Document: NUREG-0800
Document ID: 042bc5c0-5de0-44b4-9599-6c131e20eb7a
Document Type: srp
Title: FUNCTIONAL DESIGN OF CONTROL ROD DRIVE SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070413.pdf
Revision Date: 2023-06
Chapter: 4
Section ID: 4.6
CFR Part: 
CFR Title: 

Content:
erature and power and the lowest negative reactivity contributions from poisons such as Xenon. Meeting the requirements of General Design Criterion 26 ensures that the control rod drive system will be capable of providing sufficient operational control, reliability and safety during reactivity changes, including those during normal operation and anticipated operational occurrences. 5. General Design Criterion 27 requires the reactivity control systems be designed to have a combined capability, in conjunction with poison addition by the emergency core cooling system, of reliably controlling reactivity changes under accident conditions such that the capability to cool the core is maintained. The control rod drive system 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, implies that the fuel assembly retains 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 due to coplanar fuel rod ballooning. Meeting the requirements of General Design Criterion 27 for the control rod drive systems in conjunction with the emergency core cooling system enhances plant safety by ensuring that the reactor can be shutdown and core coolability will be maintained. 6. General Design Criterion 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