Tokyo Electric Power Company says it is releasing radioactive water into the ocean so as to leave space in the stricken Fukushima Daiichi nuclear power plant for water that is even more contaminated.
The company said it is releasing a total of 11,500 tons of water, starting Monday evening Japan time. The water is being dumped because the water in the Number 2 reactor (unit 2) is so highly contaminated that it had to be taken out and put in the storage site where the less radioactive water is.
The water that is going into the ocean, the company said, is about 100 times the legal limit for radioactive iodine-131. The legal limit is 0.04 becquerels per cubic centimeter, which means the water being dumped into the sea is at about 4 becquerels per cubic centimeter. A becquerel (Bq) is a unit of radioactivity that measures the number of decay events per second, adjusted for the element one is measuring. Limits for exposure differ depending on the element.
By contrast, the water in the ocean detected near the discharge canals of the reactor was thousands of times the limit allowed, approaching 57 becquerels of iodine-131 on Wednesday. TEPCO has yet to release measurements from the rest of the week. The water that is being drained from Unit 2 is 100,000 times the allowed levels of contamination -- which would be about 4,000 becquerels per cubic centimeter.
Some of the water, about 1,500 tons of it, was from the groundwater around the plant. Radioactive material was found there last week. Contamination of iodine-131 was 10,000 times higher than the government standards. It was found nearly 50 feet (15 meters) below one of the reactors, according to a statement from TEPCO.
Meanwhile, a 20 centimeter crack was found in the shaft that houses power cables near the water intakes of unit 2. The company tried injecting concrete into it to stop the leakage of radioactive water into the ocean. That didn't work, so the company said it will try injecting polymer into it. On Monday TEPCO said it was putting tracer chemicals in the water to see if it is still leaking.
The radioactive water leaking into the ground is a sign there may be more damage to the reactors than previously thought. Iodine-131 has a half life of about eight days, which means that the only way for it to show up in those amounts is for the water to come in contact with either spent fuel rods or the reactor core.