气体裂变产物88Kr的放化分离方法

为了制备满足88Kr核参数测量的样品,本工作研究了88Kr的放化分离方法。以85Kr、125Xe为放射性示踪剂研究了活性炭柱对Kr和Xe的吸附分离条件。结果显示,在0℃下Xe能被活性炭柱快速吸附而Kr不吸附。研制了一套适用于短寿命气体裂变产物分离的装置系统,使用辐照的铀靶进行了88Kr样品的分离。Kr的收率大于90%,Xe及I的去污因子大于1×104,整个操作过程可在5min内完成。     

复杂混合气体组分在低温活性炭表面的吸附特性

为实现大体积气体中微量放射性气体Kr、Xe同位素的测量,须将混合气体进行浓集并将目标气体吸附于10 mL左右的活性炭源盒中。本实验对混合气体中各组分在活性炭分离柱上的吸附性能进行研究,建立了通过去除其他杂质气体、浓集大体积气体制备放射性Kr和Xe活度源的方法。根据反应堆流出气体和核爆可能生成的气体组分,配制了模拟气体,使用活化的4A分子筛对其中的水和CO₂进行模拟去除,获得了流程中去除水和CO₂的实验条件;选择5个低温点(273、264、255、246、238 K),在低温活性炭柱上对H₂、CO、CH₄、Kr和Xe的吸附特性进行研究,测定了各气体在不同温度下的吸附穿透曲线。结果表明,室温下4A分子筛对水和CO₂有较好的吸附效果。低温下,H₂、CO不易在活性炭表面吸附;CH₄、Kr吸附性质相似;Xe吸附能力较强。低温下难以去除的CH₄可在高温下氧化去除。因此,可根据混合气体中各组分性质的不同实现杂质气体的去除和目标气体Kr、Xe的回收测量。     

多级吸附-脱附法浓缩纯化氙技术研究

为满足大气放射性核素监测的需求,利用氙(Xe)与二氧化碳(CO2)、氡(Rn)等组分在活性炭吸附柱内脱附行为的差异,采用多级活性炭吸附柱吸附-脱附的方法,对大气环境中的Xe(体积分数8.7×10-8)进行浓缩纯化,得到高浓度的Xe样品。研究了空气中的Xe、CO2及Rn等组分在多级活性炭吸附柱上的脱附曲线,选择Xe的脱附时段向下一级吸附柱转移吸附,对Xe进行逐级浓缩纯化。样品中Xe富集倍数可达105~106,Rn去污系数大于105,CO2体积分数低于4×10-5。此研究结果对于实现多组分混合气体中某一特定低含量组分的浓缩、纯化具有普遍指导意义。     

用于氙氪吸附分离的金属-有机骨架材料耐辐照性能的初步研究

由于乏燃料后处理废气中放射性氙（Xenon,Xe）和氪（Krypton,Kr）的去除需求以及高纯度Xe气体的商业价值,Xe和Kr的吸附分离越来越受到重视。目前Xe/Kr的分离主要采用能源和资本密集型的低温精馏法。以金属-有机骨架材料为吸附剂的多孔材料已经展示出在相对较高温度下选择性吸附Xe和Kr的能力,有望替代低温精馏法实现低成本的Xe/Kr分离。实验研究了三种热稳定性良好的金属-有机骨架材料(Co/DOBDC、Ni/DOBDC、Co₃（HCOO）₆)对Xe和Kr的吸附分离性能。从材料在273 K温度下对Xe和Kr的吸附等温线、亨利常数、亨利选择性和理想吸附溶液理论（Ideal Adsorbed Solution Theory,IAST）选择性等测试和计算结果来看,Co/DOBDC和Ni/DOBDC在常压下对Xe具有较大的吸附容量,适用于Xe吸附存储的应用场景;Co₃（HCOO）₆在低压吸附下具有大的Xe亨利常数、Xe/Kr亨利选择性和Xe/Kr IAST选择性,适用于Xe和Kr吸附分离的应用场景。...     

