Application of the Seebeck effect for the monitoring of neutron embrittlementand low-cycle fatigue in nuclear reactor technology

摘要

The monitoring of neutron embrittlement and low-cycle fatigue in nuclear reactor steel is an important topic inlifetime extension of nuclear power plants. We therefore investigated the application of the Seebeck effect for determiningmaterial degradation of common reactor pressure vessel (RPV) steel. The Seebeck coefficients (SC) of several irradiatedCharpy specimens made from Japanese JRQ-steel were measured. The specimens suffered a fluence from 0 up to4.5 E19 neutrons per cm2 with energies higher than 1MeV.The measured changes of the SC within this range were about 500 nV, increasing continuously in the range underinvestigation. Some indications of saturation appeared at fluencies larger than 4.5 E19 neutrons per cm2. We obtaineda linear dependency between the SC and the temperature shift . T41 of the Charpy energy vs. Temperature curve which iswidely used to characterize material embrittlement. Similar measurements were performed on specimens made from theaustenitic stainless steel X6CrNiTi18-10 (according to DIN 1.4541) that were fatigued by applying a cyclic strain amplitudeof 0.28%.Further investigations were made to quantify the size of the gauge volume in which the termoelectric power isgenerated. It appeared that the information gathered from a (_T)hermo (_E)lectric (_P)ower (TEP) measurement is very local.To overcome this problem we propose a novel TEP-method using a (_T)hermoelectric (_S)canning (_M)icroscope (TSM).Icroscope We finally conclude that the change of the SC has a potential for monitoring of material degradation due to neutronirradiation and thermal fatigue, but it has to be taken into account that several influencing parameters could contributeto the TEP in either an additional or extinguishing manner. A disadvantage of the method is the requirement of aclean surface without any oxide layer. This disadvantage can partially be avoided by using the proposed new TSM.