低温解析-液闪法检测植物中氚含量

为评价涉氚活动中氚对环境的影响,建立了低温解析—液闪法检测核设施周围植物样品中氚含量的分析方法。该方法将核设施周围植物样品中组织自由水氚(TFWT)在110~120℃解析出来,用液闪计数仪测量其氚含量。该分析方法比传统分析方法缩短约120 min,对植物样中TFWT的平均回收率优于76%,能够满足涉氚场所植物中TFWT的快速分析。     

氚化水蒸气短期暴露后胡萝卜中氚的浓度

为了研究气态氚化水(HTO)事故释放后胡萝卜对HTO的吸收和有机结合氚(OBT)的形成,在4个不同的生长发育期把盆栽的胡萝卜暴露于氚化水蒸气1 h,并于试验结束和收获时分别测量胡萝卜地上部和地下部的组织自由水氚(TFWT)和有机结合氚(OBT)的含量。结果表明大部分情况下胡萝卜地上部分的TFWT浓度在一小时内就能与周围空气中HTO的浓度达到平衡。收获时地上部和地下部的相对TFWT浓度均低于试验结束时的值,收获时的值分别为试验结束时值的1/389~1/86和1/116~1/3,地下部减少的幅度小于地上部。试验在地上部和地下部的生长旺盛期进行,试验结束和收获时相应的这两部分OBT浓度也最高。收获时地上部和地下部OBT浓度小于试验结束时的值,但是肉质根膨大期时期进行试验,收获和试验结束时地上部和地下部相对OBT的浓度差异不大。收获时地下可食部分中OBT与TFWT的比值范围为2.79~20.73,在食入剂量评价中OBT的贡献要大于TFWT。     

氚化水蒸汽短期释放后野生植物中氚的分布

为探究西北地区典型野生植物体内氚的分布情况，在密闭环境舱和阳光人工气候室内开展氚化水（HTO）蒸汽短期释放后3种代表性野生植物（梭梭、多枝柽柳和骆驼刺）体内氚的累积行为实验研究。结果表明，HTO短期释放后氚在植物体内的分布随植物种类和器官的不同而不同。相同实验条件下，骆驼刺地上部分组织自由水氚（TFWT）和有机结合氚（OBT）的活度浓度最高。对于同一植物种类而言，不同器官的TFWT、OBT活度浓度由大到小依次为：叶>茎>根。3种试验植物不同部位TFWT活度浓度随着植物的生长均呈降低趋势，其中叶片TFWT活度浓度的降低尤为显著。3种试验植物叶片OBT活度浓度随着植物的生长均呈显著降低趋势，其降幅由大变小；而茎部OBT的活度浓度则先增大后减小。     

氚化水蒸汽晚上和白天短期释放情况下花生中氚含量的研究

为研究氚化水(HTO)蒸汽晚上和白天短期释放情况下花生对HTO的吸收和有机氚(OBT)形成的差异,利用盆栽试验在花生开花下针期和结荚期分白天和晚上模拟HTO的短期释放,并在试验结束和收获时分别测量叶子和果实中组织自由水氚(TFWT)和OBT的含量。研究结果表明,花生叶子晚上对HTO的吸收小于白天。开花下针期晚上暴露试验结束时,叶子中TFWT和OBT的相对浓度分别是白天相应值的1/6和1/3;收获时叶子中的TFWT和OBT均小于暴露试验结束时的值。结荚期晚上暴露试验结束时,花生叶子和果实中TFWT和OBT的相对浓度分别是白天相应值的1/3、2/3和2/3、1.13倍,收获时果实中的TFWT大于暴露试验结束时的值,叶子中OBT的相对浓度为暴露试验结束时的1.7倍,果实中OBT相对浓度却减少为原来的1/4;而白天试验收获时叶子中OBT的相对浓度小于试验结束时的值,但果实中OBT的相对浓度大于暴露试验结束时的值。表明HTO在不同生育期白天和晚上释放情况下,花生叶子和果实中TFWT和OBT的变化趋势不同,所以在气态氚短期释放情况下预测植物中的OBT浓度时,应根据不同的释放时间选择相应的参数。     

