Document: NUREG-0800
Document ID: 0b93bfa1-19be-488b-8c78-a6c71cf3b42e
Document Type: srp
Title: MASS AND ENERGY RELEASE ANALYSIS FOR POSTULATED
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0535/ML053560191.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.2.1.3
CFR Part: 
CFR Title: 

Content:
t transfer for tube surfaces immersed in water and condensing heat transfer for the tube surfaces exposed to steam. iii. PWR Core Reflood Phase (Cold Leg Breaks Only) Following initial blowdown, which includes the period from the accident initiation (when the reactor is in a steady-state full power operation condition) to the time that the reactor coolant system broken loop pressure equalizes to the containment pressure, the water remaining in the reactor vessel should be assumed to be saturated. Justification should be provided for the refill period, which is the time from the end of the blowdown to the time when the emergency core cooling system (ECCS) refills the vessel lower plenum. An acceptable approach is to assume a water level at the bottom of the active core at the end of blowdown so there is no refill time. Calculations of the core flooding rate should be based on the ECCS operating condition during the core reflood phase, which begins when the water starts to flood the core and continues until the core is completely quenched, or the post-reflood phase, which is the period after the core has been quenched and energy is released to the RCS primary system by the RCS metal, core decay heat, and the steam generators, that maximizes the containment pressure. Calculations of liquid entrainment, i.e., the carryout rate fraction, which is the mass ratio of liquid exiting the core to the liquid entering the core, should be based on the PWR full length emergency cooling heat transfer experiments. Liquid entrainment should be assumed to continue until the water level in the core is 61 cm (2 feet) from the top of the core. An acceptable approach is to assume a carryout rate fraction (CRF) of 0.05 to the 46 cm (18-inch) core level, a linearly increasing CRF to 0.80 at the 61 cm (24-inch) level, and a constant CRF of 0.80 until the water level is 61 cm (2 feet) from the top of the core. Above this level, a CRF of 0.05 may be used. The assumption of steam quenching