Impact Of Neutron Irradiation Research Articles

Impact of neutron irradiation on the tensile properties of advanced EUROFER97-type steels

Tensile properties (strength and ductility) of three different experimental EUROFER97 variants and two standard EUROFER97 products were investigated before and after neutron irradiation performed in the temperature range 275–300 °C up to ∼3 dpa, i.e a damage dose comparable to the end-of-life of ITER operation. The grades with the chemical compositions within and outside the specifications of EUROFER97 steel followed alternative thermo-mechanical treatments (TMT) as compared to the reference EUROFER97. Mechanical properties were assessed with hardness and tensile tests, while fracture surface was investigated by scanning electron microscopy. Post irradiation examination was conducted to evaluate the hardening behavior, change in ductility and fracture surface after irradiation. Furthermore, Ductile-to-Brittle Transition Temperature (DBTT) shift due to neutron irradiation was estimated based on the correlation formerly established for EUROFER97 at the studied irradiation temperature.

Impact of neutron irradiation on SiC power MOSFETs after stress tests qualification

The failure of power devices produced by atmospheric neutrons, even at sea level, is a critical issue to assess the reliability of these devices in automotive applications. Usually, accelerated neutron tests are performed to estimate the failure in time (FIT) values of the power devices under different operating conditions, by using virgin device samples. In this work, neutron tests were performed on commercial SiC power MOSFETs which pass HTGB and HTRB qualification tests, commonly used in automotive qualification procedures to verify the gate-oxide and junction and termination integrity. The impact of these reliability qualification tests on the neutron FIT values was investigated.

Exceptional structural and functional stability of Zr-doped REBaCuO tapes with respect to neutron irradiation and overheating

The impact of neutron irradiation on the properties of second-generation REBaCuO tapes was studied. The main aim of the present study was to identify the fast neutrons irradiation fluence threshold, φ th, at which the high-field critical current at low temperatures, I c (10 K, 8 T), starts degrading. Following up on our previous publication for low irradiation fluences, two new irradiation steps were added. Up to the last but one irradiation step, the T c in all samples followed a linear dependence on the fast neutrons irradiation fluence, T c(φ) ≈ T c(0) − τφ (τ being a numerical constant in units of K/1022 m−2 and φ in 1022 m−2). In parallel, I c (10 K, 8 T) continuously grew with φ up to the threshold fluence, φ th ≈ 3× to 4.3 × 1022 m−2. The last gradual irradiation by φ≈ 1.83 × 1022 m−2 brought a severe degradation both in T c and I c (10 K, 8 T) in most samples, irrespective of their irradiation history. This effect was attributed to radiation overheating. Annealing of pristine tapes in dilute Ar confirmed this scenario. Two of the SuperPower tapes, doped by Zr, appeared to be exceptionally stable against both types of overheating. The tape doped with 7.5% Zr, T c(φ) followed the linear dependence up to the highest cumulative fluence φ =6.16 × 1022 m−2, while the I c (10 K, 8 T) drop was several orders of magnitude lower than in the samples without Zr. TEM study found that the Zr-doped tapes survived the overheating during the last irradiation step in a crystalline form, while all other samples were amorphized.

Impact of neutron irradiation on electronic carrier transport properties in Ga2O3 and comparison with proton irradiation effects

The minority charge carrier transport in beta gallium oxide (-Ga2O3) before and after exposure to neutrons from a 241Am-Be source was studied. Cathodoluminescence (CL) spectroscopy and current–voltage (I-V) characteristics were used to study minority carrier behavior. High energy radiation affects minority carrier properties through the production of carrier traps that reduce the conductivity and mobility of the material. In this paper, we report the effects of neutron radiation in silicon-doped -Ga2O3, using rectifiers or transistors as the measurement platform. The thermal activation energy of the reference (non-irradiated) sample was 40.9 meV, which is ascribed to silicon-donors. CL measurements indicate a slightly indirect bandgap energy of 4.9 eV. Neutrons create disordered regions in -Ga2O3 rather than just point defects, resulting in the lowest carrier removal rate because of the lowest average non-ionizing energy loss. The neutron irradiation caused an increase in reverse bias leakage current in rectifiers and a carrier removal rate of 480 cm−1 but had little effect on reverse recovery switching time. Differences in CL spectra were observed between vertical and lateral device structures, emphasizing the importance of impurities and defects in the starting material. The neutron energies in the Am-Be source range up to 11 MeV, with an average energy between 4 and 5 MeV (Figure 1). We also contrasted neutron damage with the effects of irradiation with 10 MeV protons. Under 10 MeV proton irradiation, the thermal activation energies increase. This is attributable to high order defects and their influence on carrier lifetimes. The measurements show that -Ga2O3 is more resistant to radiation damage than other wide bandgap semiconductors due to its higher displacement threshold energy, which is inversely proportional to the lattice constant.

