Correlation between degradation and magnetic properties under neutron irradiation in nuclear reactor materials

用磁法评价核反应堆材料的降解程度进行了研究。本研究提出的无损评价（NDE）的概念不同于目前采用的方法，是一种预测裂纹出现前时间长度的方法。主要工作是中子辐射下核反应堆压力容器（RPV）材料的原位磁测量。由于环形岩心样品的辐照胶囊空间有限，最大应用范围限制为25 Oe。在铁金属和低碳钢中建立了小环的分析方法。由小环参数之间的简单关系推导出的小环系数与磁场幅值无关，对位错的影响比矫顽力的影响更敏感。我们已经成功地利用小回路法进行了现场测量。在铁金属中，小环系数随中子通量的增加而单调增加。位错环在中子辐射过程中成核长大，通过磁弹性耦合使小环系数增大。另一方面，在A533B钢中，小环系数首先增加，在中子通量为1 × 10^<19> cm^<-2>时达到最大值，然后随着中子通量的增加而缓慢下降。在位错附近聚集的铜沉淀和位错环会补偿位错的应力场，使小环系数减小，TEM观测证实了这一点。这些固定在位错周围的辐射缺陷强烈地提高了材料的力学性能。在奥氏体不锈钢和因科内尔600合金中成功地发现了新的磁性无损检测方法，并研制了一种用于评价RPV材料退化程度的磁性装置。

The study to evaluate the degree of material degradation by magnetic method has been carried out in nuclear reactor materials. The concept of nondestructive evaluation (NDE) in the present study is different from the currently employed methods and a way to predict the length of time before the appearance of cracks. The main work is in situ magnetic measurements under neutron radiation in the material of nuclear reactor pressure vessels (RPV). The maximum applied field is limited to 25 Oe owing to the limited space of an irradiation capsule for ring core samples. An analysis method of minor loops had been found in Fe metal and low carbon steel. Minor-loop coefficients deduced from simple relations between minor-loop parameters are independent of the magnetic field amplitude and much more sensitive to dislocations than coercive force. We have succeeded in the present in situ measurement by use of minor loop method. In Fe metal, minor-loop coefficients increase monotonically with the increase of neutron fluence. Dislocation loops which nucleate and grow during neutron radiation, make the minor-loop coefficients increase through magneto elastic coupling. On the other hand, in A533B steel, the minor-loop coefficients increase initially and show a maximum at the neutron fluence of 1 x 10^<19> cm^<-2> followed by a slow decrease with neutron fluence. The copper precipitates and dislocation loops gathering in the vicinity of dislocations would compensate the stress field of dislocations and make the minor-loop coefficients decrease that is confirmed by TEM observation. These radiation defects fixed around dislocation strongly make mechanical properties increase. The new magnetic NDE methods have been successfully discovered in the austenite stainless steel and Inconel 600 alloy..A magnetic device has been developed to evaluate the degree of material degradation of RPV for Charpy test pieces.