Document: NRC Regulatory Guide
Document ID: cf64153e-7623-469c-a3f9-b57ba0f5497d
Document Type: regulatory_guide
Title: Reactor Coolant Pump Flywheel Integrity + HISTORY - HISTORY 01/2006 – Periodic Review of Revision 1 – No Issues Identified
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003739936.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.14
CFR Part: 
CFR Title: 

Content:
led with a realistic prediction of maximum rotational speed, is considered to provide adequate margin because of the low probability of occurrence of the specific LOCA conditions that would cause such overspeed. Methods of limiting potential pump overspeed are also under investi gation. If the flywheel of the reactor coolant pump is conservatively designed and made from suitable mate rials with closely controlled quality, if adequate design review of new configurations is provided, and if ade quate inservice inspection is provided, the probability of a flywheel failure is sufficiently small that the conse quences of failure need not be protected against. Materials for pump flywheels should be manufac tured by processes that minimize flaws and result in adequate fracture toughness in both the transverse and longitudinal rolling directions. Materials produced by vacuum melting and degassing or the electroslag remelt ing process are known to have improved cleanliness and toughness. Plate material should be cross rolled to a ratio of at least I to 3, sufficient to achieve acceptable isotropy. Fracture toughness is achieved more readily in thinner plates, and fabrication of laminated flywheels by assembling them from several plates is acceptable. As an example, past evaluations have shown that ASME SA-533-B Class 1 and SA-508 Classes 2 and 3 materials generally have suitable toughness for typical flywheel applications provided stress concentrations are kept within reasonable limits and the reference tempera ture RTNDT, determined in accordance with Article NB-2331(a) of Section HI of the ASME Code,' is at least 500C (900F) below the lowest temperature at which operating speed is achieved. For other materials that may be considered for flywheels, the strength and toughness properties should be evaluated and justified for this application. 'Copies may be obbtined from the American Society of Mechanical Engineers, United Engineering Center, 345 East 47th Street, New York,