Irradiation Temperature Range Research Articles

Combined Radiation and Temperature Effects on Brillouin-Based Optical Fiber Sensors

The combined effects of temperature (from −80 °C to +80 °C) and 100 kV X-ray exposure (up to 108 kGy(SiO2)) on the physical properties of Brillouin scattering and losses in three differently doped silica-based optical fibers, with varying dopant type and concentration (4 wt%(Ge), 10 wt%(Ge) and 1 wt%(F)), are experimentally studied in this work. The dependencies of Brillouin Frequency Shifts (BFS), Radiation-Induced Attenuation (RIA) levels, Brillouin gain attenuation, Brillouin frequency temperature (CT) and strain (Cε) sensitivity coefficients are studied under X-rays in a wide temperature range [−80 °C; +80 °C]. Brillouin sensing capabilities are investigated using a Brillouin Optical Time Domain Analyzer (BOTDA), and several properties are reported: (i) similar behavior of the Brillouin gain amplitude decrease with the increase in the RIA; (ii) the F-doped and heavily Ge-doped fibers do not exhibit a temperature dependence under radiation for their responses in Brillouin gain losses. Increasing Ge dopant concentration also reduces the irradiation temperature effect on RIA. In addition, Radiation-Induced Brillouin Frequency Shift (RI-BFS) manifests a slightly different behavior for lower temperatures than RIA, presenting an opportunity for a comprehensive understanding of RI-BFS origins. Related temperature and strain sensors are designed for harsh environments over an extended irradiation temperature range, which is useful for a wide range of applications.

Irradiation temperature and dose rate dependence of void swelling in RAFM steel during irradiation: Reaction rate theory analysis

Reaction rate theory analysis has performed to investigate the irradiation temperature and dose rate dependence of void swelling of RAFM steel under a wide range of irradiation temperatures and dose rates (250 to 620 °C and 10−7 to 10−3 dpa/s) with focusing on nucleation behavior of voids. In the rate theory analysis, an improved nucleation model is employed where the stable nucleus size of voids is estimated by the vacancy flux into/from voids which depends on irradiation condition and void size. The calculation says that the void swelling strongly depends on irradiation temperature and dose rate, and there is one unique peak temperature for each dose rate. As dose rate increases, the peak temperature shifts to higher temperatures and the peak swelling decreases; this results from the enhancement and suppression of void nucleation. The calculated stable nucleus size of voids remarkably depends on irradiation conditions and varies widely from 5 to about 50: the nucleus size drastically increases at higher temperatures, while it decreases at higher dose rates. For the dose rate dependence of the peak temperature of void swelling, the calculation provides a good agreement with the experiment more than a conventional model.

Defect generation mechanisms in silica under intense electronic excitation by ion beams below 100 K: Interplay between radiative emissions

Ion-beam effects on bulk silica at low temperature have been studied with the aim of understanding the routes and mechanisms leading from the initial generation of free carriers and self-trapped excitons (STEs) to the production of two stable defect structures in irradiated silica, non-bridging oxygen hole centers (NBOHCs) and oxygen deficient centers (ODCs). Ion beam induced luminescence (ionoluminescence, IL) spectra were obtained using 3 MeV H, 3.5 MeV He, 19 MeV Si, and 19 MeV Cl ions and a range of cryogenic irradiation temperatures from 30 to 100 K. The kinetic behavior of three emission bands centered at 1.9 eV (assigned to NBOHCs), 2.1 eV (assigned to the intrinsic decay of STEs), and 2.7 eV (assigned to ODCs) reveal the physical origin of these emissions under intense electronic excitation. The creation of NBOHCs is governed by a purely electronic mechanism. The kinetics curve of the NBOHC band shows two main contributions: an instantaneous (beam-on) contribution, followed by a slower fluence- and temperature-dependent process correlated with the concentration of STEs. The beam-on contribution is proportional to deposited ionization energy. The growth of the ODC band is linear in fluence up to around 2 × 1012 cm−2. The growth rate is independent of temperature but proportional to the number of radiation-induced oxygen vacancies per ion, showing, unambiguously, that the 2.7 eV emission can be associated with ODCs created in an excited state.

