RUSSELLVILLE, Ark. (AP) -- The Nuclear Regulatory Commission issued a notice of violation to Entergy Corp. over a 2013 accident at the utility's Arkansas Nuclear One plant that killed one worker and injured eight others.

Wade Walters, 24, died when a 525-ton piece of equipment fell 30 feet to the floor of the plant. The commission said Tuesday that the collapse resulted from Entergy's failure to adequately review the assembly design and conduct a load test before trying to lift the turbine generator stator — in violation of the commission's requirements. The accident happened in a non-nuclear area of the plant.

The Easter Sunday accident was "of substantial safety significance," the commission's most serious level of regulatory performance, the commission said. The determination was made following two inspections last year and this year of the accident, the Arkansas Democrat-Gazette reported Wednesday ( ).

Arkansas Nuclear One spokeswoman Sarah Millard said Entergy takes the NRC's findings "very seriously."

"We are committed to learning from this tragic incident, sharing our knowledge with the industry and ensuring that it never happens again," Millard said.

The commission said Tuesday that it will determine the appropriate level of agency oversight and notify Entergy officials of that decision in a separate letter.

Entergy owns and operates power plants with about 30,000 megawatts of electric-generating capacity, including more than 10,000 megawatts of nuclear power. The company provides electricity to 2.8 million customers in Arkansas, Louisiana, Mississippi and Texas.