A delay in resolving pump problems has loosened expectations for completion of repairs at FirstEnergy Corp.’s Davis-Besse nuclear plant (Akron, Ohio, USA). The facility was knocked off line a year ago when workers discovered that leaking boric acid had corroded a deep cavity into the carbon steel reactor lid. FirstEnergy determined that two emergency pumps, high-pressure injection pumps, needed some kind of repair. The pumps send water back into the reactor if a reactor breach causes a loss of coolant. The pumps take water from a tank, and also recirculate cooling water spilled onto the reactor containment building floor after an accident. Although FirstEnergy made major repairs to prevent debris from clogging the sump system collecting the water, the company still determined that debris could pose problems for bearings in the pumps. FirstEnergy also plans a pressure test to check for leaks on the reactor bottom and the four large coolant pumps. Last fall FirstEnergy discovered boric acid-related stains on the base of the reactor that it believes were caused by material from the corroded lid falling over the side. But because the stains were seen around 52 small nozzles on the reactor bottom, used to allow access for instruments, the pressure test will be used to determine if those nozzles are leaking. The nozzles are made of the same nickel alloy as the larger 69 control rod drive mechanism tubes that pass through the reactor lid. The nickel alloy in those tubes has proven vulnerable to cracking. FirstEnergy has overhauled two of Davis-Besse’s four reactor coolant pumps, and does not believe the other two have any problems. But if any leaks become apparent due to the testing, repairs could take weeks. Once repairs and tests are finished, FirstEnergy will need final approval from the Nuclear Regulatory Commission to bring the reactor back on line.
