Document: NUREG-0800
Document ID: 7ed8e5d3-fcfd-49cc-84ad-3b25caba06af
Document Type: srp
Title: STEAM SYSTEM PIPING FAILURES INSIDE AND OUTSIDE OF CONTAINMENT
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550006.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.1.5
CFR Part: 
CFR Title: 

Content:
ion of the stuck out control rod should be considered. Local power peaking will affect the DNBR analysis in the initial period as the safety rods are entering the core and during any subsequent return to power resulting from reactivity addition to the core from the cooldown. 6. The core burnup (time in core life) should be selected to yield the most limiting combination of moderator temperature coefficient, void coefficient, Doppler coefficient, axial power profile, and radial power distribution. 7. The initial core flow assumed for the analysis of the steam line rupture accident should be chosen conservatively. If the minimum core flow allowed by the technical specifications is assumed, the minimum DNBR margin results; however, for the analysis of steam line break accidents, this may not be the most conservative assumption. For example, maximum initial core flow results in increased reactor coolant system cooldown and depressurization, decreased shutdown margin, and an increased possibility that the core will become critical and return to power. Since it is not clear what initial core flow is most conservative, the assumed value should be justified. 8. Failure of a steam line at a plant with multiple coolant loops will cause asymmetric temperatures within the reactor core. Asymmetric core temperatures will affect the local power distribution and the DNBR analysis. Assumptions for mixing in the downcomer and the reactor vessel lower plenum will affect the predicted core temperature distributions, reactivity feedback and local power. Assumptions for mixing should be chosen so as to be conservative for predicting maximum local core power and DNBR. 9. For postulated pipe failure in nonseismically qualified portions of the main steam line (outside containment and downstream of the main steam isolation valves, (MSIVs) due to a seismically initiated event, only safety related equipment should be assumed operative to mitigate the consequences of the break. 10. For