Document: NUREG-0800
Document ID: c755e557-3a72-423f-92bc-0f0270936e27
Document Type: srp
Title: RESIDUAL HEAT REMOVAL (RHR) SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1006/ML100680577.pdf
Revision Date: 2023-06
Chapter: 5
Section ID: 5.4.7
CFR Part: 
CFR Title: 

Content:
systems have decreased the RCS temperature. In both existing plant types, the RHR is typically a low-pressure system that provides shutdown cooling when the RCS temperature is reduced to about 150 EC (300 EF). Although the RHR system function is similar for the two plant types, the system designs are different. The RHR system in PWRs takes water from one or two RCS hot legs, cools it, and pumps it back to the cold legs or core flooding tank nozzles. The suction and discharge lines for the RHR pumps have valving to provide reasonable assurance that the low-pressure RHR system is isolated from the RCS when the RCS pressure is greater than the RHR system design pressure. Relief valves are provided to protect the RHR system from an overpressure condition, although the relief capability is not sufficient to protect the RHR system from an overpressure condition if isolation valves are open when the RCS pressure is significantly greater than the RHR design pressure. To accomplish RHR heat removal, RHR heat exchangers transfer heat to the component cooling water or service water system, which then transports heat to the ultimate heat sink (UHS). In PWRs, the RHR system is also used to fill, drain, and remove heat from the refueling water cavity during refueling operations, to circulate coolant through the core during plant startup before RCS pump operation, and in some to provide an auxiliary pressurizer spray. The RHR system in BWRs is typically composed of four subsystems. SRP Sections 6.2.2 and 6.3 discuss the containment heat removal and low-pressure emergency core cooling subsystems. This SRP section covers the shutdown cooling and steam condensing (via RCIC) subsystems, which use the same hardware, consisting of pumps, piping, heat exchangers, valves, monitors, and controls. In the shutdown cooling mode, the BWR RHR system can also be used to supplement spent fuel pool cooling. The steam condensing mode of RCIC operation in BWRs (when included in the plant design)