Influence Of Neutron Irradiation Research Articles

Neutron irradiation influence on high-power thyristor device under fusion environment

Neutron irradiation influence on high-power thyristor device under fusion environment

Radiation hardness of self-powered Si/SiC heterojunction detector under neutron irradiation

When typically confronted with harsh environments in space, semiconductor radiation detectors with low-power consumption and long service life are preferred. To address this concern, a novel Si/SiC heterojunction detector is proposed in this paper. At a neutron irradiation fluence of 1 × 1012 cm−2, the detector has a charge collection efficiency of 96.2% and an energy resolution of 0.95% at 10 V bias at 243Am-244Cm alpha particle detection. It can maintain a charge collection efficiency of 44.2% in the self-powered mode. The detector's performance is improved significantly using the heterojunction structure, extending its carrier lifetime. Due to its exceptional performance in sustaining high charge collection efficiency at low bias or even in self-powered mode following neutron irradiation, the Si/SiC heterojunction detector has been established as a promising option for space radiation detection.

Studies of irradiated two-phase lithium ceramics Li4SiO4/Li2TiO3 by thermal desorption spectroscopy

Two-phase ceramics Li2TiO3-Li4SiO4 are one of the potentially promising materials for creating a ceramic blanket for DEMO reactor. However, until now, a limited number of studies have been carried out on the release of tritium from this material under the influence of neutron irradiation, which poses fundamental problems for its application.In this work, the pebbles of two-phase lithium ceramics consisting of 25 mol% Li2TiO3 and 75 mol% Li4SiO4 were studied using thermal desorption spectroscopy (TDS) after their irradiation with neutrons at the WWR-K research reactor. Under the conditions of the irradiation experiment, which lasted 21.5 days at a reactor power of 6 MW, the samples were exposed to thermal neutrons with a flux density of 2·1013n/(cm2 × s). The thermal neutron fluence accumulated as a result of irradiation was 3.7·1019 cm−2.It has been established that tritium comes out mainly in the form of HT molecules and has three visible TDS peaks, which can be described by three rates of the first-order desorption reaction with an activation energy of 90 kJ/mol. Experiments have shown that the main amount of tritium is evenly distributed throughout the pebble’s pores and voids. Its yield is determined by desorption and transfer from inner voids to the boundaries that communicate with the outer surface of the sample. The kinetics of tritium release depends on the number, size and depth of the exit paths of such areas inside the ceramic.

Influence of neutron irradiation on the electronic properties of hexagonal boron nitride measured by terahertz time-domain spectroscopy

Due to the low atomic number of B, hexagonal boron nitride (hBN) has a large neutron scattering cross section and, therefore, is an ideal material for the realization of solid-state neutron detector. Here we apply the THz time-domain spectroscopy to study the effect of neutron irradiation on electronic properties of pyrolytic (PBN) and hot-pressed boron nitride (HBN). The key electronic parameters of these samples, such as the static dielectric constant ε b , the effective carrier density N*, the carrier relaxation time τ, and the electronic localization factor α, are determined optically, and their dependences upon the neutron irradiation fluence (NIF) are examined. We find that for hBN,N* and ε b decrease while τ and |α| increase with increasing NIF. These results can be used to further understand the neutron irradiation effects on the basic physical properties of hBN material. We believe that the results obtained from this work can benefit to the design and application of hBN material for neutron detectors.

Study of Gas Swelling Processes under Irradiation with Protons and He2+ Ions in Li4SiO4–Li2TiO3 Ceramics

