球形燃料元件中包覆燃料颗粒的化学分析

报道了高温气冷堆球形燃料元件中包覆燃料颗粒的表面铀沾污、自由铀含量及包覆燃料颗粒的装铀量等性能指标的测试方法、范围及测量误差。利用激光荧光法测量并计算了包覆燃料颗粒中的自由铀含量及表面铀 沾污,利用电位滴定法测量了包覆燃料颗粒的装铀量。结果表明,经4层连续包覆的包覆燃料颗粒的质量符合并满足高温气冷堆球形燃料元件对包覆燃料颗粒的设计要求。     

包覆燃料颗粒尺寸及其标准偏差对失效概率的影响

三结构同向性型(Tristructural isotropic,TRISO)包覆燃料颗粒是目前高温气冷堆和固态燃料熔盐堆采用的燃料元件。TRISO包覆燃料颗粒破损会导致裂变产物不可接受的释放,由此影响反应堆的安全运行。基于TRISO包覆燃料颗粒压力壳式破损模型,分析了TRISO包覆燃料颗粒核芯和各包覆层的尺寸对失效概率的影响,研究了TRISO包覆燃料颗粒核芯半径、疏松热解碳(Buffer)层厚度和碳化硅(Si C)层厚度的合理设计范围。同时,利用随机抽样统计的方法分析了TRISO包覆燃料颗粒核芯半径分布和各包覆层厚度分布对颗粒失效概率的影响。研究发现,降低Buffer层厚度分布的标准差至16μm可以使TRISO包覆燃料颗粒的失效概率降低一个数量级。     

Release Behavior of Fission Gas from Coated Fuel Particles under Irradiation

TRISO coated fuel particles for HTGR were irradiated by two sweep gas capsules in order to study the release behavior of the fission gas and try to predict the failure fraction of the particles on the basis of the measurement. For verification of the predicted failure fraction, post irradiation examination was conducted, and failure fraction in a visual inspection and acid leaching fraction were measured. Agreement between the predicted failure fraction and the acid leaching fraction was good for these samples except one. From the release behavior from the intact particles, in-pile diffusion coefficients of Kr in LTI-PyC were estimated and expressed as D=(2.9–6.0)×10⁴exp(-2.55×10°/RT) (cm²/s), where R ids the gas constant (=8.314 J/K) and T the absolute temperature. It was recognized that the release from failed particles was controlled by diffusion at 1,600°C and that from intact particles, predominantly by recoil at 1,400°C.     

Improvements in Quality of As-Manufactured Fuels for High-Temperature Gas-Cooled Reactors

The mechanisms of coating failure of the fuel particles for the high-temperature gas-cooled reactors during coating and compaction processes of the fuel fabrication were studied to determine a way to reduce the defective particle fraction of the as-manufactured fuels. Through the observation of the defective particles, it was found that the coating failure during the coating process was mainly caused by the strong mechanical shocks to the particles given by violent particle fluidization in the coater and by unloading and loading of the particles. The coating failure during the compaction process was probably related to the direct contact with neighboring particles in the fuel compacts. The coating process was improved by optimizing the mode of the particle fluidization and by developing the process without unloading and loading of the particles at intermediate coating process. The compaction process was improved by optimizing the combination of the pressing temperature and the pressing speed of the overcoated particles. Through these modifications of the fabrication process, the quality of the as-manufactured fuel compacts was improved outstandingly.     

Techniques for measuring the alpha-particle distribution in magnetically confined plasmas

Methods are proposed for measuring the alpha-particle distribution in magnetically confined fusion plasmas using neutral-atom doping beams, ultraviolet spectroscopy, and neutral particle detectors. In the first method, single charge exchange reactions, A⁰+He²⁺A⁺ +(He⁺)^*, are used to populate then=2 andn=3 levels of He⁺. The ultraviolet photons from the decaying excited states are Doppler shifted by 5–10 Å from those produced by the thermalized alpha-particle ash. In the second method, double charge exchange reactions, A⁰+He²⁺A²⁺+He⁰, enable fast neutralized alpha particles to escape from the plasma and be detected by neutral particle analyzers. These methods are distinguished from similar techniques of observing plasma impurities in that, in principle, they allow a determination of the dependence of the distribution function on energy and pitch angle, as well as on spatial position. Detector configurations are analyzed, count rates are estimated, and the detector feasibility is discussed. A preliminary analysis of the feasibility of the required neutral beams is presented, and exploratory experiments on existing devices are suggested.     

