ANO flooding protection issues of substantial safety significance

27 January 2015

The Arkansas Nuclear One power plant, in Russellville, Arkansas, is coming under increased regulatory focus as a result of flood protection problems.

The US Nuclear Regulatory Commission has determined that two violations associated with flood protection at ANO, a two-unit pressurised water reactor operated by Entergy Operations Inc, are of "yellow" or of substantial safety significance.

Beginning in 2013, Entergy Operations officials and the NRC began extensive inspections of the flood protection programme at ANO. According to the NRC more than 100 previously unknown flood barrier deficiencies were found, including defective floor seals, flooding barriers that were designed, but never installed, and seals that had deteriorated over time. They are described in an NRC inspection report of 9 September 2014.

"Problems existed with the condition of some flood protection barriers at the plant," said NRC Region IV Administrator Marc Dapas. "This created the potential for water to enter the auxiliary building in the unlikely event of extreme flooding, potentially compromising safety-related equipment."

NRC says that the licensee has replaced the degraded seals or parts, implemented compensatory measures, and added appropriate instructions to procedures to ensure the protection of vital safety-related equipment, and that it has inspected these corrective measures to ensure their adequacy.

"While the deficiencies have been corrected they were of substantial safety significance and as such we will now reassess the appropriate level of oversight for the plant," Dapas added.

ANO Units 1 and 2 received yellow violations in June 2014 because electrical equipment damaged during an industrial incident increased risk to the plant. Workers were moving a 525-ton generator stator out of the plant's turbine building when a temporary lifting rig collapsed in March 2013, damaging plant equipment. Those violations moved both units from Column 1 to Column 3 of the NRC's Action Matrix.

The new violations will lead NRC to reassess whether even more inspection resources need to be focused on ANO. The NRC will determine the appropriate level of agency oversight and notify Entergy officials of that decision in a separate letter.

Photo: Arkansas Nuclear One. (Source: Entergy)

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