Effect Of Neutron Irradiation Research Articles

Effects of neutron irradiation and post-irradiation annealing on pop-in crack propagation instabilities in 6061 aluminium alloy

This study analyses the increase of crack propagations instabilities (pop-in) with irradiation during fracture toughness testing of aluminium alloy 6061 alloy after neutron irradiation. The aim is to identify if the crack propagation instabilities are related to microstructural heterogeneities, i.e. weak zones, or if they are linked to a competition between testing machine stiffness and tearing modulus.An in-depth mechanical instability analysis was performed comparing the testing machine stiffness to the tearing moduli of the irradiated materials. For this purpose an experimental program was carried out in the hot cells facility at CEA Saclay to conduct mechanical and microstructural studies, after irradiation in a Material Testing Reactor (mean conventional thermal fluence: 6.8 × 1021 nth.conv.cm−2).The material hardening was quantified in this study using tensile tests after annealing heat treatments. The effect of this hardening on crack propagation instabilities was measured by fracture toughness tests on irradiated and precracked CT12.5 samples. Damage mechanisms were studied by scanning electron microscope fractography and classical ductile fracture micromechanisms were found for all conditions without notable differences between non irradiated and irradiated materials. The evolution of toughness with irradiation and subsequent heat treatments was therefore attributed to the matrix hardening/softening and its effect on nucleation of voids on brittle second phase particles.To investigate experimentally if the crack propagation instabilities were related to the tearing moduli, annealing heat treatments of the irradiated material were applied that softened the material. It was shown that with softening, the number of crack propagation instabilities decreased and eventually the pop-ins disappeared. The instability criteria using J-Δa R-curves of the toughness tests were applied and it was concluded that the increase in pop-ins with irradiation resulted from the decrease of the material tearing modulus and its interaction with the machine stiffness.The toughness test results of the irradiated material of the present study were compared with those of the literature and show very good agreement.

Radiation hardness of Hamamatsu H12700/H8500 MAPMTs, entrance glass windows, and p-terphenyl wavelength shifting coating under neutron and [formula omitted]Co gamma irradiation

Photomultiplier tubes, in particular multianode photomultiplier tubes, are often used in current accelerator-based nuclear and particle physics experiments for spatially resolved detection of single photons. With increasing luminosity and harsh radiation background, the radiation hardness of these sensors plays an increasingly important role. In an extensive experimental study we have investigated the effects of neutron irradiation, using a fission neutron source, and energetic 60Co γ-irradiation on commercially available Hamamatsu H12700/H8500 MAPMTs. In addition, individual components were irradiated, such as their glass windows and voltage dividers. Additionally, a p-terphenyl based wavelength shifting coating, which can be applied on the MAPMT window to enhance the photon yield, was also tested for its radiation tolerance.

Assessment of Radiation Effects on Attitude Estimation Processing for Autonomous Things

This article investigates and assesses neutron radiation effects on attitude estimation (AE) processing, typically embedded in inertial navigation systems (INSs) and upcoming autonomous things. Findings highlight the importance of radiation-induced critical failures that can upset the on-board AE processing and consequently the inertial navigation. Radiation tests and analyses were conducted by considering as on-board AE processing the execution of classical AE algorithm on multi-core computer hardware exposed to 14-MeV neutron and thermal neutron radiation. Three computing strategies and different case-study scenarios were tested and compared. Results suggest that the contribution of radiation-induced soft errors to be mitigated on the embedded AE processing is essentially related to single-event functional interrupts (SEFIs) that can lead the inertial navigation to critical failures.

Development of irradiation tolerant tungsten alloys for high temperature nuclear applications

Development of refractory metals for application as plasma-facing armour material remains among priorities of fusion research programmes in Europe, China and Japan. Improving the resistance to high temperature recrystallization, enhancing material strength to sustain thermal fatigue cracking and tolerance to neutron irradiation are the key indicators used for the down selection of materials and manufacturing processes to be applied to deliver engineering materials. In this work we investigate the effect of neutron irradiation on mechanical properties and microstructure of several tungsten grades recently developed. Neutron irradiation campaign is arranged for screening purposes and therefore is limited to the fluence relevant for the ITER plasma facing components. At the same time, the neutron exposure covers a large span of irradiation temperatures from 600 up to 1000 °C. Four different grades are included in the study, namely: fine-grain tungsten strengthened by W-carbide (W–4wt.% W2C), fine-grain tungsten strengthened by Zr carbides (W–0.5% ZrC), W alloyed with 10 at.% chromium and 0.5 at.% yttrium (W–10Cr–0.5Y) and technologically pure W plate manufactured according to the ITER specification by Plansee (Austria). The strengthening by W2C and ZrC particles leads to an enhanced strength, moreover, the W–0.5ZrC material exhibits reduced DBTT (compared to ITER specification grade) and is available in the form of thick plate (i.e. high up-scaling potential). The W–10Cr–0.5Y grade is included as the material offering the self-passivation protection against the high temperature oxidation.

