A spherical harmonics—Finite element discretization of the self-adjoint angular flux neutron transport equation

The spherical harmonics (P_N) method is widely used in solving the neutron transport equation, but it has some disadvantages. One of them comes from the complexity of the P_N equations. Another one comes from the difficulty of dealing with the vacuum boundary condition exactly. In this paper, the P_N method is applied to the self-adjoint angular flux (SAAF) neutron transport equation and a set of P_N moments equations coupled with each other are obtained. An iterative method is utilized to decouple them and solve them moment by moment. The corresponding vacuum boundary condition is derived based on the Marshak boundary condition. The spatial variables are discretized on unstructured-meshes by use of the finite element method (FEM). The numerical results of several problems demonstrate that this method can provide high precision results and avoid the ray effect, which appears in the discrete ordinate (S_N) method, with relatively high computational efficiency.     

加速器中子源的中子注量测量方法

在用静电加速器中子源标定探测器的中子灵敏度实验中,采用“BF3长计数管 定标器”系统过渡,用^197Au中子活化分析方法达到了对中子注量在线、绝对监测的目的。这种方法给出与加速器束流不同角度、不同距离处的中子注量。介绍了这种中子注量测量方法。     

Simulation of a neutron scattering method for measuring void fraction in two-phase flow

Experiments have indicated that fast/epithermal neutron scattering techniques are attractive for void fraction measurement in two-phase flow. Some of these experiments have been simulated by Monte Carlo neutron transport calculations. The simulations predict results in agreement with the measurements. This suggests that the experimental technique has a sound theoretical basis, and that numerical simulations may be used to design experimental setups for different applications.     

Modelling effects on axial neutron flux in a Tokamak device

Using Monte Carlo N-Particle (MCNP5), three different Tokamak models using different geometries were simulated, maintaining some basic parameters from the ITER design. The neutron flux and the reaction rates were obtained over different volumes: FW, divertor and along the different device walls. The three geometries were compared under the same conditions. The results showed the behaviour of the neutron flux spectra along the different walls, as well as, the most suitable model taking in consideration the different analyses and the final purpose of adding a transmutation layer. Finally, the chosen geometry will be used to analyse the burnup, buildup, decay, and processing of material under irradiation.     

Fluence and flux dependence of void formation in pure aluminum

Void formation in high purity aluminum resulting from irradiation to fluences between 1.5 × 10¹⁹ and 1.6×10²² neutrons/cm² (E ⪢ 0.1 MeV) at a temperature of 55 ± 5°C was studied, primarily by means of transmission electron microscopy. Void size distribution curves were obtained for all fluences, and from these the mean void radius was found to increase in proportion to the irradiation time raised to the one-sixth power. The void concentration displayed a fluence dependence best described by a power law, N ~ (φt)^a, in which the exponent decreased from 2.0 at 10¹⁹ neutrons/cm² down to only 0.1 at 10²² neutrons/cm². Treating the swelling with an analogous power relation, ΔV/V~(φt)^b, a similar saturation effect was observed, with the fluence exponent b decreasing roughly from $\text{5}\text{2}$ to $\text{1}\text{2}$ over the range effluence studied. Increases in the microhardness of irradiated specimens were found to be consistent with an expression based upon void contributions to the impeding of dislocation motions. Irradiation at a factor-of-ten lower flux produced effects upon the void morphology (e.g., half as many but larger and more elongated voids) much like those resulting from irradiation at a higher temperature. In each case, the lowering of the vacancy supersaturation during irradiation is a consequence. When material degassed prior to irradiation was compared with similarly irradiated as-received material (containing 15–20 atomic ppm hydrogen), no difference in the void concentrations or sizes was evident.The experimental observations are compared with the current models for void formation. Two models most consistent with the experimental evidence both involve transmutation-produced helium playing a crucial role in void nucleation — one involving heliumstabilized spikes and the other small helium bubbles as the nuclei of voids.     

Direct measurement of mechanical momentum of a neutron flux

Translated from Atomnaya Énergiya, Vol. 66, No. 1, pp. 48–49, January, 1989.     

Attenuation of pile neutron flux in polyethylene

The relaxation lengthsofresearch reactor neutrons were measured in polyethyIene. The findings are in excellent accord with data computed theoretically using the method of moments. The relaxation lengths are 15% less than in the case of water.Translated from Atomnaya Énergiya, Vol. 15, No. 1, pp. 17–20, July, 1963     

用钴活化法测定反应堆中热中子积分通量

本文叙述了用钴活化法测定高通量堆中热中子积分通量的方法。测得的热中子积分通量值与计算值作了比较。本法适于测定在高通量堆中长期辐照的较高热中子积分通量。     

Capacitance changes in neutron irradiated n-type silicon: The flux effect

The influence of fast neutron flux on radiation-induced capacitance changes in heavily irradiated n-type Si has been studied by means of capacitance techniques. We have observed two regimes; flux-dependent and -independent for the case of high and low flux irradiation, respectively. A model that describes changes in the thermally stimulated capacitance as a function of time of irradiation has been proposed.     

The design of the J-type neutron flux distribution measurement system

This paper introduces the design of a J-type aeroball system that the tube penetrates the lateral wall of reactor pressurized vessel (RPV), then immediately goes down to the vessel bottom and then goes up through the lower core support plate into the reactor core. Some experimental results related to gas flowing within a thin tube are presented in the paper, such as the gas friction drag coefficient on the ball’s way and etc. From theoretical and experimental viewpoints, the feasibility of the system is proved in pneumatic holding-up and β measurement aspects. In order to ensure an enough ratio of signal to noise, the maximum distance between two measuring points in water reactors is given. The paper gives out the measuring number per two-assemblies width N_i=Int(n_i/2+0.51), which is the accuracy relation between the number of fuel assembly and the minimum one of measuring point to only reconstruct 2D neutron flux distribution completely by the measured data.