(Washington, DC) First Energy, an Ohio electric utility, drove its deteriorating Davis-Besse nuclear power station dangerously close to a catastrophic accident it was revealed today. Moreover, the Nuclear Regulatory Commission (NRC) capitulated to First Energy pressure to delay inspections of a vital safety component beyond a requested December 31, 2001 deadline in order to accommodate the industry rather than force an early shutdown to conduct inspections on deteriorating equipment.
Following the February shutdown for refueling outage and inspection at the Davis-Besse nuclear power station, 21 miles Southeast of Toledo, Ohio, operators discovered a cavity had eaten through 6-inches of carbon steel on the top of the 6½-inch thick reactor pressure vessel, the apparent result of corrosive coolant leakage from the reactor core. Less than a half inch of the reactor vessel's stainless steel liner remained in the bottom of the 4"X5"X6" cavity separating the reactor's highly radioactive and pressurized internal environment (2500psi) from blasting into the reactor containment building damaging safety equipment and possibly setting into motion a core melt accident. Initial company inspections additionally found cracks in the welds on five of the 69 nickel alloy sleeves that penetrate the reactor pressure vessel head to allow for control rod insertion to safely shutdown the reactor.
"First Energy pushed this reactor beyond all reasonable safety margins and the NRC basically allowed it," said Paul Gunter, Director of the Reactor Watchdog Project for Washington, DC-based Nuclear Information and Resource Service. "This was a dangerous nuclear experiment on public safety that came damn close to exceeding the strength of a fundamental piece of reactor safety equipment, the reactor pressure vessel," he said.
The United States Nuclear Regulatory Commission (NRC) had earlier granted operators at Davis-Besse a delay from a December 31, 2001 inspection report deadline on the same vessel head area of the reactor pressure vessel as was required of all other pressurized water reactor operators issued in a NRC industry bulletin on August 03, 2001. First Energy successfully fought NRC's request to shutdown early to inspect for damage to the region control rod drive mechanism vessel head penetrations for cracking and corrosive coolant leakage.
"Davis-Besse is a highly susceptible reactor with known deteriorating margins of reactor safety in this area," said NIRS staffer Kevin Kamps. "First Energy operators calculated the risks of running the reactor to their scheduled February outage to maximize their profits," said Kamps. "Such high-stakes risk taking means gambling with the health and safety of very large numbers of people," Kamps concluded.
The reactor coolant at Davis-Besse as at other nuclear reactors is a solution of boron and water. Reactor coolant escaping through cracks and around flanges on the control rod drive mechanisms allows the corrosive boron to drip, crystallize and attack the carbon steel exterior surface. While the corrosive action of the boron crystals apparently stopped at the stainless steel liner, given a wide enough cavity in the carbon steel, the reactor pressure vessel could have ruptured as the result of the extreme internal pressure exceeding the sheer stress of the steel liner tearing a hole through the vessel wall from the inside out. Reactor coolant released as a high-pressure jet stream of radioactive water much like a super fire hose could damage reactor safety equipment located directly above the reactor vessel and potentially introduce a shock wave sufficient to break already cracked control rods ejecting them as missiles further damaging equipment including other control rods needed to shut down the reactor.
Davis-Besse now plans to find a used reactor pressure vessel head or alternately weld metal plates on the interior and exterior sides of the vessel head to plug the hole until a new vessel head could be fabricated and installed two years from now. First Energy is also considering grinding out the cracks in welds on vessel head penetrations for control rod drive mechanisms and re-welding the sleeves.
"The First Energy repair option on the cavity in the reactor vessel has no standard or code to measure its reliability and safety by," said Gunter. "Such a repair could very well introduce additional stresses to this safety component to make the repair unreliable and risk public safety again later on down the line," Gunter concluded.