Vibro-Packing Experiment of Non-Spherical Uranium Dioxide Particles with Spherical Metallic Uranium Particles

Japan Atomic Energy Agency has developed vibro-packed fuel as one of the candidates for commercial fast breeder reactor fuels. In this study, vibro-packing experiments were carried out to investigate particle movement during vibro-packing as well as particle distribution after the completion of vibro-packing. Non-spherical uranium dioxide particles and spherical metallic uranium particles were used to simulate mixed oxide particles and oxygen getter particles, respectively. These experiments revealed the following facts. It is important to prevent segregation by means of feeding each size of the fuel particles uniformly into a cladding tube in order to disperse oxygen getter particles uniformly. “Simultaneous feeding” with volumetric powder feeders is useful to realize the above.     

单分散微米级铀氧化物微粒的制备

铀微粒同位素分析在核保障环境监测中发挥着重要作用。为保证准确测量单个微粒中铀同位素比,需使用丰度已知且尺寸适宜的标准微粒。通过将铀标准物溶解,并将溶液雾化形成液滴,再经蒸发溶剂、热分解一系列步骤,制得所需微粒。建立了1套以振动孔气溶胶发生器为核心的单分散铀氧化物微粒的制备装置。经扫描电子显微镜观测,制备的微粒呈球形;能谱分析表明,微粒为铀氧化物;微粒粒径主要集中在1.1μm左右,由于液滴的分裂与结合,导致了一定数量的较小和较大微粒存在;经二次离子质谱测定,其丰度值与标称值吻合,不同微粒间校正因子波动较小,能够满足实际测量的要求。     

Detection of Failed Coated Particles in HTGR Fuels by Acid Leaching

By acid leaching of several kinds of irradiated coated particle fuels, uranium-and ¹³⁷Cs-leaching fractions were measured. These fractions were compared with the surface failure fraction of the coated particles by a visual inspection in the post-irradiation examination. From the measurements it was found that ¹³⁷Cs was unsuitable as the objective nuclide for acid leaching, because this nuclide escaped from failed coated particles during irradiation or trapped in the graphite grains of the fuel-compact matrix, and therefore, it was difficult to relate the leaching fraction of ¹³⁷Cs to the failure fraction of the coated particles. Cesium-137 leaching fraction was less than 10% of the uranium fraction. The uranium leaching fraction agreed fairly well with the surface failure fraction. Therefore, uranium is regarded as the suitable objective nuclide for acid leaching. Also, combination of the acid leaching and the surface inspection is an useful method for detection of failed coated particles.     

Neutron Radiography Experiments at JRR-4, (II)

Experiments have been performed at JRR-4 (Japan Research Reactor) to investigate the capability of neutron radiographic techniques in applying to the nondestructive inspection of UO₂-PuO₂ mixed-oxide fuels. The object of the inspection was to detect “Pu particles” in the mixed-oxide fuels. In place of the actual fuel, two stages of TiO₂-EU₂O₃ mixed-oxide fuel dummy samples (the 1st stage for preliminary experiments and the 2nd stage for simulating the ATR fuel) were fabricated and radiographed with the direct exposure method using a Gd converter screen and high resolution films.

Neutron radiographs of the 1st stage dummy samples showed the excellent capability of the detection technique. Those of the 2nd stage dummy samples, however, revealed the detection limit of the technique, which showed that the present technique had not enough capability to satisfy the requirements in the inspection and that improvements of the detection technique especially on the contrast should be accomplished.     

