γ辐照对AG1-×8树脂吸附Mo(Ⅵ)的性能研究

为评价γ辐照对AG1-×8树脂吸附⁹⁹Mo的影响,选择吸收剂量分别为37.5、275、825 kGy的AG1-×8树脂,通过静态和动态实验,研究AG1-×8树脂对Mo(Ⅵ)的吸附性能。结果表明,经γ辐照后,AG1-×8树脂表面形态未发生变化及破损;AG1-×8树脂对Mo(Ⅵ)的静态分配系数随吸收剂量的增加而减小;AG1-×8树脂辐照前后对Mo(Ⅵ)的静态分配系数在NH₄OH介质中不随介质浓度变化,而在硝酸、氢氧化钠、碳酸铵介质中随浓度的增加而减小;在1 mol/L氨水介质中,AG1-×8树脂辐照前后对Mo(Ⅵ)吸附行为符合Langmuir等温模型,吸附过程为自发、吸热过程,饱和吸附容量分别为74.07、71.02、70.97、57.57 mg/g;Mo(Ⅵ)在NH4OH中吸附、用1 mol/L 碳酸铵溶液解吸,Mo(Ⅵ)回收率随吸收剂量的增大而降低。     

Desorption of silver atoms from benzene-covered Ag(1 1 1) by energetic Ar bombardment

Experiments have been conducted to gain insight into the processes of desorption of neutral species from surfaces covered with organic molecules due to bombardment with keV particles. The system is comprised of benzene molecules adsorbed onto Ag(1 1 1) and bombarded with 8 keV Ar⁺ ions. Molecular dynamics (MD) simulations of the same system have been performed. Results show that the presence of the benzene alters the yield, the kinetic energy distributions, and the angular distributions of the silver atoms. These changes of the desorption characteristics are the result of collisions between the Ag atoms and the benzene molecules adsorbed to the surface. As more benzene is adsorbed to the surface, the changes to the Ag atom desorption characteristics become more pronounced. The simulations reproduce the modifications to the Ag atom energy and angle distributions.     

Adsorption of Fission Products on Alumina in Organic Solutions

Metal nitrates are readily adsorbed on alumina in organic solutions such as acetone and n-butylacetate. Adsorption isotherms for such compounds as uranyl nitrate, thorium nitrate and cerium nitrate (III) were examined, and the adsorption was found to have occured monomolecularlly on the surface of the alumina.

The weakest adsorption strength on alumina was found to be that of uranyl nitrate, and the adsorbed uranyl nitrate could be substituted very easily by other nitrates such as of fission products.

The logarithmic decrease of the Kd values of fission products on alumina with increase of uranyl nitrate concentration in n-butylacetate was found to correspond to the increase of the solubility of nitrates of fission products (Ce, Sr and Zr) with increase of uranyl nitrate concentration.     

Si原子在CeO2(111)表面吸附与迁移的第一性原理研究

为探究Si原子在CeO₂(111)表面吸附的微观行为,采用第一性原理的方法研究了Si原子在CeO₂(111)表面的吸附作用、电子结构和迁移过程,计算了Si原子在CeO₂(111)表面的吸附能,最稳定及次稳定吸附位置的电子态密度与电荷密度分布、迁移激活能。计算结果表明：Si原子最易吸附于基底表层的O原子上,其中O桥位（O_bri）吸附作用最强,O顶位（O_t）和O三度位（O_h）吸附强度次之。Si原子仅对其最邻近的表层O原子结构影响较大,这与Si原子及其最邻近的O原子间电荷密度重叠程度增强的结果一致。Si原子最易围绕着O_t位从O_bri位向O_h位迁移,迁移所需激活能为0.849 eV。     

Wall analysis in PULSATOR 1

The amount of impurities deposited during the discharge on samples introduced to the liner of PULSATOR I has been measured using a combination of several surface physics techniques (AES, SIMS, EID, RIBS). The amounts are absolutely calibrated and are about 2 × 10¹³ atoms/cm² for oxygen, 5 × 10¹² atoms/cm² for Fe, Cr, Ni (liner material) and 2 × 10¹² atoms/cm² for Mo (limiter material). They depend strongly on the kind of discharges and on the position of the sample. First results using a shutter for time resolved exposure of the sample indicate that deposition of impurities takes place during the plateau of the discharge.     

