Radioactive cesium levels in groundwater have increased in an observation well at Fukushima No. 1 nuclear power plant, Tokyo Electric Power Co. (TEPCO) has said.
The surge signals that radioactive contamination is spreading under the disaster-stricken facility.
According to the Japan Times, TEPCO said water sample collected from the well on Monday contained 9,000 becquerels of cesium-134 per liter and 18,000 becquerels of cesium-137, both about 90 times the levels found on Friday.
The water collected on 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 on Friday, the report added.
According to the report 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.