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:
a damage function to determine ARTNDT versus radial distance into the wall. The most widely accepted damage func- tion at this time is dpa, and the attenuation formula (Equation 3) given in Regulatory Position 1.1 is based on the attenuation of dpa through the vessel wall. Sensitivity to neutron radiation embrittlement may be affected by elements other than copper and nickel. The original version and Revision 1 of this guide had a phosphorus term in the chemistry factor, but the studies on which this revision was based found other elements such as phosphorus to be of secondary importance, i.e., including them in the analysis did not produce a significantly bet- ter fit of the data. Scatter in the data base used for this guide is relatively signifi- cant, as evidenced by the fact that the standard deviations for Guthrie's derived formulas (Ref. 2) are 28 °F for welds and 17 °F for base metal despite extensive efforts to find a model that reduced the fitting error. Thus the use of surveillance data from a given reactor (in place of the calculative procedures given in this guide) requires considerable engineering judgment to evaluate the credibil- ity of the data and assign suitable margins. When surveillance data from the reactor in question become available, the weight given to them relative to the information in this guide will depend on the credibility of the surveillance data as judged by the following criteria: 1. Materials in the capsules should be those judged most likely to be controlling with regard to radiation embrittlement according to the recommendations of this guide. 2. Scatter in the plots of Charpy energy versus temperature for the irradiated and unirradiated conditions should be small enough to permit the determination of the 30-foot-pound temperature and the upper-shelf energy unambiguously. 3. When there are two or more sets of surveillance data from one reactor, the scatter of ARTNDT values about a best-fit line drawn as described in RegulatQry