放射性核素在裂隙岩石中的迁移模型研究

本文描述了放射性核素在裂隙岩石中的单一介质和双重介质二维迁移模式,并用Galerkin有限元与算子分裂迎风—均衡格式相结合的方法求解了数学模型,取得了较为满意的结果。为了验证模型的正确性,分别用两种模型对济南岩溶区总硬度进行了数值模拟,计算结果与测定结果符合较好,说明模型是基本正确的。为了探讨模式对预测深部库核素迁移规律的适用性,对核素~(90)Sr和~(99)Tc的迁移进行了1000年的预测,结果与文献预测的核素分布规律相符合,说明模式对深部核素迁移是适用的。在上述两种模拟计算中,结果均没有发生数值波动和浓度出现负值的奇异现象,克服了用有限元法解弥散方程时浓度出现负值和数值波动问题,为建立高放废物库安全评价中的地圈子模式及进一步研究核素迁移模式提供了理论依据。     

Pu在板岩与粘土中的动态吸附模拟实验研究

以西南某地的板岩与粘土为吸附介质,采用动态吸附法来模拟放射性Pu废液在吸附介质的扩散与迁移,得出Pu浓度随时间与淋滤柱柱深的变化曲线。实验结果表明:Pu在粘土中分配系数约是板岩中4倍左右;粘土和板岩中同一柱深时,钚在土壤中数值要稍大于板岩中的含量,且流量变化是影响核素迁移的主要因素之一。     

地质屏障在高放废物处置中的初步研究

简述了地质屏障对延缓核素迁移所起到的作用和一些国家对围岩类型的选择,介绍了地质屏障中核素迁移机理以及迁移对地质屏障的影响,对高放废物的处置有着现实指导意义。     

核素迁移的研究现状和进展

指出在高放废物深地质处置系统安全评价中,研究岩体裂隙中核素迁移行为尤为重要,介绍了核素迁移的机理,并对试验研究及进展和模拟研究内容作了概要总结,且对今后的发展进行了展望。     

我国岩洞型低中放废物处置核素迁移计算库室模型研究

关闭后核素经由处置设施释出并在环境中的迁移计算是放射性废物处置安全评价的核心内容,目前国际常用的评价方法为库室模型方法。我国低中放废物岩洞型处置尚处于选址与初步可行性研究的初期阶段,在此背景下,结合已有的岩洞型处置初步概念设计、工程屏障材料性能与预选场址地下水流动特性,开展核素迁移计算库室模型研究十分必要,研究成果弥补了我国岩洞型处置核素迁移评价的空白,为后续安全评价与工程设计迭代优化的开展奠定了良好基础。     

溶质运移与高放核废物处置

通过对溶质运移和高放核废物处置的介绍,结合核素迁移以及我国高放核废物处置的情况,介绍了在核素迁移过程中T-H-M-C四场耦合的组合分类,提出在核废物处置过程中进行四场耦合的研究,并指出在将来的四场耦合研究过程中加强化学场研究的重要性,对高放核废物处置具有一定的指导作用。     

粒径对多孔介质中悬浮颗粒迁移—沉积特性的影响

粒径变化对悬浮颗粒在多孔介质中迁移—沉积过程影响的研究有重要意义。利用自主研发的砂层迁移—沉积模拟试验系统,研究不同粒径的悬浮颗粒在不同尺寸多孔介质中的迁移—沉积特性。结果表明,对于相同尺寸的多孔介质,随着悬浮颗粒粒径的增加,到达相对浓度峰值时间增加,而对应的相对浓度峰值降低;同时,对于相同粒径的悬浮颗粒,随着多孔介质尺寸增大,相对浓度峰值增加;另外,相对于多孔介质,悬浮颗粒粒径的变化对其迁移—沉积过程影响更为显著;随着多孔介质与悬浮颗粒粒径比增大,相对浓度的峰值和终值增大;根据粒径比不同将悬浮颗粒在多孔介质中的迁移—沉积类型划分为“滤饼过滤型”、“迁移—沉积型”、“自由迁移型”3种。研究结果为水源热泵回灌过程中悬浮颗粒在地层中的迁移—沉积特性进一步研究奠定了基础。     

裂隙岩体核素迁移模型及其在高放废物地质处置库安全性能评价中的应用

通过一维迁移模型的线性叠加，提出了基于裂隙参数随机分布的多途径裂隙核素迁移模型。模型可计算任意给定点处核素的弥散通量(Bq／a)。模型从随机分布的裂隙导水系数出发，将随机分布的裂隙导水系数平均分成有限个单元，每1单元即代表1条运移途径，并具有其相应的裂隙参数(如导水系数、隙宽)和分布频率。裂隙中任意给定点处核素的弥散通量则由各运移途径的计算结果按导水系数的分布频率进行叠加得出。     