核设施氚气态释放后植物中有机氚的研究进展

从核设施释放到大气中的氚主要以氚化水（HTO）和氚化氢（HT）两种形式存在,最终以HTO的形式进入植物体。植物体中的氚有两种化学形态：自由水氚（TFWT）和有机氚（OBT）,其中OBT又被细分为交换性OBT和非交换性OBT。与TFWT相比,OBT在植物体内有较长的滞留时间和较大的剂量转换因子,在氚的食入剂量中OBT占主要份额,因此有必要对植物中的OBT展开全面研究。本文就植物中OBT的定义、交换性OBT和非交换性OBT的确定、OBT的形成过程及其影响因子、OBT预测模型的研究进行综述,同时对今后植物中OBT应重点研究的内容进行了简单分析,以期为植物中OBT的研究提供一定的参考。为准确评价OBT造成的辐射剂量,今后对OBT的研究中应着重从测量、夜间形成机理和环境中的行为等方面进行。     

尿中氚水和总氚的分析测定

用蒸馏 液闪法和氧化蒸馏 液闪法分别测量了氚污染人员尿中的氚水和总氚(氚水和有机氚)的浓度。根据72个高于本底水平的尿中氚水和总氚浓度分析结果比较,认为在氚内污染工作人员的尿中,有机氚与氚水的浓度比值为(5.4±3.7)%。     

含氚硅胶中氚回收率的测量

采用加热解吸结合催化氧化及吸附法对含氚硅胶中的氚回收率进行了精确量化.结果显示,含氚硅胶中的氚主要以化合态的形式存在,含氚硅胶中氚回收率随样品的加热解吸温度的升高而增加,在相同的解吸温度下,含氚硅胶中氚回收率随载气流速的增加而呈下降趋势,在解吸温度为500℃及载气流速为60 mL/min下仍有5%以下的氚滞留在硅胶中,...     

植物样品中有机氚测量方法的初步研究

为研究植物样品中有机氚（OBT）浓度相关测量的最佳方法,以秦山核电基地所采植物和人为氚污染的植物样品为研究对象,对去除交换性有机氚(E-OBT)所需的最合适浸泡水用量和浸泡时间及样品氧化燃烧和收集过程中氚的残留效应进行了研究。结果表明：用30倍于干物质质量的低氚水浸泡24 h,可有效去除植物样品中的E-OBT;用50 mL低氚水冲洗氧化燃烧炉1次,即可将残留在其中的氚冲洗干净;经3次大量低氚水冲洗后OBT水样收集瓶与石英舟中无氚残留。     

环境样品中自由氚和组织结合氚的收集

本文介绍了所建立的环境样品中的自由氚和组织结合氚的分别采样装置和方法。对于样品中的自由氚,用低真空干燥回收法,回收率可达98％;对于样品中的组织结合氚,用连续加样催化氧化冷凝收集法,回收率为93％。两法都能一次收集足够制两个并行测量样的水量。     

高压氘氚气氛下铜对氚的吸附

为了解氚在铜表面的吸附和解吸行为，对铜样品在n（D）∶n（T）=1∶1，503 K时，15 MPa下恒温8 h后，再在27 MPa恒温6 h下进行了氚的吸附，并对吸附氚的铜样品在室温下和加热到1 173 K时的解吸氚量和吸附总氚量进行了测量。结果表明，铜的吸附总氚量为31.89 MBq/cm²,解吸氚量为29.18 MBq/cm²，测量的标准差为6.49％；室温和加热条件下铜所释放的氚中，化学成分主要是HTO和HT，大部分以HT形式存在；铜的自由氚量占吸附总氚量的3.64 ％；铜的热解吸谱至少存在3个解吸峰，其解吸温度分别为650，750和1 173 K以上。     

金属样品残余氚测量方法

为定量评价氚在结构材料和老龄贮氢材料内部的滞留量,用化学蚀刻法测定不锈钢内部氚浓度大小、分布情况及同位素交换后老龄贮氚铀床的氚滞留量。结果表明,贮氚13年的不锈钢样品中氚主要存在于样品内表面由表及里的120μm范围内,样品蚀刻深度110.6μm范围内,不锈钢的平均氚滞留量～9.37×10-4mmol/g,贮氚铀粉平均氚滞留量～4.16×10-5mmol/g。该方法对测量金属中微量氚有较高灵敏度,可检测金属中残余氚的滞留量。     

