High Irradiation Resistance Research Articles

Strength anisotropy of rolled 11Cr-ODS steel

Materials for core components of fusion reactors and fast reactors, such as blankets and fuel cladding tubes, must offer the best possible high temperature strength and irradiation resistance because they will be exposed to high heat flux and heavy neutron irradiation. Japan Atomic Energy Agency (JAEA) has been developing 9 and 11 chromium (Cr) oxide dispersion strengthened (ODS) steels as candidate materials for advanced fast reactor cladding tubes. In this study the JAEA 11Cr-ODS steel was rolled in order to evaluate its anisotropy. The tensile tests and creep tests were carried out at 700°C in longitudinal and transverse orientations. The anisotropy of the tensile strength was negligible, though that of the creep strength was distinct. The observation results and chemical composition mapping suggested that the cause of the anisotropy in the creep strength was a previously formed columnar boundary, that is, a prior particle boundary including Ti-rich sub-micro metric precipitates.

A Brief Review of High Entropy Alloys and Serration Behavior and Flow Units

Multicomponent alloys with high entropy of mixing, e.g., high entropy alloys (HEAs) and/or multiprincipal-element alloys (MEAs), are attracting increasing attentions, because the materials with novel properties are being developed, based on the design strategy of the equiatomic ratio, multicomponent, and high entropy of mixing in their liquid or random solution state. Recently, HEAs with the ultrahigh strength and fracture toughness, excellent magnetic properties, high fatigue, wear and corrosion resistance, great phase stability/high resistance to heat-softening behavior, sluggish diffusion effects, and potential superconductivity, etc., were developed. The HEAs can even have very high irradiation resistance and may have some self-healing effects, and can potentially be used as the first wall and nuclear fuel cladding materials. Serration behaviors and flow units are powerful methods to understand the plastic deformation or fracture of materials. The methods have been successfully used to study the plasticity of amorphous alloys (also bulk metallic glasses, BMGs). The flow units are proposed as: free volumes, shear transition zones (STZs), tension-transition zones (TTZs), liquid-like regions, soft regions or soft spots, etc. The flow units in the crystalline alloys are usually dislocations, which may interact with the solute atoms, interstitial types, or substitution types. Moreover, the flow units often change with the testing temperatures and loading strain rates, e.g., at the low temperature and high strain rate, plastic deformation will be carried out by the flow unit of twinning, and at high temperatures, the grain boundary will be the weak area, and play as the flow unit. The serration shapes are related to the types of flow units, and the serration behavior can be analyzed using the power law and modified power law.

In-situ formation of complex oxide precipitates during processing of oxide dispersion strengthened ferritic steels

In fusion and fission reactor material development, ODS alloys are the most suitable candidate materials due to its high temperature creep properties and irradiation resistance properties. This paper describes the preparation of oxide dispersion strengthened alloy powder in large quantity (>1kg batch) in dual drive planetary ball mill using pre-alloyed ferrtic steel powder with nano sized Y2O3. The consolidation of the powders was carried out in hot isostatic press (HIP) followed by hot rolling. 99% of the theoretical density was achieved by this method. The vickers hardness values of pressed and rolled samples were in the range of 380±2HV and 719±2HV, respectively. Samples were further investigated using X-ray diffraction particle size analyzer and electron microscope. Initial increase in particle size with milling was observed showing flattening of the particle. It was found that 5h of milling time is sufficient to reduce the particle size to achieve the desired size. Transmission electron microscopy analysis of milled ODS steel powder revealed a uniform distribution of combustion synthesized nano-Y2O3 in ferritic steel matrix after a milling time of 5h. Preliminary results demonstrated suitability of dual drive planetary ball mill for mass production of alloy within a short time due to various kinds of forces acting at a time during milling process. Fine monoclinic Y2Si2O7 precipitates were also observed in the steel. This study explains the particle characteristics of nano Y2O3 dispersed ODS powder and formation of nano clusters in ODS ferritic alloy.

Krypton ion irradiation-induced amorphization and nano-crystal formation in pyrochlore Lu2Ti2O7 at room temperature**Project sponsored by the National Natural Science Foundation of China (Grant No. 11205128) and the Fundamental Research Funds for the Central Universities, China (Grant No. 2012121034).

