On 2 April, water with a surface radiation reading of greater than 1000 mSv/hr was found to be leaking into the sea at unit 2 of the Daiichi reactor.

The water had pooled 10-20cm deep in a culvert with power cables near the water intake, and was leaking out of a 20cm crack, according to a report by NHK news republished by the Japan Atomic Industrial Forum. TEPCO staff began injecting concrete that same afternoon to try to close the crack, but without success. On 3 April a polymer absorbent was poured into the duct to try to stop the leak. The leak was the first documented leak of radioactivity into the sea, and might account for the high readings of radioactivity in the sea around the plant. On Wednesday 30 March iodine-131 was sampled at a point 40km south of Fukushima-Daiichi. The reading was 79.4 Bq/L, twice the legal standard for water discharged from nuclear power plants. The Japan nuclear and industrial safety agency said that radioactive iodine will be diluted in seawater and does not pose a threat to human health.

In other news, temporary injection pumps at unit 1, 2 and 3 were plugged into site power connections on 3 April. The pumps will draw seawater to cool down circulating freshwater. Radiation levels remain too high to verify that on-site pumps have not been damaged by the earthquake.

TEPCO reduced the amount of water injected into units 1&2, saying that temperatures and pressures had stabilised.

On 2 April, a US military barge began pumping a store of fresh water that it has carried to tanks on land. A second US barge with 1300 tons of fresh water has arrived at the site.

The Japanese government and TEPCO have begun radiation monitoring tests inside the 20km exclusion zone around the Fukushima-Daiichi plant. Although tests have already been carried out beyond the exclusion zone, no measurements have been carried out inside that zone, since residents have evacuated the area and doing so would involve risk of radiation dose. However, at meeting with US and Japanese nuclear experts, US experts urged Japan to begin monitoring inside the zone to determine the extent to which radioactive substances are spreading, said NHK news. As a result, about 30 sites inside the zone are now being monitored.

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