One of the important areas of research in the energy sector is the study of the prospects for using new types of nuclear fuel, including tritium, which is one of the most promising types of fuel for thermonuclear energy. At the same time, for the production of tritium in the required quantities, the one that is the most optimal is the use of blanket materials based on lithium-containing ceramics. This is where tritium is released from lithium under the influence of neutron irradiation. The paper presents the results of an investigation of the influence of two-phase ceramics based on Li4SiO4–Li2TiO3 compounds on the resistance to external influences (mechanical loads) during the accumulation of hydrogen and helium (He2+) in the near-surface layer. The interest in such studies is primarily related to the search for solutions in the field of creating high-strength materials for tritium generation for its further use as nuclear fuel for thermonuclear fusion, as well as to the study of the mechanisms of the influence of different phases on the changes in the strength properties of ceramics, which provides an opportunity to expand fundamental knowledge in this area. The proposed method of obtaining two-phase ceramics by mechanical-chemical mixing and subsequent sintering into spherical particles enables the production of well-structured, high-strength ceramics of specified geometric dimensions (limited only by the dimensions of the mold) with a controlled phase ratio. During the experiments, it was found that increasing the content of Li4SiO4 phase in ceramics leads to an increase in strength characteristics (hardness, resistance to cracking) by 15–20% compared to single-phase ceramics. The most optimal composition of two-phase ceramics with high resistance to destructive embrittlement is the ratio of phases 0.75Li4SiO4–0.25Li2TiO3. One of the factors explaining the increase in resistance to destructive embrittlement under high-dose irradiation for two-phase ceramics is the increased dislocation density and the presence of interphase or intergranular boundaries, the high concentration of which leads to the creation of additional obstacles to the agglomeration of hydrogen and helium in the near-surface layer.

Study on Stiffened-Plate Structure Response in Marine Nuclear Reactor Operation Environment

As the regulations on greenhouse gas emissions at sea become strict, efforts are being made to minimize environmental pollutants emitted from fossil fuels used by ships. Considering the large sizes of ships in conjunction with securing stable supplies of environment-friendly energy, interest in nuclear energy to power ships has been increasing. In this study, the neutron irradiation that occurs during the nuclear reactor operation and its effect on the structural responses of the stiffened-plate structures are investigated. This is done by changing the material properties of DH36 steel according to the research findings on the neutron-irradiated steels and then performing the structural response analyses of the structures using analytical and finite-element numerical solutions. Results reveal the influence of neutron irradiation on the structural responses of the structures. It is shown that both the strength and stiffness of the structures are affected by the neutron-irradiation phenomenon as their maximum flexural stress and deflection are increased with the increase in the amount of neutron irradiation. This implies that strength and stiffness need to be considered in the design of ships equipped with marine nuclear reactors.

Influence of neutron irradiation on X-ray diffraction, Raman spectrum and photoluminescence from pyrolytic and hot-pressed hexagonal boron nitride

Hexagonal boron nitride (hBN) is considered as an ideal semiconductor material for solid-state neutron detector, owing to its large neutron scattering section because of the low atomic number of B and excellent physical properties. Here we study the influence of neutron irradiation on crystal structure and on intermediate energy state (IMES) levels induced by the presence of impurities and defects in hBN. Large-size and thick pyrolytic and hot-pressed hBN (PBN and HBN) samples, which can be directly applied for neutron detector devices, are prepared and bombarded by neutrons with different irradiation fluences. The SEM and TEM are used to observe the sample difference of PBN and HBN. X-ray diffraction and Raman spectroscopy are applied to examine the influence of neutron irradiation on lattice structures along different crystal directions of PBN and HBN samples. Photoluminescence (PL) is employed to study the effect of neutron irradiation on IMESs in these samples. We find that the neutron irradiation does not alter the in-plane lattice structures of both PBN and HBN samples, but it can release the inter-layer tensions induced by sample growth of the PBN samples. Interestingly and surprisingly, the neutron irradiation does not affect the IMES levels responsible for PL generation, where PL is attributed mainly from phonon-assisted radiative electron-hole coupling for both PBN and HBN samples. Furthermore, the results indicate that the neutron irradiation can weaken the effective carrier-phonon coupling and exciton transitions in PBN and HBN samples. Overall, both PBN and HBN samples show some degree of the resistance to neutron irradiation in terms of these basic physical properties. The interesting and important findings from this work can help us to gain an in-depth understanding of the influence of neutron irradiation on basic physical properties of hBN materials. These effects can be taken into account when designing and applying the hBN materials for neutron detectors.

