Document: NRC Regulatory Guide
Document ID: 5f4d6577-6c2a-473a-9a76-4033a95dba4c
Document Type: regulatory_guide
Title: Radiation Embrittlement of Reactor Vessel Materials (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740284.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.99
CFR Part: 
CFR Title: 

Content:
ance data, because generally the higher data point will be the more recent and therefore will repre- sent more modem procedures. C. REGULATORY POSITION 1. SURVEILLANCE DATA NOT AVAILABLE When credible surveillance data from the reactor in question are not available, calculation of neutron radiation embrittlement of the beltline of reactor vessels of light-water reactors should be based on the procedures in Regulatory Positions 1.1 and 1.2 within the limitations in Regulatory Position 1.3. 1.99-2 1.1 Adjusted Reference Temperature The adjusted reference temperature (ART) for each material in the beltline is given by the following expression: ART = Initial RTNDT + ARJNDT + Margin (1) Initial RTNDT is the reference temperature for the unirradiated material as defined in Paragraph NB-2331 of Section ill of the ASME Boiler and Pressure Vessel Code (Ref. 7). If measured values of initial RTNDT for the material in question are not available, generic mean values for that class* of material may be used if there are sufficient test results to establish a mean and standard devia- tion for the class. ARTNDT is the mean value of the adjustment in reference temperature caused by irradiation and should be calculated as follows: ARTNDT = (CF) f(0.28 - 0.10 log f) (2) CF ( °F) is the chemistry factor, a function of copper and nickel content. CF is given in Table 1 for welds and in Table 2 for base metal (plates and forgings). Linear interpolation is permitted. In Tables 1 and 2 "weight-percent copper" and "weight-percent nickel" are the best-estimate values for the material, which will normally be the mean of the measured values for a plate or forging or for weld samples made with the weld wire heat number that matches the critical vessel weld. If such values are not available, the upper limiting values given in the material specifications to which the vessel was built may be used. If not available, conservative estimates (mean plus one standard deviation) based on generic data may