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Atom Probe Tomography has been performed on as-irradiated and post-irradiation annealed surveillance weld samples from Ringhals Unit 3. The weld contains low Cu (0.07at.%) and high Ni (1.5at.%). A ...

We have undertaken a combined experimental and modelling study of plasticity development in samples containing notches and cracks in a reactor pressure vessel steel that exhibits the Luders phenomenon in uniaxial testing. We have used digital image correlation to study the development of plasticity in plane sided, waisted and notched samples of a mild steel that exhibits Luders behaviour. We have developed a constitutive model for use within elastic–plastic finite element analyses of structural geometries made from materials which exhibit Luders strain behaviour, and validated it against experimental data. The model is capable of describing plasticity development in smooth sided, waisted and notched specimens. With the assistance of the model we have determined that Luders behaviour affects the detailed development of plasticity not only in smooth sided and waisted specimens, which is readily observed experimentally, but also in sharp notched specimens. In sharp notched specimens the plastic zone is more constrained and stress intensification higher in the presence of Luders behaviour.

Zones of reduced long-range order created at desplacement cascade sites in well-ordered Cu 3 Au may be directly imaged in the transmission electron microscope so that quantitative information can be obtained on individual cascade events. In previous work the technique was used to characterise displacement cascade produced by fusion-neutron irradiation. More and larger zones were found than expected from the calculated recoil spectrum. In this paper we re-examined critically these results, taking into account additional heavy-ion calibration data and improvement in the analysis technique. Preliminary results for cascade created in the Argonne CP5 fission reactor are presented.

This paper describes a novel multi-scale study of stress corrosion cracking in cold-worked 304 type stainless steels, which are widely used in pressurized water reactors and boiling water reactors. The influence of cold work and Cr concentration on the stress corrosion cracking behaviour of the steel has been examined. A methodology has been developed in order to characterize the same crack tip region with nanoscale secondary ion mass spectroscopy, electron back-scattering diffraction and transmission electron microscopy. This has offered a unique insight into the chemistry and microstructure, showing that the right combination of techniques can provide much of the information needed to understand the processes involved in crack propagation. A model for crack propagation based on brittle fracture and localized oxidation and shearing near the crack tip has been proposed. © 2009 Acta Materialia Inc.

A series of TEM experiments was carried out to systematically investigate the formation of vacancy dislocation loops in displacement cascades in molybdenum. Single-crystal foils of high-purity molybdenum were irradiated with Sb+ single ions and and molecular ions to low doses (≤1016 ions m−2). Three different ion energies were employed (60, l20 and 180 keV) in order to systematically vary the total cascade energy and the energy per atom in the molecular ion. Dislocation loop sizes and defect yields were found to be larger for molecular ions than for single ions of the same energy. In (011) foils, most loops had Burgers vectors b = a/2⟨111⟩ lying in the plane of the foil. However, in molecular ion irradiations, a small fraction of loops with b = a⟨100⟩ was also found. This fraction was higher for than for ions and also increased with ion energy. In (001) foils, defect yields were much smaller because of the loss of glissile a/2⟨111⟩ loops to the surface, but a⟨100⟩ loops were still present in molecular ion...

In this chapter, the development of an understanding of the mechanisms that control reactor pressure vessel (RPV) embrittlement is explored. It is shown how these insights were strongly coupled with developments in microstructural techniques and how research in this field has underpinned the development of dose–damage correlations.

