Standard Test Method for Determination of Uranium Isotopic Composition by Modified Total Evaporation (MTE) Method Using 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 isotope amount ratios of uranium material can be measured by mass spectrometry following this test method to ensure that they meet the specification.

5.2 The MTE method can be used for a wide range of sample sizes even in samples containing as low as 20 µg of uranium. If the uranium sample is in the form of uranium hexafluoride, it has to be converted into a uranium nitrate solution for measurement by the MTE method. The concentration of the loading solution for MTE has to be in the range of 1 mg/g to 6 mg/g to allow a sample loading of 2 µg to 6 µg of uranium. A minimum loading of 3 µg uranium per filament is strongly recommended. This is needed to have a sufficient and stable ion signal especially for the two minor isotopes (²³⁴U and ²³⁶U) thus enabling the internal calibration of SEM versus the Faraday cups using the ²³⁴U ion beam signal during the measurement.

5.3 Until now, the instrument capabilities for the MTE method have only been implemented on the TRITON™ TIMS instrument.5 Therefore, all recommendations for measurement parameters in this test method are specified for the TRITON instrument. The manufacturers of other TIMS instruments (for example, IsotopX and Nu Instruments) have indicated plans to implement the modifications needed in their instruments to use the MTE method.

5.4 The MTE method described here can also be extended to measurement of elements other than uranium. Note that the MTE method has already been implemented for plutonium and calcium.

Subcomité:

C26.05

Referida por:

C1636-22, C1411-25, C1871-22, C1672-23, C1913-21, E0321-20, C1880-19

Volúmen:

12.01

Número ICS:

27.120.30 (Fissile materials and nuclear fuel technology)

Palabras clave:

certified reference materials; ion counting; isotope amount-ratios; mass fractionation correction; secondary electron multiplier; thermal ionization mass spectrometry; total evaporation; uranium;