Document: 10 CFR Part 50
Document ID: a6c1b81f-bcf5-4ef9-9e8b-2a055aaed0aa
Document Type: cfr
Title: Fracture toughness requirements for protection against pressurized thermal shock events.
Source: 10 CFR Part 50
Source URL: https://www.ecfr.gov/current/title-10/part-50/section-50.61
Revision Date: 
Chapter: 
Section ID: 50.61
CFR Part: 50
CFR Title: 10

Content:
c mean values must be used unless justification for different values is provided: 0 °F for welds made with Linde 80 flux, and −56 °F for welds made with Linde 0091, 1092 and 124 and ARCOS B-5 weld fluxes. ( iii ) M means the margin to be added to account for uncertainties in the values of RT NDT(U) , copper and nickel contents, fluence and the calculational procedures. M is evaluated from Equation 2. ( A ) In Equation 2, σ U is the standard deviation for RT NDT(U) . If a measured value of RT NDT(U) is used, then σ U is determined from the precision of the test method. If a measured value of RT NDT(U) is not available and a generic mean value for that class of materials is used, then σ U is the standard deviation obtained from the set of data used to establish the mean. If a generic mean value given in paragraph (c)(1)(i)(B) of this section for welds is used, then σ U is 17 °F. ( B ) In Equation 2, σΔ is the standard deviation for ΔRT NDT . The value of σΔ to be used is 28 °F for welds and 17 °F for base metal; the value of σΔ need not exceed one-half of ΔRT NDT . ( iv ) ΔRT NDT is the mean value of the transition temperature shift, or change in RT NDT , due to irradiation, and must be calculated using Equation 3. Equation 3: ΔRT NDT = (CF)f (0.28−0.10 log f) ( A ) CF (°F) is the chemistry factor, which is 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, “Wt − % copper” and “Wt − % nickel” are the best-estimate values for the material, which will normally be the mean of the measured values for a plate or forging. For a weld, the best estimate values will normally be the mean of the measured values for a weld deposit made using the same weld wire heat number as the critical vessel weld. If these values are not available, the upper limiting values given in the material specifications to which the vessel