No one knew it was leaking until a worker found it on May 11. The amount of radioactive materials in the leaking water was far less than the pit water gushing from the Reactor 2 back in early April.

Reactor 3 uses MOX fuel.
TEPCO announced on May 11 evening that a high concentration of cesium-134 was detected in the seawater just outside the silt fence for the water intake area for the Reactor 3 at Fukushima I Nuclear Power Plant. Cesium-134 was found to be 18,000 times the allowable limit for discharge into the ocean. It was the first time the highly contaminated water was found leaking from the Reactor 3. TEPCO carried out an emergency work to stop the leak.

According to TEPCO, at about 10:30AM (JST) on May 11, a worker found the water was leaking from the hollow ducts that house electrical wires in the pit that connects to the trench for the Reactor 3. The water was found to be highly contaminated with radioactive materials. There was a crack on the ocean-side of the pit, and the water was leaking into the ocean. TEPCO filled the ducts with concrete, and stopped the leak at 6:45PM.

The water outside the silt fence for the Reactor 3 water intake also had iodine-131 at 96 becquerels/cubic centimeter, which is 2,400 times the limit. Inside the silt fence, iodine-131 was detected at 190 becquerels/cubic centimeter (4,800 times the limit), cesium-134 at 1,900 becquerels /cubic centimeter (32,000 times the limit). Inside the pit, iodine-131 was detected at 3,400 becquerels/cubic centimeter (85,000 times the limit), and cesium-134 at 37,000 becquerels (620,000 times the limit).

The highly radioactive water sits in the basement of the Reactor 3 turbine building, and TEPCO thinks this water leaked. Junichi Matsumoto of TEPCO said “The silt fence prevents the flow of the contaminated water to some degree, but it is not perfect. In the worst case, the contaminated water could flow into the ocean [outside the silt fence].

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