Polycrystalline pyrochlore Lu2Ti2O7 pellets are irradiated with 600-keV Kr3+ ions up to a fluence of 1.45 × 1016 Kr3+/cm2. Irradiation induced structural modifications are examined by using grazing incidence x-ray diffraction (GIXRD) and cross-sectional transmission electron microscopy (TEM). The GIXRD reveals that amorphous fraction increases with the increase of fluences up to 2 × 1015 Kr3+/cm2, and the results are explained with a direct-impact model. However, when the irradiation fluence is higher than 2 × 1015 Kr3+/cm2, the amorphous fraction reaches a saturation of ∼80%. Further TEM observations imply that nano-crystal is formed with a diameter of ∼10 nm within the irradiation layer at a fluence of 4 × 1015 Kr3+/cm2. No full amorphization is achieved even at the highest fluence of 1.45 × 1016 Kr3+/cm2 (∼36 displacement per atom). The high irradiation resistance of pyrochlore Lu2Ti2O7 at higher fluence is explained on the basis of enhanced radiation tolerance of nano-crystal structure.

Swift heavy ion irradiation damage in Ti–6Al–4V and Ti–6Al–4V–1B: Study of the microstructure and mechanical properties

The α+β alloy Ti–6Al–4V (wt.%) and the boron-modified Ti–6Al–4V–1B (wt.%), due to their low activation, corrosion resistance, good mechanical properties, and their commercial availability, were chosen as candidate materials for the beam dump for the Facility for Rare Isotope Beams (FRIBs) at Michigan State University: a new generation accelerator with high power heavy ion beams. Through this study our goal is to establish the first irradiation data of the recently developed Ti–6Al–4V–1B (wt.%) alloy and investigate the changes in microstructure and mechanical properties of Ti–6Al–4V due to swift heavy ion (SHI) irradiation damage. The results of hardness measurements showed that the studied Ti–6Al–4V (wt.%) and Ti–6Al–4V–1B (wt.%) alloy, under the specified irradiation conditions, exhibited a high irradiation resistance. In fact, only a slight hardening was observed (∼13%) in the tested samples and no changes in the microstructure were observed. Temperature, dose and electronic excitation effects were also discussed.

Effect of mechanical milling on the microstructure of tungsten under He+ irradiation condition

“Pure” W was prepared through a powder metallurgy route by using hard alloy (WC–Co) milling tank and balls to mill WO3 powder, reducing with high purity H2, and sintering with spark plasma sintering technique. XRD, SEM, and TEM were used to characterize the phase and phase structures. Results showed that the cobalt tungsten carbide (Co3W10C3.4) phase was induced from the milling tank and balls. After the “pure” W bulk was exposed to helium ions for 2h, the cobalt tungsten carbide phase was found to be surrounded by the lattice distortion phase of W, which showed high irradiation resistance.

Irradiation Resistance of Multicomponent Alloys

High-entropy alloys (HEAs) are characterized not only by high values of entropy but also by high atomic-level stresses originating from mixing of elements with different atomic sizes. Particle irradiation on solids produces atomic displacements and thermal spikes. The high atomic-level stresses in HEAs facilitate amorphization upon particle irradiation, followed by local melting and re-crystallization due to thermal spikes. We speculate that this process will leave much less defects in HEAs than in conventional alloys. For this reason, they may be excellent candidates as new nuclear materials. We discuss initial results of computer simulation on model binary alloys and an electron microscopy study on Zr-Hf-Nb alloys, which demonstrate extremely high irradiation resistance of these alloys against electron damage to support this speculation.

Diffusion bonding of the oxide dispersion strengthened steel PM2000

Ferritic oxide dispersion strengthened (ODS) steels are well suited as structural materials, e.g. for claddings in fission reactors and for plasma facing components in fusion power plants due to their high mechanical and oxidation stability at high temperatures and their high irradiation resistance. PM2000 is an iron based ODS ferritic steel with homogeneously distributed nanometric yttria particles. Melting joining techniques are not suitable for such ODS materials because of the precipitation and agglomeration of the oxide particles and hence the loss of their strengthening effect. Solid state diffusion bonding is thus chosen to join PM2000 and is investigated in this work with a focus on oxide particles. The diffusion bonding process is aided by the computational modeling, including the influence of the ODS particles. For modeling the microstructure stability and the creep behavior of PM2000 at various, diffusion bonding relevant temperatures (50–80% Tm) are investigated. Particle distribution (TEM), strength (tensile test) and toughness (Charpy impact test) obtained at temperatures relevant for bonding serve as input for the prediction of optimal diffusion bonding parameters. The optimally bonded specimens show comparable strength and toughness relative to the base material.

