Document: NUREG-0800
Document ID: 8da52d2b-9980-4076-8056-2cafebb25ed6
Document Type: srp
Title: THERMAL AND HYDRAULIC DESIGN
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550060.pdf
Revision Date: 2023-06
Chapter: 4
Section ID: 4.4
CFR Part: 
CFR Title: 

Content:
for extended power uprates (EPUs) should be performed in a manner that ensures adequate safety margin. At a minimum, there should be a 95-percent probability at the 95-percent confidence level that a hot fuel rod in the reactor core will not experience a DNB or a transition condition during normal operation or AOOs. Specifically, this safety criterion should be satisfied while accounting for changes in radial and bundle power distribution, including any changes in critical heat flux ratio (CHFR) and CPR. The reviewer should confirm the adequacy of the flow-based average power range monitor flux trip and safety limit minimum critical power ratio at the uprated conditions (Review Standard RS-001). The reviewer should also ensure that the correlations used in the EPU analysis do not exceed their validation range under uprated normal operation and AOO conditions. The following are two examples of acceptable approaches to meeting this criterion: A. For departure from nucleate boiling ratio (DNBR), CHFR or CPR correlations, there should be a 95-percent probability at the 95-percent confidence level that the hot rod in the core does not experience a DNB or boiling transition condition during normal operation or AOOs. B. The limiting (minimum) value of DNBR, CHFR, or CPR correlations is to be established such that at least 99.9 percent of the fuel rods in the core will not experience a DNB or boiling transition during normal operation or AOOs. Correlations of critical heat flux are continually being revised as a result of additional experimental data, changes in fuel assembly design, and improved calculational techniques involving coolant mixing and the effect of axial power distributions. 2. Problems affecting DNBR or CPR limits, such as fuel densification or rod bowing, are accounted for by an appropriate design penalty which is determined experimentally or analytically. Subchannel hydraulic analysis codes, such as those described in “TEMP- Thermal Enthalpy Mixing