Cracks and coolant leaks in new Davis-Besse reactor vessel head
At least two new cracks leaking reactor coolant have turned up in a March 2010 inspection of FirstEnergy's (FENOC) now infamous Davis-Besse nuclear power plant. The reactor had only relatively recently replaced the pressure vessel head in 2004 when a new round of cracking was discovered in the same locations. Sixty-nine control rod drive mechanizms penetrate the thick reactor vessel head through pressure fitted sleeves of steel alloy that have proven to be vulnerable operational stress and radiation assisted cracking. At least twelve of these sleeves in the replacement component now need repair after only six years of operation. The inspection findings indicated that the Ohio reactor-as other Pressurized Water Reactors-is still vulnerable to costly repairs need to maintain dangerous and ongoing cracking and subsequent corrosion that can result in a nuclear accident. The reactor will have an extended outage to repair the cracks by welding them shut. The six-year old component part was installed in 2004 after the reactor was shut down in 2002 when it was discovered that it was severely damaged by the same cracking phenomenon. The combination of corporate and regulatory neglect of the cracking, corrosive coolant leakage and corrosion through 6 3/4 inches of carbon steel forced FENOC into a two-year outage, more than $600 million in repars and a $28 million fine paid to the Nuclear Regulatory Commission (NRC). A replacement vessel head was cannibalized off of the long-cancelled Midland reactor project in Michigan and shipped down to be fitted onto Davis-Besse. The replacement part was fabricated using the same susceptibal material (Inconnel 600) for the penetration sleeves.
In February 2002, FENOC shut down its Ohio Davis Besse nuclear power plant for refueling and found that leaking borated reactor coolant from cracks in the vessel head penetration sleeves had eaten a hole big enough to fit a gallon size milk carton. A thin 3/16th inch steel inner vessel liner, installed to prevent corrosive coolant from eating its way out of the pressure vessel, was bulging outward into the cavity from the 2200 pounds per square inch internal operating pressure and on the verge of rupture within as little as eight weeks of continued operation. The engineering staff at NRC had already surmised seven months earlier that the reactor was very likely cracked and at significant risk of an accident given that six of the seven Three Mile Island-style reactors (B&W) in the US had been inspected and found cracking in the penetration sleeves. Davis-Besse was the only one that had not inspected by 2001. A photo provided to NRC staff in April 2000 showed severe corrosion of the reactor vessel head was in advanced stages when the agency gave FENOC the green light to start up for a two-year operational cycle. By November 2001, NRC staff had finalized an Order for the early shut down of the reactor on December 31, 2001 to inspect for cracking that they believed posed an increasing risk of an accident. The 2001 Order was never issued based largely on a financial consideration to the operator that was discussed at a meeting between NRC and FENOC senior management. Davis-Besse was instead allowed to operate under deteriorating conditions for two more months in a gamble that risked a nuclear accident for corporate gain.
We almost lost Toledo due to the reactor's suscepitibility to harsh operational environment of nuclear power, greedy corporate neglect and the NRC that chose to shield a company's financial interest from its own safety regulations. Now, the technical problems keep reappearing under increasing financial pressure to drive reactors harder. Given the well documented history, FENOC will not risk another scandal with delay of repairs. However, that is not now the concern. This most recent reactor coolant leakage occurred before the reactor shut down on February 24, 2010 for regularly scheduled refueling. Beyond Nuclear asked the NRC to determine when FENOC first identified the new reactor coolant leakage and why it was not detected during reactor operation. Davis-Besse's operating license mandates a zero tolerance of primary coolant leakage and requires operators to shut down the reactor within six hours identifying leakage. The concern arises that FENOC may have once again placed production over public safety by ignoring or overlooking a violation of their operating license.
March 22, 2010
