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.     

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.     

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.     

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.     

手套箱气氛中氚化水处理的工艺研究

分子筛吸附柱和热金属镁床是手套箱气氛中氚化水 (HTO)搜集和分解处理的一种有效手段。测试了分子筛柱对气氛中水的吸附性能和热金属镁床对HTO的分解性能。结果表明 :分子筛柱对气氛中水的吸附效率 >99 99% ,在空气中水含量为 3 4× 1 0 - 3～ 4 2× 1 0 - 3条件下 ,未发现吸附柱水的贯穿现象 ;热金属镁床对HTO的分解率 >99 9% ,当金属镁的消耗量大于 80 %时 ,未见分解率明显降低。     

Adsorption and Desorption Behavior of Tritiated Water on the Piping Materials

The behavior of tritium on the surface of various piping materials must be investigated for establishment of the safety confinement technology of tritium or for development of the effective fuel handling technology in a D-T fusion reactor, because tritiated water or gaseous tritium is captured on the piping surface through adsorption or isotope exchange reaction. The present authors carried out the water adsorption and desorption experiments on 304 stainless steel, copper, and aluminum in the temperature range from 5 to 100°C and in the partial pressure range of water vapor between 11.8 and 198Pa using a breakthrough method and quantified the amount of water adsorbed and the overall mass transfer coefficients in adsorption and desorption of water. It was observed in this study that aluminum adsorbed more water than stainless steel or copper. It was also observed that the adsorption and desorption rates of water for three materials showed almost the same values. The breakthrough behavior of tritiated water in a 100 m pipe of stainless steel was also evaluated applying the results of this work. It is concluded that water adsorption and desorption reactions influence the behavior of tritiated water in the piping system under the condition where the partial pressure of tritiated water vapor is lower than several pascals.     

氢/氘气在改性分子筛上的吸附性能研究

在液氮温度下采用容积法研究了5A、ZSM-5及其改性沸石分子筛对氢同位素的吸附分离性能,探讨了过渡金属盐负载和球磨等改性方法对氢同位素气体吸附的影响。结果发现,改性后分子筛上气体的吸附量普遍降低,但某些改性有利于H₂和D₂的分离。     

Transient Behavior of Enrichment of Tritium Water in Adsorption-Distillation Column

Enrichment of tritium in an adsorption-distillation column was experimentally investigated under the two processes of simple distillation and total-reflux distillation. Adsorption of water on silica-gel pellets enhanced the total isotope separation factor in the water distillation column. The transient behavior of tritium enrichment was analyzed using material balance equations of tritium and water in each cell with a height corresponding to HETP. The experimental transient behavior was well simulated by the material balance equations with additional assumptions on vapor and liquid flow rates regardless of the different processes of simple distillation and total-reflux distillation.     

Influence of Framework Silica-to-Alumina Ratio on the Tritiated Water Adsorption and Desorption Characteristics of NaX and NaY Zeolites

The fixed-bed adsorption process has been studied as one of the promising processes for the recovery of tritiated water in the field of nuclear fusion. The influence of the framework SiO₂/Al₂O₃ ratio ranging from 2.0 to 10.0 on the tritiated water adsorption and desorption characteristics in the H₂O-HTO binary systems was systematically examined using NaX and NaY zeolites. A large difference in isotherm was observed by changing the SiO₂/Al₂O₃ ratio from 7.0to 10.0. The framework SiO₂-to-Al₂O₃ ratio has a slight effect on the isotope separation factor. The capacity of removable water from NaY10.0 around room temperature is approximately four times larger than that from NaA2.0 even though both zeolites have nearly the same capacity for absorbable H₂O at nearly P=P0= 1:0. The weaker interaction generates the isotope effect on desorption. The HTO dehydration ratio has a strong interrelation with the accumulative amount of purge gas. Dehydration is independent of the flow rate of the purge gas. On the design side of the water adsorption process with multi-absorber systems, the size of the water absorber such as a dryer or dehumidifier can be downscaled with NaY10.0 as the adsorbent since the consideration of the heating and cooling periods necessary for the temperature swing desorption process is not required in the NaY10.0 column.     

