Standard Test Method for Determination of Uranium Isotopic Composition by the Double Spike Method Using a Thermal Ionization Mass Spectrometer

Importancia y uso:

5.1 Uranium material is used as a fuel in certain types of nuclear reactors. To be suitable for use as nuclear fuel, the starting material shall meet certain specifications such as those described in Specifications C753, C776, C787, C833, C967, C996, and C1008, or as specified by the purchaser. The ²³⁵U/²³⁸U isotope amount ratios and the amount content of uranium material can be measured by mass spectrometry following this test method to ensure that they meet the specification.

5.2 The double spike method has been used for studies of uranium fractionation effects in isotope geochemistry and cosmochemistry, for uranium source attribution in nuclear forensics and for investigation of conversion or sampling processes in nuclear industry and nuclear safeguards (7-11). Most recently, the double spike method has been used for the validation of the Cristallini sampling method of UF₆ (12 and 13). The double spike method can be used for a wide range of sample sizes even in samples containing as low as 50 μg of uranium. The concentration of the loading solution for the DS method has to be in the range of 1 mg/g to 6 mg/g to allow a sample loading of 4 μg to 6 μg of uranium. A minimum loading of 4 μg uranium per filament is recommended.

5.3 The measurement of ²³⁶U/²³⁸U ratios using this method is not possible due to the large isobaric interference from the ²³⁶U ion beam of the double spike onto the ²³⁶U ion beam from the sample (>50.000 times for close to natural material, for example, like IRMM-184).

5.4 The application of the double spike method for measurements of ²³⁵U/²³⁸U ratio is limited by the isobaric interference between the ²³⁶U from the double spike material and the ²³⁶U contained in the sample. As a consequence, the method is not suitable for samples which contain significant amounts of ²³⁶U due to prior neutron capture from ²³⁵U in the predecessor materials. For samples with ²³⁶U/²³⁸U ratios higher than about 10^–6, the double spike method should be applied with care for the isobaric correction. For an appropriate isobaric correction, the ²³⁶U/²³⁸U ratios of the samples should be determined separately using a suitable measurement method, for example, the modified total evaporation MTE method (Test Method C1832, Ref (5) and (6)).

5.5 The measurement of ²³⁴U/²³⁸U ratios using this method is very limited in the analytical performance due to the isobaric interference of the ²³⁴U from the double spike with the ²³⁴U from the sample (range from 5 % to 15 %). The correction algorithms are presented in 14.3, but statements for precision and bias are not given. Other methods like MTE (Test Method C1832, Ref (5) and (6)) are better suited and more reliable for measurements of ²³⁴U/²³⁸U ratios.

5.6 The DS method described here can also be extended to measurement of elements other than uranium, if a suitable double spike material is available.

Subcomité:

C26.05

Referida por:

C1832-25, C0799-19, C1913-21, C1880-19

Volúmen:

12.01

Número ICS:

27.120.30 (Fissile materials and nuclear fuel technology)

Palabras clave:

certified reference materials; double spike; isotope amount ratios; mass fractionation correction; modified total evaporation; thermal ionization mass spectrometry; total evaporation; uranium;