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:
REVIEW RESPONSIBILITIES Primary - Organization responsible for review of transient and accident analyses for BWRs Secondary - None I. AREAS OF REVIEW The specific areas of review are as follow: 1. Coupled neutronic-thermal-hydraulic instabilities, also known as density-wave instabilities, are safety concerns for boiling water reactors (BWRs). Three recognized modes of density-wave instability are core-wide (when the power and flow of all the core channels oscillate in phase), regional (when the power and flow of half the core channels oscillate out-of-phase with the other half), and single-channel flow instability (when the flow in a single channel oscillates accompanied by small power oscillations). 2. Instability modes other than density-wave type are possible in reactors and their systems. The most common sources of unstable power oscillations are poorly-tuned control systems or control oscillations caused by partial failures like sticky valves. Other sources of unstable power oscillations are design-dependent. For example, passive natural-circulation reactors may be susceptible to oscillations or loop instabilities during the startup phase. 15.9-2 March 2007 3. Certain instability events can lead to unacceptable consequences to the fuel if the reactor is not shut down on time. Specifically, for the density-wave regional stability mode, the original reactor protection system could not guarantee a timely shutdown because the average power range monitor signal averages the positive and negative sides of the power oscillation. Thus, the oscillation amplitude sensed by the average power range monitor is significantly smaller than the actual power oscillation experienced by the channels. Methodologies for resolving BWR core-stability issues presented in General Electric topical report NEDO-31960 and Supplement 1 were approved by the NRC in Reference 2. These reports provide long-term solutions (LTSs) to BWR stability issues and present methods to support plant system