Record strontium-90 level in Fukushima groundwater sample last July

Kyodo/JIJI

Tepco says a groundwater sample taken from a well at the Fukushima No. 1 nuclear plant last July contained a record high 5 million becquerels per liter of radioactive strontium-90.

Tokyo Electric Power Co. initially said it had detected 900,000 becquerels per liter of beta ray-emitting radioactive substances, such as strontium, in the sample taken July 5 but then found problems in the measuring equipment in October.

Strontium-90 usually accounts for about a half of all beta particle-emitting substances in contaminated water at the disaster-stricken power station.

The total amount of beta particle-emitting materials in the samples are likely to be around 10 million becquerels, far higher than the previous high of 3.1 million becquerels for that well, a Tepco official said Thursday.

Tepco stopped releasing strontium-90 data after finding problems in the readings for July and August. It recently found mistakes in its calculation method and obtained new readings through rechecks.

According to Tepco officials, readings of beta particle-emitting substances in water tend to come out lower than actual amounts when concentrations are high, for instance 100,000 becquerels per liter or more. To deal with the problem, Tepco changed its measurement method in October, but it did not announce the change at that time.

Strontium tends to accumulate in bones and may cause bone cancer and leukemia.

The utility also said it will re-analyze past water samples because some of the figures can’t be trusted.

The observation well, which is 16 meters deep, is located between reactors 1 and 2, about 25 meters from the Pacific Ocean. It is also about 6 meters from an underground channel from which highly radioactive water was found to be seeping into the sea shortly after the crisis began in March 2011.