Neutron irradiation effects in uranium dicarbides

Changes of electrical resistivity and lattice parameter in UC_1.96 after neutron irradiation from $\text{9 × 10}{}^{14}$ to $\text{2 × 10}{}^{18}$ nvt were studied. The resistivity was increased with the dose up to $\text{1 × 10}{}^7$ nvt, and saturated at that dose. Above 10¹⁸ nvt a steep increase was observed. In the lattice-parameter changes, on the other hand, a gradual increase was observed in the dose range between $\text{2 × 10}{}^{16}$ and $\text{8 × 10}{}^{17}$ nvt; above that dose, an abrupt increase followed. Annealing experiments on the resistivity were performed up to 1000°C using the specimens irradiated to the low dose of $\text{5 × 10}{}^{16}$ nvt, and the increased resistivity was completely recovered in three steps. The activation energies of each step were estimated to be 0.3, 0.5 and $\text{1.6 ± 0.2}$ eV.     

Neutron irradiation effects in SiC

SiC is a wide band gap semiconductor material with potential applications in harsh environmental conditions. In this work we investigate the effects of neutron irradiation on the properties of two SiC polytypes. Changes to the optical properties were analyzed using a range of techniques including visible transmission, infra-red reflectance, Raman spectroscopy and photoluminescence.     

中子对氟聚合物力学性能的影响

对中子辐照前后氟聚合物 F2311和 F2314的静态力学性能、动态力学性能以及分子量进行了考察。结果表明,经注量为 1.5×1013/ cm2的中子辐照后,F2311和 F2314的静态力学性能稍有增强,分子量变化不大;F2311的动态力学性能基本不变,F2314的储存模量和损耗模量却有所降低,经注量为 2.5×1013/ cm2的中子辐照后,F2311的静态力学性能和 F2314的拉伸性能明显增强,F2314的压缩性能反而降低;F2311的动态力学性能基本不变,F2314的储存模量和损耗模量却明显减小。     

Thermal diffusivity of uranium monosulfide from 638 to 1823 K

The thermal diffusivity of uranium monosulfide was determined between 628 and 1823 K by a laser pulse method. Values for the thermal conductivity at 638 and 1823 K, calculated from the available data of the heat capacity, and corrected to theoretical density, were found to be 0.117 and 0.192 W/cm · K respectively. They were fitted to the sum of the electronic contribution and the lattice contribution to the thermal conductivity. The electrical resistivity was calculated by means of the Wiedeman-Franz law, using the Lorenz number for metallic conductors, assuming that the electronic part of the thermal conductivity was represented by the subtraction of the phonon part of the thermal conductivity, fitted by a computer, from the total thermal conductivity. The results agreed well with those of the direct measurements of electrical resistivity by other investigators. The Grüneisen anharmonicity parameter was also calculated from the value of the lattice contribution to the thermal conductivity, to be 1.07.     

Neutron irradiation effects on superconducting wires and insulating materials

On the progress of the Deuterium–Deuterium (D–D) or Deuterium–Tritium (D–T) burning plasma devices, the importance of neutron irradiation on superconducting magnet materials increases and the data base is desired to design the next generation devices. To carry out the investigations on the effect of neutron irradiation, neutron irradiation fields are required together with post-irradiation test facilities. In these several years, a collaboration network of neutron irradiation effect on superconducting magnet materials has been constructed. 14 MeV neutron irradiation was carried out at Fusion Neutronics Sources (FNS) in Japan Atomic Energy Agency (JAEA) and fission neutron irradiation was performed at JRR-3 in JAEA. After the irradiation, the Nb₃Sn, NbTi and Nb₃Al samples were sent to High Field Laboratory for Superconducting Materials (HFLSM) in Tohoku University and the superconducting properties were evaluated with 28 T hybrid magnet. Also, the organic insulation materials are considered to be weaker than superconducting materials against neutron irradiation and cyanate ester resin composite was fabricated and tested at the fission reactor. One clear result on Nb₃Sn was the property change of Nb₃Sn by 14 MeV neutron irradiation over 13 T. The critical current was increased by 1.4 times around 13 T but the increment of the critical current became almost zero at higher magnetic fields and the critical magnetic field of the irradiated sample showed almost the same as non-irradiated one.     

