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覆土抑氡是铀矿冶场址退役重要手段,覆土实验研究结果可为退役治理工程的设计与环境影响评价等工作提供科学依据。研究针对废石堆与尾矿库两种典型铀矿冶退役覆盖场地,设计覆土试验,确定了覆盖介质、覆土场地尺寸、压实度、监测方法等。根据覆土实验结果对比讨论两种场地氡析出率、覆土厚度、介质扩散系数之间的关系,建立了相应的函数关系表达式。结果表明,两种覆盖场地覆土厚度与氡抑制效果显著相关,但废石堆与尾矿库在覆盖过程中覆土厚度与氡抑制效果在不同的覆土层表现不同。研究结果可应用于指导覆土施工现场工作。 相似文献
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基于核反冲理论建立了铀尾矿氡析出的数学模型和蒙特卡罗模拟方法,模拟了不同含水饱和度条件下铀尾矿颗粒粒度对氡析出的影响。结果表明,镭分布于颗粒表面时,4种含水饱和度(5%、20%、50%、75%)条件下的K均随颗粒尺寸的增大先增大后趋于稳定。镭分布在距颗粒表面34 nm和68 nm时,含水饱和度为5%或20%的条件下,K先增加后趋于稳定,而含水饱和度为50%或75%的条件下,K随颗粒尺寸的增大先稍有下降然后逐渐稳定。运用蒙特卡罗方法计算了各铀尾矿样品的氡析出率,计算的氡析出率与实测铀尾矿氡析出率符合较好,相对误差为3%~9%。 相似文献
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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。 相似文献
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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。 相似文献
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氡来源于土壤、铀尾矿、岩石等多孔射气介质,铀尾矿库滩面是尾矿堆积或沉积体与大气环境直接接触的暴露面,氡气从该交界面析出并经大气弥散而污染周边环境,覆盖处置是滩面控氡的主要手段。本文以典型铀尾矿库滩面为例,综述氡析出机理及其影响因素,阐述了多孔射气介质固有特性及外部气象环境条件对铀尾矿库滩面氡析出的影响机制。结果表明,国内外学者已对多孔射气介质固有特性影响氡析出的规律开展了大量研究,但由于实验尺度、研究方法存在差异,矿物颗粒特征影响氡析出机制的解释仍存在争议,外部气象环境等因素对铀尾矿库滩面氡析出的影响机制尚不明确。为此,提出今后研究的关注点:(1)真实条件下,氡析出过程的合理表征形式;(2)开展大尺度实验探究多孔介质固有特性对铀尾矿库滩面氡析出的影响机制。 相似文献
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在土壤中添加不同比例的膨润土或石灰粉,比较添加前后土壤覆盖层厚度相同时的降氡效果。本研究利用具有稳定氡析出率的标准模块(35 cm×35 cm×12 cm)作为源项,并自制截面为正方形(30 cm×30 cm)高度可调的实验箱,实验时尽量保持含水率和压实度一致。实验结果表明:随土壤中膨润土或石灰粉添加比例的增大降氡效果越好,且添加膨润土比石灰粉降氡效果更好;对结果进行曲线拟合分析,得出了添加不同比例膨润土或石灰粉的土壤覆盖厚度与降氡效果的对数关系式,并计算出了相应的氡扩散系数;推导出了在满足退役管理限值0.74 Bq·m-2·s-1时,覆盖前氡析出率与所需覆盖土壤厚度的关系式,可用于待治理氡析出率表面的保守覆盖厚度的计算。通过经济比较分析,得出了在添加比例较低时,所需费用比原始土壤高,添加比例较高时,所需费用比原始土壤低,且所需费用随着添加比例的增加而减小。 相似文献
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随着核电的发展,天然铀需求量增大,地表尾矿大量堆积而产生的氡污染成为不可忽视的问题,如何能更加有效地降低铀尾矿氡析出量具有重要意义。一般采用地表堆积后覆盖的方法减小铀尾矿造成的地面环境危害,而氡的迁移过程经历在被覆盖材料迁移和覆盖材料中迁移两个阶段,因此研究氡迁移规律成为解决问题的关键内容。本文总结并评述了国内外学者针对氡析出影响因素、氡迁移理论、覆盖控制方法和效果、覆盖参量方面的研究,发现目前虽对氡析出机理和影响因素进行了全面分析,但是氡析出过程中多因素耦合机理和作用过程还需要更多的深入研究;覆盖材料主要为天然材料和人工合成材料,目前常采用的是天然材料,其中红土添加膨润土、砂质亚黏土、红土均为良好的降氡材料,后续还需要更多的研究,从而找到有效控制氡并对生态环境影响最小的覆盖材料。 相似文献
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^99Tc在土壤中的吸附行为研究 总被引:1,自引:0,他引:1
在有氧条件下,用静态实验法研究了放射性核素^99Tc在各种土壤中的吸附行为,并研究了土壤的特性和土壤平衡水的pH和Eh值,选择活性炭和还原铁粉作添加剂,与砂土混合作为工土壤,研究放射性核素^99Tc在人工土壤中的吸附行为,结果表明,^99Tc在天然土壤(格列土除外)中的吸附比很低,人工土壤中的吸附比很高,并且随着添加剂的质量分数和接触时间的增大而增大。对核素吸附的物理化学过程和可能的吸附机理也进行 相似文献
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植物和动电修复铀污染土壤的研究现状 总被引:2,自引:0,他引:2
核工业的发展,导致重金属铀的排放和扩散,造成了地表局部土壤的污染,对社会和环境造成了一定的影响。由于铀的特殊性和土壤成分的复杂性,如何修复铀污染的土壤成为了一个难题。本文在已有研究基础上,对土壤中铀的形态特征、植物修复和动电修复的概念、国内外的研究进展、制约因素、优势和局限性、未来的发展趋势、两者的互补性进行了讨论,提出未来的发展方向是使植物修复和动电修复相结合,植物修复用于大面积、中低浓度铀污染土壤的修复,动电修复应用于较高浓度、环境恶劣、深层的铀污染,两者的结合将有望成为解决这一难题的希望。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(8):1106-1116
