The Nuclear and Industrial Safety Agency said Wednesday that cracks in a steel reactor shroud at the Hamaoka nuclear plant in Shizuoka Prefecture do not require immediate repairs.
In a report, the agency said the No. 4 reactor at the Hamaoka plant, operated by Chubu Electric Power Co., is strong enough to hold out for five years.
But the cracks need to be checked periodically because they could widen and compromise the shroud's strength, the agency said.
As a result of the report, Chubu Electric will not carry out immediate repairs.
Chubu Electric said it hopes to resume operations between late July and early August. Operations at the reactor have been suspended since September to facilitate regular maintenance checks.
The Advisory Committee for Natural Resources and Energy, which advises the Ministry of Economy, Trade and Industry on technical matters, compiled the report.
The agency conducted an evaluation after checks revealed the cracks in the shroud and elsewhere, mainly in March and April.
Wednesday's report takes into account more cracks and adds to earlier evaluations of the cracks on the lower welded segment of the shroud, a cylindrical stainless steel device that separates the nuclear fuel from the pressurized reactor vessel.