Document: NUREG-0800
Document ID: 97120913-d26f-4324-ab62-22f3f5b73925
Document Type: srp
Title: and 8.3.2.
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0636/ML063600410.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.1
CFR Part: 
CFR Title: 

Content:
have sufficient independence, redundancy, and testability to perform their safety functions assuming a single failure. Therefore, no single failure will prevent the onsite power system from supplying electric power, thereby permitting safety functions and other vital functions requiring electric power to be performed in the event of any single failure in the power system. As documented in SECY 94-084, the preferred electrical distribution system for evolutionary light water reactor design plants should include: 1) an alternate offsite power source available for non-safety-related loads, unless the design margins for loss of non-safety-related loads are no more severe than turbine-trip-only events in current plants, and 2) at least one offsite circuit to each redundant safety division supplied directly from offsite power sources, with no intervening non-safety-related buses. Passive reactor designs incorporate passive safety-related systems for core cooling and containment integrity, and therefore, do not depend on the electric power grid connection and grid stability for safe operation. However, passive reactor designs also include active systems that can provide defense-in-depth capabilities for reactor coolant makeup and decay heat removal. The accident analysis and Probabilistic Risk Analysis (PRA) need to be reviewed to identify these non-safety related systems. Once identified, review of the electrical design of the plant needs to confirm that any offsite power requirements for thses systems are met. The AP1000 safety analyses, for example, assume that the reactor coolant pumps (RCPs) can receive power at 6.9 kV from either the main generator or the grid for a minimum of 3 seconds following a turbine trip assuming no electrical fault. Should a turbine trip occur during power operation, the generator will continue rotating at synchronous speed by acting as a synchronous motor. Anti-motoring protective relaying for the main generator will open the generator