氚的各种来源(下)

【美国《核安全》1981年9—10月第612页报道】目前世界上除轻水堆和重水堆以外,尚有其它一些堆型,它们也都释放氚。高温气冷堆每年释放氚的总量为7.8×10~9—3.1×10~(10)贝可/兆瓦(电)年。其中,84—97%以氚化水形式释出,2—8%以氚化水蒸汽释放,0.6—8%以氚气形式释放。这种堆氚的产生主要是燃料的三裂变,以及~3He 和锂杂质的中子活化。液态金属快     

氚废气的回收技术研究

采用了高温催化氧化法处理含氚废气。处理过程如下:在干燥氩气(含少量H2)的载带下,含氚废气通过高温催化氧化床转化为氚水,然后用蒸馏水或合适的干燥剂吸收。在400℃,氧化床穿透之前,Hopcalite氧化剂对H2的氧化效率接近100%;在500℃,Hopcalite氧化床对HT的氧化效率大于99%。实验测定了回收氚的分子筛在存放过程中,不同规格分子筛的氚释放系数以及存放条件与释放系数的关系。结果表明,3种分子筛在吸收氚水后的氚释放系数为(1.9～5.5)×10-6d-1·g-1。其中,4A钠型分子筛的氚释放系数最小,5A钙型分子筛的氚释放系数最大;3种分子筛在吸收氚水后释放的氚的化学形式绝大部分是氚化水(HTO),氚气(HT)含量不超过1.2%;含氚分子筛的贮存气氛对氚的再释放有一定影响,在纯氩气中氚释放系数比在含2%氢的氩气中的低。     

带自动控制功能的除氚系统

针对氚工艺尾气处理的需求和源项实际情况,根据化工原理和氚特性设计含自动控制功能除氚系统的主要部件、自动控制功能和初步性能测试,得出催化反应器、氚水吸附床等部件的结构尺寸,催化剂、干燥吸附剂的装填量等参数及控制软件界面;通过除氘和除氚实验初步测试了除氚系统的处理性能。结果表明,在循环处理模式下,1m3密闭容器中氘体积比6.0×10–4–2.8×10–2范围内时,35min内氘气浓度降低两个量级;5次对30L密闭容器内不同浓度的含氚气体处理,60min内对氚的去除效率均达到95%以上。     

含氚重水脱氚方法

CANDU6核电站慢化剂重水中的氚浓度随反应堆运行而增加,含氚重水以气态或者液态向反应堆厂房及环境中泄漏,将造成运行人员辐射剂量及环境污染。如何有效将慢化剂重水中的氚脱除受到国际上广泛的关注。本文调研国内外重水脱氚技术,对各种现有脱氚技术进行了系统的比较与分析,总结了各工艺的优缺点及经济性。     

含氚废水的处理与处置

本文叙述了氚的特性,含氚废水的处理与处置方法以及我国高通量工程试验堆(HFETR)含氚废水的处置。     

压水堆核电站含氚废液处理技术

介绍了几种可规模除氚的氢-水同位素交换工艺及其应用情况,并结合压水堆核电站含氚废液排放的实际情况,对压水堆核电站含氚废液处理的适用性进行了分析,认为联合电解催化交换技术处理压水堆含氚废液可行性较高。     

含氚气体中氚分压BIX在线测量方法研究

建立了一种聚变堆氘氚燃料循环系统燃料气及工艺气等含氚混合气体中氚分压在线快速测量方法,该方法通过测量氚衰变产生的β射线与材料相互作用发射的轫致X射线（BIX）,利用轫致X射线的计数率与含氚气体氚分压的标定关系曲线,实现含氚气体中氚分压（活度浓度）的实时测量。该方法中的轫致X射线是通过β射线与表面喷金的铍窗材料作用而产生的,X射线的测量采用NaI(Tl)探测器。研究过程中建立了轫致X射线计数率与氚分压的标定关系曲线,对于纯氚气体,氚压测量范围为1 Pa~10 kPa（氚活度浓度为10¹²~10¹⁵ Bq/m³）时,计数率（C）与氚压（p）的标定曲线为C=5.01×10⁴（1-e^-4.55×10-5p）,其指数拟合相关系数为1.000 00。对于氚体积分数为1%的氚-氦混合气体,氚分压测量范围为1~100 Pa（氚活度浓度为10¹¹~10¹⁴ Bq/m³）时,计数率与氚分压的标定曲线为C=5.24×10²(1-e^-4.69×10-3p),其指数拟合相关系数为0.998 60。对于氚体积分数为1%的氚 氢混合气体,氚分压测量范围为1~100 Pa（10¹¹~10¹⁴ Bq/m³）时,计数率与氚分压的标定曲线为C=5.18×10²(1-e^-4.61×10-3p),其指数拟合相关系数为0.999 53。利用以上标定曲线,对任意氚分压的含氚混合气体进行验证测量,结果表明,该方法测量精度较高、响应速度快、测量稳定性好,在氚测量技术中是一种很有前景的方法。     

