TEPCO has revised its estimates for the core damage in units 1, 2 and 3 of the Fukushima 1 nuclear power plant. It now estimates 55% (previously 70%) damage for unit 1, 35% (previously 30%) for unit 2 and 30% (previously 25%) for unit 3. The estimates are based on radioactivity levels measured inside the reactor containment.
TEPCO has experimented with pumping more water into the reactor core of unit 1 to fill the normally dry part of the containment vessel for cooling purposes:
TEPCO says it will raise the amount of water injected from 6 to 10 tons per hour for 6 hours, and then to 14 tons per hour. The temperature and pressure in the containment vessel will be monitored for 18 hours. The utility says it will decrease the flow back to 6 tons per hour by Thursday morning and then send robots into the reactor building to check for leaks. TEPCO also says it will make sure that the containment vessel, with the added weight of the water inside, can withstand strong aftershocks. The firm says robots on Tuesday detected radiation levels of up to 1,120 millisieverts per hour inside the No.1 reactor building. It says some contaminated water may be leaking from the reactor into external pipes. (NHK, 2011-04-27)
Radiation monitoring devices have been issued to 55 schools and kindergartens in Fukushima prefecture. Teachers will keep a log of radiation exposure of the children. At two schools in the city of Koriyama, some 50 km west of the wrecked reactor, workers are removing contaminated topsoil. The soil is first sprayed with water to prevent dust from rising through the work. The soil will be piled up and covered with sheets before later being moved to landfills.
One female worker in her 50s employed at Fukushima 1 received an accumulated dose of 17.55 mSv over the first quarter of the year, over three times the legal limit. She worked at the plant for 11 days after March 11. Most of the exposure was internal, through inhalation. By law female nuclear workers in Japan must not be exposed to more than 5 ms over any three month period.