Tokyo Electric Power Co. on Tuesday reported a surge in radioactive cesium levels in groundwater in an observation well at its Fukushima No. 1 nuclear power plant.
This signals radioactive contamination is spreading under the disaster-stricken facility.
Water sampled from the well Monday contained 9,000 becquerels of cesium-134 per liter and 18,000 becquerels of cesium-137, both about 90 times the levels found Friday, Tepco said. The well is near the turbine building for reactor 2 and about 25 meters from the plant’s harbor.
“We still don’t know why the level of radiation surged, but we are continuing efforts to avert further expansion of contamination,” a Tepco spokesman stated.
Government guidelines permit cesium-134 at 60 becquerels per liter and -137 at 90 becquerels. Once ingested, the substances accumulate in muscle and bone and are believed to cause cancers.
The water collected Monday also contained 890,000 becquerels of substances that include strontium, which emits beta radiation, compared with 900,000 becquerels found in groundwater sampled from the well Friday.
Groundwater cesium levels in the well and other observation wells had remained low until recently. Readings were often below the minimum detectable levels.
Explaining the reason for the low contamination in groundwater, Tepco had said cesium can be easily absorbed by soil.
Following the latest findings, however, Tepco officials now say they do not know why the cesium levels have surged.
“Mud that has absorbed radioactive cesium may have got mixed with the water. We will measure the (contamination of the) water again,” a Tepco official told reporters at the Fukushima Prefectural Government office.
The official also said Tepco will determine if radioactive substances are seeping into the sea after studying its seawater survey.
The company also said groundwater collected Monday from a well located near the reactor 3 turbine building and about 23 meters from the port was found to have contained 1,700 becquerels of beta radiation-emitting substances per liter.
The reading was about 20 times the level detected Thursday and the highest for such substances in the well.
The new readings came two days after Tepco said tritium, a radioactive isotope of hydrogen used in glow-in-the-dark watches, was present at levels 10 times the permitted rate.
Tepco said in late June it had detected the highly toxic strontium-90, a byproduct of nuclear fission that can cause bone cancer if ingested, at levels 30 times the permitted rate.
The substances, which were released by the meltdowns of reactors at the plant in the aftermath of the huge tsunami of March 2011, were not absorbed by soil and have made their way into groundwater.
Subsoil water usually flows out to sea, meaning these two substances could normally make their way into the ocean, possibly affecting marine life and ultimately impacting humans who eat sea creatures.