Desorption Rate of Adsorbed Tritiated Water from Molecular Sieve 5A by Exchange with Environmental Water Vapor

The desorption rate of tritiated water from molecular sieve adsorbed HTO, by exchange with the environmental water vapor, was measured. The molecular sieve, packed in a column, was initially changed with tritiated water and then humidified Ar gas was made to flow through it and the tritium concentration of effluent gas was measured. The desorption rate of tritiated water increased linearly with the water vapor pressure in the gas at constant flow rate. In the case where both the flow rate and the vapor pressure were kept constant, the amount of tritium left adsorbed on the molecular sieve decreased exponentially with time. It should be noted that the desorption rate was rather rapid even at room temperature and nearly all the tritiated water adsorbed on the molecular sieve was recovered by the flowing humidified gas at room temperature within several hours.     

氚在RAFM钢表面的吸附研究

采用气相吸附法研究了室温下RAFM钢表面对氚的吸附与释放行为,并使用316L钢、1Cr18Ni9Ti钢进行了对照实验。结果表明,RAFM钢表面的氚吸附与释放性质与316L钢、1Cr18Ni9Ti钢的非常相似,相同表面状态的样品,在相同实验条件下的吸附氚量相差不超过50%。可推测,未经深度除水处理的RAFM钢暴露于氚后,表面会形成富氚层,浓度远高于基体溶解氚,厚度不大于10 μm。表面氚的形态以化学吸附和物理吸附的氚化水为主,约占90%以上。室温下RAFM钢表面吸附的氚在干燥气氛中的释放非常缓慢,但遇水会因氚-水间的同位素交换而加速释放。     

不锈钢和铜吸氚及其干法去污

为了对不锈钢和无氧铜吸氚后氚在其内部的分布情况及除氚去污方法进行研究,对模拟吸氚及加热去污后的样品进行了酸蚀刻以考察氚在金属层中的分布情况;单独加热或加热结合通入空气、O3和紫外线(UV)进行去污,考察不同去污方式的去污效果。结果表明:金属在表层1μm内吸附了大量的氚,约占总量的42%;加热到500℃及联合去污不锈钢的最佳去污因子达到286,铜为150,通入气体在中温条件下对金属去污最有效,加热是金属去污最有效方式;氚热解吸形态分析表明氚污染不锈钢有4种吸附态。     

氚在真空贮存容器材料中的吸附和渗透行为

研究了贮存氚靶约4 a和20 a的两个316 L不锈钢真空贮存容器(以下简称贮存容器)及其垫片材料对氚的吸附行为,并对氚在贮存容器材料中的渗透速率进行了测量和分析。结果表明,贮存容器外表面氚污染为几十Bq/cm2,不锈钢与陶瓷中吸附的氚活度均为106Bq/g;热解吸至1 273 K过程中,材料中99%的氚释放出来;在解吸出的氚中,陶瓷中的HTO比例高于不锈钢;贮存温度对氚靶贮存容器的渗氚速率有较大影响,夏季约为冬季的4倍。上述结果提示,氚在贮存容器材料内表面吸附后,一部分会向晶格扩散并滞留下来;另一部分则透过材料向外环境渗透,其中温度是影响氚向外环境渗透的主要因素之一。     

Tritium sorption on concrete protective coatings and the impact on operational safety

Exposures of concrete and selected coating materials to tritiated atmospheres have shown that tritium sorption on these materials and subsequent desorption are important parameters in defining tritium sources within a tritium-handling facility. Exposure time, tritium concentration and humidity of the air atmosphere affected the amount of tritiated water vapor sorbed. Some of the selected coatings reduced the tritium sorbed to less than 1% of unprotected concrete samples.Work funded by AECL Research and the Canadian Fusion Fuels Technology Project (CFFTP).     

Removal of Tritiated Water Vapor by Adsorption

Abstract

Experiments were conducted on the dynamic adsorption of tritiated water vapor, using a column packed with either silica-gel, activated alumina, or molecular sieve 5A. The column was 4 mm I.D. and 5–30 cm long. The runs were performed at 30°–70°C. Tritiated water vapor (HTO) was loaded into the column with a concentration of 170 μμCi/ml, either in pulses of predetermined duration or continuously (breakthrough). The concentrations of H₂O and HTO at column outlet were measured. Particular interest was attached to observing the effect of differences in the pretreatment applied to the adsorbents (whether dried or saturated with water), and in the H₂O partial pressure of the carrier gas. It was found that the adsorption characteristics shown for HTO were not influenced to any appreciable extent by differences in the pretreatment applied to the adsorbents. On the other hand, adsorbent performance depended sensitively on the H₂O pressure in the carrier gas.

Adsorption models for a two-component mixture composed of H₂O and HTO were sought for describing the adsorption mechanism. For the particular case of the molecular sieve 5A, the Langmuir-type mixed adsorption model was found to give values agreeing fairly well with experiment. A model postulating chemisorption of H₂O into hydroxyl group on the adsorbent surface, to be subsequently replaced by tritium, was found suitable for explaining the adsorbent behavior in the case of silica-gel.     

