A ruling Friday by the Osaka District Court canceling central government approval for the operation of two reactors at the Oi nuclear plant run by Kansai Electric Power Co. (Kepco), saying its calculations for standards involving earthquake safety were flawed, has stunned the nuclear power industry.

The decision, which is the first of its kind, is likely to be appealed and could still be overturned. But the result has resurrected fundamental questions about nuclear power safety and the future role of the energy source.

What was at issue in the court case?