燃料破损在线探测系统在核电厂的应用与分析

国内两台核电机组分别安装了1套由中国原子能科学研究院研制的燃料破损在线探测系统（FDDS）。通过FDDS对两台核电机组发生燃料破损时的连续监测和分析,表明FDDS在核电厂一回路放射性核素活度浓度在线测量及燃料破损监测中发挥了良好的作用,弥补了化学取样分析方法的不足。     

铀钚单粒子检测技术在核保障中应用研究

综述了近年来国内外铀钚单粒子检测技术用于核保障的进展。简要介绍了铀钚单粒子检测技术用于核保障的样品采集、粒子提取、定位转移和铀同位素标准粒子的制备,重点叙述了二次离子质谱法(SIMS)、热电离质谱法(TIMS)和电感耦合等离子体质谱法(ICP-MS)法在核保障微粒检测中的应用研究现状,展望了未来的发展趋势和研究前景。     

Fabrication of the First-Loading Fuel of the High Temperature Engineering Test Reactor

The High Temperature Engineering Test Reactor (HTTR). which is the first high temperature gas-cooled reactor (HTGR) in Japan, attained its first criticality in November 1998. The fabrication of the first-loading fuel started June 1995 and in December 1997, 150 fuel assemblies were completely formed. A total of 66,780 fuel compacts, corresponding to 4,770 fuel rods, were successfully produced through the fuel kernel, coated fuel particle and fuel compact processes. Fabrication technology for the fuel was established through a lot of research and development activities and fabrication experiences of irradiation samples. As-fabricated fuel compacts contained almost no through-coatings failed particles and few SiC-defective particles. Average through-coatings and SiC defective fractions were as low as 2 × 10^–6 and 8 × 10^–6, respectively. This paper describes (1) characteristics of as-fabricated fuel, (2) the experiences obtained from the first mass-production and (3) prediction of irradiation performance of the fuel in the HTTR.     

AMS直接测量铀微粒次同位素比的方法

铀微粒同位素比测定在核保障环境取样中发挥着重要作用,目前铀微粒中次同位素比的准确测定方法尚未完善。本工作使用小型加速器质谱研究了一种直接测量铀微粒中次同位素比的分析方法,采用CRM铀系列同位素标准样品,选取不同丰度、不同粒径的铀微粒进行测量分析,CRM-U200、CRM-U970微粒²³⁴U/²³⁵U和²³⁴U/²³⁶U同位素比的测量值与标称值之间的相对误差分别小于10%和20%,该法可实现微米级铀微粒的高灵敏测定,为单铀微粒的次同位素比分析提供了新的技术路线。     

Study of individual atmospheric aerosol particles at the Debrecen ion microprobe

Aerosol samples collected in outside and indoor environments with a 9-stage PI cascade impactor were analysed using PIXE, STIM (on and off-axis) and RBS ion beam analytical techniques at the Debrecen ion microprobe. Elemental composition, size and morphology of single aerosol particles were determined.Since the quantitative determination of light element concentrations requires a support material with small or no light element content, impactor surfaces made of different materials were tested in order to optimize the sampling and analysis. Thin polymer and Al foils were found to be possibly adequate substrate materials.     

Thermal Conductivities of Granular UO2 Compacts with/without Uranium Particles

The thermal conductivities of granular UO₂ compacts with and without uranium particles were measured to evaluate the thermal performance of vibro-packed granular MOX fuels containing metallic fine particle oxygen getters. The thermal conductivity of the compact with 10 wt% of uranium particles was higher than that of the compact without uranium particles. After heating beyond 1,408 K, the melting point of the uranium particles, the thermal conductivity increased further. The evaluation model for analyzing such phenomena was developed. The model predicted that once the UO₂ compact with uranium particles was exposed to a temperature beyond 1,408 K, the uranium particles should melt and provide interconnecting areas between the UO₂ granules and uranium particles, and between other uranium particles. The resulting increase of the thermal conductivity was reasonably expressed by the effect of necks in the compact on the heat conduction.     

