Radiation Embrittlement Understanding for PLIM Activities at EC-JRC-IE

Radiation embrittlement and aging mechanisms for NPP reactor pressure vessels and vessel internals have been studied within NPP Plant Life Management (PLIM) for evaluation, prediction, and monitoring of the critical components’ service life. The main achievements of the SAFELIFE project, integrating various networks on PLIM issues, are given. Results of neutron embrittlement of model alloys are presented, and surveillance and research data on WWER reactor pressure vessel and other steels have been analyzed. Projects for the development of destructive and non-destructive testing of irradiated materials have been outlined.В рамках программы PLIM исследовано радиационное охрупчивание и механизмы старения конструкционных сталей внутрикорпусных устройств реакторов с целью оценки, прогнозирования и мониторинга ресурса ответственных узлов АЭС. Изложены результаты проекта SAFELIFE, объединяющего различные подходы к контролю ресурсом АЭС. Представлены результаты радиационного охрупчивания модельных сплавов, проанализированы данные испытаний с использованием образцов-свидетелей, а также исследована надежность корпусных и других типов сталей. Предложены перспективы развития разрушающих и неразрушающих методов радиационного охрупчивания материалов.У рамках програми PLIM досліджено радіаційне окрнхчування і механізми старіння конструкційних сталей та реакторів із метою оцінки, прогнозування і моніторинга ресурсу відповідальних вузлів АЕС. Підсумовуються результати проекту SAFELIFE, що об’єднує різні підходи щодо контролю ресурсом АЕС. Представлено результати радіаційного окрихчування модельних сплавів, проаналізовано дані випробувань із використанням зразків- свідків, а також досліджується надійність корпусних та інших типів сталей. Запропоновано перспективи розвитку руйнівних і неруйнівних методів радіаційного окрихчення матеріалів

Incorporation of Y2O3 Particles into 410L Stainless Steel by a Powder Metallurgy Route

Addition of yttria to steels has been proposed for the fabrication of oxide-dispersion-strengthened materials for nuclear power applications. We have investigated materials prepared from 12 Cr martensitic stainless steel, AISI 410L, produced by powder metallurgy. Materials were produced with and without yttria addition, and two different sizes of yttria were used, 0.9 µm and 50 nm. Tensile and mini-creep tests were performed to determine mechanical properties. Optical microscopy, SEM, TEM, and EDX analysis were used to investigate the microstructures and deformation mechanisms and to obtain information about non-metallic inclusion particles. SiO2, MnS, and Y2Si2O7 inclusion particles were observed. An SiO2 and Y2O3 interaction was seen to have occurred during the ball milling, which impaired the final mechanical properties. Small-angle neutron scattering experiments showed that the matrix chemistry prevented effective dissolution of the yttria. © The Author(s) 201

Investigation of shot-peened austenitic stainless steel 304L by means of magnetic Barkhausen noise

Different shot peening conditions were applied to an austenitic stainless steel AISI 304L in order to transform austenite to martensite α′ at different depths. Magnetic Barkhausen noise measurements performed on this steel reveal a correlation between the strength of the signal and the depth of the treatment. The combined effect of the volume fraction of martensite and the residual stress in martensite determined using X-ray diffraction analysis were found to be responsible for the evolution of the Barkhausen noise response. Using tensile plastic deformation, the residual stress in martensite was changed, giving rise to a strong increase of the Barkhausen noise activity. This variation was correlated to a modification of the sign and amplitude of the residual stress in the martensite phase. Directional measurements of the Barkhausen noise revealed the anisotropy of the residual stresses induced by the tensile plastic deformation. It is concluded that the Barkhausen noise activity recording could lead to the determination of the residual stresses in martensite induced by shot peening processes

Magnetic measurements for evaluation of radiation damage on nuclear reactor materials

It is important for the plant lifetime management to estimate the loss of toughness and other effects, e.g. increase of yield strength and hardness, caused by irradiation. This paper deals with the use of magnetic measurements to determine the irradiation effects on nuclear reactor structural materials. Three types of nuclear reactor materials were studied. Samples of the materials were irradiated with different neutron fluences. The Magnetic Barkhausen Emission was measured using stabilised flux mode, i.e., control of the magnetic flux within the sample to compensate for leakage and variations on the flux. The samples were carefully identified according to position and the cutting direction within the steel forging block. Anisotropy effect due to sample cutting direction was observed and it masks the magnetic signal results induced by the irradiation effects. The results on the specimens cut in the same direction shows correlation with irradiation induced material hardening and its dependence on fluence. Different materials show different hardening levels. Barkhausen emission results were correlated to neutron fluence taking into account the cutting direction