络合-吸附方法去除核电厂模拟废水中的钴

针对核电厂放射性废水提出一种络合-吸附处理方法。初步采用乙二胺四乙酸(EDTA)作为有机络合剂、活性炭作为吸附剂、Co~(2+)作为去除对象,对该方法的可行性及相关影响因素进行了研究。结果表明,模拟废水中加入EDTA后可显著提高活性炭对Co~(2+)的去除率,符合理论预期,证实了该方法的可行性。络合-吸附条件实验结果显示,去除率随活性炭投加量的增大而增大;振荡16h后吸附达到平衡;溶液的pH值显著影响络合-吸附过程,最适宜pH值约为7.0;EDTA与Co~(2+)摩尔浓度比为1∶1时,Co~(2+)的去除率达到最大值。吸附特性研究结果显示,活性炭对EDTA-Co络合物的吸附热力学符合Freundlich模型,其吸附过程符合准二级动力学模型。     

Mist Formation in a Water Vapor Cold Trap and Evaluation of Its Removal Rate

Mist formation conditions in a mixture of non-condensable gas (nitrogen or helium) and water vapor, mass transfer rates onto a cooled wall under the mist formation and choking time are determined in a case of a laminar flow in a vertical round tube cooled from the outside at constant temperatures of 77K to 263 K. This is a basic study of a cold trap for a fusion fuel clean-up (fcu) system. If mist is formed in the trap, it makes tritium spikes at the trap outlet, and consequently it causes tritium leakage to the outlet. The limiting condition of mist formation in the present system is quantitatively expressed by the critical supersaturation model (CSM). When the inlet vapor concentration is within the CSM mist formation condition, the outlet concentration is very high immediately after the gas supply and, afterward, it drops very quickly. When within the no-mist formation condition, the outlet concentration is almost constant throughout the frosting time. The trap shows a good removal performance for a long time until choking. This difference in the time variations is successfully explained by the relaxation of the mist formation condition with an increase in the thermal resistance of frost formed on cooled surfaces.     

碳分子筛上氪、氙的动态吸附及脱附性能

为筛选快速分离Kr/Xe的材料,研究了不同碳分子筛(CMS)对氙(Xe)和氪(Kr)的动态吸附性能与脱附性能,探讨了压力、气体流量、温度等因素对Kr、Xe的动态吸附系数与脱附率的影响。结果表明,碳分子筛Aladdin TDX-01对Xe的吸附容量最大,其次为光复TDX-01,低温时,Aladdin TDX-01对Kr的动态吸附系数大于光复TDX-01。Aladdin TDX-01碳分子筛对Kr和Xe的吸附能力均随压力升高而增强,随着原料气流量增加而减少,动态吸附系数随着温度升高而降低;采用N₂吹扫对Kr、Xe进行脱附,随着N₂流量增大、温度升高,Kr、Xe的脱附时间缩短。Aladdin TDX-01碳分子筛在25℃、100 kPa条件下对Xe的动态穿透吸附系数为1 283 mL/g,在-50℃、100 kPa条件下对Kr的动态穿透吸附系数为474 mL/g。     

分子筛的结构表征及对痕量氙的动态吸附性能

高效吸附剂是大气放射性氙取样分析系统的核心组成部分之一,为提高探测灵敏度,需获得对大气中痕量氙具有更高吸附性能的吸附剂。研究了10种分子筛对痕量氙的动态吸附性能,利用氮气静态吸附对分子筛的孔结构进行表征,分析了孔结构特征与分子筛动态吸附性能的关系。选择吸附量较高的分子筛,进一步研究了原料气流量、吸附压力和氙浓度对动态吸附性能的影响。结果表明:5A分子筛具有较适合的孔径,对氙的动态吸附性能优于13X分子筛;ZSM-5分子筛可能因晶穴内极性较强和具有较适合的孔径,对氙的吸附能力最强;痕量氙在ZSM-5分子筛上的动态吸附系数随吸附压力的增加而线性增大,随流量增大先下降而后趋于稳定,氙浓度在7.6×10^-9～3.0×10^-8 mol/L范围内对其无明显影响。     

Sorptive Removal of Cesium-137 and Strontium-90 from Water by Unconventional Sorbents

It has been shown that coal fly ash is a good adsorbent for both radionuclides of ¹³⁷Cs and ⁹⁰Sr. Radiocesium adsorption is maximal around the neutral region whereas radiostrontium adsorption increases with pH, especially above pH 8. Cesium retention sharply drops with ionic strength while strontium adsorption increases sharply and steadily at low and moderate concentrations of the inert electrolyte, respectively. The suggested mechanisms of radionuclide retention by fly ash is specific adsorption of Cs⁺ and irreversible ion-exchange uptake of Sr²⁺. The isotherm of adsorption is a Langmuir approximation of the B.E.T. multi-layered sorption. Acid pretreatment of fly ash, though not increasing radionuclide sorption capacity, may be useful in preventing the leach-out of other contaminants from the sorbent into water during the adsorption process.     