UO_2-Zr弥散燃料板氧化扩散机理研究

UO2-Zr弥散燃料板的氧化过程包括包壳与冷却剂的氧化反应和芯体中弥散的UO2燃料微球氧原子扩散过程。本文通过直接求解球坐标系下的氧化扩散方程,得到UO2燃料微球高温下向芯体中氧原子扩散强度的解析式,该式与实验数据符合良好,并结合锆水反应与UO2燃料微球高温氧原子扩散效应构建了UO2-Zr板的氧化扩散模型。新模型能预测不同的氧化结构、芯体中更高的氧原子浓度以及相对较低的氧化吸氧量,为UO2-Zr板严重事故早期行为的研究提供了理论基础。     

Single Scattering Calculations of Sky-Shine with Cylindrical Container Penetrations

Loss by deposition of aerosol particles in an air sampling pipe causes error in the estimation of aerosol concentration in the atmosphere.

For a horizontal pipe, the deposition fraction for laminar flow can be estimated by equations of deposition governed by gravity settling and diffusion. For turbulent flow, there are two methods available—one using the equation by Yoshioka et al, to express deposition velocity, the other being the “extrapolation method” proposed by the present authors.

The present paper examines the validity of the two methods, with particular reference to the contribution of gravity settling to the deposition, and the effect of roughness of the pipe wall on the deposition from turbulent flow.

The deposition fraction in a horizontal straight metal pipe can be estimated with deviation from experimental values not exceeding a factor of 2, throughout the whole region covered by the study, extending over both laminar and turbulent ranges. Use of a suitable friction factor to account for the roughness of the pipe wall gives a reasonable value of deposition fraction in the turbulent region. The deposition from turbulent flow is mainly governed by gravity settling when the Reynolds number is not very large (Re?10⁴).     

空白采样膜中210Po含量及其对样品分析的影响

分析了4种不同材质2种常用尺寸规格的气溶胶采样膜中²¹⁰Po的含量。结果表明,国产玻璃纤维膜和聚丙烯膜中²¹⁰Po的含量较高,且这2种采样膜在日常监测中采用最多。通过测定玻璃纤维膜中铀含量可知,²¹⁰Po偏高主要是由生产膜的原材料引起的。通过实际样品测定与相对合成标准不确定度的估算,量化地分析了空白采样膜对实际气溶胶样品测定的影响。玻璃纤维膜A、B（分别为国内A、B厂家生产）和聚丙烯膜A（国内A厂家生产）材质的单张采样膜中²¹⁰Po含量与气溶胶样品中²¹⁰Po含量的比值较高,对分析结果的影响不能忽略,因此建议,在分析²¹⁰Po含量大于30 mBq的气溶胶样品时,要扣除空白采样膜中²¹⁰Po含量。当气溶胶中²¹⁰Po含量低至几十μBq/m³水平时,扣除空白采样膜后的测定结果不确定度较大,应选取²¹⁰Po含量较低的采样膜（如石英纤维材质）。     

Study of emission episodes of urban aerosols by ion beam analytical techniques

The quantitative elemental composition and morphology of over 500 atmospheric aerosol particles were determined by nuclear microscopy and scanning electron microscopy (SEM). The samples originated from eight sampling campaigns, when hourly variation and sources of the urban aerosol elemental components were studied in Debrecen between 2007 and 2010. Aerosol which could be connected to heavy metal pollution episodes and high aerosol pollution levels deposits were selected for the nuclear microprobe study.Ion beam analytical methods (micro-PIXE and STIM) provided the elemental composition of coarse (particles with aerodynamic diameter between 2.5 and 10 μm) aerosols while the morphology of the different particle types was determined by SEM.Through the elemental composition, elemental correlations and morphology different particle types were identified and attributed to different anthropogenic sources like biomass burning, oil combustion, traffic or industry.