Document: NUREG-0800
Document ID: 02fef38f-79ed-4d55-825f-81551bcfdcdc
Document Type: srp
Title: LOSS-OF-COOLANT ACCIDENTS RESULTING FROM SPECTRUM OF
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550016.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.6.5
CFR Part: 
CFR Title: 

Content:
is considered insufficient to determine the worst break because the break areas associated with these integer diameters are too coarse to adequately identify the highest PCT. The analyses must also be carried out until the top of the active fuel has been recovered with a two-phase mixture and the cladding temperatures have been reduced to temperatures near the saturation temperature. The analyses must also consider the case with a severed ECC injection line, along with the degraded ECC injection into the intact loops. Break locations should include the side and top of the discharge leg to assure that the suction leg piping that fails to clear of liquid does not result in depression of the two-phase mixture level into the core and result in the worst case PCT. If operator action is required to maintain conditions within 10 CFR 50.46 limits, then the equipment and operator action times to achieve a successful core cooling condition should also be identified. An evaluation of post-LOCA long term cooling should also be performed to identify the operator actions to successfully control and prevent boric acid precipitation. Analyses of both large break and small break LOCAs should be performed to identify the timing for boric acid precipitation. The timing for the switch to simultaneous injection for large breaks should be identified using acceptable analysis methods. A spectrum of small breaks should also be analyzed to identify other means to control boric acid precipitation when RCS pressure remains too high to enable flushing of the core through a simultaneous injection line-up during the long term. All equipment and operator action times should also be clearly identified in the analyses. 15.6.5-3 Revision 3 - March 2007 The calculational framework used for the evaluation of the ECCS system in terms of core short term behavior and long term cooling performance are referred to as an evaluation model. It includes one or more computer programs, the mathematical models