HTR-10一回路放射性核素在石墨上的吸附及其微观机理研究

通过巨正则系综方法与第一性原理计算,研究了100～900 ℃下,¹³⁴Cs、¹³⁷Cs、⁹⁰Sr、¹¹⁰Ag^m、¹³¹I 5种重要核素在石墨上的吸附率随温度、压强等参数的变化,并根据工程实际参数,推算他们在HTR-10一回路中反射层、石墨碳砖以及石墨粉尘上的吸附量。研究表明,Cs和Sr倾向于吸附在石墨的H位,而Ag和I倾向于吸附在石墨的T位,且他们的吸附能也有所差异。此外,核素粒子数密度与吸附率呈线性关系,而温度与吸附率呈指数关系。最后,通过研究5种核素在HTR-10一回路中的吸附情况,发现其中的放射性主要来自于核素¹³⁴Cs、¹³⁷Cs和¹³¹I,而⁹⁰Sr和¹¹⁰Ag^m的贡献较少,这与唯象模型的保守估计结论一致。     

液态燃料氯盐快堆最小需求燃耗分析

为探究采用增殖燃烧模式运行的液态燃料氯盐快堆的平均卸料燃耗深度，基于中子平衡分析方法，选取5种常用氯盐，提出在线清除裂变气体和难溶裂变产物方案来维持增殖燃烧运行模式，主要研究分析了氯盐的重金属密度和在线处理方案对最小需求燃耗的影响以及无限栅元模型下维持增殖燃烧模式可接受的堆芯中子损失项。分析表明68NaCl-32UCl₃和20UCl₃-80UCl₄的最小需求燃耗分别是30.47%FIMA（FIMA是指已裂变原子数与初始的总装料金属原子数之比）和10.28%FIMA；清除裂变气体和难溶裂变产物后，60NaCl-40UCl₃可接受的中子损失项从3.49%提高到10.68%。结果表明氯盐的重金属密度对最小需求燃耗有明显影响，同时清除裂变气体和难溶裂变产物能够较大提高燃料盐系统的中子经济性，以及提高增殖燃烧模式运行可接受的堆芯中子损失项。      

Ag_(3)PO_(4)/P-C_(3)N_(4)材料的制备及其对铀的吸附性能北大核心CSCD

为设计一种对U(Ⅵ)具有较高吸附容量和较高选择性的吸附材料,采用石墨相氮化碳(g-C_(3)N_(4))与磷酸二氢铵作为原料,通过热共聚法制备P-C_(3)N_(4),再利用磷酸氢二钠与硝酸银通过原位共沉淀法制备Ag_(3)PO_(4)/P-C_(3)N_(4)复合吸附材料。吸附实验结果表明,Ag_(3)PO_(4)/P-C_(3)N_(4)复合吸附材料在室温下对U(Ⅵ)的吸附容量达到524.6 mg/g;在溶液中同时存在Na^(+)、K^(+)、Mg^(2+)、Ca^(2+)、Sr^(2+)、Zn^(2+)、Ni^(2+)和Co^(2+)等竞争离子时,对U(Ⅵ)的吸附分配系数达到6.13×10^(3)mL/g。XPS分析结果表明,Ag_(3)PO_(4)/P-C_(3)N_(4)复合吸附材料中的含N和含P官能团可能参与U(Ⅵ)吸附过程。因此,Ag_(3)PO_(4)/P-C_(3)N_(4)复合吸附材料是一种对U(Ⅵ)具有较高吸附容量和较高选择性的吸附材料。     

球床模块式高温气冷堆失冷事故特性研究

利用高温气冷堆专用系统分析软件THERMIX程序,对球床模块式高温气冷堆(HTR-PM)失冷失压和失冷不失压事故的动态特性进行了研究,分析了堆芯功率、燃料最高温度及堆舱水冷壁余热载出功率等关键参数的变化过程,并对影响余热排出功率和燃料最高温度的不确定性进行了评价.研究结果表明,在失冷事故下,堆芯余热可通过热传导、辐射和自然对流等非能动方式传至最终热阱大气,燃料元件和压力容器等重要部件的最高温度均在设计限值内.这为HTR-PM保持模块式高温气冷堆固有安全性不变的同时实现单堆250 MW的功率方案奠定了基础,也为后续高温气冷堆电站示范工程进一步的深入设计研究提供了依据.     

Electrolysis of Burnup-Simulated Uranium Nitride Fuels in LiCl-KCl Eutectic Melts

The electrochemical behavior of burnup-simulated uranium nitride fuels containing representative solid fission product elements, UN+Mo (Mo = 2.84 wt%), UN+Pd (Pd = 4.6 wt%) and (U, Nd)N (NdN = 8.0 wt%), was investigated in the molten LiCl-KCl eutectic salt with 0.54 wt% UCl₃ in order to clarify the effects of fission products on the dissolution of actinide nitrides and the behavior of FPs in the electrorefining of spent nitride fuel. The rest potentials of burnup-simulated UN pellets were similar to that of pure UN. The electrochemical dissolution of UN began at about _0:75V vs Ag/AgCl reference electrode in all samples as well as that of pure UN. After the electrolyses at the constant anodic potential of ?0:65––0:60V vs Ag/AgCl, most of UN was dissolved into LiCl-KCl as UCl₃ at the anode, and U was recovered in the liquid Cd cathode in all samples. Furthermore, Nd was dissolved at the anode and accumulated into LiCl-KCl as NdCl₃, while Mo and Pd were not dissolved but remained at the anode.     

