The radiation leak detected yesterday at the No.3 reactor indicated possible damage to the unit's vessel, pipes or valves, Japan's Nuclear and Industrial Safety Agency said, two weeks after the magnitude 9 quake and tsunami rocked the country's northeast leaving over 27,000 people dead or unaccounted for.
"At present, our monitoring data suggest the (No.3) reactor retains certain containment functions, but there is a good chance that the reactor has been damaged," Hidehiko Nishiyama, spokesman for the agency, told a press conference.
Three workers at the No.3 reactor's turbine building were yesterday exposed to the water containing radioactive materials 10,000 times the normal level, with two of them hospitalised with possible radiation burns to their feet.
Nishiyama said the high-level radiation is suspected to have originated from the reactor where overheating fuel rods are believed to have been partially melted, or a boiling pool that stores spent nuclear fuel, both of which are located in the same building.
Following the incident, the nuclear agency ordered the Tokyo Electric Power Company (TEPCO), the operator the nuclear plant, to improve radiation management at the crisis-hit facility. TEPCO has already begun removing the highly radioactive water from the site.
Nishiyama said that further verification is needed to find out how the radioactive water reached the underground site. Tonnes of water had been poured into the reactor and in its pool, which was substantially damaged by a hydrogen blast on March 14.
The government, which had earlier designated areas within a 20 km radius of the Fukushima plant as exclusion zone, today encouraged residents within a 30 km radius of the nuclear power station to leave voluntarily, as the release of radioactive materials is expected to continue for some time.
Though the restoration work at the troubled plant was disrupted due to the radiation exposure incident yesterday, TEPCO today prepared to inject fresh water into the No.1, No.2, No.3 and No.4 reactor cores and spent fuel pools, instead of seawater which is being currently used.
Authorities wanted to replace sea water with fresh water as crystallised salt could form a crust on the fuel rods and prevent smooth water circulation, thus diminishing the cooling effect.
Defence Minister Toshimi Kitazawa said that US forces in Japan will offer fresh water to be sprayed at the reactor cores and the fuel pools to ensure ample water supply. TEPCO currently uses fresh water from a dam near the plant.