A robot probe found sauna-like conditions inside the No. 2 reactor building at the Fukushima Daiichi nuclear power plant but lower levels of radiation than in other damaged units, the plant's owner reported Tuesday.
Reactor No. 2 is believed to be leaking water, thousands of tons of which are filling the basement of its turbine plant and utility tunnels. Workers at the plant began pumping the first of that highly radioactive fluid into a storage tank for contaminated water Tuesday, Japan's Nuclear and Industrial Safety Agency announced. But the Tokyo Electric Power Company, which owns the six-reactor plant, says it has no idea how much lies in those darkened spaces.
A robot inserted into the unit's reactor building Monday found temperatures up to 41 degrees Celsius (106 F) and humidity ranging from 94-99 percent, Tokyo Electric reported Tuesday. Those conditions fogged up the lenses of the probe's cameras, forcing operators to withdraw the device after a few minutes, company officials said.
But the radiation level it recorded was only 4.1 millisieverts per hour -- less than 10 percent of the doses found in the No. 1 and No. 3 reactor buildings.
By comparison, the average resident of an industrialized country receives a dose of about 3 millisieverts per year. Emergency standards for plant workers battling the month-old nuclear disaster limit their annual exposure to 250 millisieverts, while a CT scan produces just under 7 and a chest X-ray delivers a one-time dose of about .05 millisieverts.
Doses above 100 millisieverts can increase the long-term risk of cancer, while 1,000 millisieverts can produce radiation sickness.
Engineers began deploying the U.S.-built "Packbots" into the reactors on Sunday. It's part of an effort to get a better view of conditions inside the buildings, where high radiation readings have kept workers out for weeks.
Cooling systems at Fukushima Daiichi, about 240 km (150 miles) north of Tokyo, were knocked out by the massive tsunami that struck Japan's Pacific coast after a massive earthquake March 11. The disaster triggered the worst nuclear accident since Chernobyl as the cores of reactors 1-3 overheated and spewed huge amounts of radioactive contamination across the surrounding area.
The buildings that house reactors 1 and 3 were blown apart by hydrogen explosions in the first days of the crisis. Another hydrogen buildup is believed to have ruptured a water reservoir beneath the No. 2 reactor, and the pools housing spent but still-energetic fuel assemblies are concerns in units 1, 3 and 4.
Tokyo Electric this week laid out a six- to nine-month timetable for winding down the crisis and bringing the reactors to a complete shutdown.
The disaster has led to mandatory evacuations of about 78,000 people living within 20 km (12.5 miles) of the plant and orders to people living another 10 km away to remain sheltered, affecting another 60,000-plus. Several towns both inside and outside that radius were told to prepare to evacuate soon, while others have been directed to stand by for further instructions.