Hole in Containment Liner Could Indicate Other Problems

Background on Beaver Valley Unit 1 Steel Containment Liner Corrosion

Paul Gunter, Beyond Nuclear

July 10, 2009

Beaver Valley nuclear power station owned and operated by First Energy Generation Group is a two-unit Westinghouse Pressurized Reactor near McCandless, PA. Beaver Valley is a sub-atmospheric containment design where the pressure inside the containment is 4 psi below the pressure outside containment. There are only seven Westinghouse plants in the United States that rely on this sub-atmospheric design; Beaver Valley 1 & 2, North Anna 1 & 2, Surry 1& 2 and Millstone 3.

The Beaver Valley nuclear power plant is seeking a 20 year license extension from the Nuclear Regulatory Commission.

The design is identified as having generic issues including the small size of the reactor containment building relating to construction problems with the placement of concrete and rebar. In specific, a declaration filed by nuclear engineer Arnold Gunderson has identified that "the lack of analytical data regarding the long-term strength of the reactor building and its continual exposure to the combination of high temperatures, low pressure and low specific humidity within the sub-atmospheric containment as it has aged has led to doubts and questions regarding the strength of this critical safely-related structure in the event of an accident."

On April 21, 2009, during a Beaver Valley Unit 1 refueling outage, a visual inspection inside the reactor building of the carbon steel containment liner found a 3-inch diameter blister in the paint coating on the interior of the liner with rust protruding out of it. The area was cleaned and corrosion removed to reveal the .375 inch thick steel liner had a 1-inch X 3/8-inch hole rusted entirely through.  The interior of the concrete containment wall was visible on the other side. While the steel liner is not designed to contain the pressure increases during a nuclear accident, it is the only structure that is credited as a leak-tight structure to contain the radioactive gases within the reactor building during such an event. The corrosion was determined to have initiated from the outside of the steel liner as the result of a small piece of water-soaked wood  embedded in the concrete wall that was in contact with the steel liner buried during the original containment construction.

The corrosion event discovered in 2009 is not the only containment liner corrosion event at Beaver Valley Unit 1. According to NRC inspection reports, the first event was discovered in 2006. While removing a large section of the concrete and steel liner wall to replace one of the reactor’s three steam generators, three significant areas of pit corrosion, though not through-wall, were discovered in a 20-foot X 20-foot area on the exterior of the containment steel liner exterior wall.

The question remains “How much more and extensive is the corrosion on the exterior wall of the steel containment liner that cannot be visually inspected?  Furthermore, what assurances are there today that the aging and defective steel containment liner will not fail if there is a radiological accident? What are the implications for Beaver Valley Unit 2 and the five other PWRs using sub-atmospheric containments?

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