Effects of Annealing under High Static Pressure on Precipitation Behavior of Fission Gas Bubbles in Irradiated UO2

Annealing experiments were carried out on irradiated UO₂ in argon gas under high pressure (600 and 1,000 kg/cm²) as well as atmospheric, at temperatures of 1,400°–1,600°C. The effects of high external pressure on the behavior of fission gas bubbles in the irradiated UO₂ were studied by comparing replica electron micrographs of fractured surfaces of specimens annealed under different temperatures and pressures. The results indicate that high pressures such as above 600 kg/cm² can be effective in surpressing the growth of fission gas bubbles in both intergranular and intragranular zones, and in inhibiting the joining together of intergranular bubbles to form direct passages for fission gas release.     

哑铃型氧间隙缺陷在UO2材料内扩散的分子动力学研究

以UO2材料为对象,采用分子动力学方法模拟计算了哑铃型氧间隙缺陷的扩散行为,研究了几种温度条件下拉伸应变方向和拉伸应变对哑铃型氧间隙缺陷扩散行为的影响。研究发现,哑铃型氧间隙缺陷在UO2材料内存在扩散现象且为三维扩散,扩散能力与材料温度和拉伸应变有关。利用模拟结果计算了哑铃型氧间隙缺陷的扩散系数,结果表明：哑铃型氧间隙缺陷在扩散过程中始终沿〈111〉方向排布;材料体系温度越高扩散现象越明显;拉伸应变越大扩散现象越明显;沿〈111〉方向拉伸应变对哑铃型氧间隙缺陷扩散现象影响最大;无论有无拉伸应变,〈100〉方向始终是哑铃型氧间隙缺陷的主要扩散方向。本文的研究结果能为UO2材料的辐照损伤效应研究提供依据。     

Densification and Swelling in UO2 Pellets under Hydrostatic Pressure Condition

The effect of hydrostatic pressure on the volume change in unirradiated UO₂ pellets has been examined using an out-of-pile high pressure annealing technique. The pellet volume change was generated by annealing UO₂ pellets at 1,500°C and at higher or lower ambient external pressures of 10–150 MPa Ar/0.2%H₂ gas than the sintering pressures of 50 or 100MPa at 1,800°C. The pressure difference, Δ P, between bubble internal and external hydrostatic pressures during the annealing corresponded to a range of ?101 to 82MPa. The volume change directly depended on the sign and magnitude of Δ P. More negative Δ P caused larger densification due to the shrinkage of the as-sintered bubbles. Almost no volume change was observed at nearly zero Δ P, and fuel swelling due to the bubble growth increased at more positive Δ P. The bubble shrinkage and growth data were analyzed by the rate equation of Hull and Rimmer. The fractional volume changes calculated by the model were in good accordance with the measured values in the wide range of—8 to +10%.     

钨中自间隙原子团簇扩散行为的分子动力学模拟

钨被视为未来聚变堆中最有可能全面使用的面对等离子体材料。而在未来聚变堆真实环境下,氘氚聚变反应产生的14 MeV高能中子辐照将在材料中产生严重的原子离位损伤和各种缺陷积累。其中自间隙原子（SIA）及其团簇是中子辐照损伤中最常见的缺陷种类。本文采用分子动力学模拟系统研究钨中1/2〈111〉和〈100〉 SIA团簇的稳定结构和形成能,发现SIA团簇最稳定结构是1/2〈111〉 SIA团簇结构,SIA团簇聚集后会稳定存在。并研究了不同尺寸1/2〈111〉 SIA团簇的动力学扩散行为,发现单个SIA在温度高于700 K时易扩散和转向,而两个以上的SIA团簇在300~900 K时主要表现为一维方向的运动。为准确描述各种尺寸SIA团簇的动力学行为,给出了一套计算SIA团簇跃迁频率的经验参数。相关结果将为更大尺度的动力学蒙特卡罗和团簇动力学模拟提供准确和完备的输入参数,为正确掌握和评价钨中子辐照行为提供依据。     

粉煤灰基沸石固化体中Sr~(2+)、Cs~+的浸出行为

以电厂粉煤灰为原料水热制备粉煤灰基沸石,利用粉煤灰基沸石对模拟放射性废液中Sr~(2+)、Cs~+进行分离富集,在碱激发剂的作用下,以粉煤灰、粉煤灰基沸石制备地聚合物固化体,测试了所得固化体的抗压强度和抗浸出性能,并采用X射线衍射法(XRD)和扫描电镜(SEM)技术对浸出机理进行了初步探讨。结果表明,不同沸石掺量对固化体的抗压强度和抗浸出性能有很大的影响,当沸石掺量(质量分数)为20%~30%时,其抗压性能达到国家标准,浸出率和累积浸出分数均远低于国家标准限值。同时,固化体对Sr~(2+)、Cs~+阻滞效果不同,其中对Sr~(2+)的固化效果更加优异,42d浸出率最低为1.87×10~(-6)cm/d,累积浸出分数为3.3×10~(-4)cm。实验得出,粉煤灰基沸石固化体对Sr~(2+)、Cs~+具有较优异的固化效果。     

Study on Redox Equilibrium of UO2 2+/U2 + in Molten NaCl-2CsCl by UV-Vis Spectrophotometry

In order to enhance the understanding of the redox equilibriums of uranyl ions in molten NaCl-2CsCl eutectic salt UV-Vis absorption spectrophotometry measurements were performed for UO₂ ²⁺ in molten NaCl-2CsCl at 923 K under simultaneous electrolytic control of their ratio. A prominent absorption band at 395 nm was assigned to UO₂ ⁺, and its molar absorptivity was determined to be 832±27 mol^-1·l·cm^-1. From the dependence of the rest potential of the melt on the spectrophotometrically determined ratio of [UO₂ ²⁺]/[UO₂ ⁺], the standard redox potential of the couple UO₂ ²⁺/UO₂ ⁺ was determined to be ?0.903±0.007 V vs. Cl₂/Cl^—.     

T225NG钛合金在高温高压水质中的电化学行为

本文采用电化学测量方法测定了特殊换热器传热管用材料钛合金T225NG在高温高压不同氯离子浓度和不同溶解氧含量水质条件下的极化曲线,并探讨了钛合金T225NG在不同水质条件下的电化学行为和腐蚀机理.在本实验条件下钛合金T225NG的各阳极极化曲线没有出现活化区,但随着Cl-浓度和溶解O2浓度的增加,阳极极化曲线的维钝电流密度增大,钛合金的腐蚀增大.当Cl-＜0.005mg/L时,钛合金T225NG的阳极极化曲线只有一个电位区间氧化膜形成区A段;而当Cl-≥0.02mg/L时,各阳极极化曲线则存在两个电位区间A段和B段.