ASTM C1871-18a PDF

SIGNIFICANCE AND USE 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 to 6 mg/g to allow a sample loading of 4 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... SCOPE 1.1 This test method describes the determination of the isotope amount ratios of uranium material as nitrate solutions by the double spike (DS) method using a thermal ionization mass spectrometer (TIMS) instrument. 1.2 The analytical performance in the determination of the 235U/238U major isotope amount ratio by the DS method is five to ten times better in terms of the internal and external reproducibility compared to the (“classical”) total evaporation (TE) method as described in Test Method C1672 and the “modified total evaporation” (MTE) as described in Test Method C1832. This is due to the use of an internal rather than external mass fractionation correction by using a double spike material with a known or certified 233U/236U isotope ratio, which is mixed with the sample prior to the measurement, either during the sample preparation or directly on the TIMS filament. 1.3 The DS method cannot be applied for the determination of the 236U/238U minor isotope amount ratio, and is also not recommended for the determination of the 234U/238U minor isotope amount ratio. 1.4 In case the uranium amount concentration of the double spike is known or certified, the uranium amount concentration of the sample can be determined using the isotope dilution mass spectrometry (IDMS) method as described in Test Method C1672, by blending the sample gravimetrically with the double spike and performing a DS measurement. 1.5 An external mass fractionation correction by measurements of a certified reference material loaded on different filaments and measured in the same measurement sequence, as recommended for TE and required for MTE measurements, is not necessary for the DS method. However, for quality control (QC) purposes it is recommended to perform DS measurements of low enriched or natural uranium isotopic reference materials on a regular basis. 1.6 The DS method can only be applied to uranium samples with relative isotope ...