Tokyo Electric Power Company (Tepco) says the level of radioactivity near one underground wastewater tank at the crippled Fukushima Daiichi NPP is more than 100 times greater than earlier readings. The tanks were built three years ago to store highly radioactive wastewater produced within the crippled plant. But all of the tanks were soon taken out of use due to repeated leaks of contaminated water. Tepco pumped most of the water out of them, but has been checking radioactivity levels of groundwater near the tanks. On 6 April equipment detected 8,100 becquerels of beta-ray-emitting radioactive substances per litre of water. The next day it increased to 9,300 becquerels. The previous week it was only 87 becquerels. Tepco was unable to explain the sharp rise. It said some highly radioactive water remains in the tank, but it is isolated with waterproof protection. Tepco will continue to analyse groundwater samples around the tank, and also compare them with data on the contaminated water left in part of the tank. This is just the latest in an ongoing series of similar incidents.