According to officials, traces of radioactive strontium and other substances in the stored water react with the materials, the tank is composed of, producing X-rays.
On Friday, the Nuclear Regulation Authority held a meeting at which measures to curb the rising levels of radiation to the south of the plant were discussed.
 Radioactive water leaks at Fukushima have been a major concern to the international community, as well as the Japanese population since the outbreak of the crisis in March 2011.
When leaks from the Fukushima plant's underwater tanks were detected, TEPCO started storing contaminated waters in tanks.