广东省环境水体中的氚活度浓度水平

2012—2013年对广东省全省范围内环境水体氚活度浓度水平进行了调查,并对调查结果进行了分析研究。结果表明:(1)空气水蒸气、江河水、水库水的氚活度浓度水平显著高于海水、地下水氚活度浓度水平(p＜0.01),空气水蒸气活度浓度水平明显高于雨水氚活度浓度水平(p＜0.05);(2)江河水、雨水的氚活度浓度水平与空气水蒸气的氚活度浓度水平相关(相关系数分别为0.655和0.637, p＜0.01),雨水中的氚也会对水库水、江河水氚活度产生影响(相关系数分别为0.444和0.440,p＜0.1);(3)本次调查结果基本与历史数据相符,目前广东省环境水中氚活度浓度水平在<0.081~0.69 Bq/L之间,已基本接近核爆前天然本底水平;(4)大亚湾/岭澳核电站附近环境水中氚的活度浓度水平比广东省其他地区高5~10倍左右。     

核电厂氚的产生和排放分析

研究核电厂中氚在堆芯和主冷却剂中的产生方式,以及进入环境的途径、形态和排放量,是核电厂辐射环境影响评价非常重要的内容之一。本文通过分析压水堆核电厂中的主冷却剂系统、辅助系统、三废系统和厂房通风系统的运行模式,结合国际上的运行经验参数,研究主冷却剂中的氚排放进入环境大气的途径和形态。研究结果表明:理论计算分析结果与电厂运行经验数据相吻合,氚主要通过燃料棒中的三元裂变,可燃毒物棒中硼的活化以及主冷却剂中硼、锂和氘流经堆芯时的活化产生,主要以液态氚水形式排放,影响气液两相分配份额的主要因素取决于主冷却剂向反应堆厂房和辅助厂房的泄漏率。     

Korea's progress on the ITER tritium systems

Korea has been operating four units of CANDU nuclear power plant since 1983. Tritium generated in the heavy water of the plant has been removed by Wolsong TRF (tritium removal facility) since 2007. Korea has developed a 500-kCi BU-type tritium transport container. Furthermore, strictly controlled tritium release to the environment from the CANDU nuclear power plant in Korea will also be a helpful experience for ITER. The BU-type tritium transport container will be unpacked and the quantity of tritium in the metal tritides of the primary vessel will be measured accurately before the tritium is liberated by heating the metal tritides. In the ITER fuel cycle plant, Korea is responsible for the development and supply of the SDS (fuel storage and delivery system). We present the on-going R&D progress to use a non-nuclear material ZrCo for the storage and delivery of tritium. Especially we present the delivery characteristics of the ZrCo hydride bed by considering the fueling requirement and maintainability of the ZrCo hydride bed. We also present various test results for the experimental ZrCo beds and the test programs for the leak tight large scroll pump with a magnetic coupling-drive.     

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。     

Tritium dose criteria and radiological impact of a tritium plant

Radiation safetry criteria adopted in Russia (in the former USSR) distinguish five classes of tritium compounds. The lowest permissible tritium concentration in the air is set for insoluble tritium compounds (3.10⁵ times lower than that for HT). Russia's criteria for tritiated radioactive waste are outlined. It is explained why the tritium weighting factor of two is used as a basis for the tritium dose criteria development in this country. The ecological situation nearby a large tritium processing plant is considered. Amounts of tritiated waste produced at the plant, sources of tritium effluents, tritium content in the air, water, snow, soil and vegetation as well as HTO sorption parameters of various food products are reported. On the basis of HTO near-surface concentrations in the air and public doses measured 3 km away from the plant stack, the tritium dose factor was calculated.     

Tritium: its generation and pathways to the environment at CANDU 6 generating stations

Tritium production rates and its pathways in CANDU 6 generating stations are studied in this paper. Tritium is generated primarily by the D(n, γ)T reaction in the reactor core. The major sources of tritium are moderator and coolant heavy water which are exposed to high neutron flux levels during reactor operation. A small amount of tritiated heavy water escape from heavy water filled systems is inevitable. Most of the tritiated heavy water which escapes is recovered through well-equipped heavy water recovery and collection systems. The vaporized tritiated heavy water is controlled by the D₂0 vapour recovery and ventilation systems. Similarly, the liquid tritiated heavy water is collected by portable D₂0 recovery tools and by an active drainage system. The remaining small amount escapes as tritiated heavy water and is lost to the environment in airborne and/or waterborne form.     

