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:
ed operational occurrences. Meeting the requirements of General Design Criteria 29 for the control rod drive systems prevents occurrence of mechanisms that could result in fuel cladding damage such as severe overheating, excessive cladding strain or exceeding the thermal margin limits during anticipated operational occurrences. Preventing excessive cladding damage in the event of anticipated transients ensures that the integrity of the cladding as a fission product barrier will be maintained. 8. 10 CFR 50.62(c)(3) requires that each boiling water reactor have an alternate rod injection system that is diverse (from the reactor trip system) from sensor output to the final actuation device. In addition, the alternate rod injection system must have redundant scram air header exhaust valves. There is a potential within all reactor trip system designs for common cause failures of identical or similar components to result in a failure to trip the control rod drive system. The ATWS requirements address this potential and reduces the susceptibility to common mode failures in the scram systems. For BWRs one method of providing diversity in the alternate rod injection system is the use of an "energize to trip" circuit versus a "de-energize to trip" circuit in the output devices of the scram system and by the provision for the redundant scram air header exhaust valves (References 8 and 9). Implementing the requirements of 10 CFR 50.62(c)(3) enhances plant safety by reducing the risk due to an ATWS event at BWR plants, and by providing mitigating capability to permit a safe shutdown of the plant should an ATWS event occur. III. REVIEW PROCEDURES The review procedures set forth below are used during the construction permit (CP) review to determine that the design criteria and bases and the preliminary design as set forth in the applicant's preliminary safety analysis report (PSAR) meet the acceptance criteria given in subsection II of this SRP section. During the operating