Fact Sheet on Improvements Resulting From Davis-Besse Incident
On March 5, 2002, maintenance workers discovered that corrosion had eaten a football-sized hole into the reactor vessel head of the Davis-Besse nuclear power plant in Oak Harbor, Ohio. 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 U.S. 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.
Davis-Besse Lessons Learned Task Force
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.
With regards to the underlying corrosion mechanisms, the NRC instituted strict inspection requirements for reactor vessel heads and other susceptible components to ensure cracks and/or leaks will be detected and repaired long before corrosion could affect plant safety. Many nuclear power plants installed entire new reactor vessel heads following these inspections. The recommendations also led to NRC inspectors having additional procedures for monitoring plants’ efforts to inspect their components and appropriately deal with boric acid buildup. The NRC has contributed to additional ASME code requirements for inspecting reactor components.
In the area of operating experience review, the NRC created a “clearinghouse” group to collect and evaluate experience every day, then appropriately share it throughout the agency and the industry. The clearinghouse applies the lessons learned to the NRC’s core functions of oversight, licensing, rulemaking, and incident response. In addition, the agency is using information technology to more widely share operating experience, including a central database for managing all reported events, and an operating experience gateway that consolidates a variety of information onto a single page on the NRC Web site: http://nrcoe.inel.gov/results/. The agency has also formalized methods for integrating future lessons-learned recommendations into its operational areas.
The NRC addressed the need to adequately consider plant experience in licensing decisions by updating expectations in several areas, including:
- how long the agency’s licensing project managers are assigned to a specific plant;
- how frequently the managers visit plant sites and communicate with the resident inspectors; and
- how to maintain a questioning safety attitude about plant events.
The NRC also improved its guidance for informing the industry on issues that affect large numbers of plants generically. The agency established criteria for acceptable plant responses to such generic communication, improved its documentation while evaluating those responses, and now performs additional verification of actions the plants take to deal with generic issues. The NRC staff now devotes additional attention to how risk information is used and communicated when making regulatory decisions, particularly in ensuring that uncertainties inherent in risk calculations are considered and communicated along with risk analysis results.
The NRC enhanced its inspection procedures by increasing its evaluation of a plant’s programs and actions for resolving long-standing issues. The agency’s inspector training program now includes a Web-based system to promptly share information among the inspection staff, as well as individual study tools. Specific training topics address the lessons learned from Davis-Besse, such as the effects of boric acid corrosion and the importance of maintaining a proper safety culture in questioning how events affect plant performance. This enhanced training has led to resident inspectors promptly identifying potential safety issues, such as peeling paint inside a containment building and whether a plant crane was capable of moving a reactor vessel head.
The NRC improved its management of the Reactor Oversight Process, ensuring the routine oversight of properly performing plants remains unaffected when the agency allocates resources to monitor plants in a performance-based extended shutdown. The NRC has also ensured continuity of regulatory oversight by developing a site-staffing metric to monitor gaps in permanent resident and senior resident inspector staffing at reactor sites, with a goal of maintaining at least 90-percent inspector coverage at a site.
The NRC ensured Davis-Besse met all applicable requirements before it restarted, and the agency ensured FENOC satisfied additional requirements before closing out an order against the company. The NRC will maintain strong oversight at Davis-Besse and continue to implement the lessons learned from the incident at all U.S. commercial nuclear power plants.