Perforation and Carbon Ablation Experiments on Nano-Ceria by Electron Irradiation

ABSTRACTThe well-known high irradiation resistance of fluorite-structured oxides is examined on the nanoscale by focused electron beam irradiation of ceria nanoparticles. It is found that ceria is amongst the nanomaterials most resistant to electron beam perforation with mainly swelling and amorphisation damage observed, along with grain reorientation effects. A comparison to reference nano-materials, shows that cubic zirconia behaves similarly resistant but that ultra-fine holes can be drilled, unlike for ceria, while SiC on the other hand can be perforated easily. Ablation of carbon films around electron beam impact zones is found accelerated in ceria, as compared to SiC, and discussed as a potential catalytic effect.

Effect of mechanical alloying and consolidation process on microstructure and hardness of nanostructured Fe–Cr–Al ODS alloys

► The particle size progressively decreases with increase in milling time. ► The use of stearic acid can was found to achieve fine uniform spherical powders. ► High BPR has a significant influence on the rate of decrease of crystallite size . ► High-temperature sintering leads to relative density increase and grain growth. ► Canning-HIP technique has a significant improvement in mechanical properties. Nanostructured ferritic oxide dispersion strengthened (ODS) alloys are promising materials for both high temperature creep properties and irradiation resistance. These alloys were produced by mechanical alloying (MA) which is a complex process and a number of process variables need to be controlled to achieve the desired properties. In this study, the effect of mechanical alloying and consolidation processes on the microstructure and properties of nanostructured ferritic ODS alloy were investigated. The powder mixtures were milled in Spex mill for different milling times (1 h, 3 h, 8 h, and 15 h). The effect of process control agents (PCAs) and ball to power ratio (BPR) were studied. Two-stage sintering and canning-HIP processes were introduced as new consolidation methods to produce ODS alloys with improved mechanical properties. The results showed that crystallite size during milling decrease with milling time and higher BRP has a significant influence on the rate of decrease of the crystallite size. The use of stearic acid as PCA led to fine, uniform and spherical particles during the ball milling. Additionally, the samples sintered at the elevated temperatures over long periods resulted in a reduction in porosity; however, the microstructure became coarser, accompanied by a decrease in the hardness. The canning-HIP technique can effectively minimize the content of oxygen and carbon impurities to achieve high relative density and high hardness.

Thermo-activated Dislocation Emission at the Cu/Nb Interface Revealed by Molecular Dynamics Simulations

Nanolayered Cu-Nb composites offer a series of enhanced properties for their use in extreme conditions, e.g. high field magnets and high irradiation resistance. However, the stability of the Cu/Nb heterogeneous interface needs confirmation under various conditions. In the present work, molecular dynamics simulations were carried out to investigate the interfacial behavior under various temperatures with initial stress at the interface. It is found that the interface becomes unstable at simulation temperatures higher than 600 K, resulting in the emission of dislocations and loops within one or more slip systems. The emission process is found to be thermally-activated, i.e., the higher temperature, the shorter annealing time needed. The present study is believed to assist the experimental synthesis of the Cu-Nb multilayer nanocomposites for multiple applications.

A novel route for preparation of PVC sheets with high UV irradiation resistance

AbstractA novel acrylonitrile acrylate copolymer coating was proposed to improve the UV irradiation resistance of poly(vinyl chloride) (PVC) sheets. Its effect on the photoageing properties of the sheets was evaluated by means of Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), yellowness index test, and the oxygen permeability coefficient and mechanical properties measurement. The experimental results show that the novel acrylonitrile acrylate copolymer coating significantly improves the UV irradiation resistance of PVC sheets. Compared with the PVC sheets without coating, the coated PVC sheets show better mechanical properties, lower yellowness index, and smaller oxygen permeability coefficient after UV irradiation. The analysis on the SEM images of the PVC sheets indicates that the coating acts as a film to prevent the PVC sheets from UV energy and oxygen that can accelerate the photochemical reactions of PVC. The FTIR analysis confirms that the coating can slow down the microstructures development of the PVC sheets, also indicating that the coating impeded the photochemical reactions of PVC. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Main results of the development of dispersion type IMF at A.A. Bochvar Institute

At A.A. Bochvar Institute a novel conception of IMF to burn civil and weapon’s grade Pu is currently accepted. It consists in the fact, that instead of using pelletized IMF, that features low serviceability and dust forming route of fuel element fabrication, the usage is made of dispersion type fuel element with aluminium or zirconium matrices. Dispersion fuels feature a high irradiation resistance and reliability; they can consequently reach high burnups and be serviceable under transient conditions. Three basic fuel element versions are under development in VNIINM for both thermal and fast reactors. The first version is a fuel element with a heterogeneous arrangement of fuel (PuO 2 or YSZ granules) within an Al or Zr matrix. The second version of a fuel element has a heat conducting Al or Zr alloy matrix and an isolated arrangement of PuO 2 in a fuel minielement more fully meets the ‘Rock Fuel’ requirements. According to the third version a porous meat of zirconium metallurgically bonded to a fuel cladding is formed through which a PuO 2 powder is introduced. All the versions are technologically simple to fabricate and require minimal quantities of process operations related to treating MA and Pu. Preliminary in-pile tests of IMF prototypes are presented.

