Evaluation of Irradiation Damage Effect by Applying Electric Properties BasedTechniques

摘要

The pressure vessel of the reactor (RPV) in light water reactors (LWR) is a key component for the safe operation ofa nuclear power plant, being it part of the containment of the plant and non replaceable. Its life therefore largely delimits thelife 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 theductile to brittle transition temperature (DBTT) and its increase due to neutron irradiation can be calculated. These tests aredestructive and regularly applied to surveillance specimens to assess the integrity of RPV. The possibility of applyingvalidated non-destructive aging monitoring techniques would however facilitate the surveillance of the materials that formthe reactor vessel. On the one hand it would indeed allow in-situ inspection and on the other it would allow saving preciousspecimens 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 nondestructivelythe embrittlement state of materials. The first technique, called STEAM (Seebeck and Thomson Effects onAged Material), is based on the measurement of the Seebeck coefficient, characteristic of the material and related to themicrostructural 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 REAMmeasurements with the change in the mechanical properties due to neutron irradiation. For this purpose different sets ofalloys coveting a large spectrum of steels have been used. The alloys are characterised with parametric variation of thecontent of impurities such Phosphorus, Copper, and Nickel, elements that are known to play a significant role in materialcharacteristic and degradation.The STEAM and REAM techniques have been successfully applied to the model alloys irradiated in the High FluxReactor of Petten (The Netherlands). The results of this study are shown in the paper and will enable a better understandingof the role and the influence of the above mentioned elements on the mechanical properties of steels. These results will makepossible the improvement of such techniques based on the measurement of material electrical properties for their applicationto the irradiation embrittlement assessment.