Radiation induced amorphization of carbides in additively manufactured and conventional ferritic-martensitic steels: In-situ experiments on extraction replicas

In-situ irradiations using 1 MeV Kr2+ ions in a transmission electron microscope were performed on extraction replica samples containing M23C6 carbides and MX carbonitrides from two ferritic-martensitic (FM) steels: (i) 9%Cr-1%W-TaV based Eurofer97 and (ii) 9%Cr-1%Mo-VNb (all in wt.%) based additively manufactured (AM) Grade91 steel. The irradiations were performed between 100 and 773 K up to a maximum dose of ∼2.4 displacements per atom (dpa). The M23C6 carbides are highly susceptible to radiation induced amorphization (RIA), while the MX type nanoprecipitates are highly amorphization resistant across the entire irradiation temperature range. Between 100 and 423 K, RIA of M23C6 carbides occurs very rapidly with critical amorphization doses ranging between ∼0.35 and 0.9 dpa, increasing to higher doses at 573 K. Complete amorphization of the M23C6 carbides up to doses of ∼2.4 dpa is not possible at 773 K under the present irradiation conditions. The critical amorphization dose of M23C6 carbides increases nearly exponentially with irradiation temperature. The critical temperature for the crystalline-to-amorphous phase transformation (Tc→a) of M23C6 carbides irradiated as replica samples, i.e. without the surrounding metal matrix, was estimated to be ∼812 K. Comparing the present results with neutron irradiation data on bulk samples reveals a decrease in the critical amorphization dose for M23C6 and an increase of Tc→a, highlighting the effect of dose rate on the amorphization behavior that is qualitatively consistent with literature on other non-metals. Changes in the minor chemistry of M23C6, such as presence or absence of W, V, Nb, Mo, seems to have little effect on the amorphization behavior. In-situ irradiations on extraction replica samples provide a novel pathway to explore radiation tolerance of nanoprecipitates in nuclear structural materials

Early-stage microstructural evolution and phase stability in neutron-irradiated ferritic-martensitic steel T91

A Fe-9Cr ferritic martensitic (F/M) steel T91 was neutron-irradiated in the Advanced Test Reactor up to 3.96 dpa in two temperature ranges, 466 °C to 534 °C and 571 °C to 632 °C. The microstructure evolution including dislocation loops, precipitation, segregation of elements and phase stability were studied using analytical scanning-transmission electron microscopy and atom probe tomography. The hardening induced by irradiation was measured by nanoindentation. Ni/Si/Mn clusters were identified in all conditions except the one irradiated around 600 °C to 3.23 dpa. The compositions of Ni/Si/Mn clusters were found to be converging to G phase stoichiometrically with increasing dose, with Mn partially substituted by Cu. Significant coarsening of this phase was observed in high temperature cases, with total dissolution of intragranular G phase after prolonged irradiation. A similar trend was also identified for dislocation loops. The results obtained in this experiment provide evidences that the absence of dislocation loops in some specimens irradiated to high dose level under high irradiation temperature range (typically above 500 °C) is not due to the suppression of nucleation and growth by high point defect recombination rate, but rather fast coalescence of dislocation loops. Hardness measurements show different dose dependences for two temperature ranges. For specimen irradiated around 600 °C significant hardening before 0.5 dpa followed by softening process was observed, while in lower temperature range (450 °C ~ 500 °C) the normal hardening pattern with increasing dose was observed.

Impact of high temperature electron irradiation on characteristics of power SiC Schottky diodes

Impact of high temperature electron irradiation on the characteristics of power silicon carbide-based semiconductor devices was studied for the first time. Commercial 4H–SiC integrated Schottky diodes (JBS) with blocking voltage of 1700 V were irradiated with 0.9 MeV electrons at temperatures from 23 to 5000С in the fluence range Φ from 1 × 1016 cm−2 to 1.3 × 1017 cm−2. It was shown that ruggedness of the diodes during high temperature (“hot”) irradiation significantly exceeds the ruggedness of diodes at room temperature (“cold”) irradiation. With an increase in the irradiation temperature from 23 to 500 °C, the change in the base resistance at a fluence of 1.3 × 1017 cm−2 decreases by 6 orders of magnitude. In the entire investigated range of irradiation temperatures and fluences, irradiation does not change the height of the metal-semiconductor barrier even at the maximum fluence Φ.