Neutron-irradiated effect on the thermoelectric properties of Bi2Te3-based thermoelectric leg

Thermoelectric (TE) materials working in radioisotope thermoelectric generators are irradiated by neutrons throughout its service; thus, investigating the neutron irradiation stability of TE devices is necessary. Herein, the influence of neutron irradiation with fluences of 4.56 × 1010 and 1 × 1013 n/cm2 by pulsed neutron reactor on the electrical and thermal transport properties of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 thermoelectric alloys prepared by cold-pressing and molding is investigated. After neutron irradiation, the properties of thermoelectric materials fluctuate, which is related to the material type and irradiation fluence. Different from p-type thermoelectric materials, neutron irradiation has a positive effect on n-type Bi2Te2.7Se0.3 materials. This result might be due to the increase of carrier mobility and the optimization of electrical conductivity. Afterward, the effects of p-type and n-type TE devices with different treatments on the output performance of TE devices are further discussed. The positive and negative effects caused by irradiation can cancel each other to a certain extent. For TE devices paired with p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.7Se0.3 thermoelectric legs, the generated power and conversion efficiency are stable after neutron irradiation.

Radiation and Emission Phenomena in Combination

Radiation and emission are often decoupled in applications, methods, or specific experiments. However, the principles of these phenomena are closely interconnected. It holds both to neighboring and relatively distant branches of science and technology, allowing for interesting synergies, while considering these phenomena in combination. For example, even though light emitting diodes and photovoltaic cells are two separate branches of modern science and technology, in foundation, both sectors rely on understanding of the principles of photon-matter interactions. Concurrently, in scientific methodologies, there are numerous examples for irradiation of samples with different types of particles (e.g., with ions, electrons, positrons, X-rays) and collecting the response of the interaction used to learn the properties. At no doubt, there are excellently working well-established narrow-focused conferences in the field, however organizing a broader scope conference reaching a high level of the professional quality is challenging. Indeed, there is a risk of defocusing and losing grounds for professional discussions as it often happens with emerging conferences around the globe trying to capitalize on the generic approaches, unfortunately with relatively limited success. On the contrary, as has been proven by its 5-year-long annual operation, the International Conference on Radiation and Emission in Materials (ICREM) is one of a few successful examples of such newly established events aiming to bring several research communities closer together. This success is exactly because of considering the radiation and emission phenomena in their natural combination, as such being paradoxically focused and generic at the same time. Notably, the next ICREM will take place in Chiang Mai during December 13–15, 2023 (https://www.icrem2023.com/), keeping a tradition of hosting ICREMs in Thailand. On this occasion, we are glad to invite researchers, industrialists, and students involved into all relevant fields to participate in ICREM2023, which will provide a great forum for knowledge-sharing, networking, and collaboration. The ICREM2022 (http://www.nano.kmitl.ac.th/icrem2021/) was the 4th edition of the ICREM. The event was affected by the restrictions related to the covid-2019 pandemic, forced to move the event from 2021 to spring 2022, even though the travelling barriers were still in place in spring 2022 in many countries unfortunately. The shift of the conference from 2021 to 2022 explains why one may see puzzling referencing to 2021 in the website. Nevertheless, the conference has attracted >120 participants and resulted in a strong collection of papers comprising the present physica status solidi (a) Special Issue. The papers gathered in this Special Issue may be categorized into three divisions: accelerated particle beams, advanced optical materials, and devices. Experiments and simulations with different sorts of energetic particles attracted significant attention at the ICREM2022. Specifically, Dauletbekova et al. (pssa.202200332) have revealed and reported the influence of neutron irradiation on the infrared absorption spectra of LiF crystals as a function of the contaminations, in particular with hydroxyl and metallic impurities. Thongbai et al. (pssa.202200398) have reported on an interesting development of the magnetic field measurement system as a part of the mid-infrared and terahertz radiation free-electron laser project at the Chiang Mai University in Thailand. Tang et al. (pssa.202200426) have reported on the most recent development at the pulsed muon facility (the so-called EMuS) at China Spallation Neutron Source (CSNS). Whitlow and Nagy (pssa.202200432) have used micro-particle induced x-ray emission to study the lead-free and lead-based solders as well as their interactions with copper wires. Yu (pssa.202200512) has reported on discoveries of the suppressed defect dynamics in SiO2-Si structures under high-to-low switched dose rate irradiations. Du et al. (pssa.202200515) have studied a phenomenon of lateral scattering of high energy heavy ions in solids applying a set of membranes as samples. Mastering of the light emission was among the major topic at the ICREM2022. Reshchikov (pssa.202200402) has provided a comprehensive review on