Nucnet - Tokyo Electric Power Company (Tepco) says it has identified a source of a leak of highly radioactive water leaking into the ocean from unit 2 at the Fukushima-Daiichi nuclear plant.
The power company said today (Saturday) that water has been seeping from a 20 cm crack in the wall of a two-metre-deep pit that contains power cables near the reactor's water intake.
Water between 10 and 20 cms deep was found in the pit. The radiation level has been measured at more than 1,000 millisieverts (mSv) per hour at the surface of the contaminated water in the pit, Tepco said in a statement today at noon local time.
Tepco said it is preparing to inject concrete into the cracked pit to stop the leak.
Japan's Nuclear and Industrial Safety Agency (NISA) confirmed the crack could be one of the sources of radioactivity found in seawater near the water outlet.
NISA said it has asked Tepco to test samples of seawater at more locations near the plant and analyse them for different radioactive materials.
In the past week, the radiation detected in water in the basement of the turbine building at unit 2 has been about 100,000 times higher than the normal level. High levels of radiation were also found in puddles in a utility trench outside the turbine building.
Tepco also said it had made errors measuring the composition of radioactive isotopes in samples of contaminated water taken from plant buildings, trenches, and the sea. The total activity and the iodine-131 values were correct, but the tellurium-129 and molybdenum-99 values were too high because of a programming error in their laboratory. The corrected data have since been published on Tepco's website.
Meanwhile, NISA has said radiation dose levels around the plant are now safe in areas such as the village of Iitake, where authorities had earlier urged residents to avoid drinking tap water after tests showed it contained more than three times the maximum standard of radioactive iodine.
The International Atomic Energy Agency (IAEA) reported that on 1 April, iodine-131 was detected in seven prefectures ranging from 7 to 74 becquerel per square metre. The level of caesium-137 in nine prefectures ranged from 2.9 to 76 becquerel per square metre. Reported gamma dose rates in the 45 prefectures showed no significant changes compared to 31 March 2011.
NISA said that 106,000 people from Fukushima prefecture had been body-scanned for radioactivity and 102 were above the safe level of 100,000 counts per minute (cpm). When re-checked without their clothing, they were below the limit.
NISA reported that among the workers at the Fukushima-Daiichi plant, 21 have received doses exceeding the 100-mSv limit. No worker has received a dose above 250 mSv, which is the dose limit for urgent emergency work according to international recommendations.
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