Effect of high temperature irradiation with 15 MeV protons on characteristics of power SiC Schottky diodes

The effect of high-temperature irradiation with 15 MeV protons on the parameters of high-voltage 4H-SiC Schottky diodes has been studied at irradiation temperatures of 23–500 °C and doses in the range from 7 × 1013 to 2 × 1014 cm−2. After the irradiation with a dose of 1014 cm−2 at room temperature, the forward current at a forward voltage U = 2 V decreases by ~10 orders of magnitude. In this case, the cutoff voltage Uc, equal to ~0.6 V in unirradiated devices, decreases to Uc ≈ 0.35 V. By contrast, irradiation with the same dose at a temperature of 500 °C leads to an increase in Uc up to Uc ≈ 0.8 V. At the same reference value of the forward voltage U = 2 V, the decrease in current, compared to the value in unirradiated devices, was smaller by ~4 orders of magnitude. In the entire range of doses and irradiation temperatures under study, the forward current–voltage characteristic of diodes at U > Uc is linear up to U ≤ 2 V.

Neutronography of Irradiated Reactor Austenitic Steels

The neutron diffracttion studies of the samples of fuel element claddings made of EK-164 and ChS-600 austenitic steels in the initial state and after operation in a BN-600 fast neutron reactor are reviewed. The samples were investigated in a wide range of fast neutron doses and irradiation temperatures, up to ∼80 displacements per atoms (dpa) and 628°C, respectively. Various microstructural characteristics, such as microstresses, dislocation density, and crystallographic texture are determined using full-profile analysis of neutron diffraction data. At high doses studied in this work, the irradiation temperature is the dominant factor responsible for the dislocation density. The procedures of analyzing and revealing defect types were preliminary developed on specially prepared nickel samples and austenitic alloys upon irradiation in the IVV-2M reactor core at a temperature near 80°С, which provided a low thermal mobility of lattice defects. The results obtained in some first diffraction studies on samples after their operation in the reactor core show that neutron data can be used to characterize the microstructures formed due to irradiation and, at least, estimate the mechanical properties of irradiated materials without their destruction and with no radiation risk for personnel.

Clouds in Three-dimensional Models of Hot Jupiters over a Wide Range of Temperatures. I. Thermal Structures and Broadband Phase-curve Predictions

Abstract Using a general circulation model (GCM), we investigate trends in simulated hot Jupiter atmospheres for a range of irradiation temperatures (1500–4000 K), surface gravities (10 and 40 m s−2), and cloud conditions. Our models include simplified temperature-dependent clouds with radiative feedback and show how different cloud compositions, vertical thicknesses, and opacities shape hot Jupiter atmospheres by potentially increasing planetary albedos, decreasing photospheric pressures and nightside temperatures, and in some cases producing strong dayside thermal inversions. With decreasing irradiation, clouds progressively form on the nightside and cooler western limb, followed by the eastern limb and central dayside. We find that clouds significantly modify the radiative transport and affect the observable properties of planets colder than T irr ≈ 3000 K (T eq ≈ 2100 K) depending on the clouds’ vertical extent. The precise strength of expected effects depends on the assumed parameters, but trends in predicted phase curves emerge from an ensemble of simulations. Clouds lead to larger phase-curve amplitudes and smaller phase-curve offsets at IR wavelengths, compared to cloud-free models. At optical wavelengths, we predict mostly westward phase-curve offsets at intermediate temperatures (T irr ≈ 2000–3500 K) with clouds confined to the nightside and western limb. If clouds are vertically compact (i.e., on the order of a pressure scale height in thickness), their distributions and effects become more complicated as different condensates form at different heights—some too deep to significantly affect the observable atmosphere. Our results have implications for interpreting the diversity of phase-curve observations of planets with T irr ≲ 3000 K.

