Theoretical Study of High Radon Emanation

Radon emanation coefficients larger than 0.6 have been reported; such large values were unexpected. This led the authors to study how the maximum possible radon emanation coefficient (hereafter referred to as ‘maximum radon emanation probability’) could be determined. Theoretical calculations were repeated in which the grain configuration was changed in order to get the maximum radon emanation probability. Two types of grains were targeted. The first type consisted of two components mixed together; one component was a large amount of mother grains including no radium and the other component was a small amount of very fine grains including radium. For this type, the maximum radon emanation probability was obtained as 0.75. The second type consisted of only one grain component including radium. For this type, the maximum radon emanation probability was 0.625. In both types, the high coefficients were attributed to the extremely small size of the radium-bearing grains. This finding hinted at a possible countermeasure to suppress radon emanation, i.e., sintering at a rather low temperature, which may best be fitted to industries which process naturally occurring radioactive materials (NORM).     

Radon Emanation Dependence on Grain Configuration

Very small pores called ‘nanopores’ play an important role in enhancement of radon emanation in grains. The concept of nanopores was originally proposed by Rama and Moore. The present paper has evolved this concept into more specific grain configurations to estimate radon emanation coefficients by theoretical calculations. These configurations cover combinations of nanopore geometry and radium distribution in grains. Radium is the parent nuclide of radon. Assuming isotropic emission of radon from its birthplace with recoil energy imparted by the decay of radium, the present calculation led to nearly the same high radon emanation coefficients as measured; these were as high as 0.18 under moist conditions. Therefore, it was theoretically verified that even small pores of nanometer size may contribute to high radon emanation.     

Demonstration of a Method to Suppress Radon Emanation from Uranium-bearing Wastes

The authors have previously done a theoretical study of radon emanation and quantitatively demonstrated that a small pore of even nanometer size with moisture in its microscopic grain structure can give as high a radon emanation coefficient as around 0.18. Therefore, it was concluded necessary to remove pores of any size in the grain in order to suppress radon emanation. Melting of uranium-bearing wastes is one of the best technologies for this purpose. In order to verify this theoretical finding, a series of experiments was carried out using three test samples; unprocessed, cemented and vitrified calcium superphosphate. Calcium superphosphate was chosen because it resembles a uranium-bearing waste like sludge in terms of both radioactive nuclide adhesion on the grain surface of the waste matrix (surface contamination) and the grain geometric shape. As expected from the theory, radon emanation from the vitrified sample was extremely low compared to the unprocessed sample. On the other hand, radon emanation from the cemented sample remained very high. The present study opens doors to suppression of radiation exposure from radon and to safe disposal which does not depend on integrity of the final waste form and the site cover soil.     

Theoretical Estimation of Radon Emanation Coefficients for UO2 Particles Deposited on Surfaces of Uranium-bearing Wastes

In nuclear fuel fabrication facilities, fine particles of UO₂ deposit on the surfaces of walls, equipment, ventilation filters, etc. which may finally become uranium-bearing wastes when these items are removed or replaced. Radon is one progeny of uranium and emanates from those wastes. It is very difficult to experimentally simulate such radon emanation, which means it is difficult to measure radon emanation coefficients for those wastes. The present paper theoretically calculated radon emanation coefficients for them assuming UO₂ particles remain on the surfaces of such wastes in the distant future when radon is formed in these particles. The calculated average radon emanation coefficient was 0.03. With more complete information about particle size distribution from fuel manufacturers, this method would be able to provide better predictions.     

水浸颗粒堆积型射气介质氡析出规律的理论研究

铀尾矿库和地表浸铀铀矿堆是一种颗粒堆积型射气介质,其水位的变化和覆水厚度对氡迁移与析出的影响不容忽视。为揭示这类介质表面氡析出的规律,本文基于菲克定律和气液两相界面氡的传输理论,建立了水浸颗粒堆积型射气介质氡的一维传输-扩散数学模型,并获得稳态条件下气液两相体系中氡浓度分布的解析解和氡析出率的计算公式。通过研究,获得以下结论：1）水位为0 m时,颗粒堆积型射气介质表面氡析出率随介质厚度的增大而增大,其增长率随厚度的增大而减小;2）介质表面氡析出率随水位的增大先增大后减小;3）当水体高度大于射气介质厚度时,覆水表面氡析出率随覆水厚度的增大而减小,随覆水氡扩散系数的增大而增大。     

