The Nuclear Regulatory Commission (NRC) staff has determined that First Energy Nuclear Operating Co. (FENOC) has met the terms of a 2004 NRC order placing conditions on the restart of the Davis-Besse Nuclear Power Station after a two-year shutdown following the discovery of severe reactor vessel head degradation. The plant is located 21 miles southeast of Toledo, Ohio.
On 5 March 2002, maintenance workers discovered that corrosion had eaten a football-sized hole into the reactor vessel head of the Davis-Besse nuclear power plant. Although the corrosion did not lead to an accident, this was considered to be a serious nuclear safety incident.
The NRC kept Davis-Besse shut down until March 2004, when the agency was convinced the plant operator, FirstEnergy Nuclear Operating Company (FENOC), had performed all the necessary maintenance for safe operations. The company also agreed to an order that required several actions to reform its operations approach and ensure safety was the top priority. The NRC imposed its largest fine ever — more than $5 million — against FirstEnergy for the actions that led to the corrosion. The company paid an additional $28 million in fines under a settlement with the US Department of Justice.
The NRC closely monitored FENOC’s response and concluded in September 2009 that FENOC met the conditions of the 2004 order. From 2004 through 2009 the NRC reviewed 20 independent assessments conducted at the plant and verified the independent assessors’ credentials. The agency also conducted its own inspections and reviewed FENOC’s reactor vessel inspections conducted in early 2005. NRC inspectors paid particular attention to the order’s focus on safety culture and safety conscious work environment to ensure there were no new signs of weakness.
Lessons Learned
The Davis-Besse incident occurred despite almost a decade’s worth of agency and industry efforts to understand and prevent the underlying corrosion mechanism – cracking in certain alloys used for reactor components and the buildup of boric acid deposits on the reactor vessel head. The NRC closely examined its own actions prior to March 2002 to determine how the agency and/or the nuclear industry could do better and to avoid similar events in the future. A task force of experts from throughout the NRC, as well as an observer from the state of Ohio, reviewed five general areas, including: the reactor oversight process; the regulatory process; research activities; international practices; and the NRC’s Generic Issues Program.
The task force concluded that the corrosion occurred for several reasons:
• the NRC, Davis-Besse and the nuclear industry failed to adequately review, assess, and follow up on relevant operating experience at other nuclear power plants;
• Davis-Besse failed to ensure that plant safety issues received appropriate attention; and
• the NRC failed to integrate available information in assessing Davis-Besse’s safety performance.
The task force made 51 recommendations covering the following areas: inspection guidance; NRC and industry operating experience assessment; industry inspection requirements based on American Society of Mechanical Engineers (ASME) code; assessment of NRC programs, processes, and capabilities; NRC staff training and experience; technical requirements for reactor vessel and piping integrity; practices and capabilities for monitoring reactor vessel and piping leaks; technical information and guidance regarding stress corrosion cracking and boric acid corrosion; NRC licensing process guidance development and implementation; and previous NRC lessons-learned reviews.
“The Davis-Besse incident resulted in a number of valuable lessons for the NRC and our licensees for improving safety,” said NRC Chairman Gregory Jaczko. “We’ve implemented the task force’s recommendations over the past several years at Davis-Besse and plants around the country, and the recommendations have substantially strengthened and enhanced our evaluation and oversight process.”
Related ArticlesFrazer-Nash joins steel research panel Reactor designs submitted to UK regulators EPR design online Interview: “We will be back” in Europe, says GE Fraser-Nash fusion deal