photoluminescence bands occurring in gallium nitride and associated with point defects involving nitrogen or gallium vacancies. Jakrapong et al. (pssa.202200411) have reported on the significance of the X-ray luminescence, photoluminescence and radiation shielding properties of the Eu doped oxide glasses. Kiwsakunkran et al. (pssa.202200437) have studied photo and X-ray luminescence properties of complex glasses in particular demonstrating hypersensitive transitions at the visible and near infrared ranges, respectively. Yasaka et al. (pssa.202200438) have investigated optical properties of boro-tellurite glasses for photonic applications. Intachai et al. (pssa.202200440) have prepared Sm-doped gadolinium sodium silicoborate glasses by melt quenching process and investigated their luminescence properties suggesting feasibility for orange color emitting devices. Galeckas et al. (pssa.202200449) have reported the control of carrier lifetime on SiC films by thermal generation and annihilation of carbon vacancy, in particular using a combination of the luminescence-based depth-profiling, capacitance-voltage measurement and deep-level transient spectroscopy. Mishra et al. (pssa.202200466) have conducted cathodoluminescent imaging and secondary-ions mass spectrometry measurement on ZnO:N films under rapid thermal annealing process in N2 and O2 atmosphere and found an enhancement of acceptor-related cathodoluminescence in these films. Selim (pssa.202200712) has provided a review on advanced thermoluminescence spectroscopy, flagging it as a research tool to investigate crucial optical and electronic properties of semiconductor and photonic materials. Reports on devices for energy storage, radiation detection, photovoltaics, etc. comprised an integrated part of ICREM2022. In particular, Kornphom et al. (pssa.202200240) have reported improvements in the energy storage depending on the rhombohedral vs cubic phase balance in the samples. Thawong et al. (pssa.202200418) have demonstrated lead-free ceramics by solid-state combustion method featuring a change in magnetic properties as a function of composition. Wirunchit and Koetniyom (pssa.202200364) have employed hydrothermal process to prepare ZnO nanoparticles utilized as antibacterial materials with enhanced efficacy. Kansaard et al. (pssa.202200447) have presented the sonochemical synthesis of a composite compound and proposed it as a photocatalyst. Meejitpaisan et al. (pssa.202200441) have investigated photo- and X-ray-induced luminescence properties of Sm-doped oxyfluoroborate glasses as potential red-emitting laser medium and scintillators. Nayak et al. (pssa.202200651) have investigated sub-stochiometric nickel oxide films acting as hole selective contacts in silicon heterojunction solar cells and found that the performance of the device could be limited by the high interface defect density. Huang et al. (pssa.202200448) have reviewed the status and the challenges for the cast-mono silicon substrate technology as cost-effective wafers for solar cells. Yu and Rimjaem (pssa.202200263) have developed mid-infrared free-electron laser and terahertz emission generated by a corresponding electron accelerator. The ICREM organization with a history of already four past conferences and the 5th conference forthcoming in December 2023 (https://www.icrem2023.com/) has emerged as a prominent addition to the conference events in the community. In particular, it assists to establish cross-disciplinary links and collaborations across the boarders within the field of the radiation and emission in materials. We trust this physica status solidi (a) Special Issue comprising the highlights of the ICREM2022 can be of use for a wide and cross-disciplinary research community dealing with radiation effects, as well as for the students in the field to use the papers collected herein for studies, referencing, and inspirations. We thank all the authors and co-authors of the papers submitted to this Special Issue, as well as all participants of the ICREM2022 for attending the conference. With a great pleasure, we acknowledge the support provided to the ICREM2022 by the King Mongkut's Institute of Technology Ladkrabang as well as by all other sponsors. We also appreciate the networking opportunities partly enabled through the INTPART and UTFORSK Programs at the Research Council of Norway and the Directorate for Higher Education and Skills in Norway (NEARTEMS Project No. 322382 and SPECTRINKO Project No. UTF-2021/10210). Andrej Kuznetsov was awarded with his Ph.D. degree in physics from the Russian Academy of Sciences in 1992 and accomplished his habilitation in solid state electronics in 2000 at the Royal Institute of Technology in Sweden. In 2001 he joined the Department of Physics at the University of Oslo (UiO) in Norway as an associate professor, where he was subsequently promoted to a full professor rank in 2003. From 2018 he acts as the Chair of the UiO Centre of Excellence: Light and Electricity from Novel Semiconductors (LENS)—as a part of the Centre for Materials Science and Nanotechnology at UiO. He is an expert in the field of modern semiconductors, in particular focusing on the physics of diffusion, defects, and radiation effects. Wisanu Pecharapa received his B.S. in physics from Chiangmai University in 1992, M.S in physics from University of Central Florida, USA in 1997, and Ph.D. in physics from King Mongkut's Institute of Technology Ladkrabang (KMITL) in 2007. Currently, he is a professor at the College of Materials Innovation and Technology, KMITL. His research focus is on synthesis processes of metal oxide-based materials and composites, especially in low-dimensional structures that can be applied for optical, optoelectronics, and catalyst applications.

