Microstructural aspects of neutron embrittlement of reactor pressure vessel steels - A view from positron annihilation spectroscopy

A comprehensive review of positron annihilation studies of Cr---Mo---V reactor pressure vessel (RPV) steels (Soviet type 15Kh2MFA) in unirradiated and neutron irradiated states is presented. The influences of lattice defects, impurity atom distribution, irradiation temperature, flux and fluence of fast neutrons on positron annihilation parameters, especially during isochronal annealing, are discussed in terms of the positron trapping model. In contrast to the literature, where irradiation-enhanced Cu precipitates and solute coated microvoids are thought to be major defect types responsible for strengthening and hence embrittling of RPV steels, we suggest irradiation-induced precipitates, i.e. probably carbides, to play this role. Possibilities to probe this model are suggested.     

TEM and PAS study of neutron irradiated VVER-type RPV steels

Conventional transmission electron microscopy and positron lifetime and Doppler broadening positron annihilation spectroscopy techniques have been used to investigate the radiation-induced microstructural changes in surveillance specimens of VVER-type reactor pressure vessel (RPV) steels, and RPV steels irradiated in the research reactor. Defects visible in transmission electron microscopy consist of black dots, dislocation loops and precipitates concentrated along the dislocation substructure. Their size and density depend on the neutron flux and fluence. The parallel set of thermally aged specimens, specimens recovery annealed after irradiation and specimens irradiated in a lower neutron flux was investigated too. No defects discernible in transmission electron microscopy were found after accelerated irradiation in the research reactor. In addition to visible defects, the small-volume vacancy clusters were identified by positron annihilation spectroscopy.     

Positron annihilation study of neutron irradiated model alloys and of a reactor pressure vessel steel

The hardening and embrittlement of reactor pressure vessel steels are of great concern in the actual nuclear power plant life assessment. This embrittlement is caused by irradiation-induced damage, and positron annihilation spectroscopy has been shown to be a suitable method for analysing most of these defects. In this paper, this technique (both positron annihilation lifetime spectroscopy and coincidence Doppler broadening) has been used to investigate neutron irradiated model alloys, with increasing chemical complexity and a reactor pressure vessel steel. It is found that the clustering of copper takes place at the very early stages of irradiation using coincidence Doppler broadening, when this element is present in the alloy. On the other hand, considerations based on positron annihilation spectroscopy analyses suggest that the main objects causing hardening are most probably self-interstitial clusters decorated with manganese in Cu-free alloys. In low-Cu reactor pressure vessel steels and in (Fe, Mn, Ni, Cu) alloys, the main effect is still due to Cu-rich precipitates at low doses, but the role of manganese-related features becomes pre-dominant at high doses.     

Doppler-broadening measurements of positron annihilation with high-momentum electrons in pure elements

Doppler-broadening measurements of the electron–positron annihilation line in twenty-seven single-element samples are presented. A coincidence technique has been used to suppress the background and to evidence the contribution of positron annihilation with core electrons. Systematic dependences on the atomic number of the target material are found in ratio curves obtained dividing the measured spectra by the spectrum of a reference material. The positron lifetime technique has been used to detect the presence of positron traps in all the samples. The change in the high-momentum part of the annihilation line due to positron trapping is illustrated. The measured data are in a good qualitative agreement with recent theoretical calculation and constitute the most complete measurement series, up to now, to establish a future data-base for positron annihilation spectroscopy.     

Study of PRIMAVERA steel samples by a positron annihilation spectroscopy technique

In the present article, a positron annihilation spectroscopy investigation of VVER-440/230 weld materials is discussed. Important characteristics of metals such as Fermi energy, concentration of electrons in the conduction band, size and concentration of defects were experimentally determined for three model materials with higher level of copper (0.16 wt.%) and phosphorus (0.027-0.038 wt.%). The impact of neutron irradiation and subsequent annealing on crystal lattice parameters was investigated. The experiments with the angular correlation of positron annihilation radiation (ACAR) complement the published positron annihilation spectroscopy (PAS) studies of the radiation treated VVER materials as well as previous experiments on PRIMAVERA materials. The availability of the experimental reactor to prepare strong ⁶⁴Cu positron sources provided for unique experimental conditions, such as good resolution of spectra (0.4 mrad) and reasonable short time of measurement (36 h). The present paper aims to contribute to further understanding of RPV (reactor pressure vessel) steels behaviour under irradiation conditions as well as annealing recovery procedures, which have already been applied at several VVER NPP units in Europe.     

用正电子湮没技术研究黄玉的辐照变色机理

通过对天然无色黄玉、快中子辐照变色黄玉、高能电子辐照变色黄玉以及辐照变色黄玉退火过程的正电子湮没寿命谱的对比分析研究,结果表明：中子、电子辐照均不同程度地在黄玉中产生了相当数量的缺陷。从而造成黄玉的变色,而辐照变色黄玉高温退火后．相当数量的缺陷消失．从而导致改色后黄玉的退色。在此基础度上对黄玉的呈色机理作了探讨．并对黄玉的改色工艺作了大胆的预测。     

Positorn annihilation study on point defects in lead tungstate

A study on point defects in leas tungstate(PbWO4) by using positron annihilation lifetime method is presented,The measurement was carried out for the cases of untreated,vacuum-annealed,oxygen-annealed and La-doped PbWO4 crystals,It was found that the components T2,which reflect the positron annihilation in point defects ,are different from each other for each case,Some tentative models for the defects are dicussed.     

