Study on highly-efficient enrichment of tritium water by use of distillation column packed with hydrophilic adsorbent

氚废水将从未来聚变反应堆的氚燃料循环设施中排出，或目前从裂变反应堆的铀燃料后处理工厂中排出。当其浓度低于法定浓度（60Bq/cm^3）时，可将其原样排出设施。当浓度高于法定值时，排放的水必须用大量的淡水稀释或在设施中进行浓缩/分离。在稀释过程中困难较少。然而，当其氚浓度远高于规定水平时，我们需要开发一种新的同位素分离系统，在低于规定水平的氚废水排水口进行净化，并分离少量高氚水。用于CANDU反应堆重水分离的H_2H_2O同位素交换法虽然可以应用于氚富集，但分离氘的设施体积较大，且需要特殊且昂贵的Pt催化剂。此外，熔合设备废气中含有的CO会使Pt催化剂的性能恶化。因此，该工艺需要预处理，以减少一些污染物。本文研究了一种利用亲水吸附剂提高经典精馏塔分离性能的同位素分离新方法。作为亲水吸附剂的候选材料，本文对硅胶和沸石吸附剂进行了比较实验。基于H_2O和HTO蒸气压差的原始同位素分离因子为1.028。结果表明，亲水吸附剂可将同位素分离系数提高到1.1 ~ 1.2，从而减小了氚富集分离的规模。硅胶柱在不同汽流量范围内均具有较好的分离性能。另一方面，沸石柱（商品名林德分子筛13X）在极小蒸汽流量下的同位素分离性能最大，但在较大流量下分离系数降低。这是因为气相中的HTO与吸附剂上的H_2O之间的交换反应比较缓慢。因此，沸石柱的转移单元数（NTP）远小于硅胶柱。沸石柱被认为是有效的，特别是对于非常小的蒸汽流量。对氚的瞬态富集性能进行了实验测定，发现采用迁移单元数的平板模型的数值计算与实验结果吻合。实验和数值结果在下一页列出的研究论文中给出。目前的科学研究摘要在一份报告中进行了总结。少

Tritium-waste water will be drained from facilities for a tritium fuel cycle of a future fusion reactor or is presently exhausted from uranium fuel reprocessing plant for a fission reactor. When its concentration is lower than the legally regulated one (60Bq/cm^3), it can be drained from the facilities as it is. When it is higher than the legal value, the drain water has to be diluted by a large amount of fresh water or has to be enriched/separated in the facilities. There is less difficulty in the dilution process. However, when its tritium concentration is much higher than the regulated level, we need to develop a new isotope separation system to decontaminate the tritium-waste water drain at a lower level than the regulated level and to separate a small amount of high-level tritium water. Although the H_2H_2O isotopic exchange method that was used for a heavy water separation of CANDU reactor can be applied to the tritium enrichment, the facilities for the deuterium separation are h … More uge, and they need a special and expensive Pt catalyst. In addition, the Pt catalyst performance is deteriorated by CO that will be included in the exhaust gas of fusion facilities. Therefore, the process needs pretreatment to reduce some pollutants. In the present study, a new isotope separation method to enhance the performance of a classical distillation column with use of hydrophilic adsorbents. As candidates for the hydrophilic adsorbent, silica-gel and zeolite adsorbents were comparatively experimented in the present study. The original isotope separation factor based on the difference in vapor pressure between H_2O and HTO is 1.028. It was found that the isotope separation factor was enhanced to 1.1 to 1.2 with the use of the hydrophilic adsorbent, and therefore it can downsize the scale of the tritium enrichment and separation. The silica-gel column attained the comparatively large separation performance in the various ranges of vapor flow rate. On the other hand, the zeolite column (commercial name Linde molecular sieve 13X) attained the largest isotope separation performance at very small vapor flow rate, but the separation factor decreased at higher flow rate. This is because the exchange reaction between HTO in the vapor phase and H_2O on the adsorbent is comparatively slow. Therefore, the number of transfer unit (NTP) of the zeolite column was much smaller than that of the silica-gel column. The zeolite column is considered to be effective especially for the very small vapor flow rate. The transient tritium enrichment performance was experimentally determined, and it was found that the numerical calculation based on the plate model that uses the number of transfer unit fitted the experimental ones. The experimental and numerical results were presented in the research papers listed in the next page. The abstract of the present scientific research is summarized in a report. Less