Document: NUREG-0800
Document ID: 9738c583-ac33-4836-b8f1-580dc98eb7f0
Document Type: srp
Title: RADIOLOGICAL CONSEQUENCES OF THE FAILURE OF SMALL LINES CARRYING
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350147.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.6.2
CFR Part: 
CFR Title: 

Content:
ervatism of the assumptions used in the analysis. 2. Identification of the small lines connected to the primary reactor coolant system and penetrating the containment. The isolation provisions are IS. 6.2- 2 Rev. 2 - July 1981 identified with respect to the applicability of GDC 55 (i.e., isolation capability inside and outside containment) and Regulatory Guide 1.11 (i.e., isolation capability outside containment for lines exempt from GDC 55). The implementation of these guidelines is reviewed by the Containment Systems Branch under SRP Section 6.2.4. The AEB reviewer will coordinate his review with CSB if additional clarification is needed. 3. Performance of an independent analysis by the staff. The reviewer selects for a failure analysis those small lines that most likely will result in the highest offsite radiological consequences. The selection is largely based on the analysis performed on recently reviewed plants but should include, if appropriate, the letdown line of the chemical volume and control system (CVCS) and the largest instrument and sample line. The following conservative assumptions are made for the analysis: a. For small lines that meet GDC 55, such as the CVCS letdown line, the failure is assumed to occur downstream of the outboard containment isolation valve in conjunction with a single failure of one of the two containment isolation valves. The amount of primary coolant released outside the containment is determined by considering the method, capability and time required to detect such failure and the time required to isolate the failure (i.e., time to close the operable isolation valve). b. For small lines exempt from GOC 55, such as instrument lines, but which meet the isolation guidelines of Regulatory Guide 1.11 (i.e., containment isolation valve outside containment), the failure is postulated to occur downstream of the valve in conjunction with a single failure (i.e., valve does not close). Unless other isolation or flow reduction