Influence of γ-irradiation on mechanical behaviors of poly methyl-vinyl silicone rubber foams at different temperatures

In this study, the radiation dose effect of γ rays on the temperature-dependent mechanical behaviors of poly methyl-vinyl silicone rubber foams is investigated by uniaxial compression tests. After exposure to a wide radiation dose range from 0 to 500 kGy at room temperature, silicone rubber foams were tested at 10, 40, 70, and 100 °C. The test results show that temperature increase causes linear hardening for both unirradiated and irradiated samples due to the predominating entropy-related deformation of silicone rubber matrix. Moreover, increase of irradiation dose leads to linear hardening as a result of dominating cross-linking reactions of rubber networks. A stress hardening factor is introduced to characterize the effect of irradiation dose on temperature-related hardening behavior, which is defined as the ratio between the compressive stresses of irradiated and unirradiated samples for a given compression strain. The approximated constant stress hardening factor for each radiation dose condition implies that the irradiation dose does not affect the temperature-related hardening behavior. Based on the test findings, the Ogden Hyperfoam model was extended by correlating the initial shear modulus-related model parameters with radiation dose and temperature. The hardening exponent-related model parameters have been shown to be independent of radiation dose and temperature, and the Poisson's ratio-related model parameters are approximated to zero for the high porosity of the material. The prediction performance of the extended model is demonstrated by comparing the fitted model responses with test data over the studied irradiation doses and temperature range. The results are expected to be helpful for the safety evaluation of nuclear engineering structures.

Study of radiation-induced amorphization of M23C6 in RAFM steels under iron irradiations

The mechanical properties of reduced activation ferritic/martensitic steels (RAFMs) such as creep, thermal aging, and irradiation resistance are improved by the formation of MX and M23C6 particles. However, it is well known that these particles are unstable under irradiation. The purpose of the present study is to clarify the details of the radiation-induced amorphization (RIA) of M23C6 in F82H steels. The instability behavior of M23C6 under a wide range of irradiation temperatures from R.T. to 773 K and various ion beam energies (2.8, 3.7, 6.4 and 10.5 MeV) was systematically investigated. Two types of materials, F82H and its model alloy (F8), were utilized in this study. TEM observation and selected area electron diffraction analysis before and after irradiation were conducted to evaluate the occurrence of RIA, and the chemical composition was analyzed to reveal the possible relation between atom displacement/diffusion and RIA. In the case of the iron irradiation at the temperature below 598 K, a bilayer contrast of the particle, consisting of an amorphous-rim phase and inner crystalline core, was observed. Similar particle survived in the irradiated F82H at the temperature of 623 K, the RIA was not observed in the F8 specimen. Consequently, the critical temperature of RIA was estimated as 623–673 K. Since the melting temperature (Tm) of M23C6 is approximately 2173 K, the critical temperature corresponds to ∼0.29 Tm. From the STEM-EDS analysis, the Fe/Cr ratio of the particle decreased with increasing irradiation temperature in the range of 573–623 K. This behavior was qualitatively explained by the formation of the amorphous phase. It is clarified that the occurrence of the RIA of M23C6 particle can be evaluated by the variation of Fe/Cr ratio.

Exploitation of thermal gradients for investigation of irradiation temperature effects with charged particles

The effects of radiation damage on materials are strongly dependant on temperature, making it arguably the most significant parameter of concern in nuclear engineering. Owing to the challenges and expense of irradiating and testing materials, material property data is often limited to few irradiation conditions and material variants. A new technique has been developed which enables the investigation of radiation damage of samples subject to a thermal gradient, whereby a wealth of data over a range of irradiation temperatures is produced from a single irradiation experiment. The results produced are practically inaccessible by use of multiple conventional isothermal irradiations. We present a precipitation-hardened copper alloy (CuCrZr) case-study irradiated with a linear temperature gradient between 125 and 440 °C. Subsequent micro-scale post irradiation characterisation (nanoindentation, transmission electron microscopy and atom probe tomography) highlight the capability to observe mechanical and microstructural changes over a wide range of irradiation temperatures. We observed irradiation-softening in CuCrZr that did not occur due to irradiation-enhanced aging of the Cr-precipitates. Excellent reproducibility of the new technique was demonstrated and replicated irradiation-hardening data from several isothermal neutron irradiation studies. Our new technique provides this data at a fraction of the time and cost required by conventional irradiation experiments.

