The company said it identified a possible leak of iodine from the 1,160MW reactor’s nuclear fuel assemblies into its coolant.
According to the company, 4.2 becquerels of iodine-133 and 3,900 becquerels of xenon gas were detected per cubic centimeter, up from 2.1 becquerels of iodine and 5.2 becquerels of xenon deteced earlier.
Japan Atomic said there may be a pin hole created in a zirconium alloy encasing fuel pellets and added that there had been no radiation leak from the facility.
Tsuruga nuclear plant is located 280 miles west of Tokyo in Fukui prefecture.
The plant is located in an area that is not affected by the adverse earthquake and subsequent tsunami that hit Japan on 11 March 2011.
