NRC asks Exelon to address questions about Dresden’s flooding response plan

The Nuclear Regulatory Commission has issued a letter asking Exelon Generation Co. to address the NRC’s concerns with Dresden Nuclear Station’s response plan for external flooding events. The two-unit plant is located in Morris, Ill., 25 miles southwest of Joliet.

NRC inspectors identified multiple areas of concern during recent inspections conducted in response to the Fukushima Dai-ichi accident. The issues pertain to the plant’s plan to respond to a Probable Maximum Flood – a hypothetical flooding level which postulates the largest conceivable flood from the combination of the most severe meteorological and hydrologic conditions. Such conditions have never been known to occur in this area and are highly improbable. The issues with Dresden’s flood response plan do not represent an immediate safety issue but are an area the NRC would like additional information on to ensure it meets post-Fukushima standards.

Dresden was originally licensed for operation in 1966 for the flood value of 506.4 feet above mean sea level. The reactor and other plant structures were constructed at 517 feet above mean sea level, 10 feet above the historic flood levels. While the plant was within its design basis at this time, the NRC changed the flood design criteria in 1982 by basing it on a more stringent hypothetical flood value for the area. Dresden developed a response plan to address the disparity between the original and the revised design bases for flooding.

As the agency works to enhance the protection of nuclear plants against extreme natural disasters after the accident in Japan, the issues with Dresden’s flood plan have come into stronger focus.

“We expect the plant to address the concerns with Dresden’s flood plan NRC inspectors identified during recent inspections looking at Dresden’s ability to deal with a hypothetical flood,” said NRC Region III Administrator Charles Casto. “We expect our licensees to be in compliance with the plant’s design and licensing basis.”

The NRC has two major areas of concern with Dresden’s flood response plan:

The quality and viability of the procedure;

The availability and capability of equipment specified in the response plan to fulfill their intended functions.

The NRC asked Exelon to respond the NRC’s letter within 30 days by:

Addressing the list of specific NRC concerns;

Demonstrating that the existing procedures and strategies to respond to postulated maximum flooding events would be successful or offering alternative solutions;

Providing a schedule for the actions the plant intends to take in response to the NRC’s concerns.

After the NRC receives Exelon’s response, a public meeting will be scheduled to provide a forum for discussing these issues with members of the public.