Document: NUREG-0800
Document ID: 3006d57d-d68e-41da-8ef9-9217d041a456
Document Type: srp
Title: RADIOLOGICAL CONSEQUENCES OF A DESIGN BASIS LOSS-OF-COOLANT
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350166.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.6.5
CFR Part: 
CFR Title: 

Content:
he CSB to assure that the operation of the MSIVLCS does not adversely affect pressure transients in secondary containment regions. The system is then modeled using a computer code (Ref. 4). The source assumed i's the same as that used to estimate the containment leakage dose calculated in SRP Section 15.6.5, Appendix A, but it is assumed to be instantaneously distributed in the drywell free volume at the time of the accident. No credit for leakage of activity from the drywell to the containment (Mark III) or to the suppression pool region (Mark I and II) is assumed, but credit can be taken' for radioactive decay of the fission products in the drywell prior to operation 15.6.5-24 Rev. 1 - July 1981 of the MSIVLCS. The main steam isolation valves are assumed to leak at their technical specification limit. No release of activity from the MSIVLCS is assumed up to the time of system actuation. Leakage through valve stems or drain lines to an untreated region is assumed.to be released to the atmosphere. Releases through the MSIVLCS which are directed to treated regions are assumed to be direct to the filter intake unless the MSIVLCS flow is mechanically directed to a distribution header. If the latter is the case, then credit for mixing is given on the same basis as for other leakage to this system (see SRP Section 6.5.3). The resulting doses at the exclusion area and the LPZ boundaries are calculated using the dose model described in Regulatory Guide 1.3 (Ref. 3). The X/Q values to be used for this evaluation are the accident X/Q's used in Section 15.6.5s Appendix A. For systems which are designed for initial releases at significantly later times into the accident, application of worst meteorology at the time of release may have to be considered; this will be handled on a case-by-case basis. IV. EVALUATION FINDINGS The reviewer verifies that the applicant has provided sufficient information for an independent staff calculation of the thyroid and whole-body doses due to