Radon and its progeny are an important part of natural environmental exposure to radiation. However, little information is available about the radon contents of soil gas. We carried out a survey of radioactivity, focusing on 222Rn-concentrations in soil gas in parts of western Japan. Fifty nine samples in soil gas from 4 Prefectures of the Kinki district were analyzed with a liquid scintillation counter after the trapping of radon in soil gas into a toluene based-scintillation cocktail, together with 19 samples of interest from karst and uranium mining sites in another two Prefectures for comparison. The cumulative frequency of the 222Rn-concentrations in soil gas of the Kinki district showed a log-normal distribution. The average content was found to be 11.9kBqm?3 (arithmetic mean) and 7.5kBqm?3 (geometric mean). A maximum concentration of radon in soil gas, 2.1 MBqm?3 was found at the marker of the Ningyo uranium mining site. Surveys of natural radioactivity in soil were also carried out with a Ge(Li) detector to determine the concentrations in soil, mainly focusing on uranium and thorium series. The radon concentrations in soil gas were weakly correlated with those of uranium series in soils. There were no great differences vertically in the natural radioactivity in soils within 1 m, but a difference by one order of magnitude was found in soils horizontally even in the residence area of the Kinki district. 相似文献
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某铀尾矿库周边土壤中铀元素的空间分布与污染评价 总被引:1,自引:1,他引:0
为查明某铀尾矿库周边土壤中铀元素的空间分布特征及污染程度,对该铀尾矿库进行了现场采样,利用便携式XRF元素分析仪进行了原位测试,并采用SPSS软件对铀元素的测试数据进行了统计分析。结果表明:该铀尾矿库周边土壤中铀元素含量的平均值分别是中国及其所在省土壤中铀元素含量背景值的4倍和2.3倍,而样品中铀元素含量变异系数达到61.84%,属于强变异,且样品中铀元素含量的统计频数属于正偏态分布,这说明该铀尾矿库对其周边土壤产生了一定的污染效应。在统计分析基础上,运用单因子污染指数法与地质累积指数法,并结合Arc GIS空间分析功能对该铀尾矿库周边土壤中铀元素污染程度进行了定量评价,评价结果表明,主要污染区域集中在该铀尾矿库坝址区0~500 m范围内及尾矿库NE侧的应急处理池周围0~100 m内,该评价结果可为铀尾矿库治理及植物修复提供基础数据。 相似文献
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The mineralization and transformation of both added organic nitrogen and native soil N in red soils from four different ecological conditions 总被引:1,自引:0,他引:1
The NH4^ -N,microbial biomass-N,humus-N,and extractable orgainc N derived from the added ^15N-labelled ryegrass and soil indigenous pool were measured separately with 15N tracing techniques.Based on the recovery of NH4^ -15N and lost-15N(mainly as NH3),more than 30% of the added ryegrass ^15N was mineralized in 15d.The amount of mineralized N increased with time up to 90d for all soils except for the upland soil in which it decreased slightly.The minearlization of ryegrass N and incorporation of ryegrass-15N into microbial biomass was greatest in upland soil.The transformation of ryegrass 15N into humus 15N occurred rapidly in 15d,with higher humus ^15N occurring in the upland or tea-garden soil than the paddy and unarable soil.The addition of ryegrass caused additional mineralization of soil indigenous organic N and enhanced the turnover of both microbial biomass N and stable organic N in soils. 相似文献
