The Nuclear Regulatory Commission’s safety regulations require that nuclear reactors be designed to protect the public from postulated accidents, such as the rupture of pipes that would limit the flow of cooling water to the reactor. These regulations include General Design Criteria 34 and 35 in Appendix A to 10 CFR Part 50.
Emergency diesel generators (EDGs) are important safety systems since they provide electricity to emergency equipment if outside power is cut off to the plant—another postulated accident. This electricity, for example, would allow pumps to continue to send cooling water to the reactor vessel to prevent overheating damage to the core. So the NRC has requirements that limit how long a reactor can continue operating without one of its two EDGs under different conditions. The shortest period is 3 days while the longest period is 14 days. Read more >