Xcel Energy officials are still reviewing a Nuclear Regulatory Commission (NRC) preliminary finding assigned to the Monticello Nuclear Generating Plant.
The NRC uses a color-coded system to classify its findings, which range from green, for an issue of very low safety significance, to red, for an issue of high safety significance. Monticello plant officials were notified last week the plant had received a “yellow” for probable maximum flood preparedness planning.
A yellow finding indicates an issue with “substantial safety significance”, which would lead to additional NRC inspections and potentially other NRC action.
“We are still reviewing the NRC finding,” said Mary Sandok, Xcel Energy’s media relations manager “We’re still deciding how we are going to respond.”
In a letter to Mark Schimmel, Monticello site vice president, the NRC reported the yellow finding is not a current safety concern. “On Feb. 15, 2013, actions were completed to reduce the flood mitigation plan timeline to less than 12 days by developing an alternate plan for flood protection features, pre-staging equipment and materials and preplanning work orders,” wrote Steven Reynolds, the NRC’s division of reactor projects director in a letter dated June 11.
According to the NRC, Xcel Energy officials will have to decide before this Friday (June 21) whether or not the utility will attend a regulatory conference where it would present its perspective on the facts and assumptions the NRC used to arrive at the flood planning yellow finding and assess its significance or submit its position on the finding to the NRC in writing. If a regulatory conference is held, it will be open for public observation. “We have not decided yet,” Sandok said.
The Monticello Nuclear Generating Plant (MNGP) was built at a 930-foot elevation grade, with the exception of the site’s intake structure and screen house, which sit at approximately the 917 to 919 feet. The plant’s flood elevation is listed at 939.2 feet. That figure is based on annual rain and snow melt estimations.
NRC inspectors observed that rather than performing a walkthrough levee construction activities, Monticello plant officials referenced an evaluation performed by an engineering firm, which they believed had previously verified that a protective levee near the nuclear power plant could be constructed within 12 days.
Upon review of the evaluation, federal inspectors noted that the levee construction timeline included in the evaluation was 15 days.
Specifically, the inspectors were concerned with a lack of detailed procedure guidance, a lack of clarity in the steps provided, a lack of pre-staged equipment and materials, and the presence of several assumptions inherent in the strategy.
In addition, the NRC inspectors noted plant staff was not trained on the procedures despite the complexities of the plant’s flood prevention strategy.
“The licensee believed that they would have warning of the flooding conditions well in advance of the first day of flooding due to the site’s flood prediction procedure,” the inspectors reported. “The preferred method of protection when water levels are predicted to exceed 930 ft. would be to construct a ring levee around the entire facility. Installation would require less labor and it would be more secure.”
NRC inspectors determined that it is feasible to ring the entire facility with a levee. Preparations such as reserving earthmoving equipment and excavators would need to begin as soon as possible when environmental conditions indicate the potential for a probable maximum flood.
According to the NRC, Monticello’s flood plan failed to provide the means to carry out the levee-related actions described in the procedure in the credited 12 days, and in advance of each of the flood stages anticipated during those 12 days.
Flooding above plant grade is assumed to always lead to a station blackout since emergency procedures call for de-energizing the plant’s substation equipment when water levels exceed the 930-foot elevation.
According to the NRC, the plant would be placed in cold shutdown when flood waters were expected to reach the 921-foot level and alert would be declared. As water levels continued to rise and plant conditions worsen, most of the population would likely be evacuated.
NRC inspectors also noted in their report the plant’s flood planning effort did not include a timeline or review of the necessary actions to procure flood protection materials and equipment.
“The licensee took inventory of the few items they had stored onsite,” the inspectors wrote in their report.These items included approximately 5,000 of the 100,000 sandbags necessary and several 4-foot by 8-foot steel plates, which were stored onsite to support the flood protection method in place for the licensee up until the levee plan was developed in 2001.
The NRC inspectors also noted that peak Mississippi River water levels (913 feet above sea level) occurred at the MNGP site in 1965, 1997, 2001 and 2009. The calendar date window for potential flooding was anywhere from March 27 through May 4.
“Safety and security at our nuclear generating plants are top priorities for Xcel Energy, and at no time was the public in any danger,” stated Tim O’Connor, chief nuclear officer for Xcel Energy in an earlier email.
Flood berm wall construction procedures for a “worst case” scenario were in place. According to O’Connor, the Monticello plant had contracts with local suppliers for needed materials
“The plant now has procured those flood berm materials and has placed them on site for improved readiness for this worst case scenario,” O’Connor added. “Because the materials are on site, the potential safety concern has been resolved.”
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