Document: NRC Regulatory Guide
Document ID: 5a810f5d-d35a-4bd8-bde7-205519300c40
Document Type: regulatory_guide
Title: Thermal Shock to Reactor Pressure Vessels
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1221/ML12216A018.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.2
CFR Part: 
CFR Title: 

Content:
properties assumed in the analyses have not yet been com- pletely confirmed. The additional data needed to resolve the uncertainties in the. fracture toughness prop- erties of reactor vessel material are expected to be provided by the Heavy Section Steel Tech- nology (HSST) research and development pro- gram. Since reactor vessel materials are ini- tially ductile and their fracture toughness prop- erties are not significantly changed upon irra- diation during the initial 5 years of operation, the potential for reactor pressure vessel fail- ure as a result of cold water injection is con- sidered to be acceptably small during this period. Sufficient data should be available from the HSST Program to permit a final judgment within this 5-year period on the acceptability of the projected behavior of vessel material throughout its service lifetime. In the event that the results of the HSST Program or other research indicate that the potential for growth of defects in radiation em- brittled reactor pressure vessel n~aterial re- duces the available margin of safety against brittle fracture to an unacceptable level, an acceptable engineering solution to the problem could be applied-for example, thermal anneal- ing of the reactor vessel material. Naval Re- search Laboratory data indicate that annealing of a PWR vessel at its design temperature (650'F) for a period of 168 hours should pro- duce a recovery in fracture toughness proper- ties and reduce the transition temperature shift due to irradiation by 30 to 50 percent (i.e., a 100'F shift in transition temperature would be reduced to 70-50' after annealing). Annealing BWR vessels at design temperatures and for equivalent time periods would, if needed, pro- vide an equivalent degree of recovery. Based on the calculation of potential irradiation effects in presently designed PWRs and BWRs, this de- gree of recovery of material toughness proper- ties combined with the potential for repeating the annealing process, if