Southern California Edison Co. could be fined more than $100,000 for taking inadequate safety precautions with canisters of spent nuclear fuel at its San Onofre Nuclear Generating Station.

The Nuclear Regulatory Commission proposed the $116,000 penalty March 25, after finding the company had wedged a canister near the top of a storage vault at the San Onofre facility, near San Clemente, Calif., last August. The company was lowering the canister into storage.

“At no point during the...