Molecular dynamics simulation study of neutron irradiation damage in hexagonal boron nitride (h-BN)

; 5 8 : 5 : 8 : : 9 < 6 8 9 6 8 6 5 ; 8 6 : 4 9 > < D ; lattice atom was investigated in detail. The results are of general interest since the method used is limited only by the validity of the interatomic potential assummed. Cross sections for the displacement of lattice atoms by gamma rays up to 5 Mev were calculated. A theoretical study was made of the slowing down process for a primary displaced atom in a solid. The small amplitude motion of dislocation loops was investigated in detail, taking into account the whole elastic field interaction between different parts of the loop. The extension and interval correlations in a radiation-induced displacement cascade were investigated. The numerical data apply to copper. A special model for annealing of defects in solids is discussed. Dislocation Interactions: Studies were made of the variations of internal friction and elastic modulus during irradiation of pure copper crystals at a number of temperatures in the range 90 to 300 deg K. Using neutron irradiation as a tool, it is shown that there are at least two dislocation contributions to the Young's modulus and internal friction of Cu at low temperatures. An apparatus was developed which makes possible the continuous observation of the Young's modulus and internal friction of a metal sample. Low-temperature Irradiation Studies: Activation energies for the annealing of copper and aluminum following reactor bombardment near 4 deg K were measured. Isochronal annealing studies of Cu, Ag, Au, Pt, and Zn were made after neutron bombardment of these materials at 4 deg K. It was confirmed that the residual resistivity of high purity copper can be greatly reduced by annealing in an oxidizing atmosphere. A redetermination of the stored-energy release in reactorirradiated Cu between 30 and 50 deg K was made. The design of a new facility for irradiation damage experiments at very low temperatures is described. A helium-cooled facility was installed in the pool of the ORR, which allows samples to be irradiated at about 50 deg C in an inert atmosphere. Electron Microscope Studies: Fission fragment tracks in thin films of UO/sub 2/ were studied and found to be essentially a surface effect in which material at the surface is displaced as a result of the passage of the fission fragments. An improved replication technique for copper is described. Chemical Properties of Metal Surfaces: The kinetics of the dissolution of copper crystals in aqueous solutions were investigated. The diffusion of deuterium in deuteron-irradiated Cu was studied in the temperature range -50 < T < 50 deg C by monitoring neutrons from the D(d,n)He/sup 3/ reaction. Alloy Studies: Experiments were conducted on the effect of irradiation on atomic rearrangements in Cu-Al, Ni-Be, Ni-Cu, Au-Cd, and Fe-C. Semiconductor Studies: A model for the potential well surrounding disordered regions in neutron-irradiated Ge and Si is discussed. The different effects of Co/sup 60/gammaray and fast-neutron bombardment on the electrical behavior of Ge are discussed in terms of the distribution of lattice defects. Thermal neutron capture in Si and Ge is considered. The effect of neutron and gamma irradiation upon minority carrier lifetime in Ge was studied. The effect of 14-Mev neutron irradiation upon the electrical properties of Ge was studied. A preliminary study was made of the change in thermoelectric power of n-type germanium as a result of neutron irradiation. Annealing of radiation-induced conductivity changes in n-type Ge was found to take place in the range between 77 and 273 deg K. The charge-center concentration as a function of temperature of high-purity, n-type Ge under fast- neutron irradiation is compared to similar data obtained for Co/sup 60/ gamma-ray irradiations. The difiusivity, solid solubility, and acceptor behavior of Cu in Ge was investigated. The effect of neutron spectrum on conluctivity changes in n- type Ge was investigated. Hall coefficient and Hall mobility were

Chapter 13 - Photoacoustic studies on neutron irradiated RE oxide powders and γ-irradiated Nd-doped glasses

A refined numerical simulation approach to assess the neutron irradiation effect on the mechanical behavior of wurtzite GaN

The relationship between the irradiation induced damage and the mechanical properties of single crystal Ni

Zirconium alloys have hcp crystal structure with low c/a ratio at and below the reactor operating temperatures and exhibit preferred orientations or textures. These textures result in anisotropic mechanical properties, which in-turn affect their in-service behavior such as in-pile creep down of the cladding tubes. The purpose of the present study has been to investigate the effects of recrystallization and neutron irradiation on the anisotropic biaxial creep behavior of Zircaloy cladding tubes. The creep anisotropies of the cold-worked and recrystallized tubes were considered using results from the closed-end internal pressurization tests superimposed with axial loading. The in situ biaxial strain measurements were made using laser and linear variable differential transformer (LVDT) extensometers. Creep data were obtained at various stress ratios, and creep loci were constructed at constant energy dissipation for both cold-worked and recrystallized tubes. X-ray diffraction techniques were used to measure the textures which were then described quantitatively in terms of crystallite orientation distribution functions (CODFs). These CODFs were employed to predict the anisotropy parameters R and P, and the anisotropic creep behavior. The creep behavior of Zircaloy tubes changed with recrystallization. The effect of neutron irradiation on the recrystallized material is modeled by invoking secondary slip systems. The considerable amount of plastic anisotropy observed in the unirradiated recrystallized tubes shows a tendency to decrease and to become isotropic at high fluences. On the other hand, neutron irradiation does not produce any significant changes in the anisotropy of the cold-worked material when radiation growth is taken into consideration.

