Sampling of Uranium Hexafluoride

Some Examples of the ASTM Methods Concerning Characterization of UF for Enrichment Facilities 

Standard specification for uranium hexafluoride for enrichment Test methods for chemical, mass spectrometric, spectrochemical, nuclear, and radiochemical analysis of uranium hexafluoride Terminology relating to nuclear materials Specification for uranium hexafluoride enriched to 5% 

In some cases, when cylinders have already been filled with UFg and sampling of liquid UFg is to be avoided, a representative sample may be obtained during transfer 

Test Methods for Subsampling, Chemical, Mass Spectrometric, Spectrochemical, Nuclear, and Radiochemical Analysis of Uranium Hexafluoride UF  

Isotopic analysis by double-standard mass-spectrometer method 23-29 

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Assume that you have a sample of uranium hexafluoride with the natural abundance (0.7%) of 235U, and that you want to use gaseous effusion to separate the isotopes. 

The enrichment of uranium has to be accomplished by some physical process which depends on differential behavior of the two isotopes of uranium. The great majority of separative work has to date been carried out by the gaseous diffusion process, where the distinguishing feature between the isotopes is the rate at which the molecules of different mass diffuse through a porous barrier under an applied pressure differential. In a sample of uranium hexafluoride gas, the mean kinetic energy of the lighter molecules is equal to that of the heavier, i.e.,... 

Bostick WD, McCulla WH, Pickrell PW. 1985. Sampling, characterization, and remote sensing of aerosols formed in the atmospheric hydrolysis of uranium hexafluoride. J Environ Sci Health, Part A A20 369-393. 

Nuclear forensics also plays a role with regard to the processing of uranium ore concentrates in the UCF and fabrication of uraninm oxide for fueling nuclear reactors or of uranium hexafluoride for isotope enrichment facilities. Characterization of the nuclear materials can detect unauthorized operations and partially ascertain that no undeclared activities are taking place but one shonld always bear in mind that absence of evidence is not evidence of absence. In some cases, relevant information may be obtained from bulk samples but highly significant details may be found in analysis of single particles. Some examples will be presented here, but more details are discussed in Section 5.4. 

To increase the percentage of uranium-235 in a sample of uranium (a process called enrichment), one first prepares uranium hexafluoride, UF, a white, crystalline solid that is easily vaporized. Uranium hexafluoride vapor is allowed to pass through a series of porous membranes. Each membrane has many small holes through which the vapor can effuse. Because the UFe molecules with the lighter isotope of uranium travel about 0.4% faster than the UF molecules with the heavier isotope, the gas that passes through first is somewhat richer in uranium-235. When this vapor passes through another membrane, the uranium-235 vapor becomes further concentrated. It takes many effusion stages to reach the necessary enrichment. 

Uranium hexafluoride (UFg) is a much heavier gas than helium, yet at a given temperature, the average kinetic energies of the samples of the two gases are the same. Explain. 

C1052. (2007). Standard practice for bulk sampling of liquid uranium hexafluoride. West Conshohocken, PA ASTM. 

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