多孔介质应用于建筑结构的热质传递及制冷性能分析

本文将含湿多孔介质床层应用于建筑围护结构,利用多孔介质内水分蒸发的吸热作用,为房间提供部分冷量。本文在建立非饱和多孔介质热质迁移过程数学模型的基础上,分析了室外环境参数及多孔介质床层结构对床层内温度分布、蒸发量场及水蒸气迁移的影响,为多孔介质蒸发制冷板应用于建筑结构的推广和应用提供了理论指导。     

不同种类胶体在含水介质中沉积和释放特征

在进行粘土、高岭土和蒙脱石三种胶体在含水介质中沉积和释放试验的基础上,重点研究不同种类胶体在含水介质中迁移、沉积和释放的差异性,同时探讨了胶体的迁移-沉积机理。结果表明,相对于粘土胶体和蒙脱石胶体,高岭土胶体最不容易在含水介质中迁移。胶体开始释放浓度随孔隙体积数的增大迅速降低,随后变化缓慢,最后趋于稳定。粘土、蒙脱石和...     

Radium migration through clay liners at waste disposal sites

The migration of 226Ra through the bottom compacted clay liner of the wastewater disposal reservoirs of an industrial plant that processes uranium ore was evaluated. An instrumental method for 226Ra analysis in soils, consisting of detector calibration, the determination of detector counting efficiency, cumulative counting of both background and soil samples in regular counting intervals, and photo-peak smoothing was developed. The 226Ra was analyzed by means of its granddaughter 214Bi, at a photo-peak of 609 keV. The results showed that most of the 226Ra which diffused from the solution into the soil was retained in the upper layer of the sample, and that just a small percentage migrated to the subjacent layers. This methodology is adequate for the assessment of the migration of radionuclides through soil layers and for environmental impact studies related to contamination of soils by radionuclides.     

Impact of humic matter on sorption of radionuclides by montmorrilonite

The paper has analyzed the impact on sorption by montmorrilonite of the chemical nature of radionuclides, forms of their finding and concentration of humic matter. It has been found that for Eu(III) and Th(IV) in the presence of humic matter one can observe reduction of sorption within the pH wide interval, which is determined by the formation of fulvate and various ligand hydroxofulvate complexes, while for U(VI)—in an acid region, which indicates the formation of only fulvate complexes. It has been shown that in the presence of humic matter in the aqueous medium an increase of migration of radionuclides is determined by a decrease of their sorption on mineral suspensions and precipitation on the surface of silt sedimentations as a result of the formation of soluble complex compounds, while the presence of humic matter on the surface of clayey components of soils substantially increases immobilization of radionuclides, i.e., reduced migration of the latter to the environment.     

三维结构下全路径迭代射线追踪方法

基于Fermat原理对三维任意界面情况下的2点间射线追踪问题进行了研究。通过采用一阶Taylor不完全展开等办法,给出了三维情况下全路径迭代射线追踪算法的计算格式,并在几个三维介质模型上进行了射线追踪模拟计算。计算结果表明:它的计算速度相当快,且其计算精度可以根据需要达到任意要求,为三维结构下地震偏移和层析成像提供了一种可行的射线追踪方法。     

LNAPL在二维空间的运移机制与分布特性研究

本文利用改进多谱图象分析方法,对实验获得的图象进行处理,获取不同时刻LNAPL含量差值(LNAPL Content Difference)在二维空间上的分布图。通过图象分析探讨LNAPL在非饱和带中非均质条件下的迁移机制和分布特性。结果说明,介质的非均质性和流体特性对污染物的迁移产生重大影响;在“油-气”二相体系中,LNAPL含量差值分布呈现出较好的对称性,而在复杂的“水-油-气”三相体系中,LNAPL含量差值分布呈现出不对称性和非均匀性,这种不均匀性也反映了毛细带中含水量分布的不均匀性。     

Geochemical landscape strategy in monitoring the areas contaminated by the Chernobyl radionuclides

The Chernobyl accident led to radionuclide contamination of vast areas that now need to be monitored; the development of a regional land use strategy is now needed. Landscape geochemistry enables us to structure, classify and map the environmental factors responsible for the redistribution of radionuclides (i.e. soil-forming rocks and soil properties, vegetation cover, types of ground water migration, and vertical and lateral geochemical barriers). Combined with land use information, regional geochemical landscape maps serve as the basis to map in toposequence conditions of mass migration and accumulation in natural and cultivated landscapes. Such mapping makes it easier to choose representative monitoring sites. This type of mapping is also helpful to interrelate and extrapolate the data already obtained on radionuclides' environmental migration for different groups of geochemical landscapes with similar types of contamination, migration and accumulation patterns. A geochemical landscape approach is demonstrated using the example of part of the Bryansk region (Russia), which is considerably contaminated with ¹³⁴Cs and ¹³⁷Cs.     

