Evaluation of irradiation damage effect by applying electric properties based techniques

Abstract

The pressure vessel of the reactor (RPV) in light water reactors (LWR) is a key component for the safe operation of a nuclear power plant, being it part of the containment of the plant and non replaceable. Its life therefore largely delimits the life of the plant. The most important effect of the degradation by radiation is the decrease in the ductility of the RPV ferritic steels. The main way to determine the mechanical behaviour of the RPV steels are tensile and Charpy impact tests, from which the ductile to brittle transition temperature (DBTT) and its increase due to neutron irradiation can be calculated. These tests are destructive and regularly applied to surveillance specimens to assess the integrity of RPV. The possibility of applying validated non-destructive aging monitoring techniques would however facilitate the surveillance of the materials that form the reactor vessel. On the one hand it would indeed allow in-situ inspection and on the other it would allow saving precious specimens for those surveillance programmes which have an insufficient amount of surveillance material available. The JRC-IAM has developed two devices, focussed on the measurement of the electrical properties to assess nondestructively the embrittlement state of materials. The first technique, called STEAM (Seebeck and Thomson Effects on Aged Material), 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 REAM, measures instead the resistivity of the material. The purpose of these studies is to correlate the results of the Charpy tests, hardness, STEAM and REAM measurements with the change in the mechanical properties due to neutron irradiation. For this purpose different sets of alloys coveting a large spectrum of steels have been used. The alloys are characterised with parametric variation of the content of impurities such Phosphorus, Copper, and Nickel, elements that are known to play a significant role in material characteristic and degradation. The STEAM and REAM techniques have been successfully applied to the model alloys irradiated in the High Flux Reactor of Petten (The Netherlands). The results of this study are shown in the paper and will enable a better understanding of the role and the influence of the above mentioned elements on the mechanical properties of steels. These results will make possible the improvement of such techniques based on the measurement of material electrical properties for their application to the irradiation embrittlement assessment.

Cu effects on radiation embrittlement of Ni-containing complex model alloys and the related potentials of the thermoelectric method

“…The results, as already shown in several papers [4], are very promising for the scope of developing non-destructive radiation embrittlement monitoring methods but they are also very interesting from the point of view of mechanism understanding. In particular for the study of copper precipitation kinetics in nickel containing alloys.…”

Thermoelectric properties of carbonaceous solids

“…Investigations on the application of thermoelectric measurements for detecting modifications in microstructure of metal alloys were carried out by Acosta and Sevini [16]. They reported that structural changes of the material due to nuclear irradiation can be revealed by simple thermoelectric tests.…”