For the first time since the March earthquake and tsunami, workers on Thursday entered the No. 1 reactor at Japan's stricken Fukushima Dai-ichi nuclear power plant, according to the Tokyo Electric Power Co.
The recovery team began a project to install six ventilation machines that would absorb isotopes from the air inside the building, said company spokesman Taisuke Tomikawa. Due to the high risk of radiation exposure, teams were expected to work in shifts inside the reactor.
The goal is to lower radiation levels so that 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-controlled robots have plumbed the depths of the building to test radiation levels, the utility said. In mid April, a robot recorded radioactivity of about 50 millisieverts per hour inside Unit 1's reactor building, too high for workers to enter the structure safely. Subsequent tests have shown a drop in radiation levels.
The devastating temblor and resulting tsunami damaged four of the six reactors at the decades-old facility 140 miles north of Tokyo. Some 80,000 residents have been evacuated from the area around the plant. About 25,000 people along Japan's northeastern coast have been confirmed dead or are missing after the disaster.
The nuclear-facility workers, organized in teams of twos and threes, are dashing into the reactor for about 10 minutes at a time, in an effort to limit their radiation exposure. They are dressed in full-body protective suits and masks and are lugging 30-pound fire extinguishers in case of an explosion.
The radiation levels inside the reactor are roughly 10 to 40 millisieverts per hour, and work crews are trying to limit their exposure to around 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 that includes nausea and vomiting.
Tomikawa said it should take two or three days to install the ventilation system. He estimated that the work to install the reactor's new cooling system could begin as soon as May 16.
Thursday's development suggests that the utility is making progress in stabilizing the plant. If successfully installed, the cooling equipment would bring down the temperature inside the reactor's core and speed the process of resolving Japan's worst nuclear crisis. The company aims to have a cooling system in place by mid May and will add two more such systems for reactors Nos. 2 and 3 soon. The system would extract hot water from inside the reactor chamber and inject chilled water into the chamber and the core containing the hot nuclear fuel rods.
Officials also announced new findings of radioactive contamination. Tepco said Tuesday it had found high amounts of radioactive isotopes along the sea floor less than 2 miles off Japan's northeastern coast. The company said cesium-134, cesium-137 and iodine-121 turned up in tests performed April 29 in two places at a depth of 65 to 100 feet.