Influence of laser irradiation on deposition characteristics of cold sprayed Stellite-6 coatings

Depositing hard materials such as Stellite-6 solely by cold spray (CS) is challengeable due to limited ability of plastic deformation. In this study, the deposition of Stellite-6 powder was achieved by supersonic laser deposition (SLD) which combines CS with synchronous laser irradiation. The surface morphology, deposition efficiency, track shape of Stellite-6 coatings produced over a range of laser irradiation temperatures were examined so as to reveal the effects of varying laser energy inputting on the deposition process of high strength material. The microstructure, phase composition and wear/corrosion resistant properties of the as-deposited Stellite-6 coatings were also investigated. The experimental results demonstrate that the surface flatness and deposition efficiency increase with laser irradiation temperature due to the softening effect induced by laser heating. The as-deposited Stellite-6 tracks show asymmetric shapes which are influenced by the relative configuration of powder stream and laser beam. The SLD coatings can preserve the original microstructure and phase of the feedstock material due to relatively low laser energy inputting, which result in the superior wear/corrosion resistant properties as compared to the counterpart prepared by laser cladding.

Reprint of: Microstructural evolution of neutron irradiated 3C-SiC

The microstructural response of neutron irradiated 3C-SiC have been investigated over a wide irradiation temperature and fluence range via qualitative and quantitative synchrotron-based X-ray diffraction characterization. We identify several neutron fluence- and irradiation temperature-dependent changes in the microstructure, and directly highlight the specific defects introduced through the course of irradiation. By quantifying the microstructure, we aim to develop a more detailed understanding of the radiation response of SiC. Such studies are important to build mechanistic models of material performance and to understand the susceptibility of various microstructures to radiation damage for advanced energy applications.

Mechanisms of radiation embrittlement of VVER-1000 RPV steel at irradiation temperatures of (50–400)°C

This work summarizes and analyzes our recent research results on the effect of irradiation temperature within the range of (50–400)°C on microstructure and properties of 15Kh2NMFAA class 1 steel (VVER-1000 reactor pressure vessel (RPV) base metal). The paper considers the influence of accelerated irradiation with different temperature up to different fluences on the carbide and irradiation-induced phases, radiation defects, yield strength changes and critical brittleness temperature shift (ΔTK) as well as on changes of the fraction of brittle intergranular fracture and segregation processes in the steel. Low temperature irradiation resulted solely in formation of radiation defects – dislocation loops of high number density, the latter increased with increase in irradiation temperature while their size decreased. In this regard high embrittlement rate observed at low temperature irradiation is only due to the hardening mechanism of radiation embrittlement. Accelerated irradiation at VVER-1000 RPV operating temperature (∼300 °C) caused formation of radiation-induced precipitates and dislocation loops, as well as some increase in phosphorus grain boundary segregation. The observed ΔTK shift being within the regulatory curve for VVER-1000 RPV base metal is due to both hardening and non-hardening mechanisms of radiation embrittlement. Irradiation at elevated temperature caused more intense phosphorus grain boundary segregation, but no formation of radiation-induced precipitates or dislocation loops in contrast to irradiation at 300 °C. Carbide transformations observed only after irradiation at 400 °C caused increase in yield strength and, along with a contribution of the non-hardening mechanism, resulted in the lowest ΔTK shift in the studied range of irradiation temperature and fluence.

Microstructural evolution of neutron irradiated 3C-SiC

The microstructural response of neutron irradiated 3C-SiC have been investigated over a wide irradiation temperature and fluence range via qualitative and quantitative synchrotron-based X-ray diffraction characterization. We identify several neutron fluence- and irradiation temperature-dependent changes in the microstructure, and directly highlight the specific defects introduced through the course of irradiation. By quantifying the microstructure, we aim to develop a more detailed understanding of the radiation response of SiC. Such studies are important to build mechanistic models of material performance and to understand the susceptibility of various microstructures to radiation damage for advanced energy applications.

Evolution of dislocation loops in He ion irradiated nickel under different temperature

The effect of temperature on the evolution of loops in nickel was investigated under 30 keV He+ irradiation. The size, Burgers vector, and nature of loops were analyzed by a transmission electron microscope (TEM). In addition, the Weibull statistical analysis was introduced to analyze the size distributions of the loops. The TEM results indicate that the sizes of loops increase with increasing irradiation temperature, where they are mainly in the range of 10–30, 20–50, and 30–80 nm at 300, 400, and 500 °C, respectively. In the irradiation temperature range of 300–500 °C, the size distributions of loops fit Weibull distribution very well, which suggests that the loops tend to grow larger and/or be merged. In addition, almost all the loops formed under He+ irradiation are the interstitial loops with Burgers vectors b = a2⟨110⟩, which is ascribed to the assistance of the He atom on the formation process of loops.