Multi-scale fracture probability analysis of tungsten monoblocks under fusion conditions

Plasma facing components inside future nuclear fusion reactors are subjected to a high heat load and intense irradiation conditions. Using advanced computational material models, several problems can be solved that reflect tungsten monoblocks under fusion relevant loading scenarios. This allows for the identification of the conditions under which material failure is probable. The material model and parameters are identified such that the mechanical behaviour is in accordance with the homogenized behaviour of a previously developed crystal plasticity model on the microscopic scale. The heterogeneous stress field that follows is analysed in order to assess the probability of material failure, which is typically reflected by unstable crack propagation. Since fracture is an inherently multi-scale problem, critical regions are analysed in detail by means of a representative volume element. The resulting analysis reveals that in case the stress relaxation in the monoblock under the applied static heat load is complete, the probability of unstable crack propagation can reach values close to 35%. Finally, the impact of prolonged neutron irradiation is simulated by means of a cluster dynamics model. Although irradiation drastically increases the brittleness of tungsten, its impact on the overall monoblock performance remains limited. • The performance of tungsten monoblocks under fusion conditions is investigated. • Failure is predicted by application of the weakest-link theory on two length scales. • Stress relaxation increases the risk of failure upon shut down of the heat source. • The impact of neutron irradiation on the failure probability is shown to be limited.

Investigation of the Impact of Neutron Irradiation on SiC Power MOSFETs Lifetime by Reliability Tests

High temperature reverse-bias (HTRB), High temperature gate-bias (HTGB) tests and electrical DC characterization were performed on planar-SiC power MOSFETs which survived to accelerated neutron irradiation tests carried out at ChipIr-ISIS (Didcot, UK) facility, with terrestrial neutrons. The neutron test campaigns on the SiC power MOSFETs (manufactered by ST) were conducted on the same wafer lot devices by STMicroelectronics and Airbus, with different neutron tester systems. HTGB and HTRB tests, which characterise gate-oxide integrity and junction robustness, show no difference between the non irradiated devices and those which survived to the neutron irradiation tests, with neutron fluence up to 10 (n/cm). Electrical characterization performed pre and post-irradiation on different part number of power devices (Si, SiC MOSFETs and IGBTs) which survived to neutron irradiation tests does not show alteration of the data-sheet electrical parameters due to neutron interaction with the device.

The impact of neutron irradiation, graphite oxidation and fluorination on tritium uptake into and desorption from graphite in molten salt environments

Tritium management is necessary in both fission and fusion nuclear reactors. In fusion reactors, tritium is a fuel that needs to be produced in breeding blankets. For fission reactors, and especially Fluoride Salt-Cooled High-Temperature Reactors (FHRs) and Molten Salt Reactors (MSRs), tritium is a contaminant to be separated and removed. The current literature on high-temperature hydrogen-graphite interactions is generated predominantly by the fusion research community and does not yet cover the low-pressure interval of relevance for FHRs and MSRs. Predictions of graphite uptake capacities and uptake rates at FHR conditions of few Pa partial pressure can only be performed using extrapolations. In order to make reliable extrapolations from the available data, the impact of phenomena that take place during operation and accident scenarios, such as neutron irradiation, air oxidation and reactions with molten fluoride salts must be accounted for. This article provides a summary of hydrogen-graphite thermodynamics and kinetics of interaction and discusses the effects of irradiation, air oxidation and fluorination on uptake capacities, uptake and desorption kinetics. We find that all three phenomena increase uptake capacities in graphite. Neutron irradiation and reactions with fluoride salts are expected to reduce tritium uptake rate, while oxidation is expected to increase it. In all three cases, the changes are more pronounced at low tritium partial pressures.