A model has been produced to describe irradiation damage in high nickel submerged arc welds (1.6% Ni, 1.5% Mn, 0.5% Mo). It is fitted to a database of hardness change results obtained for 12 such welds with copper contents from about 0.02 to about 0.6% irradiated in materials test reactors. Irradiation dose rates ranged from about 6×10−9 dpa/s down to about 1×10−10 dpa/s. In addition to the hardness change data, Charpy shift data were also available. For some specimens irradiation induced changes in microstructure have been characterised using small angle neutron scattering (SANS) and energy compensated position sensitive atom probe (ECoPoSAP) techniques. The model was empirically fitted to the data, but available physical understanding and the evidence from the microstructural studies were used to guide selection of the equations fitted. Physical understanding and microstructural evidence were also used to help choose between alternative models with similar statistical goodness of fit. The model has two components. First, ‘matrix’ damage, which is insensitive to copper content and irradiation dose rate, and which appears to increase with phosphorus and sulphur. Second, ‘precipitation damage’, which increases with copper and manganese content, and reduces with increasing silicon. Precipitation damage also increases with reducing irradiation dose. The ECoPoSAP data show that the precipitates are composed of primarily of Ni, Mn, Cu and Si, with a substantial amount of iron entrained within them. In the low copper welds the same instrument shows significant compositional fluctuations in these elements, but no visible clusters. The Charpy data have been used to develop an empirical correlation between transition shift and hardness change. This is linear up to about 250 °C shift.

The effect of irradiation on microstructure of four irradiated reactor pressure vessel steels (a low copper A533B-1 plate, a low copper A508-3 forging, a high copper Linde 80 flux weld and a high copper Linde 1092 flux weld) was determined by using complementary microstructural techniques such as optical position-sensitive atom probe (OPoSAP), field emission gun scanning transmission electron microscopy (FEGSTEM) and small angle neutron scattering (SANS). In the low copper steels, irradiation resulted in small shifts in transition temperature and small changes in hardness increments. The microstructural analyzes showed that this response was dominated by matrix damage. In contrast, both copper-enriched clusters and matrix damage formed in the high copper welds. This information was then used as input to the Russell–Brown model to predict the change in hardness resulting from copper-enriched clusters. The calculated hardness increments were found to be consistent with the experimental data.

Grain size measurement is directly dependent on the ability of the microstructure to be revealed in a form that is representative of the material. A single phase, equiaxed ferritic steel was used throughout the present investigative work, this material being chosen because of the apparent simplicity of the microstructure. The lineal intercept, circular intercept, and planimetric measurement techniques were used. All the results are reported using the ASTM grain size number, G. Two aspects of grain size measurement are reported in the present paper. The first is the impact of missing boundaries on grain size measurements. The etching techniques established within industry to reveal microstructures often only partially reveal grain boundaries. An experiment is reported where the impact of missing grain boundaries on grain size measurements is assessed and hence the importance of revealing all grain boundaries is determined. An image analysis system was used to completely reconstruct the microstructu...

The principles are reviewed which underlie trend curve development for irradiated ferritic Reactor Pressure Vessel steels where the dominant embrittlement mechanism is cluster hardening. The extent to which the form of the equations employed reflect the underlying physical mechanism is assessed.

The major challenges in nuclear technology relate to the safe, efficient and economical operation over period of the order of 109 seconds (30 years). Associated with these aims are a need for minimal interruptions for maintenance and, if possible, a sound scientific basis for extending the plant life. The scientific basis requires understanding on very different timescales: certain aspects of the collision cascades (10−15 seconds) and, between these limits of atomic dynamics and of engineering, the diffusion-controlled processes which determine microstructure. We show how studies over a wide range of length and timescales can be linked to provide a basis for successful technology. In particular, we discuss the mechanisms underlying radiation induced embrittlement in reactor pressure vessels. We discuss the characteristic times of the various processes (from femtoseconds to years) and the theoretical and experimental tools available for their study. We show how the scientist can reach out to the e...

