Document: NUREG-0800
Document ID: 50ab8154-2a3c-4c0f-8ce4-06ac83096e5c
Document Type: srp
Title: ULTIMATE HEAT SINK
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550048.pdf
Revision Date: 2023-06
Chapter: 9
Section ID: 9.2.5
CFR Part: 
CFR Title: 

Content:
ign are conservative. The reviewer makes an independent evaluation of the applicant’s calculated heat loads. The UHS heat loads include heat due to decay of radioactive material, sensible heat, pump work, and the heat load from the operation of the station auxiliary systems serving and dependent upon the UHS. B. Operational data from plants of similar design confirm, where possible, the heat input values for sensible heat, pump work, and station auxiliary systems. 9.2.5-7 Revision 3 - March 2007 2. The reviewer verifies whether: A. The total essential station heat load and system flow requirements of the service water system are compatible with the UHS heat rejection capability. B. The UHS can dissipate the maximum possible total heat load, including that of a LOCA under the worst combination of adverse environmental conditions, even freezing, and can cool the unit (or units, including a LOCA for one unit of a multi-unit station with one heat sink) for a minimum of 30 days without makeup unless acceptable makeup capabilities can be demonstrated. This capability is verified by independent check calculations. C. The single failure of any SSCs will not prevent the UHS from performing its safety functions. 3. For plants with UHS cooling towers the reviewer determines, in addition, whether: A. The results of failure modes and effects analyses show that the mechanical systems (fans, pumps, and controls) can withstand a single, active failure in any of these systems, including an auxiliary electric power source failure, and deliver water in the quantities and at temperatures required for safe shutdown. B. Adequate net positive suction head can be provided to all essential pumps with water level variations in the basins. This determination is verified by independent calculations. C. The towers can provide the design cooling water temperature under the worst combination of adverse environmental conditions, even freezing, and the basins can supply water for 30-day cooling