BURNUP AND RADIATION EMBRITTLEMENT OF THE U-MO NEUTRON SOURCE TARGET

The burnup of uranium target plates of the NSC KIPT neutron source was studied. An analysis of experimental work on the effect of neutron irradiation on the strength and plastic properties of uranium and U-Mo alloys under conditions close to the operation of the target has been carried out. A description of the processes of radiation embrittlement is presented, taking into account the deformation and porosity of materials at various levels of burnup. An estimate of the expected service life of a uranium target under irradiation has been carried out.

Synergistic Effect of Electrical Stress and Neutron Irradiation on Silicon Carbide Power MOSFETs

The synergistic effect of radiation and bias voltage for the commercial silicon carbide (SiC) power MOSFETs was investigated by 14-MeV neutron irradiation in this article. The types of C3M0065090D and C2M0080120D commercial SiC power MOSFETs from CREE studied in this article show consistent changes after the 14-MeV neutron irradiation. The results show that the devices biased during irradiation experienced more degradation than that only irradiated and biased devices. Compared with the devices only irradiated and biased, the devices biased during irradiation experienced an additional decrease in saturation current and a further decrease in peak transconductance. The defects in the devices were characterized by the low-frequency noise (LFN) and deep-level transient spectrum (DLTS) methods. The results show that the synergistic effect increased the defect concentration of the device, resulting in further degradation of the electrical performance of the device compared to the control group without a bias voltage. The defect characterization shows that the drain–source voltage leads to the accumulation of carbon and silicon vacancies induced by irradiation at the interface, which results in intensified radiation damage and significant changes in the performance of the device at low neutron fluence.

DONES Systems identification and requirements allocation

• Systems identification of IFMIF-DONES for work distribution and responsbility allocation. • System-of-Systems to Group-of-Systems type mapping. • Alignment of Systems identification and requirement allocation. The mission of the DONES program is to develop a database of fusion-like neutron irradiation effects in the materials required for the construction of the Demonstration Fusion Power Reactor (DEMO) for benchmarking of radiation response of materials. In order to do this, the DONES facility will be built to provide a neutron source producing high-energy neutrons at sufficient intensity and irradiation volume. DONES will generate a neutron flux with a broad energy distribution covering the typical neutron spectrum of a (d-t) fusion reactor. This is achieved by utilizing Li(d,xn) nuclear reactions taking place in a liquid Li target when bombarded by a deuteron beam. The energy of the deuterons (40 MeV) and the current of the accelerator (125 mA) have been tuned to maximize the neutron flux to get irradiation conditions comparable to those in the first wall of a fusion power reactor. For the success of this mission, the needs of all the stakeholders shall be very clearly stated, considering the whole lifecycle of the facility. Once the needs are clear, they shall be translated into specific requirements, following a top-down approach, to be allocated to the different systems or groups-of-systems (GoS). To do this, it is essential to properly identify which parts shall be treated as a System or GoS, as they shall be designed accordingly, and the requirements allocated in consequence.

Qualitative and quantitative analysis of neutron irradiation effects in SiC/SiC composites using X-ray computed tomography

Silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composites are candidate materials for cladding of light water reactor (LWR) fuels. Loss of fission product gas retention due to the formation of microcrack networks is considered a potential failure mechanism for SiC/SiC-cladded fuels. In this study, a variety of SiC/SiC composite tubes were irradiated with and without an LWR-relevant radial heat flux in the High Flux Isotope Reactor, followed by detailed characterization with X-ray computed tomography (XCT). This first set of XCT data for neutron-irradiated samples confirmed that the internal stresses arising from a combination of temperature gradients and irradiation-induced swelling act as the primary driver for cracking. While the observed cracking patterns varied depending on the tube architectures, the sharp edges of relatively large pores were found to be the common stress concentrator. These findings are useful to help improve the design and manufacturing of SiC/SiC fuel claddings for reduced failure probability.