氚污染不锈钢、铜、铝金属干法去污研究

为了考察氚污染金属干法去污的去污效率,对氚污染不锈钢、铜和铝进行了紫外线、臭氧、加热及联合（紫外线、臭氧与加热）去污实验研究。研究结果表明：紫外线单独照射去污效率较差,加热可明显提高去污效率,500 ℃联合172 nm的紫外线去污4 h对不锈钢表面氚去污率可达99.2%;臭氧对铜有较好的去污效率,臭氧与加热（500 ℃）的组合对不锈钢、铝、铜的去污率均高于99.2%;高温（500 ℃）较低温（300 ℃）去污效率高;氚去污后金属放置30 d表面氚有所增加,主要是氚的扩散和渗透所致;氚污染不锈钢存在4种氚吸附态。     

Multi-column Adsorption Systems with Condenser for Tritiated Water Vapor Removal

Two types of multi-column adsorption system are proposed as the system for removal of tritiated moisture from tritium process gases or/and handling room atmospheres. The types are of recycle use of adsorption columns, and are composed of twin or triplet columns and one condenser which is used for collecting the adsorbed moisture from columns in desorption process. The systems utilize the dry gas from a working column as the purge gas for regenerating a saturated column and appropriate an active column for recovery of the tritiated moisture passing through the condenser. Each column hence needs the additional amount of adsorbent for collecting the moisture from the condenser. In the modeling and design of an adsorption column, it is primary to estimate the necessary amount of a candidate adsorbent for its packed-bed. The performance of the proposed systems is examined here by analyzing the dependence of the necessary amount of adsorbent for their columns on process operational conditions and adsorbent moisture-adsorption characteristics. The result shows that the necessary amount is sensitive to the types of adsorption isotherm, and suggests that these systems should employ adsorbents which exhibit the Langmuir-type isotherms.     

Isotope exchange reaction between tritiated water and hydrogen on SiC

SiC has been considered as a primary candidate material for a first wall component in future fusion reactor because it has been claimed that SiC has excellent high-temperature properties, good chemical stability and low activation. However, the behavior of tritium on SiC has not been discussed yet. In this study, tritium trapping capacity on the surface of SiC was experimentally obtained at the temperature range of 25-800 °C in consideration of tritium trapping to the experimental system. The capacity, which was independent of the water vapor pressure in the gas phase and the temperature, was determined as about 10⁶ Bq/cm². The isotope exchange reaction rate between tritiated water in a gas phase and hydrogen on the surface was quantified at the temperature of 25, 500 and 700 °C in consideration of the behavior of tritium trapping at change of experimental condition by the numerical curve fitting method applying the serial reactor model. The reaction rate was observed to be constant as 3.48 × 10⁻⁵ m/s. Additionally tritium release behavior from the surface of SiC in water vapor atmosphere was predicted and compared with that for graphite and stainless steel.     

Study on behavior of tritium in concrete wall

It is required to understand the tritium behavior in concrete for establishment of tritium safety technology of a fusion reactor or a tritium handling facility because the concrete wall is used as the final containment to prevent tritium release to the environment. This paper discusses about the effect of adsorption and diffusion of water and isotope exchange reaction between physically adsorbed water and chemically adsorbed water or structural water. It is known in this study that a large amount of tritium can be trapped to the concrete wall because cement paste has the nature of porous hydrophilic material.     

Effect of Tritium and Dissolved Oxygen on Anodic Polarization of SUS304 Stainless Steel in Sulfuric Acid Solution

Since exotic corrosion of stainless steels in tritiated water can be expected, the anodic polarization of a SUS304 stainless steel sample in approximately 5 wt% sulfuric acid solution was performed at various concentrations of tritium and dissolved oxygen (hereafter DO) in the electrolyte. The inhibitory effect of tritium on the passivation could be observed with DO even at a tritium concentration in the electrolyte of as low as 2.2 kBq cm^?3. This effect became more pronounced as the tritium concentration increased. It was suggested that the inhibitory reaction depending on tritium concentration would compete with the self-passivation depending on the DO concentration (hereafter [DO]), since it was found that there is a threshold [DO] for self-passivation at each tritium concentration.     

The Second International Symposium on Advanced Nuclear Energy Research

The diffusion of tritiated water vapor into concrete walls of a fusion reactor building is studied to evaluate the capability of the tritium containment of concrete materials.

First, depth profiles of tritiated water in concrete are calculated to evaluate the capacity of the tritium containment by the sound concrete without cracks, and a 0.5-m-thick concrete wall is sufficient to prevent tritiated water releases to the environment in a normal operation of a fusion reactor over 50 yr. Second, simulations of the cleanup of tritiated water in the concrete reactor hall atmosphere taking into account the soaking are performed. Concrete porosity should be decreased to shorten the cleanup time of the reactor hall atmosphere. Surface coatings on the concrete, which apparently decrease the surface porosity, are effective measures to prevent the diffusion of tritiated water vapor into concrete during accidental releases.     

