A record high level of radioactive cesium has been found in groundwater beneath the crippled Fukushima No. 1 nuclear power plant, it operator TEPCO revealed.

On February 13, Tokyo Electric Power Co. reported 37,000 becquerels of cesium-134 and 93,000 becquerels of cesium-137 were detected per liter of groundwater sampled from a monitoring well earlier that day.

Water samples were taken from the technical well, located next to the second power unit, some 50 meters from the coast. These figures (the total reading) are the highest of all the cesium measurements taken previously.

Experts do not rule out that radioactive water is leaking from an underground tunnel, which is located close to the second power unit on the seashore.

However, no exact reason for such a significant increase of radioactive cesium content in the groundwater has been given so far.

Japanese newspaper The Asahi Shimbun reported that the amount of radioactive chemicals seems to be increasing. On Feb. 12, the same sampling well had produced a combined cesium reading of 76,000 becquerels per liter.

Earlier Japan's nuclear regulator slammed the stricken Fukushima plant operator for incorrectly measuring radiation levels in contaminated groundwater at the site.

The Nuclear Regulation Authority (NRA) accused TEPCO of lacking basic understanding of measuring and handling radiation almost three years since the reactor meltdowns at the Fukushima No. 1 nuclear power plant.

On Thursday, fears of new leaks surfaced in Japanese media, as the same newspaper reported two cracks in a concrete floor of the No. 1 facility near radioactive water storage tanks.

TEPCO suggested some contaminated water from the melting snow may have seeped into the ground through the cracks, stretching for 12 and 8 meters.

The leakage of radiation-contaminated water is posing a major threat to Japan’s population and environment and to the international community since the March 2011 disaster.