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。     

高纯氘中杂质的低温气相色谱分析

实验研究采用5A分子筛和氧化铝充填色谱柱分别在常温和低温（77K)下对D₂中的O₂、N₂以及H₂、HD等杂质进行定量分析测量，以建立1种准确实用的分析方法。研究结果表明，该方法对H₂、HD的最低检测浓度可达（150～200）×10^－6，能够满足高纯氘制备过程中对杂质的定量分析要求。     

Enrichment and Volume Reduction of Tritiated Water Using Electrolysis Cell Having Hydrogen Permeable Cathode

The electrolysis rate and the separation factor for hydrogen isotopes are measured using the electrolysis cell having the hydrogen permeable cathode. As the hydrogen gas without the vapor of electrolyte is obtained by this method, decrease of the apparent separation factor by mixing with vapor can be avoided. It is also observed in this study that enrichment and volume reduction of tritiated water using the bipolar electrode electrolysis cell is effective because it gives small loss of tritium from the cell during volume reduction. The separation factor obtained in this study indicates that attachment of two or three sub-cells is enough for volume reduction of tritiated water.     

Storage of Krypton-85 by Adsorption Method

Several fundamental experiments were performed on adsorption process of ⁸⁶Kr storage at the ordinary condition of temperature and pressure. A long-term test for storage was then performed with radioactive ⁸⁵Kr and the safety was confirmed by hot run of 38 days. Of many adsorbents adopted in preliminary experiments, the largest amount of adsorbed Kr was AW-500 (16.4 cc STP/g) among molecular sieves and Tsurumi HC-30E (33.2 cc STP/g) among charcoals. The amount of adsorbed Kr decreased slightly with the addition of Rb and with the irradiation of the order of 10⁵ Mrad. It was found that adsorption rate is effected larger by Xe than by air. In ⁸⁵Kr storage test of 100 Ci, the pressure in storage vessel varied in the range of about ±4%, and the ⁸⁵Kr leak rate from the vessel was the order of 10^?12cc·atm/s. It was found that there is no considerable temperature rise due to β disintegration. From these results, the adsorption process may be useful for storage of ⁸⁵Kr for long-term.     

Adsorption Equilibria of Krypton,Xenon, Nitrogen and Their Mixtures on Molecular Sieve 5A and Activated Charcoal

The adsorption equilibria of Kr, Xe and N₂, which are constituents of the off-gas from nuclear reprocessing processes, on representative adsorbents (Molecular Sieve 5A (MS5A) and activated charcoal) were studied. Adsorption experiments were conducted in the temperature range of 77 to 323 K using a packed bed column. The adsorption isotherms for the activated charcoal adsorbent were successfully correlated by the vacancy-solution model. The adsorption isotherms for the MS5A adsorbent were properly correlated by the Langmuir model and the vacancy solution model. The adsorption experiments for the binary component systems (Kr—Xe, Kr—N₂ systems) were also performed, and the results suggest that the coexistence of Xe greatly inhibits the adsorption of Kr. The coexistence of large amounts of N₂ was also found to inhibit the adsorption of Kr. The experimental results for the adsorption equilibrium of binary component systems on the activated charcoal adsorbent were well reproduced by the vacancy solution model without parameter fitting. The binary adsorption equilibrium on the MS5A adsorbent is rather well predicted by the ideal adsorbed solution model without parameter fitting. The use of the vacancy solution model for this adsorption system requires the optimization of parameters, but the binary adsorption equilibrium is well reproduced with the optimized parameters.     

Reaction of Titanium Beryllide with Water Vapor

The Doppler reactivity effect of 238U was measured in simulated MOX fuel using the FCA facility for the purpose of obtaining data on the ²³⁸U Doppler reactivity effect in light-water-moderated MOX fuel and evaluating the prediction accuracy of the current analysis code systems and nuclear data library. Experimental data on the Doppler reactivity effect from room temperature up to 800°C were obtained for a uranium fueled core and mockup cores for MOX-fueled LWR using cylindrical natural-uranium samples. With the use of various samples with various neutron spectra, ²³⁸U Doppler reactivity effects at energies generally in the low range below 1 keV were evaluated. Analyses were performed using the current standard analysis code systems for fast and thermal reactors, with the JENDL-3.3 data library. Both analyses yielded calculated/experimental value (C/E) ratios of 0.96 to 1.06 for the MOX cores, a good agreement within the experimental error, and those in the uranium core were similar.