Boron environments and irradiation stability of iron borophosphate glasses analysed by EELS

The coordination and stability under electron irradiation of boron in glasses with nominal molar composition 60P 2O 5 − (40 − x)Fe 2O 3 − xB 2O 3, for which x = 0, 5, 10, 15 and 20, have been investigated for the first time by electron energy loss spectroscopy (EELS) with transmission electron microscopy (TEM). Analyses confirm that boron is present in un-irradiated samples as tetrahedral BO 4 units; there is no evidence of any trigonal BO 3 units. TEM analysis reveals no tendency for sub-micron phase separation of the as-annealed glass. Iron borophosphate glasses exhibit high resistance to structural damage by electron beam irradiation by comparison with literature values for a range of other silicate and phosphate glasses. Large doses of highly intense irradiation result in the conversion of BO 4 to BO 3 units. The high irradiation resistance of these glasses could be related to the absence of mobile classical network modifiers such as alkalis and their associated non-bridging oxygens.

Mechanical, thermal and morphological behaviour of the polystyrene/polypropylene (80/20) blend, irradiated with γ-rays at low doses (0–70 kGy)

The effect of low doses (0–70 kGy) of gamma irradiation on the mechanical, morphological and thermal behaviour, at room temperature and in the presence of oxygen, of a polystyrene/polypropylene (PS/PP) blend (80/20) with and without compatibilizer (block SBS) at 7.5 wt.% has been studied, to solve different problems related to the radiation stability of polymeric articles and purposeful radiation-induced modifications of polymeric materials. The effect of gamma irradiation on the tensile behaviour of the PS/PP blend (80/20) with and without SBS indicates that the blends present a high irradiation resistance at low doses (⩽70 kGy); this implies that adding PP to PS to modify its mechanical behaviour is a proper procedure, since PS is one of the most stable polymers regarding radiation, and very large doses are required to produce any noticeable change. Therefore, with an irradiation dose ranging between 0 and 70 kGy, PP is protected against a strong oxidative degradation (chain scission), which coincides with the values of the relative concentration of radicals obtained through EPR. In addition, according to the thermal studies, T g shows no variations which could point to changes in the PS structure in the blends; however, variations in T f of PP of the blends were detected, which lead us to conclude that PP shows chain scission degradation. It can be inferred that this decrease in fusion temperature occurs in the blends at irradiation doses (⩾50kGy) higher than that of non-compatibilized PP (⩾10kGy).

Mechanical properties and damage behavior of non-magnetic high manganese austenitic steels

Fe–Cr–Mn steels have been considered as materials of structural components for fusion reactor because of their low induced-radio-activity compared with SUS316 stainless steels. It has been expected to develop a non-magnetic steel with a high stability of the austenitic phase and a strong resistance to irradiation environments. For these objectives, a series of the Fe–Cr–Mn steels have been examined by tensile tests and simulation irradiation by electrons. The main alloying compositions of the steels developed are; C:0.02–0.2 wt%, Mn: 15 wt%, Cr: 15–16 wt%, N: 0.2 wt%. These steels were heat-treated at 1323 K for 1 h. The structure of the steels after the heat-treatment was austenite single phase. The yield stress of the steels was 350–450 MPa and the elongation were 55–60%. When the steels of high C and N was electron-irradiated at below 673 K, no voids were nucleated and only small dislocation loops were formed with high density. The austenite phase was also stable during irradiation below 673 K. Thus, newly developed high manganese steels have excellent mechanical proprieties and high irradiation resistance at relatively low temperature.

高速炉炉心材料用改良オーステナイト鋼の開発

Advanced austenitic stainless steel beyond the standard composition region of SUS316 stainless steel PNC1520 has been successfully developed. Optimization of the steel leads to a composition of 15Cr-20Ni-0.06C-2.5Mo-1.7Mn-0.25Ti-0.1Nb-0.028P-0.004B through the alloying design and fabrication tests. An extensive series of evaluation tests including out-of-pile, sodium environment, neutron irradiation and fission product corrosion has confirmed that PNC1520 is superior in high temperature strength and irradiation resistance to PNC316 as a core material for the prototype reactor MONJU. PNC1520 is the best candidate material for the Demonstration reactor and will be tested on the whole core scale in JOYO MK-III to obtain the proven data.