Advances, Challenges, and Future Perspectives of Microwave Reflectometry for Plasma Position and Shape Control on Future Nuclear Fusion Devices.

Providing energy from fusion and finding ways to scale up the fusion process to commercial proportions in an efficient, economical, and environmentally benign way is one of the grand challenges for engineering. Controlling the burning plasma in real-time is one of the critical issues that need to be addressed. Plasma Position Reflectometry (PPR) is expected to have an important role in next-generation fusion machines, such as DEMO, as a diagnostic to monitor the position and shape of the plasma continuously, complementing magnetic diagnostics. The reflectometry diagnostic uses radar science methods in the microwave and millimetre wave frequency ranges and is envisaged to measure the radial edge density profile at several poloidal angles providing data for the feedback control of the plasma position and shape. While significant steps have already been given to accomplish that goal, with proof of concept tested first in ASDEX-Upgrade and afterward in COMPASS, important, ground-breaking work is still ongoing. The Divertor Test Tokamak (DTT) facility presents itself as the appropriate future fusion device to implement, develop, and test a PPR system, thus contributing to building a knowledge database in plasma position reflectometry required for its application in DEMO. At DEMO, the PPR diagnostic's in-vessel antennas and waveguides, as well as the magnetic diagnostics, may be exposed to neutron irradiation fluences 5 to 50 times greater than those experienced by ITER. In the event of failure of either the magnetic or microwave diagnostics, the equilibrium control of the DEMO plasma may be jeopardized. It is, therefore, imperative to ensure that these systems are designed in such a way that they can be replaced if necessary. To perform reflectometry measurements at the 16 envisaged poloidal locations in DEMO, plasma-facing antennas and waveguides are needed to route the microwaves between the plasma through the DEMO upper ports (UPs) to the diagnostic hall. The main integration approach for this diagnostic is to incorporate these groups of antennas and waveguides into a diagnostics slim cassette (DSC), which is a dedicated complete poloidal segment specifically designed to be integrated with the water-cooled lithium lead (WCLL) breeding blanket system. This contribution presents the multiple engineering and physics challenges addressed while designing reflectometry diagnostics using radio science techniques. Namely, short-range dedicated radars for plasma position and shape control in future fusion experiments, the advances enabled by the designs for ITER and DEMO, and the future perspectives. One key development is in electronics, aiming at an advanced compact coherent fast frequency sweeping RF back-end [23-100 GHz in few μs] that is being developed at IPFN-IST using commercial Monolithic Microwave Integrated Circuits (MMIC). The compactness of this back-end design is crucial for the successful integration of many measurement channels in the reduced space available in future fusion machines. Prototype tests of these devices are foreseen to be performed in current nuclear fusion machines.

Influence of Neutron Irradiation on Microstructure and Mechanical Properties of Coarse- and Ultrafine-Grained Titanium Grade 2

The influence of neutron irradiation on the microstructure and related mechanical properties of Ti Grade 2 in coarse- and ultrafine-grained conditions was investigated. It was found that mechanical properties of the coarse-grained (CG) state were significantly affected by neutron irradiation. At room temperature (RT), the yield stress increased by more than 30%, whereas the ductility decreased by more than 50%. An even bigger difference in the mechanical properties between irradiated and non-irradiated states was observed at a temperature of 300 °C. Changes in the mechanical properties can be attributed to the high density of defect clusters/dislocation loops induced by neutron irradiation. On the other hand, the ultrafine-grained (UFG) state is more resistant to radiation damage. The mechanical properties at RT did not change upon neutron radiation, while at a temperature of 300 °C, the yield stress increased only by about 10%. Enhanced radiation resistance of the UFG state can be attributed to the presence of a high density of dislocations and dense network of high-angle grain boundaries, which act as traps for radiation-induced defects and, thus, prevent the accumulation of these defects in the microstructure.

