TOKYO — Japan’s nuclear regulator on Wednesday upgraded the rating of a leak of radiation-contaminated water from a tank at its tsunami-wrecked nuclear plant to a ‘‘serious incident’’ on an international scale, and it castigated the plant operator for failing to catch the problem earlier.
The Nuclear Regulation Authority’s latest criticism of Tokyo Electric Power Co. came a day after the operator of the Fukushima Dai-ichi nuclear plant acknowledged that the 300-ton leak probably began nearly a month and a half before it was discovered Aug. 19.
In a meeting with agency officials and experts Tuesday night, TEPCO said radioactivity near the leaky tank and exposure levels among patrolling staff started to increase in early July. There is no sign that anyone tried to find the source of that radioactivity before the leak was discovered. Full story for BostonGlobe.com subscribers.