Photoneutron Cross Sections for Au Revisited: Measurements with Laser Compton Scattering γ-Rays and Data Reduction by a Least-Squares Method

Photoneutron cross section measurements were made for Au in the entire energy range of the (γ,n) channel based on a direct neutron counting with quasi-monochromatic γ-rays produced in inverse Compton scattering of laser photons with relativistic electrons. The data were analyzed by a least-squares method to deduce photoneutron cross sections. The analysis significantly reduced experimental uncertainties compared with those resulting from the photon difference method. The result is compared with the previous data by direct neutron counting with γ-rays produced in positron annihilation in flight and by photoactivation with bremsstrahlung. The present data are in good agreement with the previous data near the neutron threshold, while there remain some discrepancies between the present and the previous data above 10 MeV.     

High-dose neutron induced radiation swelling simulated by heavy ion irradiation and its microscopic study with positron annihilation technique

1IntroductionStainlesssteel(SS)isanimportantreactorstructuralmaterial.SSusedinreactorsexperiencesneutronirradiationandtheaccumulateddosemayreach1022-23n'cm--2alleryearsofreactoroperation.Consequently,severeradiationeffectsoccurinSSandwouldleadtoareactorbreakdownorevenaccident.RadiationsWellingisamajorradiationeffectinSSwhichshouldbetakenintoaccountinreactordesignandoperation.Severeswellinggenerallyoccursatneutrondosesof2102on'cm--2.Thelackofneutronproducingson-rsesofsuchhighdoseshampersits…     

金属氢化物的正电子湮没研究

采用正电子湮没方法在７７－３００Ｋ温区和ｘ为０－０．８６氢浓度范围研究了Ｐｄ０．７５Ａｇ０．２５Ｈｘ和ＮｂＨｘ两种金属氢化物，叙述了获得的实验结果。     

辐射损伤的正电子湮没和扰动角关联研究(英文)

用正电子湮没和扰动角关联二种方法研究了Si和Nb的辐射损伤。采用正电子湮没方法得到的结果与扰动角关联的完全一致。     

Application of Electron–Positron Annihilation for Determining the Thickness of the Barrier Layer on VVÉR Fuel-Element Cladding

The possibility of using the nuclear-physical method of positron annihilation to determine the thickness of a barrier layer consisting of zirconium on the inner surface of VVÉR fuel-element claddings is examined. The basic principles and possibilities of the method and the results of investigations are presented.     

含卤素高聚物的正电子湮没特性

用正电子湮没辐射一维角关联实验装置和正电子湮没寿命谱仪观察了全氟乙烯丙烯共聚物(FEP)系列试样和不同含氯量的聚乙烯系列试样的正电子湮没特性,并分别与聚四氟乙烯均聚物(PTFE)和聚乙烯(PE)进行了对照。结果表明:分子材料的介电性质对正电子湮没特性有明显的影响。极性基团的加入改变了分子链上的电荷密度分布,导致微观偶极电场的产生,使在自由体积内部或陷落在缺陷巾的0-Ps正电子波函数与分子链上轨道电子波函数的重迭几率增加,长寿命τ_3减小;同时,由于卤素原子的电负性较强,抑制了Ps的形成,增加了自由正电子的数目,使角关联曲线低动量成分减小。     

Positron annihilation study of effect of aluminum on iron－based amorphous alloys

Seven Fe-based amorphous alloys have been studied by Doppler broadening and lifetime techniques of the positron annihilation.It is shown that the parameters of positron annihilation in the Fe-based amorphous alloys containing more aluminum are larger than those in the alloys with less aluminum,which means that the existence of element Al in Fe-based amorphous alloys results in more vacancy-like defects.     

辐照接枝氟塑料的正电子寿命谱研究

用正电子湮没寿命谱研究了对聚四氟乙烯和聚合氟乙丙烯进入γ辐照接枝的反应机理。结果表明：γ辐照和辐照接枝使聚合物的凝聚态结构发生了变化。随着辐剂量的增加，接枝率不断提高，而正电子湮没长寿命产生明显改变。说明了辐照接枝主要发生在非晶区以及非晶区和晶区的交界处，将实验结果与红外光谱进行了比较。     

正电子湮没多普勒展宽数据的稳定和修正

本文介绍了在正电子湮没多普勒展宽测量中如何利用参考谱线去稳定和修正正电子湮没谱线的线型参数。     

APPLICATION OF THE POSITRON ANNIHILATION TECHNIQUE

The principles of positron annihilation and four positron experimental techniques are described. The application of positron annihilation technique in material science. atomic physics and other related fields are discussed.     

Recent applications of small-angle neutron scattering in the characterization of irradiated steels for nuclear technologies

Small-angle neutron scattering (SANS) is a powerful experimental tool to investigate the microstructural evolution under irradiation in steels for fission and future fusion reactor systems. We present recent SANS results concerning the modelling of helium bubble growth in F82H-mod. steel implanted with α-particles and the dose dependence of microstructural radiation damage in Eurofer-97 steel for fusion reactors irradiated at 250 °C. The discussion of these results is focussed on the quality of the metallurgical information obtained by such SANS measurements and consequently on their usefulness also for engineering and design purposes.     

液态轧制Fe-3%Si中的正电子湮没参数

用正电子湮没方法研究非晶态合金对认识非晶态的结构模型、电子结构、缺陷分布、结构弛豫、晶化过程起了不可忽视的作用。近年来,在急冷淬火制备非晶态合金带材的基础上又发展了一种崭新的工艺,即液态急冷轧制。因为它降温速率比急冷淬火的慢,且轧制出的带材有较大的厚度,制备的带材呈晶态结构,换句话说,它克服了急冷淬火制备非晶态带材中所存在的热稳定性问题,从而可望短期内在工业生产中得到实际广泛应用,并大大减少生产工序,节约能源和成本。本文报道了用正电子湮没多普勒展宽能谱对液态急冷轧制的Fe-3％Si(工业中所用的一种矽钢的成分)的测量结果,以探索正电子湮没方法在该类合金中的适用性。