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High-level radiation in trench water may have come from reactor coreTOKYO —
High levels of radiation exceeding 1,000 millisieverts per hour have been detected in water in a trench outside the No. 2 reactor’s building at the troubled Fukushima Daiichi nuclear plant, with the contaminated water suspected to have come from the reactor’s core, where fuel rods have partially melted, authorities said Monday.
The government’s Nuclear and Industrial Safety Agency said the plant operator Tokyo Electric Power Co (TEPCO) is expected to pump out similarly highly contaminated water that has been piling up in the basement of the No. 2 reactor’s turbine building, which is connected to the tunnel-like trench, to eventually remove the trench water.
TEPCO said the high radiation level in water in the trench connected to the No. 2 complex was detected Sunday, adding the radiation level in the air of the trench stood at 100 to 300 millisieverts.
TEPCO also found a trench connected to the No. 1 reactor building was filled with radioactive water on Sunday afternoon.
The radiation level at the surface of the trench water adjacent to the No. 1 complex was 0.4 millisievert per hour but the level could not be measured at the gutter linked to the No. 3 unit as rubble prevented the firm from checking it, the company added.
Although it remains unknown whether the contaminated water has flowed into the sea from the trenches that are 55 to 70 meters away from the shore, TEPCO suspects the high concentration of radioactive substances found in seawater near the plant reactors’ drainage outlets may be linked to the trench water.
Haruki Madarame, chairman of the Nuclear Safety Commission of Japan, a government panel, told reporters he is ‘‘very worried’’ about the high-level radiation detected in water in the trenches, which are outside of the radiation controlled area set by TEPCO.
‘‘We must control the water well so it won’t ever go outside’’ the complex, said Sakae Muto, vice president of TEPCO, at a news conference.
TEPCO revealed the elevated radiation levels in trench water a day after it first detected them, but Muto denied any intention of withholding information from the public, noting he was briefed on the readings Monday afternoon.
On Monday, TEPCO continued to remove highly radioactive water from inside reactor buildings at the crisis-hit plant, in an effort to enable engineers to restore the power station’s crippled cooling functions. The turbine buildings are equipped with electric equipment necessary to cool down the reactors.
TEPCO has found the concentration of radioactive substances in a pool at the No. 2 reactor’s basement was 100,000 times higher than usual for water in a reactor core.
Chief Cabinet Secretary Yukio Edano told a press conference the highly radioactive water found at the basement of the No. 2 reactor’s turbine building is ‘‘believed to have temporarily had contact with fuel rods (in the reactor’s core) that have partially melted.’‘
The safety commission chaired by Madarame said in its recommendations to Prime Minister Naoto Kan that highly radioactive water in the No. 2 reactor’s containment vessel could have directly leaked, raising concerns that polluted water could spread to the building’s underground and to the sea.
Hidehiko Nishiyama, a spokesman for the nuclear agency, however, denied the possibility that the No. 2 reactor’s vessel has cracks or holes, saying no data suggest such conditions. It is rather likely that radioactive water has leaked from pipes or valves, he said.
Nishiyama said it is now necessary to strike a balance between two missions—injecting coolant water into the reactor cores and spent nuclear fuel pools to prevent them from overheating, and removing radioactive water in the turbine buildings and trenches.
He said the water contamination may have been caused by operations to pour massive amounts of coolant water into the reactors and pools.
Since Sunday, TEPCO has been trying to move the radioactive water in the basement of the No. 1 reactor’s turbine building to a tank in the unit by using three pumps.
But the operator has yet to start such work at the remaining three reactor buildings due to difficulties in securing enough space in tanks to accommodate the polluted water, according to the nuclear agency.
In a related development, the nuclear agency said radioactive iodine-131 at a concentration 1,150 times the maximum allowable level was detected Sunday in a seawater sample taken around 1.5 kilometers north of the drainage outlets of the troubled No. 1-4 reactors.
Nishiyama said it is highly likely that the polluted water spotted near the No. 5-6 reactors flowed from the sea area near the No. 1-4 reactors along the coastline.
He said there were no health concerns so far because fishing would not be conducted in the evacuation-designated area within 20 kilometers of the plant and radioactive materials would be ‘‘significantly diluted’’ by the time they are consumed by marine species and then by people.
Removal of highly radioactive water is also meant to reduce the risk of more workers being exposed to radioactive substances. The number of workers who have been exposed to radiation exceeding 100 millisieverts at the plant came to 19 as of Monday, TEPCO said.
Exposure to 100 millisieverts is the legal limit for nuclear plant workers dealing with an emergency, but the limit has been raised to 250 millisieverts during the ongoing crisis, the worst Japan has seen, at the plant some 220 kilometers northeast of Tokyo.
Among the 19, three received treatment at a radiation research center in Chiba Prefecture after they were exposed to radiation of 173 to 180 millisieverts Thursday. They were discharged Monday, with officials of the center saying the exposure has not affected their health.
Source Japan Today