我国部分地区食品氚的分布规律初探

调查了我国北京、兰州、上海和成都四个城市的食品氚浓度，其中食品的游离水氚（ＴＦＷＴ）和有机结合氚（ＯＢＴ）浓度的平均值分别为４．５６Ｂｑ·Ｌ＾－１和２９．５１Ｂｑ·Ｌ＾－１，食品ＯＢＴ与ＴＦＷＴ含量的比值（ＳＡＲ）为６．４７。食品ＯＢＴ浓度由北往南逐渐下降（Ｐ〈０．０５），与纬度呈高度线性关系。植物类食品的ＯＢＴ浓度较动物类食品高，且地面生长食品的ＯＢＴ浓度最高，灌溉类食品最低。     

Role of microstructure and heat treatments on the desorption kinetics of tritium from austenitic stainless steels

The liquid scintillation counting of solid samples (LSC-SS technique) was successfully used to study the role of microstructure and heat treatments on the behavior of residual tritium in several austenitic stainless steels (as-cast remelted tritiated waste, 316LN and 321 steels). The role of desorption annealing in the 100-600 °C range on the residual amount of tritium in tritiated waste was investigated. The residual tritium concentration computed from surface activity measurements is in good agreement with experimental values measured by liquid scintillation counting after full dissolution of the samples. The kinetics of tritium desorption recorded with the LSC-SS technique shows a significant desorption of residual tritium at room temperature, a strong barrier effect of thermal oxide films on the tritium desorption and a dependance of the tritium release on the steels microstructure. Annealing in the 300-600 °C range allows to desorb a large fraction of the residual tritium. However a significant trapping of tritium is evidenced. The influence of trapping phenomena on the concentration of residual tritium and on its dependance with the annealing temperature was investigated with different recrystallized and sensitized microstructures. Trapping is evidenced mainly below 150 °C and concerns a small fraction of the total amount of tritium introduced in austenitic steels. It presumably occurs preferentially on precipitates such as Ti(CN) or on intermetallic phases.     

Study on the tritium behaviors in the VHTR system. Part 2: Analyses on the tritium behaviors in the VHTR/HTSE system

Tritium behaviors in the very high temperature gas reactor (VHTR)/high temperature steam electrolysis (HTSE) system have been analyzed by the TPAC developed by Idaho National Laboratory (INL). The reference system design and conditions were based on the indirect parallel configuration between a VHTR and a HTSE. The analyses were based on the SOBOL method, a modern uncertainty and sensitivity analyses method using variance decomposition and Monte Carlo method. A total of 14 parameters have been taken into account associated with tritium sources, heat exchangers, purification systems, and temperatures. Two sensitivity indices (first order index and total index) were considered, and 15,360 samples were totally used for solution convergence. As a result, important parameters that affect tritium concentration in the hydrogen product have been identified and quantified with the rankings. Several guidelines and recommendations for reducing modeling uncertainties have been also provided throughout the discussions along with some useful ideas for mitigating tritium contaminations in the hydrogen product.     

Effect of outside tritium source on tritium balance of a D-T fusion reactor

Attainable tritium breeding ration in the blanket system must be larger than the required breeding ratio when no effective tritium resources from outside are expected. It is revealed recently that a considerable amount of tritium can be trapped to the re-deposition layer of the first wall materials and that the time constant of this phenomenon is rather long. Then, the tritium breeding ratio around 1.1 is required in the blanket system when 3 years is claimed for the tritium doubling time to prepare tritium for the initial inventory of a next reactor. Construction of an outside tritium supply is one of the possible ways to compensate the lack of tritium because it is generally considered that the attainable tritium breeding ratio in the solid breeder system is around 1.05. It is reported recently that a high-temperature gas-cooled reactor can produce 10 kg of tritium per year. The preferable amount of tritium production rate of the outer tritium supply is discussed in this study from the viewpoint of tritium balance in a D-T power reactor.     

