Raising fresh concerns about its ability to bring the nuclear crisis under control, Tokyo Electric Power Co. announced June 3 that highly radioactive water pooled in underground pits could start rising above ground in less than three weeks.
The company said there were 105,100 tons of stagnant water with high levels of radioactivity within the power plant as of the end of May.
The water contained an estimated 720,000 terabecquerels of radioactivity (1 tera is 1 trillion), according to the operator of the plant battered by the earthquake in March. That is more than the amount of radioactivity released from the plant into the atmosphere in the wake of the accident, which is estimated at 370,000 to 630,000 terabecquerels.
TEPCO warned that the contaminated water pooled in the basement of the buildings could start flowing out as early as June 20.
The company plans to treat the radioactive water in a new facility to be completed June 15 to prevent the overflow of polluted water, but it will also consider reducing the amount of fresh water being injected into the reactors.
Radioactive water is flowing into the basement of facilities within the compound as well as the buildings housing the Nos. 1 and 4 reactors, their turbine buildings, and the radioactive waste treatment facility, according to a report submitted by TEPCO to the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry.
The total radioactivity of the pools of contaminated water is equivalent to one seventh of the 5.2 million terabecquerels released into the atmosphere from the Chernobyl nuclear power plant disaster in 1986.
As TEPCO continues injecting water into the reactors at the Fukushima plant to cool their nuclear fuel, the amount of highly radioactive water leaking from the reactors is expected to continue increasing.
The utility made estimates of when the contaminated water in buildings' basements could leak aboveground, under several different scenarios, suggesting that it could happen as early as June 20.
It has been confirmed that highly radioactive water was leaked into the sea twice during the crisis: first 500 tons containing 4,700 terabecquerels gushed out, with 250 tons containing 20 terabecquerels following later.
TEPCO is building a new facility to treat the highly radioactive water while storing it in equipment located within the turbine buildings.
The expected overflow could take place earlier if there is heavy rain in the area, the utility said. In that case, the company will buy time by cutting the amount of water being injected into the reactors. The polluted water in the turbine buildings of reactors 2 and 3 had been transferred to the radioactive waste treatment facility until the company stopped this operation May 26 as the total amount approached the planned capacity of 14,000 tons.
Levels of contaminated water have since been rising, partly because of rainfall.
Radioactive water in the pits to the underground tunnels coming from the reactors 2 and 3 was 21.8 centimeters from the surface of the ground as of 7 a.m. on June 3, according to the company.
Workers collect data inside the control room of reactors Nos. 1 and 2 at the Fukushima No. 1 nuclear power plant in March. (Provided by the Nuclear and Industrial Safety Agency)
2 TEPCO workers exposed to high-level radiation
Two TEPCO workers at the crippled Fukushima No. 1 nuclear power plant were exposed to levels of radiation exceeding standards established by the government.
In the worst case, one of the workers may have been exposed to 650 millisieverts, more than double the upper limit of 250 millisieverts established by the government for workers dealing with the nuclear accident.
Tokyo Electric Power Co. officials on June 3 announced the results of a study conducted by the National Institute of Radiological Sciences.
One of the employees is in his 30s while the other is in his 40s. Since the Great East Japan Earthquake struck March 11, the two have been working at either the central control room in a reactor or the building away from the reactors where work is overseen during emergencies.
The study estimated that the man in his 30s has been exposed to internal radiation at levels between 210 and 580 millisieverts while the man in his 40s has been exposed to levels between 200 and 570 millisieverts.
The man in his 30s was found to have been exposed externally to 73.71 millisieverts while the man in his 40s was exposed externally to 88.70 millisieverts.
Combining the internal and external exposure levels would mean that both men had been exposed to more the 250 millisieverts.
Health Ministry officials will conduct an investigation at TEPCO offices and issue recommendations to improve worker safety.
The two men took stable iodine agents March 13 to prevent radioactive iodine from accumulating in the thyroid gland. However, after taking two pills that day, neither took the pills again.
Because an extended period of working under exposure to high levels of radiation was never envisioned, it was not until March 19 that the Nuclear Safety Commission of Japan asked workers to continually take the iodine agents.
According to ministry officials, by then there were 130 TEPCO workers engaged in work similar to that of the two men found to have been exposed to radiation.
A study by TEPCO found 52 workers with radiation exposure internally of levels exceeding 20 millisieverts. Of those individuals, three were exposed to radiation levels exceeding 100 millisieverts.
The water level in the pits had been rising at a daily rate of 5.9 centimeters for the No. 2 reactor and 2.1 centimeters for the No. 3 reactor.