In-Situ Measurement of Fission Product Plateout in In-Pile Gas Loop Using Portable Ge(Li) Gamma-Ray Spectrometer

A nondestructive and quantitative method of measuring fission products deposited on inside surface of the primary duct has been developed. A portable Ge(Li) detector with a lead collimator was used for the external scanning of γ-rays emitted from the fission product plateout in the duct.

Upon termination of the first irradiation cycle for the coated particle fuels in the high temperature in-pile gas loop OGL-1 installed in JMTR (Japan Material Testing Reactor), in-situ measurements of the plateout were carried out by the above method at different points in the primary system.

Identified nuclides in the measured γ-ray spectra were ¹³¹I, ¹³³I, ⁹⁵Zr, ⁹⁵Nb, ¹³⁷Cs, ^110mAg, ⁹⁹Mo, ¹⁴⁰La, ⁶⁰Co, ⁵⁸Co, ⁵⁴Mn, ⁵¹Cr, ⁶⁵Zn, ⁵⁹Fe, ¹²²Sb, ¹²⁴Sb, ¹⁸²Ta, ¹⁸¹Hf, ²²Na and ⁴⁶Sc. The plateout densities of these nuclides were obtained using conversion coefficients determined by detector calibration and calculation, which were from 10^-5 to 10^-2 μCi/cm².

It was shown clearly by the experiment that the present measuring method using an in-situ γ-ray spectrometer is useful in the studies of fission product plateout in the primary cooling system of a high temperature gas cooled reactor.     

Al2O3色层法从低浓铀靶件中分离99Mo条件研究

在裂变⁹⁹Mo的生产工艺中,常用Al₂O₃色层法分离纯化⁹⁹Mo。为建立Al₂O₃色层法从低浓铀(LEU)靶件中分离裂变⁹⁹Mo的工艺,考察吸附时间、温度、酸度、预处理方式等对Al₂O₃吸附Mo效果的影响。研究采用Al₂O₃色层法从不同浓度HNO₃溶液中分离Mo。测定Al₂O₃色层法对Al和主要杂质元素Sr、Ru、Zr、Te、Cs、I的去污系数。研究结果表明,在0.05~0.1 mol/L HNO₃介质中Al₂O₃对Mo有出色的吸附性能,Mo吸附率在99%以上,在NH₄OH溶液中Al₂O₃不吸附Mo。经500 ℃活化3 h预处理得到的Al₂O₃-C具有更大的比表面积,且在HNO₃浓度大于0.1 mol/L时相比于150 ℃活化3 h预处理得到的Al₂O₃-B以及未经高温预处理得到的Al₂O₃-A对于Mo有更好的吸附性能。采用该工艺,通过Al₂O₃色层法从模拟的LEU靶件溶液中提取Mo,Mo回收率大于90%,Al₂O₃色层法对裂变杂质元素Ru、Sr、Zr、Te、Cs等的去除率均大于99.99%,对¹³¹I的去除率大于92%。由此可见,Al₂O₃在HNO₃介质中对Mo的吸附率高,能够有效地去除⁹⁹Mo产品中的杂质核素,适用于从低浓铀靶件中分离裂变⁹⁹Mo。     

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。     

Near-surface and bulk behavior of Ag in SiC

The diffusive release of fission products, such as Ag, from TRISO particles at high temperatures has raised concerns regarding safe and economic operation of advanced nuclear reactors. Understanding the mechanisms of Ag diffusion is thus of crucial importance for effective retention of fission products. Two mechanisms, i.e., grain boundary diffusion and vapor or surface diffusion through macroscopic structures such as nano-pores or nano-cracks, remain in debate. In the present work, an integrated computational and experimental study of the near-surface and bulk behavior of Ag in silicon carbide (SiC) has been carried out. The ab initio calculations show that Ag prefers to adsorb on the SiC surface rather than in the bulk, and the mobility of Ag on the surface is high. The energy barrier for Ag desorption from the surface is calculated to be 0.85–1.68 eV, and Ag migration into bulk SiC through equilibrium diffusion process is not favorable. Experimentally, Ag ions are implanted into SiC to produce Ag profiles buried in the bulk and peaked at the surface. High-temperature annealing leads to Ag release from the surface region instead of diffusion into the interior of SiC. It is suggested that surface diffusion through mechanical structural imperfection, such as vapor transport through cracks in SiC coatings, may be a dominating mechanism accounting for Ag release from the SiC in the nuclear reactor.     