The evolution of irradiation damage cascades in copper has been simulated by molecular dynamics, using a many-body potential. Nearly 200 cascades have been produced with random knock-on directions and primary knock-on atom (PKA) energies in the range from 60 eV to 10 keV. The starting temperature for these simulations was 100 K and 600 K, this report will confine itself to the data obtained at 100 K. The cascade evolution has been followed for times typically up to ∼10 psec and in some cases up to ∼30 psec. The cascades are characterised by the sudden emission of replacement collision sequences and with shape variations due to local channelling events. At the higher energies the core has been shown to be liquid-like structure with cavitation. The annealing phase leaves loosely clustered vacancies at the cascade centre but collapse to a vacancy loop is not generally observed. A feature of the more energetic cascades is the production by a ballistic mechanism of interstitial atom clusters at the pe...

Understanding the key corrosion mechanisms in a light water reactor primary water environment is critical to developing and exploiting improved zirconium alloy fuel cladding. In this paper, we report recent research highlights from a new collaborative research programme involving 3 U.K. universities and 5 partners from the nuclear industry. A major part of our strategy is to use the most advanced analytical tools to characterise the oxide and metal/oxide interface microstructure, residual stresses, as well as the transport properties of the oxide. These techniques include three-dimensional atom probe (3DAP), advanced transmission electron microscopy (TEM), synchrotron X-ray diffraction, Raman spectroscopy, and in situ electro-impedance spectroscopy. Synchrotron X-ray studies have enabled the characterisation of stresses, tetragonal phase fraction, and texture in the oxide as well as the stresses in the metal substrate. It was found that in the thick oxide (here, Optimized-ZIRLO, a trademark of the Westinghouse Electric Company, tested at 415C in steam) a significant stress profile can be observed, which cannot be explained by metal substrate creep alone but that local delamination of the oxide layers due to crack formation must also play an important role. It was also found that the oxide stresses in the monoclinic and tetragonal phases grown on Zircaloy-4 (autoclave testing at 36°C) first relax during the pre-transition stage. Just before transition, the compressive stress in the monoclinic phase suddenly rises, which is interpreted as indirect evidence of significant tetragonal to monoclinic phase transformation taking place at this stage. TEM studies of pre- and post-transition oxides grown on ZIRLO, a trademark of the Westinghouse Electric Company, have used Fresnel contrast imaging to identify nano-sized pores along the columnar grain boundaries that form a network interconnected once the material goes through transition. The development of porosity during transition was further confirmed by in situ electrochemical impedance spectroscopy (EIS) studies. 3DAP analysis was used to identify a ZrO sub-oxide layer at the metal/oxide interface and to establish its three-dimensional morphology. It was possible to demonstrate that this sub-oxide structure develops with time and changes dramatically around transition. This observation was further confirmed by in situ EIS studies, which also suggest thinning of the sub-oxide/barrier layer around transition. Finally, 3DAP analysis was used to characterise segregation of alloying elements near the metal/oxide interface and to establish that the corroding metal near the interface (in this case ZIRLO) after 100 days at 360C displays a substantially different chemistry and microstructure compared to the base alloy with Fe segregating to the Zr/ZrO interface. Copyright © 2011 by ASTM International.

Displacement cascades produced by energetic lattice recoils are the primary damage state in neutron-irradiated metals, among which austenitic stainless steels are an important class of technological alloys. The vacancy constituent of this damage that survives in the form of collapsed vacancy loops is a major component of this damage state, and has been investigated in the present work as a function of alloy composition and the temperature. This has been done by irradiating single crystal foils of a range of high-purity model ternary Fe - xNi -15% Cr alloys ( x = 15–70%) with heavy ions, and then analysing the resulting damage by transmission electron microscopy. A full analysis has been achieved by measuring the areal density of loops and their size distribution for each irradiation condition, and hence obtaining the important parameters defect yield and collapse efficiency. By appropriate choice of ion energy, ion mass, ion dose and specimen temperature, we have been able to vary the factors such as cascade size, cascade energy density, cascade defect density and cascade overlap, and thus study their influence on cascade collapse. The results have been assessed in terms of current models of cascade processes in pure metals and alloys.