医用裂变99Mo分离纯化工艺中131I-和131IO-3的去除

为评价已建立的裂变⁹⁹Mo分离纯化工艺,即AgNO₃沉淀法、α-安息香肟沉淀法、阴离子交换色层法与活性炭色层法联用工艺流程,对放射性碘的去除效果,本研究以¹³¹I为放射性示踪剂,研究两种不同放射性碘化学形态¹³¹I^-与¹³¹IO^-₃在⁹⁹Mo分离纯化工艺中的行为及其去除效果。结果表明,对于¹³¹I^-,AgNO₃沉淀能够去除模拟溶液中98.2%¹³¹I^-,α-安息香肟沉淀法分离⁹⁹Mo工艺能够去除97.9%¹³¹I^-,AG1-×8树脂上阴离子与I-发生交换可以除去Mo样品中99.9%的¹³¹I^-,活性炭色层法通过吸附作用除去75%的¹³¹I^-,最终¹³¹I^-的累积去污系数为1.90×10⁶,¹³¹I^-的去除率大于99.99%。对于¹³¹IO^-₃,加入AgNO₃对其去除没有影响,ɑ-安息香肟沉淀法能除去99%以上的¹³¹IO^-₃,AG1-×8树脂上阴离子与¹³¹IO^-₃发生交换可以除去Mo样品中99.9%的¹³¹IO^-₃,活性炭色层法能除去约70%¹³¹IO^-₃,最终¹³¹IO^-₃的累积去污系数为2.52×10⁵,¹³¹IO^-₃的去除率大于99.99%。已建立的裂变⁹⁹Mo分离纯化工艺流程对¹³¹I^-与¹³¹IO^-₃均具有出色的去除效果。     

复杂混合气体组分在低温活性炭表面的吸附特性

为实现大体积气体中微量放射性气体Kr、Xe同位素的测量,须将混合气体进行浓集并将目标气体吸附于10 mL左右的活性炭源盒中。本实验对混合气体中各组分在活性炭分离柱上的吸附性能进行研究,建立了通过去除其他杂质气体、浓集大体积气体制备放射性Kr和Xe活度源的方法。根据反应堆流出气体和核爆可能生成的气体组分,配制了模拟气体,使用活化的4A分子筛对其中的水和CO_2进行模拟去除,获得了流程中去除水和CO_2的实验条件;选择5个低温点(273、264、255、246、238 K),在低温活性炭柱上对H_2、CO、CH_4、Kr和Xe的吸附特性进行研究,测定了各气体在不同温度下的吸附穿透曲线。结果表明,室温下4A分子筛对水和CO_2有较好的吸附效果。低温下,H_2、CO不易在活性炭表面吸附;CH_4、Kr吸附性质相似;Xe吸附能力较强。低温下难以去除的CH_4可在高温下氧化去除。因此,可根据混合气体中各组分性质的不同实现杂质气体的去除和目标气体Kr、Xe的回收测量。     

乏燃料溶解尾气中氙的取样分离及稳定同位素比的测量

采用活性炭低温收集的方法对空气中的氙（Xe）进行收集,经活性炭初步分离后,再用5Å分子筛进一步分离纯化,获得可用于气体质谱仪测量的Xe样品,然后采用气体质谱仪对Xe的稳定同位素比（R）进行准确测量。研究确定了活性炭、分子筛对Xe的分离性能与操作条件,建立了Xe的收集和纯化方法。对空气中R(¹³⁴Xe/¹²⁹Xe)、R(¹³¹Xe/¹²⁹Xe)、R(¹³²Xe/¹²⁹Xe)测量的相对标准偏差分别为0.32%、0.15%、0.14%(n=3)。采用该法对乏燃料剪切、溶解尾气中的Xe进行了取样、纯化、测量,并利用Xe同位素比计算了乏燃料燃耗。结果表明：采用R(¹³²Xe/¹³⁴Xe)推算的燃耗比R(¹³¹Xe/¹³⁴Xe)更接近真实值,与真实值的偏差在20%左右。     

乏燃料溶解尾气中氙的取样分离及稳定同位素比的测量

采用活性炭低温收集的方法对空气中的氙（Xe）进行收集，经活性炭初步分离后，再用5Å分子筛进一步分离纯化，获得可用于气体质谱仪测量的Xe样品，然后采用气体质谱仪对Xe的稳定同位素比（R）进行准确测量。研究确定了活性炭、分子筛对Xe的分离性能与操作条件，建立了Xe的收集和纯化方法。对空气中R(¹³⁴Xe/¹²⁹Xe)、R(¹³¹Xe/¹²⁹Xe)、R(¹³²Xe/¹²⁹Xe)测量的相对标准偏差分别为0.32%、0.15%、0.14%(n=3)。采用该法对乏燃料剪切、溶解尾气中的Xe进行了取样、纯化、测量，并利用Xe同位素比计算了乏燃料燃耗。结果表明：采用R(¹³²Xe/¹³⁴Xe)推算的燃耗比R(¹³¹Xe/¹³⁴Xe)更接近真实值，与真实值的偏差在20%左右。     

