DOE Order 5480.11 and ANSI N13.30 require that internal dose assessments be made as part of the bioassay program for nuclear facility workers. For indirect bioassay of uranium workers, the uranium isotopes must be measured along with the total uranium in urine samples. The RMDA for each uranium isotope is 0.1 pCi/L.

This method is applicable for measuring ²³⁵U and ²³⁸U at the RMDA. Because of extremely low mass concentration (because of the high specific activity), ²³⁴U cannot be measured without additional sample preconcentration.

Note 2—Column chromatography separations and concentration of ²³⁴U using manual or flow-injection preconcentration followed by ICP-MS isotopic determination are described in Test Methods C 1310 and C 1345. These methods focus on environmental soil sample analysis, but with some development, may be applicable to digested urine samples. The ²³⁴U concentration can be calculated based on an enrichment gradient for workers in uranium enrichment plants, and internal dose assessments can be made.

Note 3—Use of high resolution ICP-MS may also be used to obtain lower detection limits, see 1.

1.1 This test method covers the determination of the concentration of uranium-235 and uranium-238 in urine using Inductively Coupled Plasma-Mass Spectrometry. This test method can be used to support uranium facility bioassay programs.

1.2 This method detection limits for ²³⁵U and ²³⁸U are 6 ng/L. To meet the requirements of ANSI N13.30, the minimum detectable activity (MDA) of each radionuclide measured must be at least 0.1 pCi/L (0.0037 Bq/L). The MDA translates to 47 ng/L for ²³⁵U and 300 ng/L for ²³⁸U. Uranium- 234 cannot be determined at the MDA with this test method because of its low mass concentration level equivalent to 0.1 pCi/L.

1.3 The digestion and anion separation of urine may not be necessary when uranium concentrations of more than 100 ng/L are present.

This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

The ICP-MS is a source of intense ultraviolet radiation from the radio frequency induced plasma. Protection from radio frequency radiation and UV radiation is provided by the instrument under normal operation.