Some recent research results and their implications for RPV irradiation surveillance under long term operation
During the last decade the irradiation behaviour of characteristic RPV steels used in Pressurized Water Reactors has been extensively investigated in the international research programs CARISMA, CARINA and LONGLIFE. Whereas the CARISMA and CARINA programs were mainly focused on material testing of German RPV steels and data base applications by the RTNDT and Master Curve concepts, the main emphasis of the LONGLIFE project was placed on microstructural examinations of a wide range of RPV steels used in European NPP. Atom Probe Tomography, Small Angle Neutron Scattering, Transmission Electron Microscopy and others belonged to the techniques applied. Four of those RPV steels which are particularly interesting under the point of view of long term irradiation behavior have been studied at different irradiation levels up to 8×10 n/cm (E > 1 MeV) in all three research programs. In this way it was possible to get a comprehensive understanding of the material behavior induced by neutron irradiation and the responsible mechanisms behind. By means of the material properties and microstructural data obtained, in particular the impact of chemical composition (copper and nickel), and neutron flux on the material’s fracture toughness was quantified. Moreover, the most important mechanisms such as formation of element specific precipitations, segregations, and matrix defects could be demonstrated in relation to the change of material properties. For one material the occurrence of late irradiation effects has been observed in both material properties and microstructural appearance. All the available data are discussed thoroughly by consulting the relevant literature in the light of the practical implications they have for RPV irradiation surveillance under long term operation of 60 years and beyond. Specific issues like material specific application of reference temperature concepts, data scattering, prediction of high fluence behavior and use of material test reactor data are addressed. Finally, based on the results obtained by the research programs concerned, best practices for RPV irradiation surveillance programs are suggested and exemplified by industrial experience and adopted measures already in use.
Final Results from the Crack Initiation and Arrest of Irradiated Steel Materials Project on Fracture Mechanical Assessments of Pre-Irradiated RPV Steels Used in German PWR
Pre-irradiated original reactor pressure vessel (RPV) materials covering all four German pressurized water reactors (PWR) construction lines were tested in the Crack Initiation and Arrest of Irradiated Steel Materials program to create a database of fracture toughness and arrest values for neutron fluences beyond the end of life range. The new database comprises data from both unirradiated and irradiated RPV base and weld materials generated by tensile, Charpy-V impact, fracture toughness KJc, and crack arrest KIa tests. The test matrix consists of materials with optimized chemical composition and with high Copper or high Nickel content, respectively. Based on the generated and already existing data the RTNDT and the RTT0 (Master Curve) concepts are applied with specific view on reference temperatures, transition temperature shifts, and on possible correlations between the criteria used in both concepts. In this context the consequences of some influencing factors like type and chemical composition of the RPV steel, its manufacturing conditions, and the specimen type and size on the reference temperatures are discussed. Moreover, the test results are assessed with respect to the American Society of Mechanical Engineers (ASME) code and German Nuclear Safety Standards Commission safety standards. The crack arrest characteristics for these typical RPV materials are also determined in a twofold way by testing Compact Crack Arrest specimens and by evaluation of instrumented Charpy-V impact test data. The available results made a good point that crack arrest is a reliable phenomenon that doubtless exists. It is also shown that the obtained KIa data can be enveloped by applying the ASME KIc lower bound curve indexed by different reference temperatures. Finally, the results show that the used RPV materials are well designed in terms of material behavior under irradiated conditions and that optimized manufacture specifications are of great benefit particularly after long operation times.
AN ANALYSIS OF POLYMERIC THICK-FILM RESISTORS AS PRESSURE SENSORS
Abstract The strain-sensing characteristics of thick-film polymer-based resistors printed and cured on 96% alumina are presented. Two layout configurations have been analysed: planar and sandwich. Various strain-gauge characteristics have been studied, including the mechanical and temperature-dependent properties of the polymeric films. It has been shown that the planar polymer resistors exhibit low sensitivity, comparable to that of metal-foil gauges, whereas the MRM (metal-resistor-metal) configurations exhibit similar characteristics to those of cermet thick-film MRM gauges. It has also been observed that the mechanical properties of the polymeric films are significantly poorer than those of cermet-based gauges. This degradation in performance is attributed to the epoxy/pseudo-plastic structure of the polymeric thick-film resistor layer.