Plaintiffs seeking to halt the restart of two Kansai Electric Power Co. reactors now more than 40 years old filed a lawsuit in the Nagoya District Court on Thursday to challenge the government-appointed Nuclear Regulation Authority's restart review process, warning that running the units for another two decades would be dangerous.

Kepco's Takahama No. 1 and 2 reactors in Fukui Prefecture began operation in 1974 and 1975, respectively, and the original plan was to decommission them after 40 years.

However, the government has authorized a one-time, maximum two-decade extension if the old reactors pass new safety tests.

The NRA essentially cleared the two Takahama reactors in February, but will conduct other specialized checks to determine their condition before deciding whether or not to officially grant approval for an extension.

"In a serious accident at the Takahama reactors, there is a danger of radiation damage from the effects of a westerly wind," said lawyer Sakae Kitamura, who is representing the plaintiffs, at Thursday's news conference in Nagoya.

Kepco is racing against time to finish the safety review and secure approval before the July 7 regulatory deadline. If Kepco misses the deadline, the utility will be forced to permanently shut both reactors.

The major issues the plaintiffs are contesting include concerns about the condition of the reactors' pressure vessels, and questions about whether the seismic risks for the old reactors have been fully considered.