Session: CS-20-01 Master Curve Method and Applications

Paper Number: 125225

125225 - An Examination of Margins Needed to Ensure Conservative Application of T0 to Rpv Fracture Toughness 

Variation in fracture toughness of a heavy-section reactor pressure vessel (RPV) steel plate, forging or weld can be caused primarily by processing and chemical composition variation. Understanding the variation is paramount to enable application of the ASTM E1921 measured ductile-brittle transition temperature, T₀, to RPV integrity evaluations. Variation in toughness in thick section forgings and plates can be caused by carbon segregation and through thickness by the quenching process. Variation in toughness can also be caused by variation in chemical composition of the elements that enhance irradiation
embrittlement, primarily copper and nickel. The geometric scale of these variations varies. For example, carbon segregation in large ring forging might be limited to one region while it is well documented that toughness increases near the surface  here the cooling rate was high when quenching. For welds, copper and nickel might vary within and between weld beads and at least a significant portion of the variation is captured in a typical set of toughness specimens used to determine T₀. This paper will look at many datasets where at least two sets of specimen tests from which T₀ can be calculated are available from the same heat of steel. It will be assumed that one T₀ measurement is used as the direct fracture toughness measurement and the 2nd (or more) are measurements from the irradiated RPV represented by the irradiated ductile-brittle transition temperature fracture toughness test results. One T₀ measurement will be adjusted to the condition of the 2nd (or more) measured datasets with assessment of the margin needed to ensure an evaluation of the RPV would be bounding. This information will enable development of necessary margins in applying unirradiated and irradiated master curve fracture toughness measurements to an RPV component using relatively small samples.

Presenting Author: J. Brian Hall Westinghouse

Presenting Author Biography: Brian has unique experience in the nuclear power industry gained over the last 30+ years, enabling him to understand the interrelationship between material mechanical behavior, fracture mechanics, and aging/embrittlement. Brian’s experience includes: material specifications for component replacement and new plants, failure analysis, materials testing, fracture mechanics, and material aging evaluations for uprates, repairs and license renewal for nuclear power plants. His contributions have been in the areas of reactor pressure vessel (RPV) integrity, RPV internals aging, and other reactor coolant system materials. He has supported materials reliability programs for individual utilities, the Pressurized Water Reactor Owners Group Materials Committee, and the Electric Power Research Institute (EPRI). He is the chair of the ASTM E10.02 Subcommittee, “Behavior and Use of Nuclear Structural Materials,” which is responsible for standards related to RPV embrittlement surveillance, and is the chair of ASTM E10 Committee, “Nuclear Technology and Applications.” Through publications and leadership in industry activities, he is recognized internationally. He has advanced the use of the master curve method (direct fracture toughness) for the benefit of the utilities, enabling operation beyond 40 years and improved operation.

Authors:

J. Brian Hall Westinghouse
Brian Golchert Westinghouse
Derek Simpson Westinghouse