Analysis of displacement damage effects on the charge-coupled device induced by neutrons at Back-n in the China Spallation Neutron Source

Displacement damage effects on the charge-coupled device (CCD) induced by neutrons at the back-streaming white neutron source (Back-n) in the China Spallation Neutron Source (CSNS) are analyzed according to an online irradiation experiment. The hot pixels, random telegraph signal (RTS), mean dark signal, dark current and dark signal non-uniformity (DSNU) induced by Back-n are presented. The dark current is calculated according to the mean dark signal at various integration times. The single-particle displacement damage and transient response are also observed based on the online measurement data. The trends of hot pixels, mean dark signal, DSNU and RTS degradation are related to the integration time and irradiation fluence. The mean dark signal, dark current and DSNU2 are nearly linear with neutron irradiation fluence when nearly all the pixels do not reach saturation. In addition, the mechanisms of the displacement damage effects on the CCD are demonstrated by combining the experimental results and technology computer-aided design (TCAD) simulation. Radiation-induced traps in the space charge region of the CCD will act as generation/recombination centers of electron–hole pairs, leading to an increase in the dark signal.

Investigation of the Influence of Neutron Irradiation on the Fault Tolerance of a Microcircuit

Investigation of the Influence of Neutron Irradiation on the Fault Tolerance of a Microcircuit

Investigation of Irradiation Effect on REBCO Coated Conductors for Future Radiation-Resistant Magnet Applications

Construction of a second target station of the Materials and Life Science Experimental Facility is one of the future plans of the Japan Proton Accelerator Research Complex. A superconducting magnet called a pion capture solenoid, which requires 100 MGy class high radiation resistance, will be installed for the muon beamline in the second target station. Therefore, we are researching and developing radiation-resistant magnets based on high temperature superconductors. As one of the research subjects, we have been investigating the effect of irradiation on rare-earth barium copper oxide (REBCO) conductors. Results of irradiation using the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co gamma-ray facility indicated no significant degradation in superconductivity up to 27.4 MGy. However, decreases in the superconducting transition temperature and critical current were confirmed with a neutron irradiation fluence of 8.23 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sup> n/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Influence of neutron irradiation on the mechanical and dielectric properties of epoxy/ titanium oxide nanocomposite

The exposure of polymeric insulation in nuclear power plants necessitates the study of the effect of neutron irradiation on the mechanical and dielectric properties of neat and nano-filled polymeric-based insulation materials. The exposure of the materials to ionizing radiation can influence their dielectric and insulating properties. This work presents the influence of neutron irradiation on the dielectric behavior of neat and nanoparticle-filled Epoxy-TiO2 nanocomposite. The prepared neat and nanocomposite samples were exposed to neutron radiation in the Nigeria Research Reactor I (NIRR-I). The mechanical and dielectric analyses of the samples were performed before and after irradiation. The presence of 2 wt% TiO2 nanoparticles in the epoxy matrix resulted in optimum mechanical and dielectric behavior. While the presence of the nanoparticles seems to have a significant influence on the reduction of the mechanical degradation of the composite (39.96%–12.11% after exposure to 4.5 kGy), it does not have much influence on the reduction of the dielectric loss of the composite. The variation of temperature of the sample revealed that the 2 wt% nanoparticles filled polymer displayed higher relaxation activated energy. The research suggests that the filling of the epoxy polymer with 2 wt% TiO2 nanoparticles can modify the mechanical and dielectric relaxation behavior of the polymer composites. This could enhance the resistance of the composite material to the effect of radiation-induced degradation in the polymeric insulation.

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.

