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Tuesday, April 19, 2011
Robots detect dangerous spike in reactor 3 radiation
French-style air coolers eyed in effort to bring down the heat
Robots sent in to explore the Fukushima No. 1 nuclear plant have found high radiation levels in three reactor buildings that may seriously hinder efforts to bring the plant under control, Japan's nuclear watchdog said Monday.
On Sunday, two U.S.-made robots checked radiation, temperature and oxygen concentrations in reactors 1 and 3 to see if they were safe for repair crews to enter to get the crippled cooling systems back online
In the No. 3 reactor building, the robots detected a radiation level of 28 to 57 millisieverts per hour on the ground floor.
In the No. 1 reactor building, radiation was measured at between 10 and 49 millisieverts per hour.
"It's difficult to work for a long time under these conditions," said Hidehiko Nishiyama, spokesman at the Nuclear and Industrial Safety Agency.
The maximum allowable annual radiation does for nuclear workers is 250 millisieverts, which is two and a half times the precrisis limit. This means each worker can only spend a maximum of five hours inside the building. Many have already passed the standard annual limit of 100 millisierverts and many subcontractors are reportedly refusing to adhere to the higher radiation limit set for the crisis.
On Saturday, workers detected 270 millisieverts per hour on the south side of the same floor in the No. 1 unit, Tepco said.
Tepco will analyze the data and find ways to improve access. The utility was to check the radiation in reactor 2's building Monday.
NISA meanwhile unveiled plans for Tepco to set up a new air-cooling system to cool the coolant water to be stored inside the reactors' containment vessels.
The system, similar to air conditioners used in French nuclear power plants, will remove heat from the coolant water that will circulate inside the containment vessel and keep the core cool.
It will be the first air-cooling system to be used in a Japanese reactor, most of which use water-based cooling systems.
To start the new system, which will hopefully stabilize the reactors' temperatures, however, will take six to nine months, Tepco said Sunday in announcing its plan for ending the crisis.
Meanwhile, a more urgent task awaits at the No. 2 reactor, where radioactive water is flooding its turbine building and an adjacent underground trench.
Tepco plans to pump the highly radioactive water into a nearby facility on the premises that can store about 30,000 tons of water so that workers can resume repairs.
The water level in the trench is rising day by day and went up 3 cm from Sunday to 82 cm as of 7 a.m. Monday.
Tepco is trying to finish water-proofing the storage facility as soon as possible.
The utility is also considering pouring adhesive concrete into the suppression chamber of reactor 2 to patch the hole that is believed to be causing radioactive water to leak into the turbine building and the trench.
The prime cooling systems of the 1, 2, 3 and 4 units have been out of action since the March 11 mega-quake and tsunami hit the six-reactor complex.
Massive amounts of water have been poured into the reactors and their spent nuclear fuel pools as a stopgap measure to cool them down. But pools of contaminated water have been detected in various parts of the site, an apparent side effect of the emergency measure.
Tepco has said the amount of polluted water at the reactor 1, 2 and 3 turbine buildings and nearby areas totals an estimated 67,500 tons.
Information from Kyodo added