Calibrating a gas chromatograph to measure tritium using calorimetry

The availability of calibrated gas mixtures in a tritium plant is an important precondition for correct analysis of unknown gas samples because a quantitative analysis with a gas chromatograph (GC) requires frequent calibration checks. To calibrate a GC for tritium, certified gas mixtures with different tritium concentrations are necessary. These mixtures can be produced directly in a laboratory. In this case an independent method is needed to determine the tritium concentration in the mixture with high accuracy. Calorimetry is the method of choice because its accuracy is better than 1% and it is non-destructive method.Using the closed tritium loop of the Tritium Laboratory Karlsruhe (TLK), different mixtures containing tritium in the range 1–100% have been produced and measured with one of the in-house calorimeters. After that the GC of the CAPER facility at TLK has been calibrated several times with an uncertainty of a few percents.     

Overview of tritium safety technology at the Tritium Process Laboratory of JAERI

The Tritium Process Laboratory of the Japan Atomic Energy Research Institute is the only laboratory in Japan where grams of tritium can be handled to carry out R&D on tritium processing and tritium safety handling technologies for fusion reactors. The tritium inventory is approximately 13 grams. Since 1988, basic research has been performed using gram-level tritium quantities. During the past 5 years, approximately 1 kilogram of tritium has been handled in experimental apparatus. The total amount of tritium released through the stack of TPL was controlled to less than 1 Ci without any accidents. In order to establish more complete tritium safety for DT fusion reactors, main R&D areas on tritium safety technology at TPL were focused on a new compact tritium confinement system, reliable tritium accounting and inventory control, new tritium waste treatments, and tritium release behavior into a room.     

Untersuchungen zur rückhaltung von tritium in HTR-brennelementen

In a nuclear reactor tritium is produced by ternary fission and a number of further neutron-induced nuclear reactions. The liberation of the tritium so produced from the ceramic fuel of a high temperature reactor was examined. Fuel particles with pyrocarbon coatings are able to retain tritium to a large extent under reactor operating conditions. The amounts of tritium found in reactorirradiated fuel particles correspond within the limits of error with the calculated concentrations. The activation energy of the liberation factor for tritium from fuel particles is 106 kcal/mol in the temperature range 1400–1900°C. The release of the tritium found according to ${}^6\text{Li (n, α)}{}^3\text{H}$ from a reactor graphite was measured and the concentration of tritium in graphite samples from the AVR nuclear power station was determined.     

Effect of water adsorption on tritium release from Li4SiO4

As a ceramic material proposed for tritium breeding in a fusion reactor blanket, lithium orthosilicate (Li₄SiO₄) is being examined in view of the influence of water uptake on tritium release behavior. In this work, out-of-pile tritium release experiments were performed on Li₄SiO₄ samples that were transferred and stored under different moisture environments. The water content was measured on the samples that were treated in similar conditions. Effects of water adsorption on the chemical form and temperature of released tritium were investigated. It is found that with the water content increases, the gaseous tritium fraction decreases and the proportion of low-temperature desorption of HTO increases. The results of this study can be used later for engineering and design activities for fusion reactor blankets.     

Effect of hydrophobic paints coating for tritium reduction in concrete materials

The effects of hydrophobic paint coating on a concrete material of cement paste on the tritium transport are investigated. The cement paste is coated with two kinds of paints, acrylic-silicon resin paint and epoxy resin paint. We investigated the amount of tritium trapped in the samples exposed to tritiated water vapor by means of sorption and release. It was found that both the hydrophobic paints could reduce effectively tritium permeation during 50 days exposure of tritiated water vapor. The effect of tritium reduction of the epoxy paint was higher than that of silicon while the amount of tritium trapped in the epoxy paint was larger than that of silicon due to difference of the structure. Based on an analysis of a diffusion model, the rate-determining step of tritium migration through cement paste coated with the paints is diffusion through the paints respectively. It was found that tritium was easy to penetrate through silicon because there were many pores or voids in the silicon comparatively. In the case of tritium released from the epoxy paint, it is considered that tritium diffusion in epoxy is slow due to retardation by isotope exchange reaction to water included in epoxy paint.