The irradiation-induced changes occurring at the nanometer level in the microstructure of the reactor pressure vessel have been shown to be responsible for a degradation in mechanical properties that occur in large structures with dimensions in the tens of metres. These changes can place severe restrictions on the reactor both at the startup and under continual operation; and in the long term could compromise the safe operation of the plant. The large financial and safety related matters have given the necessary driving force to study the factors controlling the microstructural evolution, resulting in a multi disciplinary approach to the problem. This paper aims to review the current understanding of the subject, giving were possible examples of the approach and techniques used to obtain this. We also highlight areas of current research activity and indicate the type of work still required to provide information on aspects that currently lack a full understanding.

In this paper we review the approach employed in the UK to characterise the embrittlement of thermal reactor pressure vessels (RPVs). The experimental techniques developed to characterise the neutron energy spectrum and fluence are described; these include the use of multifoil activation packs and a direct damage monitor. The techniques for the retrospective assessment of the exposure of service irradiated components and the methods for the prediction of end-of-life doses in RPVs are discussed. Displacements per atom (dpa) is the main exposure and correlation parameter employed and the success of using it to measure damage dose is evaluated. A variety of techniques is used to characterise the changes in mechanical properties in both materials test reactors and power reactors. These include fracture toughness, Charpy impact and tensile testing. Mechanical properties inter-relationships are particularly helpful when evaluating the condition of irradiated materials; the Charpy-tensile, Charpy-hardness and Charpy-fracture toughness correlations are reviewed. An important aspect of research into materials behaviour in the UK has been the development of mechanistic models of the embrittlement phenomena. These models have been reasonably successful in the interpretation of embrittlement in copper-containing materials, particularly in rationalising data obtained at different dose rates. The approaches are summarised. Microstructural techniques based on transmission electron microscopy, small angle neutron scattering and atom probe/field ion microscopy have been developed to characterise the microstructure and microchemistry of unirradiated and irradiated copper-containing materials. The contributions these techniques have made to the understanding and prediction of embrittlement processes are described.

The many-body potential of Ackland et al. is currently being used to investigate the production of displacement damage cascades in irradiated copper, using the molecular dynamics computer program MOLDY. The effect of adopting this potential on both the static and the dynamic properties of irradiation-induced defects is evaluated here. It is shown that this potential provides a good representation of the well known properties of point defects. However, for dynamic events involving the close approach of atoms, a short-range ion core repulsive term needs to be incorporated. The modified core term has been optimized to give an excellent fit to the measured threshold displacement energies without significantly affecting the fit to other physical properties.

The evolution of irradiation damage cascades in a metal has been simulated by molecular dynamics, using a many-body potential. Over 100 cascades have been produced with random knock-on directions and primary knock-on atom (PKA) energies ranging from 60 to 2 keV. The cascade evolution has been followed for times typically up to about 10ps and in some cases up to about 30 ps. The cascades are characterized by the sudden emission of replacement collision sequences and with shape variations due to local channelling events. At the higher energies the core has been shown to be a liquid-like structure with cavitation. The annealing phase leaves loosely clustered vacancies at the cascade centre but collapse to a vacancy loop is not observed. The onset of this thermal spike occurs for cascades with energy of 100 eV or higher; below this the cascade is made up of a series of closely coupled short replacement collision sequences. A feature of the more energetic cascades is the production by a ballistic mech...

Recent results on neutron-irradiated RPV submerged-arc welds have revealed grain boundary segregation of phosphorus during irradiation, which may lead to intergranular fracture. However, the experimental database is insufficient to define the dependence of the process on variables such ad dose, dose-rate and temperature. This paper describes work in which two existing models of phosphorus segregation, under thermal or irradiation conditions, have been developed to obtain predictions of these dependencies. The critical parameters in the models have been adjusted to give consistency with the available reference data, and predictions have been made of the dependence of segregation on a number of variables.