中子活化法测定~(232)Th裂变产物产额

采用中子活化法测量了~(232)Th的裂变产物及其累积产额。利用加速器T(d,n)~4He反应产生的14.9 MeV高注量中子长时间照射ThO_2样品,用高纯锗γ谱仪测量其特征γ谱,求得较长半衰期核素~(99)Mo、~(141)Ce、~(143)Ce、~(131)I、~(140)Ba等的裂变产额,实验结果的典型误差为4%。其中,利用MCNP程序对中子的多次散射效应和自屏蔽效应进行修正,同时考虑了中子注量波动及γ射线在样品中的自吸收影响。     

A review of revaporisation behaviour of radioactive Cs deposits and its impact on the source term in severe nuclear accidents from Phébus FP results and single effect testing

ABSTRACT

Revaporisation of the fission products deposited in the primary circuit of a reactor was identified as a possible late source of fission product release during a severe accident: e.g. loss of coolant accident (LOCA). Subsequent testing has shown that revaporisation is very likely to occur given a breach of the reactor and is an important contributor for the source term release to the containment and biosphere. The first part reviews the revaporisation mechanisms of Cs and other volatile or semi-volatile fission products transported in the primary circuit that were derived from the Phebus FP and associated programmes. The second part examines the separate effects testing to determine the high temperature chemistry of volatile and semi-volatile fission products (I, Mo, Ru) and structural materials (Ag, B), as well as atmospheric effects that substantially affect the source term. Finally, it examines Cs data from reactor accident sites that is providing additional knowledge of longer-term fission product chemistry. The results have been summarised in the form of a table and schematic diagram. This accumulated knowledge and experience has important applications in minimising contamination during decommissioning and site remediation techniques, as well as improving SA simulation codes and raising nuclear safety.     

Fuel components and fission products diffusion on the surface of communicating cavities of a thermionic electricity-generating channel

The diffusion of fuel components and fission products on the surface of communicating cavities of a thermionic electricity-generating channel of a nuclear power facility is studied analytically. The Arrhenius constants are determined for the electricity-generating channel. A model is developed for the diffusion of the atoms of the fuel components and fission products on the surface of fuel element cladding. The results are used to determine the negative effect of the diffusion of uranium, as the main component of the fuel, and the uranium fission products molybdenum, niobium, and zirconium on the emission-adsorption characteristics of the electrodes of the electricity-generating channel and the electrical properties of the nuclear power facility. Proposals are made for reducing the effect of the phenomenon analyzed.     

The influence of iodine vapour on creep rupture properties of 20%Cr/25%Ni/Nb stabilised stainless steel

Interactions between volatile fission products, such as iodine, and fuel cladding have been observed in a number of reactor systems. To determine the effect of iodine on the mechanical properties of the 20Cr/25Ni/Nb steel used as fuel cladding in UK advanced gas-cooled reactors, stress rupture tests have been performed in environments of iodine vapour, air and vacuum under initial stresses of 47 to 130 MN/m² at 750° C. Iodine vapour promoted surface-nucleated, intergranular cracking which significantly reduced the specimen rupture life and strain at fracture compared with tests in air or vacuum. Increasing the iodine vapour pressure from 0.04 to 56 mbar resulted in further embrittlement. Examination of the surface regions of a specimen after long-term exposure to iodine vapour revealed a porous duplex surface scale and significant depletion of chromium from the metal associated with sub-surface void formation. Embrittlement mechanisms and some possible implications for fuel clad behaviour are discussed.     

Cluster size effect on reactive sputtering by fluorine cluster impact using molecular dynamics simulation

The mechanism of high-yield sputtering induced by reactive cluster impact was investigated using molecular dynamics (MD) simulations. Various sizes of fluorine clusters were radiated on clean silicon surface. At an incident energy of 1 eV/atom, F atom and F₂ molecule are only adsorbed on the surface and sputtering of Si atom does not occur. However, fluorine cluster, which consists of more than several tens molecules causes sputtering. In this case, most of Si atoms are sputtered as fluorinated material such as SiF_x. This effect is due to the fact that cluster impact induces high-density particle and energy deposition, which enhances both formation of precursors and desorption of etching products. The deposition of atoms and energy becomes denser as the incident cluster size increases, so that larger clusters have shown higher sputtering yield.