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:
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 Position 2.1 normally should be less than 28 °P for welds and 17 °P for base metal. Even if the fluence range is large (two or more orders of magnitude), the scatter should not exceed twice those values. Even if the data fail this criterion for use in shift calculations, they may be credible for determining decrease in upper-shelf energy if the upper shelf can be clearly deter- mined, following the definition given in ASTM E 185-82 (Ref. 1). 4. The irradiation temperature of_ the Charpy specimens in the capsule should match vessel wall temperature at the cladding/base metal interface within ± 25 °P. 5. The surveillance data for the correlation monitor material in the capsule should fall within the scatter band of the data base for that material. To use the surveillance data from a specific plant instead of Regulatory Position 1, one must develop a relationship of ARTNDT to fluence for that plant. Because such data are limited in number and subject to scatter, Regulatory Position 2 describes a procedure -in which the form of Equation 2 is to be used and the fluence fac- tor therein is retained, but the chemistry factor is determined by the plant surveillance data. Of several possible ways to fit such data, the method that minimizes the sums of the squares of the errors was chosen somewhat arbitrarily. Its use is justified in part by the fact that "least squares" is a common method for curve fitting. Also, when there are only two data points, the least squares method gives greater weight to the point with the higher ARTNOT; this seems reasonable for fitting surveillance 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