BS ISO 24459:2021 pdf download – Determination of uranium content in samples coming from the nuclear fuel cycle by L-absorption edge spectrometry
6.1 X-ray tube.
The maximum working voltage of X-ray tube is higher than 25 kV, voltage-controlled, current- controlled. It shall be stable over time and shall reach an intensity (adjustable, usually lower than 100 μA) high enough to ensure satisfactory total count rate for fast and accurate measurement (as described in Clause 4).
6.2 Shielding and collimator. The shielding body is made of brass or other shielding materials. X-ray tube, X-ray detector and sample cell are directly mounted in the shielding body. The thickness of the shielding is chosen to ensure no X-ray leakage, and to satisfy the radioprotection requirements. The collimator is made of tungsten, or other materials, whose fluorescence X-rays do not interfere with the region of interest.
6.3 Sample cell. The sample cell can be made of glass or polycarbonate (PC), which can withstand nitric acid and TBP- DILUANT or in quartz that is resistant to nitric acid. The optimum path length and the specifications of the cell depend on the characteristic of the apparatus and the analytical needs. Examples of cell specifications:
— for process control purposes, disposable 4mm long PC cell;
— for high accuracy purposes, fixed flow-through cell with a path length of 2 mm and a volume of 125 μl.
6.4 X-ray detector and multichannel analyser. The X-ray detector should have an energy resolution better than 135 eV (for the 55 Fe peak at 5,9 keV). For example, a Peltier-cooled, high-resolution 10 mm 2 × 0,5 mm silicon drift detector.
6.5.1 For data acquisition. Commercial or non-commercial spectroscopy software can be used to collect the X-ray spectrum.
6.5.2 For data processing. At the time of writing this document, no commercial solutions are available for the fitting of L-edge transmission spectrum. Examples of fitting algorithm are described in 7.5.
7.1 Pre-checks Ensure that the temperature sensor is working properly and that the temperature is close to the temperature of reference. Setup the multi-channel analyser: — adjust the gain so that the peaks for energy calibration and the L III edge of uranium are evenly distributed across the spectrum; — perform the energy calibration by using induced X-rays in the spectrum, such as the characteristic lines of the X-ray tube target (silver or molybdenum) or the target positioned in a side path (germanium), and the collimator (titanium or brass). Ensure that the HV cut-off and the total count rate are as expected. If not, adjust the voltage and the intensity of the X-ray generator.
7.2 Reference spectrum The matrix of the solution used to obtain the reference spectrum shall be similar to the one of the sample. Prepare a solution with HNO 3 , 3 mol/l using the reagents described in 5.1. For process control, 3 mol/l HNO 3 can be used as the matrix solution for both nitric acid and TBP-DILUANT solutions. Acquire the reference spectrum with a counting time long enough to ensure low statistical counting uncertainty. For high accuracy measurement, the count rate shall be similar to the one used to measure the samples and the reference solutions.
7.3 Calibration Prepare one or more uranium reference solutions with concentration close to the expected concentration of the samples. For process control, the uranium reference solutions also can be used to analyse TBP-DILUANT samples. The solutions shall be prepared with the materials and reagents as described in Clause 5. Dissolution and dilutions shall be performed gravimetrically on a calibrated analytical balance. Measure the relevant reference solution(s) in replicates with a counting time long enough to ensure low statistical counting uncertainty.
7.4 Sample measurement
If feasible, and if there is prior knowledge of the concentration of uranium in the sample, the lattershould be prepared with the materials and reagents (as described in Clause 5) to reach the optimum concentration between reasonable counting time and high enough L-edge.BS ISO 24459 pdf download.