Effect of Neutron Irradiation on the Critical Event Size of Cleavage Fracture of the Chinese A508-3 Steel

In order to analyze the influence of neutron irradiation on the critical event of cleavage fracture for the Chinese A508-3 (RPV) steel, the fracture morphology, microstructure and grain size of the irradiated specimens are observed and analyzed by optical microscope (OM) and scanning electron microscope (SEM). The results show that with the increase of neutron doses, the fracture mode of Chinese RPV steel material changes gradually from ductile fracture to ductile-brittle mixed fracture transformation. The brittle part for fracture mode of ductile-brittle fracture is cleavage fracture, and the non-metallic inclusions, microstructure and grain size grades are not significantly different from those of the specimens without cleavage fracture. In the same material, with increasing of neutron doses, the critical event size of the cleavage fracture will be reduced, and the percentage of the grain that satisfies the grain size of the cleavage critical event will increase correspondingly, resulting in an increase of the probability of cleavage fracture of the material. The fine grain with uniform distribution can improve partly the fracture toughness of the material and withstand higher neutron doses under the same conditions.

Fast neutron irradiation effects on Si- and GaN-based avalanche photodiodes

We report the behaviour of the dark current and gain characteristics of Si- and GaN-based avalanche photodiodes (APDs) irradiated by fast neutrons. For Si-based APDs, the dark current increases with the increase of neutron fluence, indicating that the avalanche property has been seriously affected. The gain values of Si-based APD slightly increase after irradiation by a low neutron fluence of 1.0 × 1012 cm−2, while the device exhibits gain degradation as the fluence increases to 1.0 × 1013 cm−2 or even above at high reverse bias voltage, unlike the previous studies where only degradation was observed. The steep increase of dark current and gain when approaching the breakdown voltage after neutron irradiation indicate that the avalanche property is almost unaffected for GaN-based APDs. Furthermore, we infer that the optical absorption between acceptor state and conduction band in the p-type layer plays an important role in influencing the change of dark current and gain at high reverse bias voltage. The findings not only enrich the understanding of neutron irradiation effect on Si- and GaN-based APDs, but also experimentally prove that GaN-based APDs hold better radiation resistance than Si-based devices.

Analysis of Dimensional Change in Zr-2.5%Nb CANDU Pressure Tube Material aged at 300-400°C using Neutron Diffraction

The primary boundary of the CANDU reactor consists of Zr-2.5%Nb alloy pressure tubes and SA106 alloy feeder pipes. The pressure tubes are exposed to fast neutron (E>1Mev) irradiation during reactor operation, and experience dimensional changes. The actual dimensional change in the pressure tube during in-service operation is greater than the design estimate. It is not fully understood what is responsible for the dimensional changes in the pressure tubes. In this study, to accelerate the aging effect on the pressure tube material, aging was performed at 300-400°C for up to 20,000 hours and neutron diffraction was used to track variation in lattice spacing, thereby identifying the reason for the dimensional change. The analysis result showed that α-Zr, the main phase of Zr-2.5%Nb, had little dimensional change at 350°C or lower. On the other hand, the aging treatment at 400°C resulted in anisotropic expansion in the α-Zr of the HCP crystal, of 0.02% and 0.08% in the (1010) and (0002) directions, respectively. It was confirmed that above 350oC the β-phase in the Zr-2.5%Nb alloy was decomposed to precipitate β-Nb . The driving force of the lattice expansion may be due to the diffusing out tendency of the super saturated Nb in α-Zr and due to the residual cold working effect applied during the manufacturing process. The enhancing effects of fast neutron irradiation on lattice diffusion are discussed in detail.

Neutron irradiation effect on critical current and critical temperature of Nb3Sn wire

The ITER project is ongoing in France, and it is expected that a lot of high energy neutrons will be generated, and some neutrons will reach to superconducting magnets. To keep the safe and stable operation of the superconducting magnets, the neutron irradiation data must be piled up and the mechanisms of the irradiation effect must be investigated. A 15.5 T superconducting magnet and a variable temperature insert were installed in a radiation control area at Oarai centre in Tohoku University, and the superconducting properties of the irradiated Nb3Sn wires have been evaluated. The critical current was improved once and drastically dropped after irradiation of 1023 n/m2, and the critical temperature degraded monotonically, and the critical magnetic field decreased around 17 T after the irradiation of 1023 n/m2. The mechanism of the irradiation effect was discussed based on a flux pinning concept.