Dynamic magnetostriction for material characterisation of micro structure states of degraded structural steel

The magnetostriction effect has been known for over 100 years. The first observation was made by Joule in 1842; while applying a magnetic field to a nickel rod specimen the length changed. Magnetostriction is the change of the dimensions and the Young modulus of a magnetic material caused by a change in its magnetic state. Magnetostriction is classified as linear or longitudinal; transverse and volume magnetostriction. Linear magnetostriction is also referred to as Joule magnetostriction, where deformation occurs in the direction of the applied field while the volume of the distorted magnetic domains remain constant. During transverse magnetostriction the dimension change is perpendicular to the applied field. Volume magnetostriction is mainly caused by the increase of distance between the atoms by the applied magnetic field. If the volume of an iron-based material expands with an increase in magnetisation the volume magnetostriction is defined as positive. The magnetisation state of a material can also be changed by temperature variations or by applied mechanical stress. Spins in excited state can transfer their excess energy to the lattice so a disturbance of the coupled magnetic and crystal lattice affects the magnetostriction. Moreover, in Joule magnetostriction the dimensional change is associated with the distribution of distorted magnetic domains so it could be expected that domain movement hindrance would affect magnetostriction. Magnetisation state changes can cause a strain just as strain can cause a change in the magnetisation state. Thus magnetostriction effects are reciprocal causing a magnetostrictive material to behave as piezoelectric materials due to magneto elastic interaction. A sound wave is generated by the change in the magnetic state while the sound wave strains change the magnetisation state of the material. This principle of the reciprocity of magnetic state - strain was used as the theoretical background of the dynamic magnetostriction test. By applying the dynamic magnetostriction test the effect of the precipitates on the crystalline of a ferromagnetic polycrystalline can be recognised by its interaction on the magnetisation state. Dynamic magnetostriction tests have been further developed at the Fraunhofer Institute for NDT, Saarbrücken, in order to define material properties. A 15NiCuMoNb5 copper content ferritic steel material was submitted to isothermal thermal ageing and the material properties changing because of copper precipitation were studied. Mechanical and physical properties, e.g. hardness, electrical conductivity were tested. The objective was to provide a basis for developing a non-destructive testing technique for this type of steel, which is widely used in the energy industry as pipeline and vessel material. This contribution discusses the physical background, the NDE-approach and the results

Micromagnetic testing of model alloys specimens evaluating irradiation effects

The Model Alloy project, carried out by the JRC (Joint Research Centre) within the frame of the European Network AMES (Ageing Material Evaluation System), has the objective to study the influence of elements, i.e. Phosphorus, Cooper and Nickel on the mechanical properties of steels by different content alloys. As these model alloys are a representative of a large spectrum of ferritic steels with parametric variation of elements known to play a significant role in material characteristic and degradation, they provide an opportunity also to study the elements influence on the steels when exposed to degradation by irradiation

Investigation of nuclear reactor steel by magneto-acoustic emission method

At KFKI Atomic Energy Research Institute, Budapest, investigations have been done since many years for studying how steel material of nuclear reactors degrade during operation. Part of these studies is to investigate the applicability of novel destructive and non-destructive testing methods as well as to introduce them in the measurement of reactor steel properties such as neutron-induced embrittlement, fatigue and ageing. In addition to acoustic emission and magnetic Barkhausen noise testing, experimental investigations have been commenced to apply magneto-acoustic (acoustic Barkhausen) noise testing technology in the research project. At this method high-frequency mechanical stress waves are detected and analysed which erase in the material specimen being exposed to alternating magnetic excitation. For these experiments a novel, multi-purpose micromagnetic analyser has been designed, built and put into production permitting to compare different magnetic parameters and response functions to magnetic excitation. The paper gives a short overview on the magneto-acoustic emission effect and its potential to assess steel properties by presenting some results of calibration experiments executed by the authors. Several measurements have been performed on two large-size specimens cut from nuclear pressure vessel material blocks (Soviet type 15CH2MFA and IAEA reference steel JRQ). The profiles of the transition temperature along the wall thickness are known from previous measurements: these profiles are compared to that of the measured magnetoacoustic emission curve. BY comparison correspondence has been found between these and other magnetic parameters, which may lead to promising non-invasive methods for assessing the grade of embrittlement caused by neutron irradiation. A generally employed testing method of reactor steel materials is the Charpy test. The paper presents magneto-acoustic experiment results both on broken and unbroken Charpy specimens as well as compares the micromagnetic response and other magnetic parameters with the measured mechanical properties