Document: NUREG-0800
Document ID: 061b3f99-1bfd-4e65-be97-7e9affac9aef
Document Type: srp
Title: UNCONTROLLED CONTROL ROD ASSEMBLY WITHDRAWAL AT POWER
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0636/ML063600414.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.4.2
CFR Part: 
CFR Title: 

Content:
d the approximations used differ for a PWR and a BWR. 2. For a BWR, past analyses and reviews have shown that at maximum rod worths and rates of reactivity addition, the reactor power increases slowly and the total increase is relatively small, so that the AOO may be approximated by steady-state analyses. Because of changes in local power distribution attributable to rod motion and strong void 15.4.2-6 Revision 3 - March 2007 feedback effects on the power distribution, three-dimensional, steady-state, coupled neutron distribution, thermal-hydraulics calculations that take account of these effects are required. The AOO is halted by action of a rod block system, which should block rod withdrawal before fuel safety limits are reached. The review process for a BWR, discussed above, is concentrated on the steady-state aspects of the AOO to ensure that initial and subsequent power distributions are maximized, that the reactor conditions produce MCPR and that the response of the rod block system is conservatively calculated considering minimum operation of the associated local power range monitoring system. 3. A PWR analysis, on the other hand, generally involves larger power changes and requires AOO calculations. Because power distributions in the course of the AOO can frequently be predicted conservatively using design-limit peaking factors, point kinetics may be used for the nuclear AOO. The nuclear AOO is coupled, however, to core and system thermal-hydraulic response to the power changes (fuel and moderator thermal feedback and system instrumentation response). For a PWR, the reviewer ascertains that a full range of AOO conditions are analyzed; the AOO calculation models are adequate; and that scram response of the flux, temperature, or pressure instrumentation is correctly calculated. The range of parameters to be considered includes: A. Initial power levels from low to full power. B. Reactivity insertion rates from very low to maximum possible for the control