Document: NUREG-0800
Document ID: 9c7116dd-39cd-47a9-b121-dce6f51adc77
Document Type: srp
Title: SUBCOMPARTMENT ANALYSIS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0706/ML070620009.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.2.1.2
CFR Part: 
CFR Title: 

Content:
hin the subcompartment is modeled as a homogeneous water-steam mixture with an average density equivalent to the dry air model. This approach should be limited to subcompartments that have choked flow within the vents because the adequacy of this simplified model for subcompartments having primarily subsonic flow through the vents has not been established. 3. Vent Flow Path and Distribution of Mass and Energy Released. Assumptions with regard to the distribution of mass and energy release should be biased towards maximizing the subcompartment pressure. The vent flow behavior through all flowpaths within the nodalized compartment model should be based on a homogeneous mixture in thermal equilibrium, with the assumption of 100-percent water entrainment. In addition, the selected vent critical flow correlation should be conservative with respect to available experimental data. Currently acceptable vent critical flow correlations are the “frictionless Moody” (Ref. 2), with a multiplier of 0.6 for water-steam mixtures, and the thermal homogeneous equilibrium model for air-steam-water mixtures. If vent flowpaths are used that are not immediately available at the time of pipe rupture, the following criteria apply: 6.2.1.2-5 Revision 3 - March 2007 A. The vent area and resistance as a function of time after the break should be based on a dynamic analysis of the subcompartment pressure response to pipe ruptures. B. The validity of the analysis should be supported by experimental data, or a testing program should be proposed at the construction permit or DC stage that will support this analysis. C. To meet the requirements of GDC 4, the safety analysis should consider the effects of missiles that may be generated during the transient. 4. Design Pressure. For the review of a construction permit (CP) preliminary safety analysis report (PSAR) or a factor of 1.4 should be applied to the peak differential pressure which is calculated in a manner acceptable to the reviewer for