Investigation of the Influence of Neutron Irradiation on Cladded Nuclear Reactor Pressure Vessel Steel Blocks by Magnetic Adaptive Testing

The influence of neutron irradiation degradation on reactor pressure vessel steel was investigated. Large blocks were irradiated by neutrons in the BR2 reactor at a low irradiation temperature. They were measured by a nondestructive magnetic method, magnetic adaptive testing, before and after the neutron irradiation. It was shown that the modification of the magnetic parameters due to the neutron irradiation was well detectable by this nondestructive method. It was also shown that the influence of neutron irradiation could be detected with a reasonable signal-to-noise ratio through the cladding. The present results are considered as a first step towards the application of magnetic adaptive testing in the nuclear industry.

Investigation of Al-B4C Metal Matrix Composites Produced by Friction Stir Additive Processing

Aluminium—boron carbide metal matrix composites (Al-B4C MMCs) belong to the class of materials extensively used in the nuclear industry as a thermal neutron absorber in spent fuel casks. This article investigates a novel production method of Al-B4C MMCs—Friction Stir Additive Processing (FSAP)—as an alternative production method to casting or sintering. FSAP is derived from friction stir welding, which can be used to local modifications of microstructure, or it can be used to incorporate the second phase into the processed material. During this study, a variant of FSAP for MMC production was proposed, and its mechanical and thermal neutron absorbing properties have been investigated. Further, the influence of neutron irradiation on mechanical properties has been studied. Results show that FSAP can successfully produce Al-B4C MMCs with 7 mm thickness. Neutron irradiation causes only a slight increase in hardness, while its effect on tensile properties remains inconclusive.

Radiation embrittlement of clad-HAZ of RPV of a decommissioned BWR plant

Radiation hardening/embrittlement was investigated for clad-heat affected zone (clad-HAZ)) of reactor pressure vessel (RPV) of Hamaoka unit-1 boiling water reactor (BWR) under decommissioning process. The neutron irradiation fluence in the HAZ of the RPV steel was 1.5 × 1022 n/m2 (E > 1MeV). The shift in ductile-brittle transition temperature, ΔDBTT, was measured to be +26 °C using 1/3-sized Charpy specimens, while the increase in Vickers hardness, ΔHv, was 19 HV in the clad-HAZ of 1.6 mm depth from the clad boundary. Atom probe tomography (APT) was conducted at the locations 0.1, 0.8, 1.6. 4 and 10 mm away from the clad boundary, and revealed that solute clusters were formed in both clad-HAZ and base metal (10 mm depth), and the clusters were rich in Mn, Ni, Si, Cu with the averaged diameter of about 2.5 nm and the number density of 2 × 1022/m3, being almost independent of depth location. As for the chemical compositions of the clusters, Mn content increased with decreasing Cu content. This suggests that there might be site completion between Mn and Cu for clustering. Radiation hardening of clad-HAZ induced by the formation of solute clusters was estimated on the bases of the dispersed barrier hardening (DBH) model in terms of N·d, and well interpreted with α = 0.06–0.08. The ΔDBTT-Vf plot, of which the data was measured with 1/3 size specimens sampled from the clad-HAZ at 1.6 mm depth, agreed with the previous surveillance test results measured in surveillance tests with standard size specimens of base metal.

Effect of irradiation temperature on the fracture-mechanical behaviour of tungsten irradiated to 1 dpa

We investigate the influence of neutron irradiation on the fracture-mechanical behaviour of ITER-specification conform stress relieved tungsten bar. The neutron irradiation of miniaturized Disc-shaped Compact Tension specimens with electrical discharge machined notches was performed in the Material Testing High Flux BR2 reactor of SCK CEN in Mol. Damage doses close to 1 dpa were achieved at multiple irradiation temperatures of 400, 600 and 1000°C. Suppression of thermal neutrons fluence by applying stainless steel capsules resulted in reduction of Re (Os) content down to fusion application relevant level of 2 at% (0.2 at%). Neutron irradiation strongly impacted fracture-mechanical behaviour of the material. Depending on the irradiation temperature, the DBTT increases by about 650°C or even higher as has been deduced on the basis of the load-displacement curve analysis. The degradation of the mechanical properties is attributed to the alteration of the microstructure and fracture mode. The results are compared with the fracture-mechanical data on irradiated tungsten obtained previously in the course of same neutron irradiation campaign.