###### Abstract  
The influence of neutron irradiation degradation on reactor pressure vessel steel was investigated. Large blocks were irradiated by neutrons in the BR2 reactor at a low irradiation temperature. They were measured by a nondestructive magnetic method, magnetic adaptive testing, before and after the neutron irradiation. It was shown that the modification of the magnetic parameters due to the neutron irradiation was well detectable by this nondestructive method. It was also shown that the influence of neutron irradiation could be detected with a reasonable signal-to-noise ratio through the cladding. The present results are considered as a first step towards the application of magnetic adaptive testing in the nuclear industry.  
neutron irradiation; reactor pressure vessel steel; magnetic nondestructive evaluation; magnetic adaptive testing +
Footnote †: journal: Applied  
0000-0001-8882-2233]C. C.  
One of the non-destructive techniques is the magnetic adaptive testing (MAT) [5, 6]. This is a special type of measurement of magnetic hysteresis loops. The main advantages of this method are the following: In contrast to the traditional hysteresis measurement, it is not the major loop and its few key parameters that are measured, but a series of minor ones. This way, a big data pool is generated and those descriptors are chosen from this data pool, which characterize the best degradation of the investigated material. As is shown in [6], this method offers parameters that characterize the correlation between magnetic descriptors and independent variables (embrittlement, ageing, fatigue, the degree of thermal treatment, plastic and elastic deformation, neutron irradiation, etc.) more sensitively and more reliably than traditional magnetic parameters. In addition, there is no need for magnetic saturation of the investigated samples, which can be hardly carried out in practical applications. Evidently, this method also has some drawbacks, which are as follows: The method does not provide absolute magnetic quantities, as it is suitable only for comparative measurement. However, if the method is \"taught\" on a series of reference samples, a calibration curve can be generated. Thus, parameters of any unknown sample from a similar series of samples can be characterized by one single measurement, if the parameters of the measurement is kept fixed. Another drawback of the method is (similarly to any other magnetic measurement, where a magnetizing yoke is placed on the samples' surface) that the surface condition has a great influence on the detected magnetic signal. This problem can also be handled somehow by using a non-magnetic spacer between the sample and the yoke, as described in detail in [6].  
Recently, several papers were published, where neutron embrittlement of RPV steels was investigated by MAT [7, 8, 9] on Charpy specimens. DBTT values were compared with MAT parameters on RPV steels, which were irradiated by neutrons.  
In this work, instead of measurement of Charpy specimens, the MAT is applied on neutron irradiated RPV steel blocks in order to simulate the direct measurement on the reactor vessel. Measurements were performed on two sides of the blocks--one from the base material side and one on the cladded sides of the blocks.