Tritium Safety-Related Studies at TPL of JAERI

Activities regarding tritium safety technology in the Tritium Process Laboratory (TPL) at Tokai Establishment of Japan Atomic Energy Research Institute are reviewed. Research and development of a new tritium removal system is being carried out by using a gas separation membrane which enable to make the ITER atmosphere detritiation system more compact and cost-effective. Techniques of gas flowing calorimetry and laser Raman spectroscopy are applied to develop new tritium accountancy methods. Studies of tritium-material interaction, such as plasma material interactions, radiochemical reaction of tritium in gas phase, radiolysis of tritiated water, and waste processing are being carried out under ITER/EDA and U.S.-Japan collaboration. Tritium release experiments for research of tritium behavior in confinements and environment and demonstration of safety related components are planned.     

Tritium handling, breeding, and containment in two conceptual fusion reactor designs: UWMAK-II and UWMAK-III

Tritium is an essential component of near-term controlled thermonuclear reactor systems. Since tritium is not likely to be available on a large scale at a modest cost, fusion reactor designs must incorporate blanket systems which will be capable of breeding tritium. Because of the radiological activity and capability of assimilation into living tissues, tritium release to the environment must be strictly controlled. The University of Wisconsin has completed three conceptual designs of fusion reactors, UWMAK-I, UWMAK-II, and UWMAK-III. This report discusses the tritium systems for UWMAK-II, a reactor design with a helium cooled solid breeder blanket, and UWMAK-III, a reactor design with a high-temperature liquid breeder blanket. Tritium systems for fueling and recycling, breeding and recovery, and plant containment and control are discussed.     

氚长期大气释放后小麦中氚浓度预测模型的比较研究

通常对于气态氚的长期释放,如植物中含水量多的情况下,可采用比活度模型估算植物中自由水中氚的浓度进而对食入剂量进行评价。然而对于籽粒作物来说有较低的含水量和较高的有机物质,浓度和剂量的计算必须把有机结合氚(OBT)考虑进去。本文以小麦为例对气态氚的长期释放情况下植物中氚浓度的几种计算方法及其所做的假设进行比较研究,对用不同的方法计算所得的小麦中氚的浓度和导致的食入剂量进行了对比。结果表明,采用比活度模型过高估算了小麦中氚的浓度但是过低估算了食入剂量,因为他们没有明确考虑OBT。在估算植物中氚的浓度时应同时考虑空气水分和土壤水分中氚对植物氚浓度的贡献;因为OBT的剂量转换因子是HTO的两倍多,在估算籽粒作物的食入剂量时应把HTO和OBT分开单独处理,这样估算出来的浓度和剂量才能更符合实际情况。     

Tritium uptake in graphite tiles exposed to EAST plasma and then tritium gas

Tritium exposure experiments were carried out for three kinds of EAST SiC coated doped-graphite (SiC/C) samples, one from the original graphite tiles without being irradiated, and the other two from erosion and deposition areas of first wall after the 2009 campaign in EAST. β-ray-induced X-ray spectrometry (BIXS) was used to characterize the exposed samples. It is showed that the significant amount of tritium was absorbed in the surface of deposition sample in comparison with that of original sample, which was also supported by the results of imaging plate (IP) measurements. In addition, it was found that drastic decrease in tritium retention appeared by lowering exposure temperature, and the trapped tritium was maintained stably with time. Computer simulation is used to analyze the details of depth profile of tritium in different kinds of samples.     

压水堆主冷却剂中氚源项计算分析

压水堆主回路冷却剂流经堆芯时,水中固有及特加核素受中子辐照后会产生氚,氚几乎全部以气体和液体的形式排入环境,造成氚污染。因此,氚是压水堆辐射环境影响评价的主要关注内容之一。本文以AP1000为例,根据压水堆主回路冷却剂中氚的产生途径及其随时间的变化情况建立详细的计算模型,计算压水堆主回路冷却剂中的氚活度并分析各产氚途径对氚产生量的贡献。计算结果表明：主回路冷却剂中的氚主要来源于可溶性硼的中子活化和铀裂变,对氚产生量的贡献达80%以上;在⁷Li纯度为99.9%时,AP1000主回路中的年产氚量为5.23×10¹³ Bq,锂产氚量占总量的14.01%,随⁷Li纯度的增加,锂产氚量的贡献呈线性减小,在⁷Li纯度为99.99%时,锂产氚量占总量的3.18%。其他途径对氚的产生量贡献很小,可忽略。根据以上结果,可通过控制主回路冷却剂中添加的初始硼浓度、提高燃料包壳质量、增加LiOH中⁷Li的纯度等多种途径来降低主冷却剂中氚的产生量,从而减少氚对环境的放射性污染。     

Study on oxidation of hydrogen over commercial catalyst for tritium recovery system