A specially designed and characterized oil-free cryogenic UHV experimental system has been used to irradiate pre-thinned orientated copper and molybdenum single crystals at 4.2 and 78 K with very high doses (5 x 1012to 5 x 1015ions cm-2) of low-energy (0.2-20 keV) self-ions and xenon ions. Populations of dislocation loops were produced, after subsequent warm-up to room temperature, within a few hundred ångströms of the irradiated surface. The loop depth distributions were measured using stereo transmission electron microscope (TEM) techniques and correlated with possible displacement damage production and retention mechanisms, including replacement collision sequences (RCSS), incident ion channelling and near-surface loop losses. In copper, both near-surface vacancy-loop populations at depths up to about 100Å and deeper interstitial loops up to about 400Å in depth could be produced. In molybdenum only interstitial loops were visible, at depths up to about 250Å. The depth distributions depended critically on the incident ion mass, ion energy and the specimen surface orientation used. In all the copper and molybdenum irradiations at doses greater than 1013ions cm-2only a very small fraction (not more than 2%) of the point defects theoretically created during the irradiations at 4.2 K were retained in visible loops after warm-up to room temperature. The results are consistent with displacement cascades, initiated by incident ions, injecting some interstitials along RCSS directed away from the irradiated surface, which may subsequently aggregate into interstitial loops. It is concluded that the loop depth distributions are determined more by the fraction of incident ions channelled at the irradiated surface than on RCS orientation effects relative to the surface. The low point defect retention efficiency in the present study is consistent with RCS ranges of only a few tens of ångströms at most. However, the lattice is highly damaged during the irradiation, possibly leading to enhanced RCS defocusing. Irradiation at 78K provides results consistent with interstitial mobility at this temperature.

The production of vacancy loops by the collapse of displacement cascades is of particular importance in radiation damage, for these loops are known to play a major role in subsequent microstructural development, and yet little is known of the cascade processes in them. In this study, attention has been focused on cascade collapse to form vacancy loops in five of the h.c.p. metals, namely Ti, Co, Re, Ru and Mg, chosen for their wide-ranging material properties. Sb+ ions of either 100 of 150 keV have been used to produce cascades, which may collapse to form vacancy dislocation loops. These loops have been studied using transmission electron microscopy, and this has enabled detailed analysis to be undertaken of loop geometry, size and number density. For the foil orientation used, all the loops observed lay on the prism planes, and from the size distributions of faulted and perfect loops we have estimated values for the prism plane stacking-fault energy. The efficiency of collapse varies dramaticall...

A Cameca NanoSIMS 50 has been used to map trace elements in stainless steels from nuclear reactors. The results prove that it is an ideal technique to map elements in small concentrations such as boron, sulphur or phosphorous which remain inaccessible to conventional microanalysis techniques. Especially remarkable is the ability to map boron, revealing segregation to grain boundaries or to carbides in sensitized samples. © 2008 Elsevier B.V. All rights reserved.

High-resolution analysis using a Cameca NanoSIMS 50 has been used to map the oxide chemistry in intergranular cracks in stainless steels. The technique has proven ideal for this type of sample, as it is able to discern between the different oxide layers and clarify the role of minor segregants such as boron and sulphur. Results are compared with analysis of the same sample by scanning auger microscopy and its interpretation discussed. The short time required to prepare and examine multiple regions present the NanoSIMS as an optimum tool for corrosion characterization. © 2007 Elsevier B.V. All rights reserved.

Vacancy loop formation in cascades formed during heavy-ion irradiation of the h.c.p. metal ruthenium at room temperature has been investigated by transmission electron microscopy. The ion energy and the ion mass were varied between 10 and 100 keV and 84 (Kr+) to 184 (W+) respectively to produce a wide variety of cascade morphologies. Information about the cascade collapse process has been obtained from the measurement of defect yield and cascade efficiency values. The former defines the probability that an incident ion forms a visible loop, and the latter the proportion of vacancies per cascade that remain in the form of a dislocation loop. The defect yield increases with increasing ion energy and has a complex dependence on ion mass, first increasing and then decreasing with increasing mass at low and high energies respectively. Cascade efficiency is not as complex and increases with increasing ion mass and decreasing ion energy. These effects have been interpreted in terms of current cascade co...