Effect of neutron irradiation on the mechanical properties of weld overlay cladding for reactor pressure vessel

X-ray detectors based on conventional semiconductors with large atomic numbers are suffering from the poor stability under a high dose rate of ionizing irradiation. In this work, we demonstrate that a wide band gap ceramic-boron nitride with small atomic numbers could be used for sensitive X-ray detection. Boron nitride samples showed excellent resistance to ionizing radiation, which have been systematically studied with the neutron- and electron-aging experiments. Then, we fully analyzed the influence of these aging effects on the fundamental properties of boron nitride. Interestingly, we found that the boron nitride samples could maintain relatively good charge transport properties even after large dose of neutron irradiation. The fabricated X-ray detectors showed decent performance metrics, and the neutron-aged boron nitride even showed improved operational stability under continuous X-ray irradiation, suggesting the great potential for real applications.

Composite materials have made far‐reaching changes in the space industry since they have been adopted into the structural and thermal control subsystems of space vehicles because of their several multi‐functions, including being lightweight as well as having advanced mechanical and thermal properties. The use of composites as space radiation shielding materials is also one of the most crucial applications because space radiation is a major impediment for current and future deep‐space missions. Investigation of carbon fiber composites with a diverse array of element and nanoparticle reinforcements has revealed their potential as an alternative to conventional radiation shielding materials in space. This study focused on the alleviation of gamma‐ray and neutron radiation by carbon fiber/epoxy composites incorporated with various weight ratios of carbon nanotube (CNT) and boron nitride (BN) nanoparticles. A narrow beam geometry setup was used for gamma radiation tests with a Cs‐137 gamma‐ray source, while neutron radiation experiments were conducted in a neutron howitzer with a 239Pu‐Be neutron source. Six groups of specimens, namely, pure carbon fiber/epoxy, 0.5 wt% CNT, 0.5 wt% BN, 0.5 wt% CNT + 0.5 wt% BN, 1 wt% CNT + 1 wt% BN, and 2 wt% BN, were examined against these two types of radiation. Results have indicated that the 2 wt% BN specimen showed the best attenuation properties against both gamma‐ray and neutron radiation among all tested specimens; furthermore, it was almost three times more effective against neutron radiation than against gamma‐ray radiation.Highlights Varying weight ratios of CNT and BN nanoparticles used for radiation shielding. A Cs‐137 gamma‐ray source used in narrow beam geometry. Neutron radiation studies were conducted in a 239Pu‐Be neutron howitzer. The 2 wt% BN sample showed the best attenuation against gamma‐ray and neutron radiation. It resulted in an HVL of 6.86 cm for gamma‐ray radiation and 2.13 cm for neutron radiation.

Swelling on neutron induced hexagonal boron nitride and hexagonal boron nitride-titanium diboride composites

Annealing and neutron-irradiation effects on the permeability of Fe 86Zr 7B 6Cu 1

The microstructure and microhardness of niobium and commercial prototype niobium-base alloys have been investigated following fast neutron irradiation to a fluence of 1.1 × 1022 neutrons (n)/cm2 (&amp;lt;0.1 MeV), 4 displacements per atom (dpa), at 482°C. The purpose of this work was to determine the effects of molybdenum and zirconium alloy additions on the resistance of niobium-base alloys to neutron irradiation. Neutron irradiation of the niobium and Nb-1Mo alloy produced very small voids whose mean diameters were in the range of 30 to 35 Å. In all other alloys, however, no voids were observed and the principal effect of the neutron irradiation was to form a high density of 30 to 40 Å diameter dislocation loops which are believed to be primarily of interstitial character. The effect of fast neutron irradiation was to increase the microhardness of both niobium and all its alloys, with the largest increase in the Nb-1Zr alloy and the smallest increase in the ternary Nb-5Mo-1Zr alloy. Previous work on niobium and Nb-1Zr alloy has shown that a vacancy trapping mechanism is particularly effective at irradiation temperatures up to 600°C for fast neutron fluences of 2.5 × 1022 n/cm2 (&amp;gt;0.1 MeV). The observation from the present experiments that molybdenum and zirconium additions were effective in the suppression of void formation suggests that a vacancy trapping mechanism was operative in the present alloys. The smaller hardness increase observed for the ternary alloys suggests that these alloys may maintain good engineering properties in addition to their improved resistance to void formation.

ABSTRACTThe mechanism of damage production in solids during irradiation is of great practical interest in nuclear technology. The need to increase the life time of current nuclear plants as well as extreme conditions (high temperature and high neutron flux) in new generations of nuclear plants leads to have a deep insight into radiation damage in solids. In fact, the slowing down of particles in solids leads to a non homogeneous distribution of defects in solids, giving rise to complex microstructures with unusual properties. Numerous experiments, Molecular Dynamics (MD) and Monte Carlo (MC) simulations have clearly shown that highly damaged areas called displacement cascades are produced by neutron or impinging ions in solids. It is now clearly established that the number and the distribution of these subcascades dictate the long term evolution of the microstructure under irradiation. In this work, we present a new model to calculate the mean number of displacement cascades produced in a mono-atomic solid by an incident particle within the Binary Collision Approximation framework (BCA) taking into account all information extracted from MD simulations. To reach such a goal, the notion of subcascade threshold energy is introduced and discussed on some examples. Within this formalism, we exhibit a new way to estimate the number of defects created in a displacement cascade integrating results of MD simulations of cascades.

Radiation damage studies in fusion reactor steels by means of small-angle neutron scattering (SANS)

Characterization and qualification of neutron radiation effects – Summary of Japan-USA Joint Projects for 40 years –

Effects of neutron irradiation on tensile properties of oxide dispersion strengthened (ODS) steel claddings