For the establishment of the D-T fusion reactor technology, recovery of tritium released into the working area of fusion power plants is quite important. When tritium leaks to working areas, the last barrier is the wall of the building. Due to higher diffusion coefficient of tritium, it diffuses through the wall and would be readily liberated to the environment. Thus, the tritium recovery system is indispensable for the D-T fusion reactor. The objective of the present study is to develop the advanced technology of the tritium recovery system.In the near future, deuterium plasma discharge experiments scheduled be conducted with Large Helical Device (LHD) in National Institute for Fusion Science. A small amount of tritium is produced by D-D reaction in LHD. Tritium in plasma exhaust gases and process gas during discharge needs to be recovered, and thus the design and construction of the tritium recovery system used for that purpose is a matter of considerable urgency.The tritium recovery system usually consists of catalysts and adsorbents, which is the most conventional and reliable method for removing tritium that is accidentally released into the working area of these facilities. However, more recent and advanced type of catalysts on the market cannot be directly applied to the design of tritium recovery system, because of paucity of design data for tritium recovery system. In this study, the authors performed oxidation experiments of hydrogen over a catalyst. The experiments were performed by changing various experimental parameters.     

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.     

Tritium permeation experiment at IFMIF Medium Flux Test Module

Tritium release experiments using different breeding material candidates are planned for the medium flux region of the IFMIF Test Cell. Nowadays, only ceramic breeder materials have been suggested to be tested in the Tritium Release Module located in the Medium Flux Test Module of IFMIF. Liquid breeder blankets are very promising and for that reason, several concepts will be tested in ITER. One of the main problems concerning the liquid blankets is the permeation of the generated tritium in the breeder throughout the walls. Since tritium permeation is highly influenced by irradiation conditions, IFMIF is a suitable scenario to perform tritium permeation related experiments.In this paper, a preliminary design of a tritium permeation experiment for the Medium Flux Test Module of IFMIF is proposed, in order to contribute to the progress of the liquid breeder blanket concept validation.The conceptual design of the capsule in which the experiment will be performed is carried out, taking into consideration the experiment necessities and its implementation in the Tritium Release Module. In addition to this, some thermal hydraulic calculations have been performed to evaluate the thermal behaviour of the irradiation capsule.     

Oxidized Tritium around a Research Reactor Site

The concentration and distribution of tritium in environmental samples obtained from sites near the Kyoto University Research Reactor were studied. About 5 GBq of tritium is discharged yearly from the KURR stack. The concentrations of tritium in the exhaust air, atmospheric moisture and precipitates were monitored to estimate not only any effects of tritium sources on the concentrations in the nearby environment but also the dilution factor of pollutants at the site boundary. The concentrations of tritium in surface water at the site were also monitored to identify the possibility of pollution in the water system. In both cases, there was slight contamination in samples near the site. The increased annual dose to an adult from tritium discharged in the atmosphere was estimated to be about five orders of magnitude lower than that from natural background radiation.     

Tritium permeation experiments using reduced activation ferritic/martensitic steel tube and erbium oxide coating

Low concentration tritium permeation experiments have been performed on uncoated F82H and Er₂O₃-coated tubular samples in the framework of the Japan-US TITAN collaborative program. Tritium permeability of the uncoated sample with 1.2 ppm tritium showed one order of magnitude lower than that with 100% deuterium. The permeability of the sample with 40 ppm tritium was more than twice higher than that of 1.2 ppm, indicating a surface contribution at the lower tritium concentration. The Er₂O₃-coated sample showed two orders of magnitude lower permeability than the uncoated sample, and lower permeability than that of the coated plate sample with 100% deuterium. It was also indicated that the memory effect of ion chambers in the primary and secondary circuits was caused by absorption of tritiated water vapor that was generated by isotope exchange reactions between tritium and surface water on the coating.     

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.     

Diffusion analysis on the thermal release of tritium from a neutron absorbing material

Tritium released from neutron irradiated borosilicate glass was determined by a specially designed sampling system and a liquid scintillation counter at temperatures in the range of 200–700°C. It was found that the chemical form of tritium released was tritiated water (HTO, T₂O) for the most part. Tritium produced in the glass would react with oxygen to form OT and diffuse out by a similar mechanism as the molecular diffusion of water in glasses. The diffusion coefficient of tritiated water in borosilicate glass obtained is expressed by D (cm²/s) = 5.3 × 10⁻⁴ exp( −128 kJ/mol)/RT). It is concluded from the diffusion analysis that the greater part of tritium produced in a neutron absorber, which is made of borosilicate glass, would remain in the glass for a few years of irradiation.     

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。