Operators of the Fukushima Daiichi nuclear plant say the filter is intended to cut down the high radiation level so workers can go in and set up a system to cool the troubled reactor, Kyodo News reported.
Tokyo Electric Power Co. said workers could be allowed in the building as early as Thursday. It would be the first time anyone has set foot inside since March 12, the day after the plant was crippled by the devastating 9-magnitude quake and tsunami.
Kyodo also reported a source said Japan's system to predict the volume of radioactive materials emitted in a nuclear accident failed to work as designed because power to the measuring equipment was lost.
In another development, the Fukui prefectural government said Monday it is suspected radioactive substances from fuel rods has leaked from a nuclear power plant in Tsuruga.
Increased radioactivity in coolant water has been detected at the plant, Kyodo said.
Japan Atomic Power Co. will manually shut down the No. 2 reactor of the plant and examine its primary cooling system, the news agency said. The local government said the radioactivity is not a threat to the nearby environment.
Japan Atomic said 4.2 becquerels of iodine-133 and 3,900 becquerels of xenon gas were detected per cubic centimeter Monday, up from 2.1 and 5.2 becquerels, respectively, April 26.