Evaluation of Mechanical Properties of Primary Circuit Components Using SPT Technique

Abstract

The paper deals with the evaluation of mechanical properties of safety-related components of the primary circuit of nuclear power plants (NPPs). During a long-term operation of NPPs, changes of mechanical properties occur. To ensure the safe operation of NPP it is necessary to monitor and evaluate these changes. One possibility how to solve this problem is a direct sampling and the assessment of the actual mechanical properties using the small punch test (SPT) technique. By the SPT technique it is possible to evaluate the basic tensile properties such as the ultimate tensile strength and the yield stress of the tested materials as well as the transition temperature. The authors describe model examples of surface sampling using the special Rolls Royce equipment SSam™-2. The SPT specimens were prepared from the removed samples by application of the wire electrical discharge machining and fine grinding. The prepared specimens were tested and the obtained data were evaluated. Original pieces of primary tubes with diameter 500 mm made of stainless steel type 08Ch18N10T (AISI 321) were used for these model examples. Another experimental material used was a block of the reactor pressure vessel wall cut from NPP Greifswald Unit 7 which contains a weld joint. Those experiments were a part of the preparatory activities for the planned sampling and the assessment of the actual mechanical properties of primary components such as the main primary coolant piping, the steam generator shell and the reactor pressure vessel.