放射性惰性气体分离与分离材料研究进展

放射性惰性气体氙(¹³³Xe)、氪(⁸⁵Kr)与氩(³⁷Ar)是重要的气体裂变产物,主要产生于核电站反应堆、地下核试验、乏燃料后处理等人类核活动中。放射性惰性气体的快速高效分离、分析与检测在核军控核查、核环境监控、核燃料循环等领域中均有重要意义。利用固体多孔吸附材料在室温环境下从复杂环境气氛中选择性地将目标放射性惰性气体高效吸附分离出来是目前最简单与高效的方法。近些年发展的金属有机框架材料、多孔有机框架材料、多孔有机聚合物等新型多孔材料在惰性气体Xe与Kr的分离上已经展现出优异的性能与良好的应用前景。本文系统性地综述了放射性惰性气体(Xe、Kr、Ar)分离与分离材料的研究进展,并对未来研究趋势进行了展望。     

吸附法净化高温气冷堆He载气中Kr、Xe的研究

用椰子壳活性炭吸附剂固定床吸附法去除高温气冷堆He载气中Kr、Xe杂质。获得了Kr、Xe在椰子壳活性炭上的动吸附规律。考察了吸附温度、浓度、流速及床高等因素对保护作用时间、完全饱和时间、吸容量的影响,获得最佳运行参数。结果表明：采用椰子壳活性炭可以除去高温气冷堆He载气中Kr、Xe等有害杂质,满足净化系统的要求。     

用制备色谱法分离氪氙

叙述了通过改变填充5A分子筛色谱柱的载气流速和色谱柱温度,改变氪、氙的保留时间,实现氪、氙分离。分离后,在低温下分别用活性炭收集。结果表明,延长氪、氙色谱柱保留时间的间隔,可提高氪、氙的去污系数;在–80oC低温下,活性炭能很好地收集氪和氙,回收率>95%。     

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。     

Atmospheric 85Kr and 133Xe activity concentrations at locations across Japan following the Fukushima Dai-ichi Nuclear Power Plant accident

Atmospheric ⁸⁵Kr and ¹³³Xe activity concentrations were determined from weekly air samples collected at Sapporo, Akita and Chiba, Japan, throughout 2011. The results demonstrated that the Fukushima Dai-ichi Nuclear Power Plant accident in early March 2011 resulted in high ¹³³Xe activity concentrations as well as elevated levels of ⁸⁵Kr activity; there was a striking increase in the concentrations of both isotopes over the week running from 14 to 22 March as the radioactive plume released from the plant was captured. At Chiba, following the accident, the ⁸⁵Kr activity concentration increased from 1.38 to 17.7 Bq/m³, while the ¹³³Xe levels increased from below the minimum detectable concentration (MDC ≤ 1.9 × 10^?3 Bq/m³) to 1.3 × 10³ Bq/m³. Conversely, at Sapporo and Akita, high ⁸⁵Kr activity concentrations were not observed, due to differences in air transportation mechanisms based on wind directions. Duplicate samples were collected at Chiba to allow the simultaneous analyses of ⁸⁵Kr and ¹³³Xe at the Japan Chemical Analysis Center and the Bundesamt für Strahlenschutz in Germany and the results were in good agreement. The external effective radiation doses resulting from ⁸⁵Kr and ¹³³Xe releases following the accident were estimated to be approximately 7.0 × 10^?3 and 1.3 μSv, respectively, based on the activity concentrations of these nuclides from March to June in 2011 at Chiba.     

