The use of miniature specimen techniques for the assessment of materials condition

The demonstration of the structural integrity of key safety related components has been a primary objective of the nuclear industry for several decades. In particular, attention has been focused on the reactor pressure vessel (RPV) and primary circuit boundary of gas and water cooled reactors. This paper describes the role and development of techniques for the characterization of in-service materials degradation. Emphasis is placed on the use of small test samples which may be obtained from conventional surveillance test pieces or extracted from operational plant. Potential in-service embrittlement mechanisms of RPV and primary circuit steels are reviewed and used to illustrate the role of microstructural characterization to determine and quantify the embrittlement mechanisms and underpin degradation modeling. Degradation mechanisms considered include the effects of neutron irradiation on ferritic RPV steels and the effects of thermal aging on ferritic and duplex steels. The combination of mechanical and micro-analytical testing from miniaturized specimens is perceived as having substantial potential for assisting in the evaluation and justification for plant life management and extension issues