Document: NUREG-0800
Document ID: 33a67dd5-21e3-4458-9085-803f75466a73
Document Type: srp
Title: OVERPRESSURE PROTECTION
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070540076.pdf
Revision Date: 2023-06
Chapter: 5
Section ID: 5.2.2
CFR Part: 
CFR Title: 

Content:
REVIEW RESPONSIBILITIES Primary - Organization responsible for the review of reactor thermal-hydraulic systems in BWRs and PWRs. Secondary - None I. AREAS OF REVIEW The application of safety and relief valves (SRVs) and the reactor protection system ensures overpressure protection for the reactor coolant pressure boundary (RCPB) during operation at power. The application of pressure-relieving systems that function during low-temperature operation ensures overpressure protection for the RCPB during low-temperature operation of the plant (startup, shutdown). The pressure-retaining portions and supports of mechanical equipment shall be Safety Class 1 if they form part of the RCPB and have requirements that fall within the scope of Section III of Division 1 of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code). Different allowable stress limits (service limits) for pressure-retaining components provide different margins of failure and hence different reliability levels for the pressure-retaining function of the RCPB. Plant conditions and the operating status of the reactor determine the allowable ASME Code service limits. For normal plant operation, the design pressure limit (stress limit) of the RCPB shall not be exceeded. However, the ASME Code allows the design pressure to be exceeded by 10 percent for anticipated operational occurrences (AOOs) such as an inadvertent emergency core cooling system actuation. The ASME Code also permits the design pressure to be exceeded by 20 percent for infrequent events such as the loss of offsite alternating current power. These transient pressure load allowances are based on the frequency and duration of the event and should be reviewed and 5.2.2-2 Revision 3 - March 2007 approved by the NRC staff. American National Standards Institute (ANSI)/American Nuclear Society (ANS) 51.1 and ANSI/ANS 52.1, respectively, include useful discussions of overall plant design requirements. Additional