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我国表层土壤中存在的钚主要来自于20世纪中后叶大气层核试验之后的全球沉降。本研究以土壤中现存的钚为研究对象,利用加速器质谱(AMS)和电感耦合等离子体质谱(ICP-MS)对环境中痕量水平钚同位素精准测量技术,在我国部分典型地区进行了现场土壤纵向分层采样和实验室测量。在此基础之上,将对流-弥散方程在单次瞬时输入情况下的解与我国不同地区土壤柱中钚核素的垂直分布数据进行了拟合,得到新疆、湖北、贵州、重庆、甘肃土壤中钚核素的表观对流系数为0.046~0.163 cm/a,表观扩散系数为0.058~0.339 cm2/a,土壤中239+240Pu浓度峰的迁移速率为0.063~0.187 cm/a。实测结果表明,钚同位素在土壤中的迁移速率与土壤有机质含量有明确的负相关关系。 相似文献
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Radionuclides, such as ~(238)U,~(232)Th and ~(40)K, can be found in urban soil. To evaluate the natural radioactivity in the environment, soil samples were collected form Shihezi city and radioisotope concentrations were determined by X-ray fluorescence. The dose rate of urban soil (mGy per year, mGy/a) was calculated. The results indicate that the U, Th and K concentrations of the urban soils were, respectively, 1.2-3.2 mg/kg, 6.4-12.3 mg/kg and 2.05%-2.24%, with the mean values of 2.47 mg/kg, 10.47 mg/kg and 2.16 %. Dose rates of urban soils were 10.04-19.55 mGy/a with the mean value of 16.31 mGy/a. This dose rate is the perfect and maximum value of natural radiation in soil and different with the air absorbed dose rate from terrestrial γ-rays. The mean value of air absorbed dose rate was about 57.42 nGy/h. The annual effective dose rate in air was about 0.07 mSv/a and the average value of Ra_(eq) in urban soil was 120.37 Bq/kg. The relative contribution of a particle to the dose rate is higher than that derived from β- and γ-rays in the urban soils. 相似文献
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Momo Takada Toshihiro Yamada Teruhiko Takahara Satoru Endo Kenichi Tanaka Tsuyoshi Kajimoto 《Journal of Nuclear Science and Technology》2017,54(4):452-458
Downward migration of 137Cs in soils was studied in three mixed deciduous forests c.a. 40 km northwest of the Fukushima Daiichi Nuclear power plant (FDNPP), Japan. We selected three different types of forest regarding to environmental condition such as slope inclinations and snow coverage conditions at the time of deposition. We examined temporal changes in the vertical distribution of 137Cs from litter layers to 10 cm soil depth for two years (2.3 to 4.3 years after the FDNPP accident in 2011). At all three study sites, the 137Cs in the litter layer had largely migrated to surface soil by 2013. After 2014, about 80% of the 137Cs in forest soils (litter layer to 10 cm soil depth) remained within 0–5 cm soil layer. The vertical distribution had not changed substantially since 2014, suggesting that changes to the downward migration rates of 137Cs in soils drastically decreased with time. In addition, small amounts of migrating 137Cs could not be detected by the present method because there was a large spatial variation in the distribution of soil 137Cs. The results showed similar patterns of soil 137Cs distribution among the three study sites although there were differences in the environmental conditions. 相似文献