The cascade processes are discussed which potentially give rise to a dependence of microstructural evolution on the recoil spectra set up by a flux of fast particles. It is emphasised that the thermal spike phase of cascade development is central to these processes. Recent results from Molecular Dynamics simulations are presented to highlight the potential importance of interstitial clustering in cascades and the impact of cascades on pre-existing features of the microstructure. A qualitative discussion is presented of the likely importance on microstructural evolution at low and high doses of the different cascade processes.

Analyses of reactor pressure vessel (RPV) surveillance data from Charpy V-notch shift results coupled with our latest knowledge of the mechanisms of radiation embrittlement have led to new predictive correlations/models that have a strong technical underpinning. In this paper we examine how well the new CRIEPI embrittlement predicts US RPV surveillance data. Secondly, we note that within the US surveillance data sets there are indications that the data may follow the same form as the predictive models, but the data may be offset by a constant amount (either positive or negative) from the predictive values. This offset can be attributed in some cases to inadequate baseline data. In other cases, there does not appear to be a constant offset, or such an offset is hidden by data scatter. This paper also reviews the potential use of an offset adjustment and focuses on several surveillance datasets for comparisons.Copyright © 2006 by ASME

Two high copper irradiated welds, one containing very low Ni and the other containing very high Ni, have been examined using 3-D atom probe (3DAP) microscopy, small angle neutron scattering (SANS) and field emission gun-scanning transmission electron microscopy (FEG- STEM).Irradiation induced clusters were observed in both welds. They were found to be significantly smaller and exist at a higher number density in the high Ni weld. A new algorithm was developed to precisely identify the shape, composition and size of clusters observed in the atom probe data. Representative irradiation induced clusters from each weld were then examined in greater detail. They were shown to be ramified and have a significant Fe content (∼60at.%). Cu was found to be more strongly associated with the core of the clusters than Mn or Ni. In the low Ni weld, there was evidence for P at the interfaces between the clusters and matrix. Cluster composition estimates from FEG-STEM analyses were consistent with those observed by 3DAP microanalysis. For each weld, the mean radius of gyration of the clusters was found to be almost identical to the radius of gyration determined directly from SANS analyses of these materials. Finally, the number density of features was estimated from the SANS data by using the compositional information from the 3DAP observations. Consistency with the number density calculated directly from the 3DAP data was obtained provided that it is assumed that the clusters exhibit some magnetic properties.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

In this paper we review the advances in understanding ofmicrostructural evolution during irradiation in pressure vessel steels. A particular focus is the benefits that arise from combining microstructural techniques on characterising the microstructure, especially the copper clusters. In addition to experimental techniques the importance of developing microstructurally based models linking the microstructural features to mechanical properties behaviour will be demonstrated. This paper will consider the recent advances in understanding in this area, and highlight the potential benefits that can be gained from a thorough understanding of the materials response to irradiation.

We report here on studies by weak-beam electron microscopy of the evolution of microstructures at and near preexisting line dislocations in a number of Fe-Ni-Cr alloys under electron irradiation in a high-voltage electron microscope (HVEM). The detailed observations are discussed in terms of dislocation climb mechanisms in these materials and a model based on interstitial pipe diffusion.