破碎射气介质内氡渗流运移和析出规律的实验研究

渗流是破碎介质内氡运移的主要方式之一,研究氡在破碎射气介质内的渗流运移和析出规律对氡的防护设计具有重要意义。为此,本文以粒径为4～5 mm的铀矿石为实验样品,利用自制的一维渗流实验装置研究了不同渗流速度下破碎射气介质内孔隙氡活度浓度和介质表面氡析出率的变化规律。实验结果表明,破碎射气介质的气体渗透率较大,氡的运移很容易由渗流主导。当破碎射气介质内氡主要以渗流方式运移时,可通过测量介质内同一位置不同渗流速度的孔隙氡活度浓度或同一渗流速度不同位置的孔隙氡活度浓度,运用氡在射气介质中的浓度分布解析式和非线性最小二乘法,估算出介质的可运移氡产生率。一定渗流速度范围内,同一高度的氡活度浓度随渗流速度的增大呈负指数减小,同一渗流速度的氡活度浓度随离介质渗流入口距离的增大近似呈线性增大。介质渗流出口表面氡析出率随渗流速度的增大呈指数增大,最终趋于稳定。     

铀废石堆放场地的氡析出特征

根据铀废石堆放形式,分析了平坦型、沿山坡堆放型、山型三类铀废石堆放场地的氡析出特征,得出了平坦型废石场以扩散析出为主,沿山坡堆放型和山型废石场既要考虑氡的扩散析出,还要考虑氡掺流的影响。但废石含水量是影响三类废石场氡析出的主要因素。     

Modeling Radon Flux Density from the Earth's Surface

In order to make the idealized model for predicting soil radon flux more practically and accurately, two central variables (radon emanation power and soil water content) controlling the amount of radon transportation in soil were formulated. The reformulated model for predicting radon flux density was verified by the field measurements carried out in 10 different sites. The result indicates that the reformulated model is useful for improving the prediction feasibility and accuracy of radon flux density from the earth's surface.     

794矿尾矿渣场镭比活度计算法参数试验结果分析

介绍了利用镭比活度计算法确定核工业794矿铀尾渣场氡析出率所用参数——氡射气系数和氡扩散系数的测量结果及其分析对比,野外采样室内化学分析镭比活度与γ能谱测量镭比活度对比,探讨了在北方气候条件下,铀尾渣场氡射气系数和扩散系数的变化规律和特点,以及这些参数测量的最佳气候和季节,并对镭比活度计算法的特点和测量结果进行了分析。     

灼烧温度对氡射气析出率的影响

通过了解锆英砂、铀矿粉、石英砂一铀矿粉混合物等含铀地质材料中^222Rn的析出情况,探索了降低这些材料中氡射气析出率的方法,并应用灼烧法研究了灼烧温度对上述材料中氡射气析出率的影响。实验结果表明,上述地质材料的氡射气析出率随灼烧温度升高而减小。灼烧法是一种有效降低氡射气析出率的方法,可作为对氡射气及放射性子体的防护手段加以利用。     

煤样射气系数的测定及其影响因素的探讨

介绍了煤样氡射气系数测量方法,应用该方法测量了全国不同地区多个煤样的氡射气系数。根据测量结果分析了镭-226比活度、煤样粒径、样品含水率等因素对氡射气系数的影响,研究结果表明:氡的射气系数与煤样中镭-226比活度没有相关性;但与样品的粒径有关,且随粒径减小而增大;样品含水率对测量结果有明显影响,当样品含水率5%时,氡的射气系数随着含水率的增加而增加,当样品含水率5%时呈下降趋势。     

Effect of Soil Moisture Content on Radon and Thoron Exhalation

In this study, the authors considered the effect of soil moisture in the emanation process of radon and thoron gases. Weathered granite soil was selected as the test soil and it was packed in a polypropylene container (275 × 210mm² and 100mm in height), up to 50mm in depth from the bottom. The container was covered with the exhalation rate measuring instrument adopting the accumulation method and γ-particles were counted at 30 s intervals for 30 min to estimate the exhalation rates. A sporadic increase in the radon and thoron exhalation rates was caused by the increase in the moisture content up to 8%. However, the exhalation rates showed a decreasing tendency with the increase in moisture content over 8%. Although the measured radon exhalation rate was about 25% of the calculated one, both measured and calculated radon exhalation rates had similar trends with an increase in the moisture content in the soil. The measured thoron exhalation rate agreed well with the calculated one. When the moisture content was in the range of 3.5–18%, it was considered that applying the correlation between the moisture content and the measured thoron exhalation rate is useful for estimating the thoron effective diffusion coefficient.     

The Effect of Some Soil Characteristics on Soil Radon Concentration and Radon Exhalation from Soil Surface

To find out the impacts of soil characters on radon concentrations in soil and radon exhalation from soil, field measurements on soil radon concentrations (60 cm under the soil surface) and radon exhalation rate from soil surface were carried out in totally 31 points with different types of soil in three cities in both South and North China. Soil radium contents, water contents, soil porosity and grain size were concretely analyzed in our laboratory. The linear simulation was used to analyze the above data. The results showed that radon exhalation rate from soil and radon concentrations in soil have direct proportion to soil radium contents. Rather high radium content and radon exhalation rate were measured in Guiyang area, 67±28Bq/kg and 40±59mBq/m²-s, however no high soil radon concentration was found due to the difficulties in the measurements on clay soils with high water saturation. Compared with soil radium contents, radon exhalation rate from soil and soil radon concentrations are more easily impacted by soil characters and change in a rather large range.     

