用于六氟化铀泄漏事故后果评估的化学物质推荐限值

在六氟化铀泄漏事故后果的评估中,除了关注铀的放射性后果外,还需要关注泄漏物质的化学毒性影响。在进行化学毒性影响评估时,如果采用半致死浓度作为评估标准,则低估了六氟化铀泄漏事故的影响半径。在进行六氟化铀泄漏事故的环境影响评估时,不仅要考虑泄漏物质的致死效应,更应该考虑泄漏物质对事故地点周边公众的健康影响。美国环保署、美国工业卫生协会等机构均提出了相应的化学浓度限值系列。对六氟化铀事故后果评价,推荐采用美国能源部推出的保护行动限值(PACs)。     

A study of the properties of uranium hexafluoride in organic solvents

Studies have been made of the solubility and kinetics of solution of uranium hexafluoride in carbon tetrachloride, chloroform, dichloromethane, asymmetrical dichloroethane,symmetrical tetrachloroethane, pentachloroethane, trifluorotrichloroethane, symmetrical trichloropropane,and tetrachloropropane. It has been shown that solutions of uranium hexafluoride in carbon tetrachloride, tetrachloroethane, pentachloroethane,and trifluorotrichloroethane are completely stable for two weeks at 20 °C; at this temperature solutions of uranium hexafluoride in chloroform, dichloroethane,and dichloromethane are unstable. It has been shown that reactions of uranium hexafluoride with these studied organic solvents at 60–100 °C occur in the following way: at first uranium pentafluoride is formed which is reduced at first to the intermediate uranium fluor ides, containing a large amount of tetravalent uranium.and then to uranium tetrafluoride.     

Electromagnetic isotope separation at the China Institute of Atomic Energy

Electromagnetic isotope separation at the China Institute of Atomic Energy (CIAE) is described. Calutron, Nier-Bernas and Freeman ion sources were constructed for ion implantation systems. It was found that some enriched isotope samples were contaminated more by lighter than by heavier neighbors. This phenomenon may be explained if the sputtered particles consist of a considerable percentage of ions. A computer inspection system for recording and processing operation data has been designed.     

Model of the effect of uranium hexafluoride on the human body under industrial conditions

A method for calculating certain quantities characterizing the effect of uranium hexafluoride (UF₆) on the human body under industrial conditions in uranium enrichment plants is described. It is assumed that the effect is determined by uranium and fluorine inhaled together with the products of hydrolysis of uranium hexafluoride. The proposed complex model consists of three models, the first of which describes the contamination of the industrial environment and the second and third describe inhalation and percutaneous intake. A relation is obtained between uranium and fluorine intake and the uranium hexafluoride concentration in air at the moment the compound is discharged. __________ Translated from Atomnaya énergiya, Vol. 103, No. 2, pp. 103–106, August, 2007.     

铀离心浓缩厂铀丰度在线监测仪本底自动测量方法研究

铀丰度在线监测仪是对铀浓缩厂工艺管道中UF6气体235U丰度进行在线监测的装置,本底是其核心关键技术指标,直接关系到丰度值的测量精度。原有本底测量方法需监测仪停止工作,人工将容器内的气体抽空进行测量。而本底自动测量方法通过改变测量容器内UF6气体的压力,用Na I(TI)探测器测量容器内UF6气体中235U发射的特征γ射线,利用压力传感器测量容器内UF6气体的压力值,最后对不同压力下的数据进行拟合获得监测仪的本底。实验结果表明,采用本底自动测量方法,监测仪铀丰度在线监测结果的相对标准偏差小于0.30%,与气体质谱计测量结果的最大相对偏差小于0.25%,表明该方法测量本底的准确度高;监测仪本底测量由软件自动完成,提高了监测仪的自动化程度,增强了监测仪的适用性。     

Radiochemical separation of thorium from 18O induced reaction with natural uranium

A radiochemical procedure used to separate and purify trace concentration thorium produced in heavy ion reaction with uranium targets is presented.The procedure can rapidly yield thorium fraction suitable for gamma-ray spectroscopy studies.The resultant gamma-ray spectra showed that Th was isolated from a large number of elements produced in the reaction,and there were only a few contaminating activities of isotopes of Sc,Cd,In,etc.The decontamination factors for the main reaction products are given.     

Physico-mathematical models for evaluating the flow of dangerous chemical substances into the atmosphere as a result of depressurization or rupture of a container holding depleted or natural uranium hexafluoride

The objective of the present work is to evaluate the emission of dangerous chemical substances upon depressurization and partial or complete rupture of a container holding depleted or natural uranium hexafluoride. An algorithm is presented for calculating the emissions of dangerous chemical substances during emergencies which are not associated with fires or explosions. The expressions for evaluating the emissions in the primary cloud and during stationary emission, which include a dependence on the state parameters of atmospheric air – temperature, pressure, moister content, and wind velocity – are obtained. The assessment of the stationary emission is based on an analysis of the heterogeneous chemical reaction of water vapor with the solid surface of uranium hexafluoride.