Characteristics of radiation porosity and structural phase state of reactor austenitic 07C–16Cr–19Ni–2Mo–2Mn–Ti–Si–V–P–B Steel after neutron irradiation at a temperature of 440–600°C to damaging doses of 36–94 dpa

The phase composition and the characteristics of vacancy voids in cold-worked steel 07C–16Cr–19Ni–2Mo–2Mn–Ti–Si–V–P–B (CW EK164-ID) after neutron irradiation at damaging doses of 36–94 dpa and temperatures of 440–600°C are investigated. In the entire range of damaging doses and temperatures, voids with different sizes are observed in the material. The maximum void size increases with irradiation temperature up to ~550°C, whereas their concentration decreases. At higher irradiation temperatures, almost no coarse voids are observed. The concentration of fine voids (to 10 nm in size) sharply increases with temperature from 440 to 480°C. Further increases in the temperature do not result in the noticeable concentration growth. In the irradiation temperature range of 440–515°C, second phases precipitate (G phase, γ’ phase, and complex fcc carbides). At higher irradiation temperatures, there are Laves-phase particles, fine second carbides of the MC type, and needle shape precipitates identified as phosphides in the material.

Microstructural stability and mechanical behavior of FeNiMnCr high entropy alloy under ion irradiation

In recent years, high entropy alloys (HEAs) have attracted significant attention due to their excellent mechanical properties and good corrosion resistance, making them potential candidates for high temperature fission and fusion structural applications. However there is very little known about their radiation resistance, particularly at elevated temperatures relevant for energy applications. In the present study, a single phase (face centered cubic) concentrated solid solution alloy of composition 27%Fe-28%Ni-27%Mn-18%Cr was irradiated with 3 or 5.8 MeV Ni ions at temperatures ranging from room temperature to 700 °C and midrange doses from 0.03 to 10 displacements per atom (dpa). Transmission electron microscopy (TEM), scanning transmission electron microscopy with energy dispersive x-ray spectrometry (STEM/EDS) and X-ray diffraction (XRD) were used to characterize the radiation defects and microstructural changes. Irradiation at higher temperatures showed evidence of relatively sluggish solute diffusion with limited solute depletion or enrichment at grain boundaries. The main microstructural feature at all temperatures was high-density small dislocation loops. Voids were not observed at any irradiation condition. Nano-indentation tests on specimens irradiated at room temperature showed a rapid increase in hardness ∼35% and ∼80% higher than the unirradiated value at 0.03 and 0.3 dpa midrange doses, respectively. The irradiation-induced hardening was less pronounced for 500 °C irradiations (<20% increase after 3 dpa). Overall, the examined HEA material exhibits superior radiation resistance compared to conventional single phase Fe-Cr-Ni austenitic alloys such as stainless steels. The present study provides insight on the fundamental irradiation behavior of a single phase HEA material over a broad range of irradiation temperatures.

The relation between circulation types and regional Alpine climate. Part II: the dependence of the predictive skill on the vertical level of the classification for Trentino

ABSTRACTThis study investigates the effect of varying the vertical level of a synoptic circulation classification on its predictive skill with respect to surface temperature, rainfall, solar radiation and wind in Trentino, a mountainous region in the South‐Eastern Alps. A synoptic climatology based on the same data set and classification method presented in part I of the present article, in fact, showed that seasonal anomalies of mean daily temperature, daily rainfall, daily solar irradiation and mean daily wind intensity vary not only among weather types and seasons but also within the same type and season for different vertical levels. This analysis quantifies the ability of the method to classify synoptic circulation in classes associated with distributions of atmospheric variables different from climatology and to identify the occurrence of extreme events. The statistical metrics presented in the article demonstrate that the differences in predictive skill between classifications applied to distinct levels are comparable in magnitude to those between different atmospheric variables and seasons for the same level. The level of 500 hPa generally provides the largest predictive skill with respect to total daily rainfall, daily solar irradiation and daily temperature range in all seasons. On the other hand, the largest skill with respect to wind intensity is found for sea level pressure and 850 hPa circulation types. Large seasonal variations are also evident, with the colder seasons providing the largest predictive skill. Combinations of circulation types derived at two vertical levels increase the skill, although an optimal combination of levels could not be found even for the same atmospheric variable and season.