Removal of Tritiated Water Vapor by Molecular Sieves 5A and 13X,Silica Gel and Activated Alumina

The adsorption of tritiated water vapor on molecular sieves 5A and 13X, silica gel and activated alumina was investigated in the small column experiments. The results were analyzed by a simple first order kinetic equation. The adsorption characteristics of the adsorbents are rationalized by the two important parameters, maximum adsorption capacity and adsorption rate constant, which were determined at various temperatures for each adsorbents. The column exhaustion experiments were also carried out. An equation was derived to express the correlation between breakthrough time and column length. A reasonable consistency has been noticed between the calculated and the observed results.     

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.     

高温气冷堆用含硼碳对水蒸气的吸附特性研究

高温气冷堆中使用了大量的碳材料,其中含硼碳（BC）因其优秀的物理特性而被大量用于堆芯的结构材料。BC是一种典型的多孔材料,暴露于空气中会吸附水分等杂质,其对水蒸气的吸附和脱附特性将直接影响初装堆芯的除湿过程。通过动态吸附和脱附实验详细测定了BC的水蒸气吸附等温线,使用低相对湿度的吸附数据拟合BET方程,并得到高相对湿度下的BET预测值。研究结果表明,水蒸气在BC表面属于多层物理吸附,脱附曲线较吸附曲线有一定的滞后,水蒸气能深入进材料内部,这也导致在较高的相对湿度下很难达到吸附和脱附平衡。     

Adsorption Characteristics of Water Vapor on Gamma-Lithium Aluminate

Lithium aluminate (LiAl0₂) is one of the probable candidates for tritium breeding material because of its potential to give a fair tritium breeding ratio, stability at high temperature and stability in atmosphere containing water vapor. Clarification of the adsorption performances of water on LiAl0₂ is important for optimization of the way to recover bred tritium from LiAl0₂ and for estimation of the tritium inventory in the breeding blanket and for quantification of the hydrogen isotope exchange reaction. The amount of water captured on LiAl0₂ was studied in the temperature range of 373~1,100K using the breakthrough curve method, and adsorption isobar and isotherm of water on LiAl0₂ were proposed based on the data obtained. The water capture phenomena of LiAl0₂ was attributed to the dissociative chemisorption, and the apparent activation energy was determined to be 32.2 kJ/mol.K. The tritium inventory by sorption for LiAl0₂ was compared with that for Li₂0.     

充氚不锈钢中氦泡长大行为的加热效应

以室温贮存经历的充氚不锈钢试样为研究对象,计算了充氚不锈钢中氚、氦浓度的深度分布,利用透射电镜观察了充氚不锈钢在加热过程中氦泡的演化行为。结果表明:在氚压0.131MPa、780℃充氚8h后,不锈钢中氚在深度方向分布均匀,平均浓度为110μL/L;在空气室温环境下放置6a后,不锈钢中氚衰变的氦浓度在深度方向分布均匀,平均浓度为60μL/L;对充氚不锈钢加热处理后,在550℃/1h时效即可观察到氦泡;在950℃/1h和1050℃/1h时效时,氦泡明显长大,大的可达100nm,小的可达30nm,在晶界、晶内和位错处均可见氦泡。     

Li transfer from a Li2O blanket

Lithium oxide is one of the most potential breeding materials among the various candidates because of its high melting point and high lithium atomic density and preferable capability to give a large tritium breeding ratio. Leak of a fair amount of water to the blanket purge gas from the cooling water system is anticipated from the experience at the cooling system of fission reactors. Then, the behavior of lithium hydroxide formed in the lithium oxide blanket must be understood because lithium oxide is highly reactive with water vapor. In this work, the relation of the partial pressure of LiOH(g) with temperature or pressure of water vapor is studied experimentally, and the effect of Li transfer from the blanket on tritium recovery is also discussed.     

氚污染部件干法去污技术

针对核退役工程中存在的大量含氚废物处理问题,利用设计组装的干法去污处理装置对氚污染的金属进行了加热、紫外线、臭氧去污研究.结果表明,升高温度可明显提高去污效果;220 ℃用365 nm紫外线照射3 h对不锈钢的表面去污效率可达99%;臭氧与加热联合作用更有利于提高去污效率,220 ℃时去污3 h,臭氧对不锈钢、铝、黄铜的去污效率可达95%以上;而去污完毕经放置后,金属的氚表面活度会有所增加.     

Effect of water vapor on tritium permeation behavior in the blanket system

It is found that most hydrogen supplied to the purge gas changed to water vapor due to the water formation reaction in the early stage of the blanket operation and that physical or chemical adsorbed water is released in the high concentration into the blanket purge gas when the blanket temperature becomes higher than several hundreds of degrees K if the pre-treatment is not applied to the solid breeder materials. Effect of coexistence of water vapor in the purge gas on permeation behavior of hydrogen through F82H ferritic steel in the breeding part and palladium–silver (Pd–Ag) in the recovery part is discussed because use of them is generally considered for recovery of bred tritium from the solid blanket. Almost no decrease in permeation rate of F82H is observed in this study when water vapor exists in the blanket purge gas. The permeability of hydrogen isotopes through the Pd–Ag pipe gradually decreases when water vapor exists in the blanket purge gas. Properties required in estimation of the hydrogen permeated to the purge gas are experimentally obtained in this study.