Impact of neutron irradiation on hardening of baseline and advanced tungsten grades and its link to initial microstructure

Six tungsten grades were irradiated in the Belgian material test reactor (BR2) and characterized by Vickers hardness tests in order to investigate the irradiation-induced hardening. These tungsten grades included: Plansee (Austria) ITER specification tungsten, ALMT (Japan) ITER specification tungsten, two products from KIT (Germany) produced by powder injection molding (PIM) and strengthened by 1% TiC and 2% Y2O3 dispersed particles, and rolled tungsten strengthened by 0.5% ZrC from ISSP (China). The materials were irradiated face-to-face at three temperatures equal to 600 °C, 1000 °C, and 1200 °C to the dose of ∼1 dpa. The Vickers hardness tests under 200 gf (HV0.2) were performed at room temperature. The Vickers hardness increases as the irradiation temperature increases from 600 to 1000 °C for all materials, except for the ZrC-reinforced tungsten, for which the increase of hardness does not depend on irradiation temperature. The irradiation-induced hardness decreases after irradiation at 1200 °C. This is a result of defect annealing enhanced by thermally activated diffusion. However, even at 1200 °C, the impact of neutron irradiation on the hardness increase remains significant; the hardness increases by ∼30 to 60% compared to the non-irradiated value. In the case of TiC-strengthened material, the irradiation hardening progressively raises with irradiation temperature, which cannot be explained by the accumulation of neutron irradiation defects solely.

Impact of neutron irradiation on the thermophysical properties of additively manufactured stainless steel and inconel

This paper presents the initial results of a multi-year irradiation project to evaluate the impact of manufacturing method and neutron irradiation (at doses up to 1.63 displacements per atom) on the heat capacity and thermal diffusivity of Additively Manufactured (AM) stainless steel 316 L, Inconel 718, and Inconel 625 samples at temperatures between 50 °C and 400 °C. When complete, the project will have tested 48 irradiated Laser Flash Analysis (LFA) and 48 irradiated Differential Scanning Calorimetry (DSC) specimens. At the current time, the project has tested 10 irradiated DSC and 11 irradiated LFA specimens. The unirradiated AM specimens have heat capacity values similar to, or lower than, the reference values, regardless of manufacturing method or material. The irradiated AM specimens have average heat capacities greater than the unirradiated specimens and reference values in every case. The thermal diffusivities of the unirradiated AM specimens are either larger or statistically similar to the reference values obtained from materials manufactured in conventional methods. The irradiated AM specimens exhibit lower thermal diffusivities compared to the reference unirradiated thermal diffusivity values. One of the stainless steel 316 L laser powder bed fusion samples exhibited thermal diffusivity values with statistically significant anisotropy prior to and after irradiation.

Impact of neutron irradiation on the strength and ductility of pure and ZrC reinforced tungsten grades

The strength and ductility of two tungsten products, developed for application in nuclear fusion environment, are studied before and after neutron irradiation using uniaxial tensile tests. The first product is a commercially pure tungsten, produced by AT&M company according to ITER specification, and the second one is reinforced with zirconium carbide (W–ZrC) particles. The addition of ZrC particles leads to a reduction of the ductile to brittle transition temperature (DBTT) in non-irradiated conditions down to 50–100 °C without loss of strength and of other attractive properties of tungsten.The neutron irradiation was performed in the range 625–700 °C up to 1.125 dpa. The tests were performed to screen the shift of the DBTT as well as to characterize the evolution of the strength and ductility at the irradiation temperature. In addition, a series of interrupted tensile tests were performed in order to determine the variation of the yield strength as a function of temperature using an original single specimen test method.The neutron irradiation causes the reduction of the total elongation of both tungsten products. The DBTT range, which was evaluated from the tensile test results, of W–ZrC lies in the 300–500 °C range (while it is ∼100 °C in non-irradiated state). The DBTT range of pure tungsten is between 400 and 575 °C i.e. higher than that of W–ZrC. The irradiation hardening, measured at ∼600 °C, which is close to the irradiation temperature, leads to an increase of the proof stress by a factor of two in both studied grades. Despite that the irradiation induced hardening, both products retain a total elongation of about 10% prior to fracture. W–ZrC exhibits a similar total elongation at 500 °C, thus maintaining a significant ductility resource, while pure W becomes brittle at 500 °C and below.

Influence of ions irradiation on the microstructural evolution, mechanical and tribological properties of Zr-4 alloy

The wear of fuel cladding due to flow induced vibration in nuclear reactor presents a safety concern, and the impact of neutron irradiation on wear behavior is not fully understood. In this study, Kr+ and Zr+ ions bombardment were used to simulate the neutron irradiation on Zr-4 alloys, and the impacts of ion irradiation on the microstructure evolution, mechanical and tribological behaviors of Zr-4 alloy were investigated. The HRTEM observation reveals that high density of point defects, dislocations as well as small dislocation loops formed below the surface within 260 nm depth after Zr+ irradiated with the damage level up to 30 dpa. The nano-indentation tests suggests that the hardness of Zr-4 alloy increases with increasing of irradiation dose, resulting from the inhibition of slip of dislocation under the large amount of defects induced by irradiation. The fretting wear tests show that the friction coefficient of Zr-4 alloy increases significantly from 0.4 to above 1, due to the irradiation hardening and embrittlement, the repeated sliding during fretting wear leads to intergranular fracture at surface and the growth of cracks under load contact area, leaving deeper furrows and higher hardness debris, which results in higher friction coefficient and severe wear of Zr-4 alloy after irradiation.