A Multi-Scale Simulation Study of Irradiation Swelling of Silicon Carbide.

Silicon carbide (SiC) is a promising structural and cladding material for accident tolerant fuel cladding of nuclear reactor due to its excellent properties. However, when exposed to severe environments (e.g., during neutron irradiation), lattice defects are created in amounts significantly greater than normal concentrations. Then, a series of radiation damage behaviors (e.g., radiation swelling) appear. Accurate understanding of radiation damage of nuclear materials is the key to the design of new fuel cladding materials. Multi-scale computational simulations are often required to understand the physical mechanism of radiation damage. In this work, the effect of neutron irradiation on the volume swelling of cubic-SiC film with 0.3 mm was studied by using the combination of molecular dynamics (MD) and rate theory (RT). It was found that for C-vacancy (CV), C-interstitial (CI), Si-vacancy (SiV), Si-interstitial (SiI), and Si-antisite (SiC), the volume of supercell increases linearly with the increase of concentration of these defects, while the volume of supercell decreases linearly with the increase of defect concentration for C-antisite (CSi). Furthermore, according to the neutron spectrum of a certain reactor, one RT model was constructed to simulate the evolution of point defect under neutron irradiation. Then, the relationship between the volume swelling and the dose of neutrons can be obtained through the results of MD and RT. It was found that swelling typically increases logarithmically with radiation dose and saturates at relatively low doses, and that the critical dose for abrupt transition of volume is consistent with the available experimental data, which indicates that the rate theory model can effectively describe the radiation damage evolution process of SiC. This work not only presents a systematic study on the relationship between various point defect and excess volume, but also gives a good example of multi-scale modelling through coupling the results of binary collision, MD and RT methods, etc., regardless of the multi-scale modelling only focus on the evolution of primary point defects.

Effect of neutron irradiation on the structure and strength of the SAV-1 aluminum alloy

The aluminum alloy SAV-1 was studied before and after inducing the radiation damage by means of neutrons with the following values of doses: 1016 - 1018 n/сm2. The measurements were carried out by neutron diffraction methods to analyze the correlation of the structural state with the results of measurements of the strength of the sample obtained using a loading machine. It was found that the changes in the strength characteristics of aluminum alloys were associated with modifications at the grain boundary during irradiation of the samples. Thus, the obtained experimental data allows us to conclude that the SAV-1 alloy represents an interstitial solid solution, and the strength of the alloy changes nonlinearly depending on the radiation dose.

Irradiation hardening of advanced tungsten grades: An experimental and inverse finite element method study

The effect of neutron irradiation on mechanical properties of various advanced W grades (pure, doped by K, alloyed by Re) was assessed by means of mechanical testing using miniaturized tensile and sub-miniaturized three-point bending (3PB) specimens. Different irradiation conditions in terms of temperature (400, 600, 800 and 1100 °C) and irradiation dose (0.2–0.25 dpa, 1.0–1.1 dpa) were considered. In order to extract the yield stress from the flexural load-displacement data, the empirical correlation between the flexural stress at a specific reference point on the flexural stress-strain curve and uniaxial tensile yield stress was established. The empirical ratio identified can be applied for the 3PB testing in a wide range of temperatures and plastic properties of un-irradiated and irradiated W alloys. The accuracy of the yield stress determination deduced using the empirical correlation from the 3PB tests was compared with the inverse FEM modelling procedure applied to the 3PB tests carried along with reference data extracted from the dedicated tensile tests. The information on the tensile yield stress and work hardening rate of all studied materials at different irradiation conditions was summarized and discussed in the view of the irradiation hardening.

Neutron irradiation effects on gallium nitride-based blue LEDs

Gallium nitride (GaN) is a promising material for radiation-hardened electronics in outer space environment. This work focuses on radiation hardness evaluation of GaN device using commercial GaN quantum-well light-emitting diodes (LEDs). Both the electrical and optical properties of GaN LEDs were characterized before and after neutron irradiation. The light emission intensity was found to increase significantly after 1014n/cm2 of neutron irradiation in the Ohio State University Research Reactor (OSURR) at room temperature. The extracted values from the I-V curve after irradiation also demonstrate such optical improvements of the GaN LED after 1014n/cm2 of neutron irradiation.