Performance evaluation of a resonance ionization mass spectrometer developed for the FFDL system of fast reactors

To prevent a fuel failure event from becoming a serious radiation accident, sodium-cooled fast reactors are equipped with a system for failed fuel detection and location (FFDL). The FFDL instrument employed in the prototype fast breeder reactor Monju is based on the gas tagging method, in which precise and accurate measurements of krypton and xenon isotope ratios (⁷⁸Kr/⁸⁰Kr, ⁸²Kr/⁸⁰Kr and ¹²⁶Xe/¹²⁹Xe) must be performed in a short time. Burnup measurements also contribute to accurate determination of ⁸²Kr/⁸⁰Kr. We have developed a highly sensitive resonance ionization mass spectrometer for the isotopic analyses, which uses resonance ionization of Kr and Xe atoms by a pulsed laser at wavelengths of 216.7 and 249.6 nm, respectively. In evaluating the performance of our spectrometer, we find that systematic errors caused by isotope shifts can be reduced to negligible levels, and that statistical errors of 3% at a nuclide concentration of 7 ppt can be achieved with a single measurement time of about 40 minutes for each Kr and Xe isotope ratio. This means that, within one hour, about 200 fuel assemblies can be individually identified with a probability of 99%, verifying the applicability of our spectrometer to the FFDL system of fast reactors.     

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.     

Studies of Ceramic Fuels with the Use of Fission Gas Release Loop, (II)

The γ-ray spectra of fission gases released from UO₂-graphite pellets under neutron irradiation were measured. With and without separating fission gases into xenon and krypton, 25 kinds of γ-ray were observed and assigned to nine nuclides, ^85mKr, ⁸⁷Kr, ⁸⁸Kr(⁸⁸Rb), ¹³³Xe, ¹³⁵Xe, ^135mXe and ¹³⁸Xe (¹³⁸Cs). A value of 15 min is proposed for the half-life of ¹³⁸Xe, based on analysis of the decay curves. Discussion is given on problems related to determination of the release rate of each fission product through measurement of the height of each peak in the γ-ray spectrum.     

Post-irradiation studies on knock-out and pseudo-recoil releases of fission products from fissioning UO2

By using post-irradiation techniques, in-pile releases of ¹³³Xe, ^85mKr, ⁸⁸Kr, ⁸⁷Kr and ¹³⁸Xe from UO₂ fissioning at low temperatures below about 200° C are studied: these are analyzed into a time-dependent knock-out and time-independent pseudo-recoil releases. For the latter, a “self knock-out” mechanism is proposed: when a fission fragment loses thoroughly its energy near the UO₂ surface and stops there, it will knock out the surface substances and accordingly the fragment (i.e. the fission product) will be released. The effective thickness of the layer where the self knock-out occurs is found to be ~7Å. As for the knock-out release, the following is estimated from its dependence on various factors: the knock-out release of fission products occurs from the surface layer with the effective thickness of ~20Å: the shape of UO₂ matrix knocked out by one fission fragment passing through the surface is equivalent to a cylinder ~32Å diameter by ~27Å thick, (i.e. the knock-out coefficient for UO₂ is ~660 uranium atoms per knock-out event). On the basis of the above estimations, the conclusions derived from the past in-pile studies of fission gas releases are evaluated.     

The mechanisms of in-pile fission gas release from UO2

In-pile release mechanisms of fission gas from UO₂ at low temperatures were studied. The release of ¹³³Xe, ¹³⁵Xe, ¹³⁸Xe, ^85mKr, ⁸⁸Kr and ⁸⁷Kr from a sintered UO₂ pellet was measured at temperatures ranging from 250 to 930°C using a graphite specimen holder. The release from the holder, in which a fraction of fission gas was recoil-implanted, was subtracted to obtain the net release from the UO₂ pellet. Knock-out release from the UO₂ was measured directly, and it was found that it was not the main release mechanism, at least not for short-lived nuclides. A ‘pseudo-recoil’ release model is proposed to explain the low temperature release under irradiation. In the model, some of the defects produced by fission fragments act as short-lived carriers for fission gas.     

The characteristics of fission gas release from monocrystalline uranium dioxide during irradiation

Release rates for ^85mKr, ⁸⁷Kr, ⁸⁸Kr, ¹³³Xe, ¹³⁵xe and ¹³⁸Xe were measured in the temperature range 700–1550°C. The data were analysed in terms of diffusion of the rare gases and their halogen precursors. The diffusion coefficients for xenon and iodine were found to be similar whilst krypton also had a similar mobility at ~1200°C but otherwise diffused more slowly. Bromine had a high mobility compared with the rare gases (X 200).