contained up to 170 billion becquerels of contaminants, but the Nuclear and Industrial Safety Agency estimated the total amount released to fall around 150 billion becquerels (Kyodo News III, April 15).
The U.S. Energy Department was sending five massive steel containers and a tractor trailer for holding contaminated water from the plant, the U.S. Embassy in Tokyo indicated on Thursday (Kyodo News IV, April 14).
Fukushima University experts have plotted out the spread of air-based radioactive materials from the plant using samples taken late last month from 370 points around Fukushima prefecture, the Asahi Shimbun reported on Friday (Asahi Shimbun II, April 15).
In excess of 100 academic specialists intend next month to launch an investigation of the ecological and safety implications of radioactive contaminants released from the facility, Kyodo News reported. Members of the team are expected to help the Fukushima government gather soil samples from 1,500 points along 62 miles of coastline and as far as 37 miles from the ocean (Kyodo News V, April 14).
Russian Prime Minister Vladimir Putin on Friday said specialists in his country “will assess the impact of the Fukushima Daiichi nuclear plant accident on the environment and will also conduct environmental monitoring” (Kyodo News V, April 15).
Participating agencies would include the Russian Atomic Energy Ministry and Russian Meteorological Service, ITAR-Tass quoted Russian Geographical Society Vice President Artur Chilingarov as saying. The monitoring “starts on April 22 and will continue 24 days,” he said (ITAR-Tass, April 15).