Robots that entered two crippled buildings Monday at Japan’s Fukushima nuclear plant found an environment still too radioactive for workers to enter.
Nuclear officials said the radiation data for Unit 1 and Unit 3 at the tsunami-flooded Dai-ichi plant collected by U.S.-made robots do not alter plans for stabilizing the complex by year’s end under a “road map” released by the plant operator Sunday.
Workers have not gone inside the two reactor buildings since the first days after the plant’s cooling systems went down after the earthquake spawned tsunami hit the nuclear site March 11. Hydrogen explosions in both buildings in the first few days destroyed their roofs and littered them with radioactive debris.
But a pair of robots, called Packbots, haltingly entered the two buildings Sunday and took readings for temperature, pressure and radioactivity. Officials will need to collect more data and radioactivity must go down further before workers can go inside, said Hidehiko Nishiyama of Japan’s Nuclear and Industrial Safety Agency.
“It’s a harsh environment for humans to work inside,” Nishiyama said.
Officials said the radiation findings should not hamper the goal of achieving a cold shutdown of the plant within six to nine months as laid out in a timetable TEPCO unveiled Sunday. Rather, the new information would help the company in figuring out how to push ahead with the plan.
“We have expected high radioactivity inside the reactor buildings, which was confirmed by data collected by the robot,” Chief Cabinet Secretary Yukio Edano said. “Even I had expected high radioactivity in those areas. I’m sure TEPCO and other experts have factored in those figures when they compiled the roadmap.”
TEPCO official Takeshi Makigami said the robots will pave the way for workers to be able to re-enter the building.
“What robots can do is limited, so eventually, people must enter the buildings,” Makigami said.
The robots investigated Unit 2 later Monday.
In addition, readings from a water tank in Unit 2 showed an increase in radiation that indicates likely damage to the fuel rods inside the spent fuel pool there, TEPCO officials said. That was the first indication of damage to those rods.
The radiation was far higher than that measured in the spent fuel pool of Unit 4, suggesting the damage to the fuel in Unit 2 is greater.
Bedford, MA-based iRobot made the robots the Japanese are using. Traveling on treads, the devices opened closed doors and explored the insides of the reactor buildings, coming back with radioactivity readings of up to 49 millisieverts per hour inside Unit 1 and up to 57 millisieverts per hour inside Unit 3.
The legal limit for nuclear workers more than doubled since the crisis began to 250 millisieverts. The U.S. Environmental Protection Agency recommends an evacuation after an incident releases 10 millisieverts of radiation, and workers in the U.S. nuclear industry have an upper limit of 50 millisieverts per year. Doctors say radiation sickness sets in at 1,000 millisieverts and includes nausea and vomiting.
The robots, along with remote controlled miniature helicopters, allowed TEPCO to photograph and take measurements of conditions in and around the plant while minimizing the workers’ exposure to radiation and other hazards.