A preliminary evaluation of irradiation damage in model alloys by electric properties based techniques

The most important effect of the degradation by neutron irradiation is a decrease in the ductility of reactor pressure vessel (RPV) ferritic steels. The main way to determine the mechanical behaviour of the RPV steels is tensile and impact tests, from which the ductile to brittle transition temperature and its increase due to neutron irradiation can be calculated. These tests are destructive and are regularly applied to surveillance specimens to assess the integrity of the RPV. The possibility of applying validated non-destructive aging monitoring techniques would however facilitate the surveillance of the materials that form the reactor vessel. The Institute for Energy of the Joint Research Centre has developed two devices, focussed on the measurement of the electrical properties which prove to give a good non-destructive assessment of the embrittlement state of ferritic steels. The first technique, called Seebeck and Thomson Effects on Aged Material (STEAM), is based on the measurement of the Seebeck coefficient, characteristic of the material and related to the microstructural changes induced by irradiation embrittlement. With the same aim, the second technique, named Resistivity Effects on Aged Material (REAM), measures instead the resistivity of the material. This paper explains (i) preliminary STEAM and REAM results and (ii) results compared with Charpy impact energy temperature shifts due to neutron irradiation. These results will make possible the improvement of such techniques based on the measurement of material electrical properties for their application to non-destructive irradiation embrittlement assessment. (C) 2004 Elsevier Ltd. All rights reserved.