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:
ons 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, including those during normal operation and anticipated operational occurrences. 5. GDC 27 requires that the reactivity control systems be designed to have the combined ability, in conjunction with poison addition by the emergency core cooling system, to reliably control reactivity changes under accident conditions such that the capability to cool the core is maintained. The CRDS provides the method for inserting the control rods into the reactor core when monitored plant conditions reach specified safety system setpoints. Insertion of the control rods, in conjunction with the poison addition by the emergency core cooling system, provides the means of inserting negative reactivity to rapidly shut the reactor down and ensure core coolability. Coolability, or coolable geometry, refers to the fuel assembly’s ability to retain its geometry with adequate coolant channels to permit removal of residual heat. Loss of coolability can result from cladding embrittlement, violent expulsion of fuel, generalized cladding melting, structural deformation, and flow blockage because of coplanar fuel rod ballooning. Meeting the requirements of GDC 27 for the CRDS in conjunction with the emergency core cooling system enhances plant safety by ensuring that the reactor can be shut down and core coolability can be maintained. 6. GDC 28 requires that the reactivity control systems be designed with appropriate limits on the potential amount and rate of reactivity increase to prevent the adverse effects of postulated reactivity accidents. A postulated failure of the control rod system, such as rod ejection or rod dropout, has the potential to result in a relatively high rate of positive reactivity insertion which, if large enough, could cause a prompt power excursion. Such a prompt power