Impact of neutron irradiation on mechanical performance of FeCrAl alloy laser-beam weldments

Oxidation-resistant iron-chromium-aluminum (FeCrAl) alloys demonstrate better performance in Loss-of-Coolant Accidents, compared with austenitic- and zirconium-based alloys. However, further deployment of FeCrAl-based materials requires detailed characterization of their performance under irradiation; moreover, since welding is one of the key operations in fabrication of light water reactor fuel cladding, FeCrAl alloy weldment performance and properties also should be determined prior to and after irradiation. Here, advanced C35M alloy (Fe-13%Cr-5%Al) and variants with aluminum (+2%) or titanium carbide (+1%) additions were characterized after neutron irradiation in Oak Ridge National Laboratory's High Flux Isotope Reactor at 1.8–1.9 dpa in a temperature range of 195–559 °C. Specimen sets included as-received (AR) materials and specimens after controlled laser-beam welding. Tensile tests with digital image correlation (DIC), scanning electron microscopy-electron back scatter diffraction analysis, fractography, and x-ray tomography analysis were performed. DIC allowed for investigating local yield stress in the weldments, deformation hardening behavior, and plastic anisotropy. Both AR and welded material revealed a high degree of radiation-induced hardening for low-temperature irradiation; however, irradiation at high-temperatures (i.e., 559 °C) had little overall effect on the mechanical performance.

Improved a-B10C2+xHy/Si p-n heterojunction performance after neutron irradiation

The impact of neutron irradiation, in the energy range of ∼0.025 eV, on amorphous semiconducting partially dehydrogenated boron carbide (a-B10C2+xHy) on silicon p-n heterojunction diodes was investigated. The heterojunction devices were created by synthesizing a-B10C2+xHy via plasma enhanced chemical vapor deposition on n-type silicon. Unlike many electronic devices, the performance of the a-B10C2+xHy heterojunction diode improved with neutron irradiation, in spite of the large neutron cross section of 10B. There is also increased charge carrier lifetime of more than 200% with modest neutron irradiation of approximately 2.7 × 108 to 1.08 × 109 neutrons/cm2.

Impact of neutron irradiation on the structural and optical properties of PVP/gelatin blends doped with dysprosium (III) chloride

Polymer composites of a system of Polyvinylpyrrolidone (PVP)/gelatin/DyCl3·6H2O were prepared in three groups that have different concentrations of PVP/gelatin contents to study the effect of neutron irradiation on their structural and optical properties. Results showed that the interaction of neutrons led to various complex phenomena, mainly bond breaking, main chain scission and intermolecular cross-linking. These processes introduced defects inside the material that were responsible for the changes in their optical and structural properties. All the calculated parameters were found to be dependent on the irradiation fluence in a uniform manner that makes these materials excellent candidates in the applications of dosimetry and radiology. Moreover, the sensitivity of the three groups of composites to the irradiation doses was found to be different. The variation in the structure of the composite group that contains the least PVP content was found to be less significant; hence, these materials were more stable against high doses that make them suitable for high radiation dose applications.

Vibratory Processes in Vessel Steel Damage Kinetics in Nuclear Reactors

The possible reasons for nonstandard embrittlement and significant variance of the experimental data in the study of the impact of neutron irradiation on the properties of reactor vessel materials are analyzed. The authors assume on the basis of experimental data and analysis of foreign research that the fluence dependence of the degree of radiation embrittlement can be of nonmonotonic as well as cyclic. The observation of vibratory processes in the embrittlement kinetics of vessel steel attests periodic transformation of structure and change in the properties of the metal. It is expected that the defect structure formed as a result of neutron bombardment undergoes transformation once or periodically in the direction of losses as well as restoration of the initial properties. The mentioned data shape the search for methods of regulating the radiation resistance of materials.

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.