VTI介质地震成像技术在地质勘查中的应用

随着地震勘探目标复杂程度的提高,基于各向同性介质假设的基本成像方法越来越难以满足生产实际需要。因此研究在各向异性介质情况下的成像方法,对于各种地下构造勘探以及矿产开发,都有着极为重要的意义。论文推导适用VTI各向异性介质的SSF延拓算子并实现VTI介质炮域单程波叠前深度偏移,对VTI-HESS模型进行了计算验证。相比各项同性介质情况下的偏移成像方法,VTI介质炮域偏移方法加入了各向异性参数的影响因素,其结果与实际勘探资料更加符合,具有更好的成像效果。     

分层填埋垃圾体中气体一维稳态运移规律

针对垃圾填埋场分层填埋特点,提出了填埋垃圾产气率和导气系数分层计算方法,建立了分层填埋垃圾体中气体一维稳态运移分析模型,分析了垃圾的产气率、导气系数和封顶覆盖层的气密性对气压力大小及分布的影响,并探讨了垃圾填埋龄期对气压力分布的影响规律。分析结果表明:对于均质垃圾体,产气率与导气系数的比值越大,则填埋气压力越大;对于含封顶覆盖层的垃圾体,产气率主要控制气压力大小,导气系数控制气压力沿填埋深度分布梯度。封顶覆盖层厚度的增加或其导气系数的降低将使填埋气释放量减少,则气压力整体提高。垃圾填埋龄期越大,则垃圾体中气压力越小。     

The recent sedimentation history of the esk estuary,Cumbria, U.K.: The application of radiochronology

The sediments of the Esk estuary, Cumbria, contain a variety of radionuclides which are derived from the British Nuclear Fuels Ltd (BNFL) reprocessing plant at Sellafield, Cumbria. In principle the total ecosystem of the Esk estuary is labelled with a variety of radionuclides which we have studied in order to investigate fundamental process which take place in estuaries; also to improve our knowledge of relationships which exist between the rate of release of radionuclides in the BNFL source term and their distribution in the Esk. On the basis of defined sampling procedures we have dated the rate of sedimentation for the major sediment types of the system using six different radionuclides, and four independent methods, including a procedure of statistical modelling. The model is based upon procedures for matching the shape of the BNFL radionuclide release profile over a period of ～ 10 y, with that for the distribution of radionuclides in profiles of sediment cores. Good agreement is obtained for the match.In the Esk a large proportion of the radionuclides which are retained in sediments are associated with particulate matter and surfaces of sediment debris; in accreting sediments these deposits have not been disturbed during the past ～ 30 y.In modelling the releases of radionuclides from point sources, attention needs to be paid to the chemical and physical composition of the source term, as this can influence the subsequent distribution of radionuclides in nearshore and estuarine marine ecosystems.     

Performance assessment model development and parameter acquisition for analysis of the transport of natural radionuclides in a Mediterranean watershed

This paper describes the methodology developed to construct a model for predicting the behaviour of the natural radioisotopes of U, Th and Ra in a Mediterranean watershed. The methodology includes the development of the performance assessment model, obtaining water flow and radiological parameters based on experimental data and analysis of results. The model, which accounts for both water flows and mass balances of the radionuclides in a semi-natural environment, provides assessments of radionuclide behaviour in grassland and agricultural soils, rivers and reservoirs, including the processes of radionuclide migration through land and water and interactions between both. From field and laboratory data, it has been possible to obtain parameters for the driving processes considered in the model, water fluxes, source term definition, soil to plant transfer factors and distribution coefficient values. Ranges of parameter values obtained have shown good agreement with published literature data. This general methodological approach was developed to be extended to other radionuclides for the modelling of a biosphere watershed in the context of performance assessment of a High Level Waste (HLW) repository under Mediterranean climate conditions, as well as for forecasting radionuclide transport under similar Mediterranean conditions that will occur in the future in other areas. The application of sensitivity and uncertainty analysis was intended to identify key uncertainties with the aim of setting priorities for future research. The model results for the activity concentration in the reservoir indicate that for (238)U and (230)Th the most relevant parameter is the initial concentrations of the radionuclides in the reservoir sediments. However, for (226)Ra the most important parameter is the precipitation rate over the whole watershed.