Document: NUREG-0800
Document ID: 67e3fd64-e6a4-4522-b90f-4184c2f5b357
Document Type: srp
Title: FUNCTIONAL DESIGN OF CONTROL ROD DRIVE SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070540139.pdf
Revision Date: 2023-06
Chapter: 4
Section ID: 4.6
CFR Part: 
CFR Title: 

Content:
ity control. Meeting the 4.6-7 Revision 2 - March 2007 requirements of GDC 25 by designing these systems to withstand single failures ensures that a single malfunction of the rod control drive system, such as accidental withdrawal, will not prevent proper control of core reactivity and therefore will not result in exceeding acceptable fuel design limits. Maintaining acceptable fuel design limits enhances plant safety by preventing the occurrence of mechanisms that could result in fuel cladding damage such as severe overheating, excessive cladding strain, or exceeding the thermal margin limits. Preventing excessive cladding damage ensures maintenance of the integrity of the cladding as a fission product barrier. 4. GDC 26 requires the provision of two independent reactivity control systems of different design principles. Each system must have the capability of reliably controlling reactivity changes resulting from normal operation. One of the systems shall use control rods and be capable of reliably controlling reactivity changes during anticipated operational occurrences, with appropriate margin for malfunctions such as stuck rods. In addition, one of the systems must be capable of holding the reactor core subcritical under cold conditions. The CRDS provides one of the methods for controlling reactivity changes. The CRDS is designed to control reactivity during both normal operation and anticipated operational occurrences. The CRDS should be capable of rendering a reactor subcritical under conservative conditions with the control rod with the highest rod worth fully withdrawn from the core. The conservative conditions include the highest positive reactivity contributions resulting from effects such as temperature and power and the lowest negative reactivity contributions from poisons such as xenon. Meeting the requirements of GDC 26 ensures that the CRDS will be capable of providing sufficient operational control, reliability, and safety during reactivity changes,