How Risk-Informed Decisions Can Fail: Lessons from a Nuclear Power Plant Incident

In 2002, a large hole was discovered in the reactor vessel head of the Davis-Besse plant located in Ohio, US. Had the reactor pressure vessel ruptured, a major public safety event would have occurred. Further investigations revealed that, by the end of 2001, a shutdown order was drafted by the Regulatory Agency. Nonetheless, through a risk-informed decision-making approach, the Agency changed the decision related to the issuance of the order. Operations were then allowed to continue for six more weeks, despite the high likelihood that the reactor was operating with leaking cracks in the nozzles located at the reactor head. The reactor vessel head wastage, which had evolved unnoticed for years, was primarily due to borated water that leaked through a nozzle crack onto the carbon steel portion of the reactor head, resulting in boric acid corrosion. This paper aims to explore the Agency’s decision-making to identify factors that might have contributed to the flawed decision. A better comprehension on the organizational factors and social processes that can adversely affect risk-informed decisions is crucial to enhance operational safety in high hazard industries. The paper concludes by suggesting possible ways to guard against the identified factors.