April 10, 2002 — Representatives from FirstEnergy Nuclear Operating Company (FENOC) met with Nuclear Regulatory Commission (NRC) officials Wednesday in Washington, D.C., to discuss proposed repairs to the reactor vessel head at the Davis-Besse Nuclear Power Station. The NRC must review and approve the repair prior to the work beginning.
Carbon steel in the reactor head was corroded by boric acid seeping through cracks in two Control Rod Drive Mechanism nozzles. Corrosion adjacent to one nozzle near the top of the reactor head will require a significant repair effort. A second corroded area, however, is minor and warrants a relatively simple repair.
Davis-Besse’s repair approach for the more significant corrosion at the top of the reactor head will be to cut out the damaged area, using robotic equipment and a high-pressure, water jet abrasion technique. The opening will be covered with a stainless steel plate, 12 to 13 inches in diameter, about five inches thick and weighing between 300 to 400 pounds. The plate will be welded in place using robotic equipment.
The nozzle penetration with the minor corrosion will be capped with a stainless steel plug and welded over. Additionally, another nozzle near the first corroded area also will be removed, capped and welded shut. This nozzle is being capped due to its proximity to the corrosion damage.
A team consisting of Davis-Besse personnel, as well as experts from Framatome ANP Inc., and Welding Services, Inc., will perform the work. All repairs will be designed to last the remaining plant life and must comply with NRC requirements.
Prior to beginning the work, mock-ups will be used to demonstrate the effectiveness of the cutting, welding and inspection techniques. The welds will be subjected to dye penetrant testing and ultrasonic or radiographic examination. The three Control Rod Drive Mechanisms displaced by these repairs will be moved to spare nozzle locations on the reactor head.
Once started, the repair work itself is expected to take three to four weeks. Based on more detailed information now available, the repair is estimated to cost $16 million.
Davis-Besse officials expect to submit a detailed repair plan to the NRC within the next few weeks for its review.
The reactor head, which covers the reactor vessel, is a dome-shaped structure seven feet high, about 17 feet in diameter, and weighing about 150 tons. It is made from six-inch thick carbon steel and lined inside with stainless steel. It has 69 stainless steel nozzles welded into the top of the head, which enable control rods to move in and out of the reactor vessel to control reactor power levels. The nozzles are three to four feet long, four inches in diameter and weigh about 150 pounds.
The Davis-Besse, Perry and Beaver Valley plants are owned by FirstEnergy Corp., Akron, Ohio, and operated by its subsidiary FirstEnergy Nuclear Operating Company. FirstEnergy is a registered public utility holding company. Its various subsidiaries produce more than $12 billion in annual revenues and sell 124 billion kilowatt-hours of electricity.