Document: NUREG-0800
Document ID: f813a982-efc9-4295-a0ff-eb6a289f39ba
Document Type: srp
Title: BOILING WATER REACTOR STABILITY
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550017.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.9
CFR Part: 
CFR Title: 

Content:
nale for application of these requirements to reviewing this SRP section is discussed in the following paragraphs: 1. GDC 12 states, “The reactor core and associated coolant, control, and protection systems shall be designed to assure that power oscillations which can result in conditions exceeding specified acceptable fuel design limits are not possible or can be reliably and readily detected and suppressed.” GDC 12, therefore, sets two types of generic LTS requirements: (A) exclusion region solutions that reduce the operating domain by defining an exclusion region where the reactor is not allowed to operate and (B) D&S solutions that scram the reactor if oscillations develop. 2. For plants with D&S solutions, unstable power oscillations are AOOs. GDC 20 requires effective reactor protection system protection against SAFDLs for AOOs. Thus, the success criteria for protection system actuation during unstable power oscillations are avoidance of boiling transition and other criteria specified in SRP Sections 4.2 and 4.4 even though during short events fuel damage may not occur. 3. The LTS protection should be automatic. Manual and administrative actions are acceptable as backup systems when the primary licensed LTS is declared inoperable for a period of up to 120 days. Manual actions are acceptable for a short time if only a small probability of an instability that would challenge SAFDLs can be shown in reasonable operator action times. If this small probability cannot be demonstrated, 15.9-6 March 2007 there should be an automatic backup. For example, in operations at MELLLA+ conditions, calculations show that large unstable power oscillations may develop rapidly and violate SAFDL within approximately one minute following a recirculation pump trip. An automatic backup system is required in this situation. 4. There is a third acceptance option for instability modes other than density-wave stability. Criteria in this SRP specify that the GDC 12 intent is that the