April 15, 2011
The concentration levels of radioactive iodine and cesium in groundwater near the troubled Nos. 1 and 2 reactors at the Fukushima Daiichi nuclear power plant have increased up to several dozen times in one week, suggesting that toxic water has seeped from nearby reactor turbine buildings or elsewhere, Tokyo Electric Power Co. said Thursday.
The announcement came as the plant operator continued to grapple with pools of highly radioactive water found on the plant’s premises, with the level of polluted water filling an underground trench edging up again after the company finished pumping out around 660 tons of water.
According to the latest findings, a groundwater sample taken April 6 near the No. 1 reactor turbine building showed radioactive iodine-131 of 72 becquerels per cubic meter, with the concentration level growing to 400 becquerels as of Wednesday. The concentration level of cesium-134 increased from 1.4 becquerels to 53 becquerels.
The government’s nuclear regulatory agency said it had ordered the utility firm known as TEPCO to enhance monitoring of groundwater inside the plant, which is located on the Pacific coast.
A total of around 60,000 tons of contaminated water is believed to be flooding the basements of the Nos. 1 to 3 reactor turbine buildings as well as trenches connected to them, and the water is hampering work to restore the cooling functions of the reactors lost since the March 11 earthquake and ensuing tsunami.
The pools of contaminated water are believed to be a side effect of TEPCO’s emergency efforts to continue injecting water into the reactors and their spent nuclear fuel pools from outside to cool them down.
TEPCO pumped out around 660 tons of highly radioactive water Tuesday and Wednesday from one of the trenches to a ”condenser” inside the nearby No. 2 reactor turbine building, where during normal operation steam from the reactor is converted into water.
But the Nuclear and Industrial Safety Agency said the water level in the vertical part of the trench as of 11 a.m. Thursday had increased by about 4.5 centimeters from the level observed at 6 p.m. Wednesday.
The level of the water is now only 1.5 centimeters lower than shortly before the water-transfer mission started at 7:35 p.m. Tuesday.
Hidehiko Nishiyama, the agency’s spokesman, told a press conference Thursday morning that the rise in the water level is likely linked to the continued injection of water into the No. 2 reactor core, which is necessary to prevent the nuclear fuel inside from overheating.
”As there is believed to be around 20,000 tons of water (in the No. 2 reactor turbine building and the trench connected to it), we’re feeling the difficulty of lowering the level of the water in a stable manner,” he said.
TEPCO is preparing to transfer more of the highly radioactive water into a facility for nuclear waste disposal at the plant, which can accommodate 30,000 tons of liquid.
Work is under way to ensure that the facility will be able to contain highly radioactive water safely without fear of the stored liquid leaking outside, but Nishiyama told the press conference that he was not sure when it would end.
The water in and around the No. 2 reactor turbine building is believed to contain higher concentrations of radioactive substances than other contaminated water found at the site, and is believed to originate from the No. 2 reactor’s core, where fuel rods have partially melted.
The agency decided to remove water from the trench first as it feared that the water inside the trench would overflow and leak into the Pacific Ocean.
TEPCO also started looking into how to check the quake resistance of already heavily damaged reactor buildings at the site in line with an order issued Wednesday by the nuclear regulatory agency, in light of a series of strong aftershocks of the March 11 quake.
The agency has told the utility to immediately examine the buildings and consider reinforcement work if they are judged as not sufficiently quakeproof.
TEPCO, however, has said that it cannot ”immediately conduct an investigation” unless it confirms the safety of areas where checks will be conducted.
To enhance preparation for tsunami waves triggered by aftershocks and other emergency situations, emergency diesel power generators and vehicle-mounted power sources are to be placed on higher ground, while backup units for water injection at the troubled Nos. 1 to 3 reactors are expected to be installed, according to the nuclear agency.
Meanwhile, concern grew over the state of the No. 3 reactor at one point, as the agency said in the afternoon that the temperature of part of its reactor pressure vessel was found to be rising suddenly.
But TEPCO officials said the data were likely due to a glitch in a measuring instrument, because other temperature data related to the vessel has not shown a similar rise.