Document: NUREG-0800
Document ID: 853719df-a6ea-408b-8d43-5956155abc38
Document Type: srp
Title: and 8.3.2.
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1007/ML100740246.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.1
CFR Part: 
CFR Title: 

Content:
fety buses in the event the non-safety bus(es) fail. The design should also include an alternate power source to non-safety loads, unless it is demonstrated that existing design margins will result in transients for loss of non-safety power events that are no more severe than those associated with the turbine-trip-only event specified in plant designs. See SRP Section 8.3.1 for further details. For passive reactor design applications, such as the AP 1000, the passive safety-related systems require electric power for valves and related instrumentation which can be supplied from the onsite Class 1E batteries and associated dc and ac distribution systems. If no offsite power is available, it is expected that the non-safety-related diesel generators would be available for important plant functions. However, this non-safety-related ac power is not relied on to maintain core cooling or containment integrity. Therefore, the passive reactor design supports an exemption to the requirements of GDC 17 for two physically independent offsite circuits, by providing safety-related passive safety systems for core cooling and containment integrity. As documented in SECY 94-084 & SECY-95-132, the staff addressed technical issues associated with the regulatory treatment of non-safety systems (RTNSS) process in passive plant designs. Risk-important, non-safety-related, active systems in passive light water reactors may have a significant role in accident and consequence mitigation by providing defense-in-depth functions to supplement the capability of the safety-related passive systems. For example, in the AP 1000 passive reactor design, ac power from an offsite system is required to power the normal residual heat removal system (RNS) and also to provide a means of supplying power to post-accident monitoring and ac input power for Class 1E dc battery chargers. The RNS provides a non-safety-related means 8.2-16 Revision 5 - May 2010 available to inject water into the reactor coolant