基于换气量和氡析出率计算的排氡风量在某水电地下工程通风设计中的比较研究

以某水电地下工程项目为例,根据换气量和氡析出率两种方法对地下厂房系统排氡风量进行了计算,并将排氡风量与排湿降温风量进行比较。得出:对于地下工程氡析出率大于200 Bq/(m³·h)时,可按实测氡析出率计算排氡风量,对于地下工程氡析出率小于200 Bq/(m³·h)时,可按GBZ 116—2002《地下建筑氡及其子体控制标准》中排氡通风率计算排氡风量,而地下工程设计风量应选取排氡风量与排湿降温风量两者最大值。该计算方法为水电行业地下工程通风降氡设计提供了技术支持。     

Transient-Diffusion Measurements of Radon: Fick's Law Confirmation and 218Po/214Po Behavior Determination

Usually, radon diffusion coefficients in soils are measured based on the assumption that Fick's law holds true. But, unlike in a free volume, strictly speaking, there is no guarantee that Fick's law holds in soils. Transient-diffusion measurements of radon in soils are best employed in order to confirm Fick's law. Alpha-particles from ²¹⁸Po/²¹⁴Po and from ²²²Rn cannot be distinguished in the course of those measurements. Therefore, the relevant portions of the detector reading must be allocated to each of these nuclides. For that purpose, the behaviors of ²¹⁸Po and ²¹⁴Po in the detection volume were determined and their ratios of contribution to the detector reading were also determined by Monte Carlo calculations and a verification test. This information was used to confirm Fick's law for representative Japanese sand and loam samples through indicial transient-diffusion measurements and a theoretical interpretation of the measured data.     

活性炭对土壤氡吸附饱和性能研究

选用六组不同类型的活性炭,通过室外对土壤氡的吸附饱和实验,研究了活性炭对低射气土壤氡的吸附行为。实验结果表明:不同类型的活性炭对土壤氡的吸附饱和时间不同,均远小于30 d,吸附性能较好的椰壳活性炭在第八天即达到吸附饱和;不同类型活性炭的吸附饱和浓度差异也较大。因此,在低射气区进行活性炭吸附氡气测量时,应选择小粒径的椰壳活性炭作为吸附载体。     

气溶胶对氡室氡浓度影响的探讨

通过实验测试往氡室中充入气溶胶对氡室氡浓度的影响,及测试在不同氡浓度及气溶胶浓度的条件下气溶胶对氡子体的吸附.实验结果显示:气溶胶对氡室氡浓度的稳定性没有影响,不同气溶胶浓度则会改变氡子体的结合状态,从而影响氡子体的扩散系数,所以会影响总量测量仪的测量结果.     

Transient-Diffusion Measurements of Radon: Practical Interpretation of Measured Data

The mathematical calculation to obtain a radon diffusion coefficient from measured radon transient-diffusion data is usually done by fitting a difference equation to the data. The difference equation is obtained through transformation of the time-dependent diffusion equation based on Fick's law. But, actual measured transient-diffusion data often have much scatter. Therefore just fitting over the whole range of the measured data through the method of least squares may not always be valid, because the method offers a mathematical interpretation rather than a physical one. Instead, the actual radon diffusion coefficients must be otherwise obtainable from measured radon transient data. Taking this viewpoint, the present paper claims that about a 90% leveling-off time is often easily discernible regardless of the shape of the radon transient curve obtained from the measured data and it can be a decisive factor for determining the radon diffusion coefficient. Alternatively, transient diffusion data during the taking-off period of the transient for a ramp-wise introduction of radon into the targeted soil column are not so scattered and can also be decisive. The present paper provides theoretical justifications to support these claims.     

小体积氡室中氡子体状态参数调控的模拟研究

基于空气中氡子体和气溶胶粒子的行为规律,研究了一种小体积氡室中氡子体状态参数稳定调控方法,即通过调节小体积氡室总换气率和气溶胶粒子数浓度实现氡及氡子体浓度、平衡因子和未结合态份额等状态参数稳定调控方法。建立了调控物理模型,根据模拟条件甄选氡子体和气溶胶粒子行为参数,采用Matlab模拟计算了小体积氡室氡子体状态参数的调控范围,并将模拟计算值与实验值进行比对,部分验证本文建立的调控方法。模拟计算结果表明,本研究所建立的调控方法可在小体积氡室内实现氡子体浓度、平衡因子和未结合态份额的稳定调控。本研究建立的调控方法为实验研究提供了初步的理论基础。     

广东省部分大型建设工程中环境氡浓度调查研究

本文对地处广东省境内铀矿发育地段的五指山隧道和飞来峡水利枢纽,两大工程项目在涉及大量的土石方开挖和搬运的大规模的施工活动中,导致含铀地段放射性核素赋存条件的改变和转移,由此引起的工程区域内的环境氡浓度及变化规律进行了调查,并对其结果进行对照分析。