Impact of neutron irradiation on the RF properties of oxidized high-resistivity silicon substrates with and without a trap-rich passivation layer

This work investigates the influence of high-energy neutrons on oxidized high-resistivity silicon substrates (HR-Si). Two oxide thicknesses as well as the presence of a trap-rich passivation layer are considered. The impact of neutron irradiation is directly related to the competition between the generation of interface traps added to the mobility and carrier lifetime degradation, which are beneficial to reduce parasitic surface conduction (PCS) into the Si substrate similarly to the passivation layer, and accumulation of radiation-induced positive charges in oxide, which would unfortunately increase PSC. It is shown that under neutron irradiation, RF losses are strongly reduced in the case of thin oxide ( t ox = 50 nm), while substrates with a polysilicon passivation layer are almost insensitive to the neutron irradiation.

Mechanical properties–microstructure correlation in neutron irradiated heat-affected zones of austenitic stainless steels

The effects of neutron irradiation on austenitic stainless steels, usually used for the manufacturing of internal elements of nuclear reactors (e.g. the core shrouds), are the alteration of the microstructure, and, as a consequence, of the mechanical properties. The present study is aimed at extending knowledge upon the impact of neutron-irradiation on the heat-affected zone of welded materials, which was influenced by the thermal cycles upon fusion welding. An austenitic stainless steel weld type AISI 304 from a decommissioned experimental pressurised water reactor has been used in the present study. The welded material has been irradiated during 11 reactor cycles to a maximum dpa dose of 0.35 and a temperature of around 573K. The mechanical properties and microstructure are determined on specimens from heat-affected zone and base materials, with different dose levels. The mechanical properties were determined by performing tensile tests on small flat specimens at two deformation temperatures: room temperature and about 573K. The characterisation of the microstructure was made by transmission electron microscopy. The correlation between mechanical properties and microstructure after neutron irradiation is made using the dispersed obstacle hardening model. It was found that the measured radiation hardening cannot be explained solely by the presence of the irradiation-induced defects observed in TEM. Smaller irradiation-induced features not resolvable in TEM may also contribute to radiation hardening.

Impact of neutron irradiation on optical performance of InGaAsP laser diodes

Results are presented of an extended study on the degradation and recovery behavior of optical and electrical performance and on induced lattice defects of 1.3 μm InGaAsP double channel planar buried heterostructure laser diodes with an In0.76Ga0.24As0.55P0.45 multi-quantum well active region, subjected to a 1 MeV fast neutron and 1 MeV electron irradiation. The degradation of the device performance increases with increasing fluence. Two hole capture traps with near midgap energy level in the In0.76Ga0.24As0.55P0.45 multi-quantum well active region are observed after a 1×1016 n/cm2 irradiation. These deep levels are thought to be associated with a Ga vacancy. The decrease of optical power is related to the induced lattice defects, leading to a reduction of the non-radiative recombination lifetime and of the carrier mobility due to scattering. The difference in radiation damage between 1 MeV fast neutrons and 1 MeV electrons is discussed taking into account the non-ionizing energy loss (NIEL). The radiation source dependence of performance degradation is attributed to the difference of mass and the probability of nuclear collision for the formation of lattice defects. The decreased optical power recovers by thermal annealing, and the recovery increases with increasing annealing temperature. The optical power recovers by 45% for 1 MeV neutron irradiation with a fluence of 1×1015 n/cm2 after a 300°C annealing.

Mechanical properties and microstructure of neutron irradiated cold worked Al-6063 alloy

The impact of neutron irradiation on the mechanical properties and fracture morphology of cold worked Al-6063 were studied, using scanning and transmission electron microscopy, and tensile measurements. Specimens (50 mm long and 6 mm wide gauge sections) were punched out from an Al-6063 23% cold worked tubes, which had been exposed to prolonged neutron irradiation of up to 4.5 × 10 25 thermal neutrons/m 2 ( E < 0.625 eV). The temperature ranged between 41 and 52°C. The tensile specimens were then tensioned till fracture in an Instron tensiometer with strain rate of 2 × 10 −3 s −1. The uniform elongation and the ultimate tensile strength increase as functions of fluence. Metallographic examination and fractography reveal a decrease in the local area reduction of the final fracture necking. This reduction is accompanied with a morphology transition from ductile transgranular shear rupture to a combination of transgranular shear with intergranular dimpled rupture. The intergranular rupture area increases with fluence. No voids could be observed up to the maximum fluence. The dislocation density of cold worked Al decreases with the thermal neutron fluence. Prolonged annealing of unirradiated cold worked Al-6063 at 52°C revealed similar results. It thus appears that under our irradiation conditions the temperature during irradiation is the major factor influencing the mechanical properties and the microstructure during irradiation.