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)%。     

氢—水液相催化交换法脱氚

对疏水催化剂的设计与制备方法及氢－水液相交换反应过程进行了讨论,并概要评述了以常温氢－水催化交换法进行重水脱氚的液相催化交换（LPCE）及其联合电解的催化交换（CECE）工艺流程。     

中国先进研究堆回路系统设计总结

目前，研究堆的类型曰趋多样化，有重水堆、轻水堆、气冷堆和正在研制的核聚变堆，不同的堆型，回路系统的配置相差很大，如101重水堆有与重水氦气有关的几个回路系统，49．2游泳池式堆也有与轻水有关的几条回路。但采用轻水作冷却剂，重水作反射层的堆，至少需设置十几条回路。CARR是一座轻水作冷却剂、重水作反射层的研究堆，回路系统设计时主要参考了国内外一些研究堆，如HWRR、ORPHEE堆，HANARO堆、FRM—Ⅱ等。     

Design Study of Feasible Water Detritiation Systems for Fusion Reactor of ITER Scale

Two types of water detritiation systems have been designed for fusion reactors of ITER scale. One of the systems is a combination of WD (Water Distillation) and VPCE(vapor phase catalytic exchange) columns. The other is a combination of a WD column and a CECE(combined electrolysis catalytic exchange) column. Three water distillation columns are needed for the former system. The total height of the three columns is 106 m. The height of the water distillation and CECE columns for the latter system are 20 and 24m, respectively. These large water distillation columns result in the larger tritium inventory of the former system than for the latter system. However, there have been the results for the operation of the actual scale of the water distillation and VPCE columns. No demonstration test has been carried out for the CECE column. From these reasons, the WD+VPCE system should be the first candidate for the fusion reactor. The WD+CECE system is superior to the WD+VPCE system for the flexibility in design as well as the tritium inventory. It is desired to demonstrate the CECE column to develop the water detritiation system best suited to the fusion reactors.     

Effect of hydrocarbons on the efficiency of catalytic reactor of detritiation system in an event of fire

Detritiation system of a nuclear fusion plant is mandatory to be designed and qualified taking carefully into consideration all the possible extraordinary situations in addition to that in a normal condition. We focused on the change in the efficiency of tritium oxidation of a catalytic reactor in an event of fire where the air accompanied with hydrocarbons, water vapor, and tritium is fed into a catalytic reactor at the same time. Our test results on the effect of these gases on the efficiency of tritium oxidation of the catalytic reactor indicated; (1) tritiated hydrocarbon produces significantly by reaction between tritium and hydrocarbons in a catalytic reactor; (2) there is little possibility of degradation in the detritiation performance because the tritiated hydrocarbons produced in the catalyst reactor are combusted; (3) there is no possibility of uncontrollable rise in the temperature of the catalytic reactor by heat of reactions; and (4) saturated water vapor could temporarily poison the catalyst and degrades the detritiation performance. Our investigation indicated a saturated water vapor condition without hydrocarbons would be the dominant scenario to determine the amount of catalyst for the design of catalytic reactor of the detritiation system.     

联合电解催化交换系统的动态模型及理论计算

为探求联合电解催化交换系统各单元中氚浓度空间分布和动态变化的内在规律，建立了D／T体系的气-液两元模型。根据不同的催化剂传质性能，计算了为达到特定脱氚率和电解池浓缩倍数所要求的交换床总高度和进液位置。理论计算得到的氚在交换床上的空间分布趋势与文献报道的中试结果一致，电解池中的氚浓度随时间呈线性增长。     

Processing highly tritiated water desorbed from molecular sieve bed using PERMCAT

Tritium handling facilities use molecular sieve beds (MSB) to collect and recover tritiated water. After reaching the capacity limit of the MSB, the water is desorbed and decontaminated in a water detritiation system (WDS). In the case of highly tritiated water (HTW) absorbed into a MSB, an inherent safe option for processing is necessary due to the HTW specific properties. Ideally, HTW should be processed immediately in a continuous mode. With this in consideration, the water desorption process from a zeolite bed was developed and optimized in a dedicated non active facility. The results of this experiments were applied into the regeneration of a MSB previously loaded with HTW containing an activity of 1.9 × 10¹⁴ Bq kg^?1. The water was desorbed, by step increasing the temperature bed and fed by helium carrier gas into the PERMCAT for detritiation and tritium recovery. The processed water was collected in a dry MSB downstream of the PERMCAT. These initial studies successfully demonstrate the viability of the process. The obtained results of the preliminary study and the subsequent tests with tritium, will provide useful information for the design of tritium processes relying on MSB, such as the water processing foreseen for the test blanket modules in ITER.     

