For the first time since the magnitude 9 earthquake and the tsunami struck Japan nearly two months ago, workers on Thursday entered a damaged reactor at the stricken Fukushima Daiichi nuclear power plant, Tokyo Electric Power Co. said.
The recovery team began a project to lower radiation levels by installing six ventilation machines that would absorb isotopes from the air in the No. 1 reactor, said company spokesman Taisuke Tomikawa. Because of the high danger of exposure, teams were expected to spend only 10 minutes at a time inside.
The ventilation is needed before workers can replace the facility’s cooling systems that were damaged by the tsunami, causing a hydrogen explosion that released damaging radioactivity into the air, soil and water.
In recent weeks, remote-control robots have plumbed the depths of the building to test radiation levels, the utility said. In mid-April, a robot recorded radioactivity readings of about 50 millisieverts per hour in Unit 1’s reactor building, a level still too high for workers to enter. Subsequent tests have shown a drop in radiation levels.
The devastating quake and resulting tsunami March 11 damaged four of the six reactors at the decades-old facility 140 miles north of Tokyo. About 80,000 residents have been evacuated from the area around the plant. Along Japan’s northeast coast, 25,000 people have been confirmed dead or missing in the disaster.
The nuclear facility workers, organized in teams of two and three, are dressed in full-body radiation suits and masks and are equipped with fire extinguishers.
The radiation levels in the reactor are about 10 to 40 millisieverts per hour, and work crews are trying to limit their exposure to about 3 millisieverts. U.S. nuclear workers are allowed an upper limit of 50 millisieverts per year. Experts say that a dose of 1,000 millisieverts causes radiation sickness, with symptoms including nausea and vomiting.
Tomikawa said it should take two or three days to put in the ventilation system. He estimated that the work to install the reactor’s new cooling system could begin as soon as May 16.
If successfully installed, the cooling equipment would bring down the temperature in the reactor’s core and speed the process of resolving Japan’s worst nuclear crisis. The company plans to add cooling equipment for reactors Nos. 2 and 3 sometime in the next two months, it said.
The system would extract hot water from the reactor chamber and inject chilled water into the chamber and the core containing the hot nuclear fuel rods.
Officials this week announced new findings of radioactive contamination.
Tepco said it found high amounts of radioactive isotopes along the seafloor less than two miles off Japan’s northeastern coast. The company said cesium-134, cesium-137 and iodine-131 turned up in tests performed in April in two places at a depth of 65 feet to 100 feet.
The company said that before the plant began leaking radiation, only trace levels of cesium-137 had been found in the ocean, and that the latest readings were more than 600 times higher. Significant levels of cesium-134 or iodine-131 had not previously been detected on the seafloor, Tepco said.
“We continue to monitor radioactivity levels in fish and other sea organisms,” said Tomikawa, adding that the tests will be conducted once a month for the foreseeable future.
According to Japanese news reports this week, the nation’s system to predict the volume of radioactive materials emitted in a nuclear accident failed to work as designed because power to the measuring equipment was lost.
Highly radioactive cesium turned up in sewage sludge and slag, a byproduct of incinerated sludge, at treatment facilities in the city of Koriyama, in Fukushima prefecture, according to the prefectural government. The amount of cesium was about 1,400 times the levels in the sewage before the quake.
Fukushima officials worry that the sewage treatment might contribute to airborne radiation. The government has no guidelines for how to dispose of radioactive sludge, and the slag has been kept in storage facilities. About 550 tons of sewage sludge have been shipped to cement makers, and officials are trying to track where they have gone.
Tepco said last month that it hoped to stabilize the facility’s reactors by the beginning of next year. Under a two-phase plan, the company expects to spend three months cooling the reactors and plugging radiation leaks. It will also set up equipment to decontaminate water that was used to cool the reactors and has been pooling in underground tunnels.
During the second phase, which is expected to take about six months, Tepco hopes to put the reactors into a stable state known as a cold shutdown, but deactivating the reactors could take years to complete.
Times staff writer Glionna reported from Sendai and special correspondent Hall from Tokyo.