Risk-informed applications and online maintenance in France and the United States

Abstract

During the past twenty-five years, the US Nuclear Regulatory Commission has been progressing toward a more risk-informed, performance-based regulation. This regulatory framework has effectively supported the development of online maintenance practices. In France, while the safety authority has been encouraging particular risk-informed applications, PRA (Probabilistic Risk Assessment) techniques have not penetrated the nuclear regulatory framework and industry to the same extent. After presenting relevant differences between the French and US nuclear industries and regulatory frameworks, the development and use of risk-informed applications in both countries are reviewed. In the United States, these techniques are usually well-accepted and have brought positive results regarding operational performance, plant safety and regulatory efficiency. In France, there have been in some cases difficulties regarding the acceptability of these techniques with the safety authority, but also within the operating company. While PRA results are commonly used in the US at the operational level through the use of risk-monitors, there appear to be in France obstacles to such practices. Online maintenance regulations and practices are then presented. US technical specifications provide much flexibility to voluntarily enter technical specifications action statements for online maintenance. As a result, following the implementation of the Maintenance Rule, online maintenance has been increasingly applied, leading to operational as well as safety improvements. In France technical specifications are more restrictive regarding these aspects, and online maintenance of safety-significant systems is often not allowed or allowed under restrictive conditions. A case study concerning the maintenance of emergency diesel generators and emergency core cooling systems is presented to illustrate and study these points in more detail. Finally, possible directions to facilitate the implementation of an online maintenance strategy in France are identified, and their implications are discussed.