Document: NUREG-0800
Document ID: ea7ce8f5-32bf-4d8c-a653-e964bff0ef48
Document Type: srp
Title: EMERGENCY CORE COOLING SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070448.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.3
CFR Part: 
CFR Title: 

Content:
of the reactor coolant pressure boundary are not exceeded during anticipated operational occurrences (AOOs). The ECCS is dependent upon the availability of electrical power supplied from the Class IE emergency electrical busses. The power supplies for the ECCS must maintain voltages at electrical equipment within the design limits. With voltages below design limits, electric equipment may not have sufficient capacity or capability to reliably perform their intended safety function during a design basis event. Thus, meeting the requirements of GDC 17 enhances plant safety by ensuring that the ECCS capacity and capabilities will be sufficient to ensure that the fuel design limits and reactor coolant pressure boundary integrity are maintained during AOOs and that the core is cooled during accidents. 5. GDC 27 establishes requirements regarding the combined reactivity control system capability. Upon actuation the ECCS in PWRs provides rapid injection of borated water to ensure reactor shutdown and adequate core cooling with appropriate margins for stuck control rods. Injection of borated water provides negative reactivity to reduce reactor power to residual levels and ensures sufficient cooling flow to the core. Requiring compliance with GDC 27 for the ECCS augments the protection for the primary fission product barrier by providing a means to ensure that the core, under postulated accident conditions, can be safely shutdown and will be maintained in a coolable geometry. 6. GDC 35 requires that an emergency core cooling system be provided that is capable of transferring heat from the reactor core, following a loss of reactor coolant, at a rate sufficient to ensure that the core remains in a coolable geometry and that the clad metal- water reaction is limited to negligible amounts. Following a breach in the reactor coolant pressure boundary, reactor coolant is lost at a rate determined by several factors, including break size and RCS pressure. The emergency core cooling