三代压水堆内陆厂址放射性流出物排放问题及改进建议

由于内陆厂址受纳水体容量有限,使得核电内陆厂址面临的一个关键问题就是液态流出物排放。本文通过对比分析三代压水堆内陆厂址液态流出物排放与现有排放国家标准要求,发现三代压水堆两项指标不能满足内陆厂址要求,即除氚、¹⁴C外其他放射性核素和氚排放均不能满足内陆厂址要求。针对除氚、¹⁴C外其他放射性核素排放,建议增加化学絮凝、离子交换床和反渗透装置以满足100 Bq/L的排放要求。针对氚排放,通过调整排放方式能满足2台机组氚排放要求,使得下游1 km处氚浓度不超过71 Bq/L;多机组内陆电厂的氚排放建议利用联合电解催化交换(CECE)和水精馏(WD)技术,以达到分离氚的目的。     

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.     

基于两级钯膜反应器的氚水处理技术

为了处理高浓氚水,搭建了一台氢-水同位素交换串联水汽变换的两级钯膜反应器装置,可以实现级联处理工艺。以天然水代替氚水为源项,以D₂代替H₂开展了除氢实验,最高获得了207.4的除氢因子,验证了两级钯膜反应器用于处理氚水的可行性。通常情况下,水汽变换反应的除氢因子大于氢-水同位素交换反应。其中,氢-水同位素交换中D₂/H₂O体积流量比越大,该反应除氢因子越大;氢-水同位素交换中原料侧压力越大,该反应除氢因子越大;原料水流量越大,两个反应的除氢因子均会下降。由于一级膜反应器采用氢-水同位素交换可将氚水浓度降低1个量级以上,因而可以尽量避免二级膜反应器中CO与高浓氚接触,抑制含氚有机物的生成。由此可见,两级钯膜反应器有望成为一种高效的氚水处理装置。     

Preliminary results from a detritiation facility dedicated to soft housekeeping waste and tritium valorization

Nuclear waste management has to be taken into account for fusion machine using tritium as fuel. Soft housekeeping waste (e.g. gloves, tissues, protective clothes, etc.) is produced during the whole life as well as during the dismantling of the reactor and is contaminated by tritium under reduced (HT) and oxidized (HTO) forms.In collaboration with ENEA, a lab-scaled facility has been built at CEA Cadarache for soft housekeeping waste detritiation and tritium valorization. The previously milled waste is placed in a reactor to be heated up to a temperature lower than the housekeeping melting point. A carrier gas is then injected in the detritiation reactor to remove tritium, thanks to the combined effects of temperature and carrier gas (type and feed flow). The tritiated gas exhausted from the detritiation reactor is then sent through a catalytic Pd–Ag membrane reactor (CMR) where tritium is recovered via isotopic exchange reaction and permeation phenomenon.Based on previous studies that have allowed defining the most efficient operating conditions for the detritiation process, this work presents the results obtained by the coupling of the detritiation facility with the CMR. Due to safety considerations, restrictions on the nature of the carrier gas were applied, rejecting air as the carrier gas even though air was the best candidate for the detritiation part of the process. The performance of the whole system was estimated by means of a parametric study on the influence of flow rates in the CMR and transmembrane pressure.     

Influence on moisture and hydrocarbons on conversion rate of tritium in catalytic reactors of fusion-DEMO detritiation system

Thoughtful consideration of abnormal events such as fire is required to design and qualify a detritiation system (DS) of a nuclear fusion facility. Since conversion of tritium to tritiated vapor over catalyst is the key process of the DS, it is indispensable to evaluate the effect of excess moisture and hydrocarbons produced by combustion of cables on tritium conversion rate considering fire events. We conducted demonstration tests on tritium conversion under the following representative conditions: (I) leakage of tritium, (II) leakage of tritium plus moisture, and (III) leakage of tritium plus hydrocarbons. Detritiation behavior in the simulated room was assessed, and the amount of catalyst to fulfill the requirement on tritium conversion rate was evaluated. The dominant parameters for detritiation are the concentration of hydrogen in air and catalyst temperature. The tritium in the simulated room was decreased for condition (I) following ventilation theory. An initial reduction in conversion rate was measured for condition (II). To recover the reduction smoothly, it is suggested to optimize the power of preheater. An increase in catalyst temperature by heat of reaction of hydrocarbon combustion was evaluated for condition (III). The heat balance of catalytic reactor is a point to be carefully investigated to avoid runaway of catalyst temperature.