Neutron irradiation effects on the mechanical properties of organic composite materials

Neutron irradiations with low γ-ray flux in the Intense Pulsed Neutron Source were carried out on four kinds of cloth-filled organic composites (filler: E-glass or carbon fiber; matrix: epoxy or polyimide resin) and a unidirectional alumina fiber/epoxy composite. These composites were examined with regard to the mechanical properties at room temperature. Following irradiation at room temperature, the Young's (tensile) modulus of these composites remains practically unchanged up to a total neutron fluence of $\text{5.0 × 10}{}^{18}\text{n/cm}{}^2$ ($\text{1.4 × 10}{}^{18}\text{n/cm}{}^2$ for $\text{E > 0.1 MeV}$). The shear modulus and the ultimate strength, on the other hand, decrease significantly at this neutron fluence for the glass/epoxy and glass/polyimide composites, whereas for the other composites both properties do not degrade. This result is most likely ascribed to the radiation damage at fiber/matrix interface due to recoil particles produced by a ${}^{10}\text{B(n,α)}{}^7$ Li reaction in the boron-containing E-glass fibers. Only for the E-glass fiber composites, in fact, the fracture propagation energy is appreciably increased by irradiation, while for the other composites the propagation energy is scarcely changed, thus confirming the significant contribution due to the ¹⁰B reaction. As to the 5 K irradiation, degradation of the present composites was not observed up to a total neutron fluence of $\text{1.0 × 10}{}^{18}\text{n/cm}{}^2$ ($\text{7.0 × 10}{}^{17}\text{n/cm}{}^2$ for $\text{E > 0.1}\text{MeV}$) when tested at room temperature.     

Minimization of uranium load in Miniature Neutron Source Reactors

The uranium load in the Syrian MNSR is minimized by reducing the clad thickness to a standard value of 0.38 mm instead of 0.60 mm based on a 3-D model of the reactor that included all reactor components. More than 31 fuel rods are saved. The effects of the reduction of the fuel load in the core on both the reactor safety and performance, in relation to its use as a tool for Neutron Activation Analyses, are analyzed.     

Neutron irradiation of dilute aluminium alloys

Aluminium alloys containing up to 0.4% silicon and 0.1% indium were irradiated at various doses up to 10²¹ n/cm² (E > 0.1 MeV) at pile temperature. Indium was found to enhance and silicon to suppress the nucleation of voids. The reasons for this are discussed in terms of possible nucleation processes. The changes in 0.2% proof stress were correlated with the change in microstructure.     

A review of irradiation effects on LWR core internal materials - Neutron embrittlement

Austenitic stainless steels (SSs) are used extensively as structural alloys in the internal components of light water reactor (LWR) pressure vessels because of their relatively high strength, ductility, and fracture toughness. However, exposure to neutron irradiation for extended periods not only changes the microstructure and microchemistry of these steels, but also degrades their fracture properties. The existing data on irradiated austenitic SSs are reviewed to determine the effects of key parameters such as material type and condition and irradiation temperature, dose, and dose rate on neutron embrittlement. Differences in the radiation-induced degradation of fracture properties between LWR and fast-reactor irradiations are also discussed. The results are used to (a) define a threshold fluence above which irradiation effects on fracture toughness of the material are significant, (b) evaluate the potential of neutron embrittlement under LWR operating conditions, and (c) assess the potential effects of voids on fracture toughness.     

抗菌素和柑桔的快中子辐射育种

辐射育种在国内外已进行了多年,但国内辐射育种过去大多用X射线、γ射线、电子束和激光束等射线源,以快中子作为辐射育种的一种手段时间不长,国内以复旦大学和广东测试分析所等单位开展得较早,并取得了较好的成果。从1979年开始,我们应用快中子射线源为抗菌素和浙江柑桔等开展辐射育种工作,经过几年的努力取得了一点效果。     

Neutron irradiation hardening and microstructure changes in Fe-Mn binary alloys

Irradiation hardening and microstructure changes in Fe-Mn binary alloys were investigated after neutron irradiation at 290 °C and up to 0.13 dpa. Significant irradiation hardening comparable to that of Fe-1 at.%Cu alloy was observed in Fe-1 at.%Mn alloy. Manganese increases the number density of dislocation loops, which contributed to the observed irradiation hardening. Manganese serves as a nucleus of the loop by trapping interstitial atoms and clusters, preventing 1D motion of the loops.     

Neutron flux optimization in irradiation channels at NUR research reactor

Optimization of neutron fluxes in experimental channels is of great concern in research reactor utilization.The general approach used at the NUR research reactor for neutron flux optimization in irradiation channels is presented.The approach is essentially based upon a judicious optimization of the core configuration combined with the improvement of reflector characteristics.The method allowed to increase the thermal neutron flux for radioisotope production purposes by more than 800%. Increases of up to 60% are also observed in levels of useful fluxes available for neutron diffraction experiments (small angle neutron scattering (SANS), neutron reflectometry, etc.).Such improvements in the neutronic characteristics of the NUR reactor opened new perspectives in terms of its utilization. More particularly, it is now possible to produce at industrial scales major radio-isotopes for medicine and industry and to perform, for the first time, material testing experiments.The cost of the irradiations in the optimized configuration is generally small when compared to those performed in the old configuration and an average reduction factor of about of 10 is expected in the case of production of Molybdenum-99 (isotope required for the manufacturing of Technetium-99 medical kits).In addition to these important results, safety analysis studies showed that the more symmetrical nature of the core geometry leads to a more adequately balanced reactivity control system and contributes quite efficiently to the operational safety of the NUR reactor.Results of comparisons between calculations and measurements for a series of parameters of importance in reactor operation and safety showed good agreement.