Study of neutron irradiation effects in Depleted CMOS detector structures

In this paper the results of Edge-TCT and I-V measurements with passive test structures made in LFoundry 150 nm HV-CMOS process on p-type substrates with different initial resistivities ranging from 0.5 to 3 kΩcm are presented. Samples were irradiated with reactor neutrons up to a fluence of 2·1015 neq/cm2. The depletion depth was measured with Edge-TCT. The effective space charge concentration Neff was estimated from the dependence of the depletion depth on bias voltage and studied as a function of neutron fluence. The dependence of Neff on fluence changes with initial acceptor concentration in agreement with other measurements with p-type silicon. A long term accelerated annealing study of Neff and detector current up to 1280 minutes at 60°C was made. It was found that Neff and current in reverse biased detector behave as expected for irradiated silicon.

Effect of Neutron Flux on an Irradiation-Induced Microstructure and Hardening of Reactor Pressure Vessel Steels

The existing knowledge about the effect of neutron irradiation on the mechanical properties of reactor pressure vessel steels under reactor service conditions relies to a large extent on accelerated irradiations realized by exposing steel samples to a higher neutron flux. A deep understanding of flux effects is, therefore, vital for gaining service-relevant insight into the mechanical property degradation. The existing studies on flux effects often suffer from incomplete descriptions of the irradiation-induced microstructure. Our study aims to give a detailed picture of irradiation-induced nanofeatures by applying complementary methods using atom probe tomography, positron annihilation, small-angle neutron scattering and transmission electron microscopy. The characteristics of the irradiation-induced nanofeatures and the dominant factors responsible for the observed increase of Vickers hardness are identified. Microstructural changes due to high flux conditions are smaller nm-sized solute atom clusters with almost the same volume fraction and a higher concentration of vacancies and sub-nm vacancy clusters compared to low flux conditions. The results rationalize why pronounced flux effects on the nanofeatures, in particular on solute atom clusters, only give rise to small or moderate flux effects on hardening.

Effect of neutron irradiation on ductility of tungsten foils developed for tungsten-copper laminates

Severe plastic deformation of tungsten (W) is known to be an efficient way to reduce its inherently high ductile-to-brittle transition temperature (DBTT), what is essential for its use in components of a fusion reactor. Thin rolled W foils possess superior mechanical behaviour at room temperature (RT), as demonstrated in previous works. It was then proposed to expand the beneficial mechanical properties of the foil to bulk by fabricating tungsten-copper (W-Cu) laminate composites, which can be used for structural applications. Neutron irradiation in HFIR resulted in embrittlement of the laminate already after 0.016dpa, with the W foil determining the composite behaviour.In this work, for the first time, we investigate the effect of neutron irradiation on individual W foil, and determine the resulting DBTT shift with the help of cantilever bend tests, using bulk W and the W-Cu composite as reference. The W foil and the bulk samples were irradiated to 0.15dpa at 400 °C in the BR-2 reactor in Mol (Belgium). We also hypothesise that diffusion of Cu atoms into W could modify the response to irradiation in these materials. We substantiate it with complementary density functional theory (DFT) ab initio calculations to analyse the Cu-vacancy and Cu-self-interstitial interaction, which helps to elucidate co-alignment of the fluxes of point defects and Cu solutes in W matrix.Irradiated foil was found to retain its ductility at RT. No significant irradiation hardening or DBTT shift were detected in the irradiated W foil compared to the bulk W. The different irradiation effect on embrittlement in individual foils and in the laminate may be attributed to the irradiation-assisted diffusion of Cu solutes in W foil, which could form intermetallic phases and affect the accumulation of lattice defects.

Effects of neutron irradiation at different fluencies on nanosized anatase titanium dioxide

Nanosized anatase polymorph of titanium dioxide was irradiated at normal conditions at different fluencies. Neutron irradiation was conducted at IBR–2 high–flux pulsed reactor at fluencies of 4.0 × 1012 n/cm2, 8.0 × 1012 n/cm2, 1.3 × 1013 n/cm2, 4.0 × 1014 n/cm2 and 1015 n/cm2 (neutron energy E > 0.1 MeV). X-ray diffraction, neutron diffraction analysis, Raman and FTIR spectroscopy were used to examine the crystal structure and the surface of the anatase polymorph after irradiation. X-ray and neutron diffraction analysis show deviations in the values for the unit cell volume with increasing fluence and some anneling effect for the highest fluence. Raman spectra analysis show that no phase transition occurs in the material at all irradiation fluences investigated. FTIR spectra analysis unveil that water molecules adsorbed on the material surface disintegrate under the influence of fast neutrons, converting to briged hydroxils on the surface of TiO2.