热中子注量率测量方法研究

研究了金箔激活法和热释光法测量热中子注量率的方法,并对中国原子能研究院101重水反应堆某热中子通道热中子注量率的大小进行了测量,结果表明两种方法测量结果一致性很好,偏差仅为8．8％。     

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.     

Examination of reactor grade graphite using neutron powder diffraction

Graphite is of principal interest in Generation IV nuclear reactor concepts. In particular, graphite will be the moderator for the Very High Temperature Reactor. In support of experimental and computational investigations that aim at understanding the behavior of reactor grade graphite under operating conditions, neutron powder diffraction experiments have been performed at the North Carolina State University PULSTAR reactor. The collected diffraction patterns exhibit intense broadening of several of the reflections, characteristic of turbostratic stacking. In order to quantify this disorder structurally, a model combined with a Rietveld-like refinement approach was implemented, which includes several refinable parameters that aim at describing this type of structure. Stacking parameters representing the probabilities of a random and registered shift between stacking packages were defined. The results indicate that the studied reactor grade graphite specimens contain a small fraction of layer disorder. The inferred interlayer spacing for the specimens is slightly larger than the theoretical value for graphite of 0.335 nm and the lattice constant is slightly less than 0.246 nm. The developed methodology is found to be successful in fitting the neutron diffraction patterns of reactor grade graphite.     

Standardization of neutron sources in the graphite prism of a reactor

A method of standardizing neutron sources is described in which a comparison is made in a graphite prism of the strength of the source and the neutron loss produced by an absorber placed in the neutron field. The experimental apparatus and the measurements carried out by the author in 1951 are described; Ra--Be and Ra--Be sources were calibrated with an accuracy of ± 3%.     

热中子透射法测定湿玻璃纤维材料含硼量时的水分干扰

报道了用热中子透射法测湿玻璃纤维材料含硼量（B2O3含量）时水分干扰的理论计算和实验研究的结果。推导了水分干扰的关系式。对于质量为16g的样品,水分变化1％（百分质量）时影响测量的含硼量值为0．28％（百分质量）。     

Porosity effects on the neutron total cross section of graphite

For subthermal neutron energies, polycrystalline graphite shows a larger total cross section than predicted by existing theoretical models. In order to investigate the origin of this discrepancy we measured the total cross section of graphite samples of three different origins, in the energy range from 0.001 to 10 eV. Different experimental arrangements and sample treatments were explored, to identify the effect of various experimental parameters on the total cross section measurement. The experiments showed that the increase in total cross section is due to neutrons scattered around the forward direction. We associate these small angle scattered neutrons (SANS) to the porous structure of graphite, and formulate a very simple model to compute its contribution to the total cross section of the material. This results in an analytic expression that explicitly depends on the density and mean size of the pores, which can be easily incorporated in nuclear library codes.     

Annealing of neutron damage in graphite irradiated and stored at room temperature

Nimonic PE16, a gamma-prime Ni₃(Al,Ti) precipitate-strengthened alloy under consideration for fast reactor structural applications, has been neutron irradiated in three heat treatment conditions: solution treated, aged, and overaged. After irradiation at 600° C to 5.4 × 10²²n/cm² (E > 0.1 MeV), or 27 dpa, specimens were characterized for gamma-prime precipitate stability by transmission electron microscopy. The precipitate microstructures after irradiation reflected the influence of the preirradiation heat treatment; and indeed the precipitate particles present prior to irradiation remained stable. However, additional precipitation occurred during irradiation in each of the specimens examined. The in-reactor gamma-prime precipitation process decorated such microstructural features as voids, dislocations and carbide precipitates. Examples were found in the solution-treated condition where gamma prime in the form of Archimedes' screws had precipitated on climbing screw dislocations. The precipitation behavior observed is compared with predictions from existing models. It is concluded that models for solute diffusion to point-defect sinks and for Ostwald coarsening can account for the observations, but that the models for precipitate stability controlled by cascade dissolution during neutron irradiation do not.     

Application of unified composite detectors for measuring neutron spectra

The results of computational-experimental studies of the parameters of the energy spectra of neutrons from the nuclear facilities of the Russian Science Center Kurchatov Institute which have different core structures, reflectors, parameters, and type of fuel elements are presented. The measurements were performed using the methods of resonance activation unified composite detectors. Individual measurement results are presented. __________ Translated from Atomnaya énergiya, Vol. 104, No. 4, pp. 227–233, April, 2008.     

Study of the neutron multiplication effect in an active neutron method

The neutron multiplication effect appears when an item contains large amounts of nuclear material. The neutron multiplication effect in this paper means the effect of subsequent fission reactions which are caused by fission neutrons produced by interrogation neutrons from a neutron generator. The previous active neutron method could not distinguish between first-fission and subsequent-fission neutrons and might overestimate the amount of nuclear material. However, the neutron multiplication effect in the active neutron method has not been adequately investigated. We discuss the evaluation method of the multiplication effect in the fast neutron direct interrogation method, one of the active neutron methods, using simulations with the Monte Carlo code MVP and experiments involving uranium waste drums. The first-generation neutrons from an external neutron source generate fission neutrons called second-generation neutrons, the second-generation neutrons generate third-generation neutrons, and so on. This study supposes that the neutron multiplication effect is mainly caused by the third-generation neutrons under the condition that the fourth-generation neutrons are much fewer. This paper proposes a correction method for the neutron multiplication effect in the measured data.