The mechanistically-guided embrittlement correlation model adopted in ASTM E 900-02 was based on U.S. surveillance results current through calendar year 1998. There now exists an extensive amount of new surveillance data that includes a large amount of boiling water reactor (BWR) results from a supplemental surveillance program designed to augment the plant-specific BWR surveillance programs. These recent data allow a statistical check of the ASTM E 900-02 embrittlement correlation, as well as the NRC correlation model currently being used in the pressurized thermal shock (PTS) re-evaluation effort and the older Regulatory Guide 1.99, Revision 2 correlation. Even though the ASTM E 900-02 embrittlement correlation is a simplified version of the NRC model, a comparison of the two embrittlement correlation models utilizing the new database has proven to be revealing. Based on the new BWR data, both models are inadequate in their ability to predict BWR results. Other aspects of the two models are presented, as well as plans to develop a revised embrittlement correlation.

This paper reviews the current state of knowledge on attenuation of damage parameters in reactor pressure vessels (RPVs). There are two methods for evaluating attenuation of properties through a reactor pressure vessel wall. The first is by direct measurement of the change in mechanical properties from decommissioned RPV sections or from simulated RPV wall experiments. It is shown that, although this approach is appealing, issues associated with knowledge of the start-of-life properties throughout the vessel wall sample and material property data scatter have made past measurements non-definitive in establishing attenuation changes. There is a need for further data on the direct measurement of attenuation, and an experiment is described, that is planned in 2002 under IAEA sponsorship. An alternative method for evaluating embrittlement is the use of a neutron damage exposure parameter and attenuation model coupled with an embrittlement correlation developed from surveillance capsule testing. The significant change in neutron flux spectrum when neutrons are attenuated through the RPV wall defines the need for a suitable neutron exposure damage parameter. The best available neutron exposure damage parameter is dpa. It is shown that plant-specific calculation of dpa through the RPV wall is the best method to be used for the neutron exposure. However, it can lead to slightly less attenuated values for damage at ¼-T and ¾-T for the vessel, as compared to using the simple exponential model quoted in Regulatory Guide 1.99, Rev. 2. Finally it is concluded that when using a surveillance correlation model to predict the attenuation of mechanical properties through the RPV wall, the use of a mechanistically guided model appears to be more appropriate than the embrittlement correlation provided in Regulatory Guide 1.99, Revision 2.

Displacement-cascade collapse to form vacancy loops is of fundamental importance to the development of damage structures in irradiated metals. In the present experiments, displacement cascades have been generated in ruthenium, a high melting-point hexagonal metal with a c/a ratio of 1.58, by irradiation with heavy ions having a range of masses and energies. A detailed transmission electron microscopy analysis of the vacancy loops formed by cascade collapse has shown that four distinct sets of loop geometries are present. In a majority of cases the cascades collapse initially on to the {1010} prism planes to form loops with Burgers vector b=½〈1010〉 and it is shown that these can subsequently unfault to form perfect ⅓ 〈1120〉-type loops. When the incident-ion-beam direction lies in the basal plane, a minority of the cascades collapse on to the basal planes to form faulted ½[0001] loops and these can transform to a lower-energy faulted loop with b of the type ⅙〈2023〉. From determination of the loop s...

Irradiation damage structures induced in α-iron by low-dose fisson-neutron irradiation at reactor ambient temperature have been investigated by transmission electron microscopy. Materials of three purities were irradiated to doses between 1022 and 1024 neutrons (with E > 1 MeV) m−2 in the PLUTO experimental reactor at Harwell. In a high-purity iron no visible damage was observed below a dose of 8 × 1022 neutrons m−2. Above this dose the damage was restricted to the decoration of in-grown dislocations and low-angle boundaries by dislocation loops. No visible damage was found in the less pure materials after irradiation to doses

The influence of small amounts of Cu on the neutron irradiation induced embrittlement of reactor pressure vessel steels is of considerable practical importance. Previous work has shown that the embrittlement is associated with the formation of copper rich precipitates but uncertainties remain regarding their composition and form. The present paper reports preliminary results from a study of such precipitates in solution treated and aged Fe-Cu alloys with additions of Ni and P, using a combination of atom probe analysis in a Field Ion Microscope (FIM) and Small Angle Neutron Scattering (SANS).