Quantification of uranium, plutonium, neodymium and gadolinium for the characterization of spent nuclear fuel using isotope dilution HPIC-SF-ICP-MS.

A method was developed for the determination of the nuclide-specific concentrations of U, Pu, Nd and Gd in two types of spent nuclear fuel (UOx and Gd-enriched). High-performance ion chromatography (HPIC) was used to separate the target elements from one another while sector-field inductively coupled plasma-mass spectrometry (SF-ICP-MS) was used for their determination relying on isotope dilution for calibration. In order to obtain the best possible precision for these isotope ratios extracted from the transient HPIC-SF-ICP-MS signals, the SF-ICP-MS data acquisition parameters were optimized and the most suitable method for calculating the isotope ratios from the transient signals was identified. The point-by-point (PbP), linear regression slope (LRS) and peak area integration (PAI) approaches were compared in the latter context. It was found that data acquisition in the flat centre of the spectral flat top peak using a mass window of 25%, a dwell time of 10 ms and 20 samples per peak, while using PAI for isotope ratio calculation, gave the best precision on the isotope ratios extracted from the HPIC-SF-ICP-MS transient signals. These parameters were used in the determination of the nuclide-specific mass fractions of Pu, Nd and Gd in two types of spent nuclear fuel using isotope dilution HPIC-SF-ICP-MS. For U, which was present at a higher concentration, the element fraction was collected and analyzed off-line after dilution. For the other target elements, an online approach was used. An uncertainty budget estimation was made using the bottom-up approach for the resulting mass fractions, and the accuracy and precision obtained when using isotope dilution HPIC-SF-ICP-MS were compared with those obtained with the routinely used techniques, isotope dilution TIMS & alpha spectrometry (an ISO 17025 accredited method).

Development of 'on-site' measurement methods for assay of plutonium isotopes.

Over the past decades, radioanalytical methods for environmental monitoring of plutonium (Pu) isotopes from contaminated soils were developed to respond in case of a nuclear accident but also for routine analyses. In this paper we prove the possibility of on-site analysis of plutonium using alpha particle spectrometry. Tests are performed with two types of soils: a "brown" soil and a "sandy" soil, both spiked with 242Pu. The proposed method starts with leaching the soil, then separating the radionuclides of interest through a TEVA column and finally preparing counting planchets for alpha-spectrometry analyses. The aim of this work was to obtain a fast and reliable procedure, from the sample preparation to the analysis, applicable directly in the field and lasting no longer than a working day. The testing involved several parameters, such as the soil-to-liquid ratio, the acid molarity, the influence of a purification step, the source preparation. For each procedure defined, the time and the recovery rates of 242Pu were recorded and compared. Results have proven that the recovery rates increase with the solid-to-liquid ratio, with the acid molarity, with the purification step but decrease with the mixing time. The two methods used for source preparation showed similar results and the sources were measured by alpha spectrometry, using two different counting devices. The final selected sample preparation procedure has a throughput of 3 h, with recovery rates of 33.8 ± 3.1% for the "brown" soil and 77.3 ± 9.2% for the "sandy" soil and is suitable for a field application.

Determination of the lanthanides, uranium and plutonium by means of on-line high-pressure ion chromatography coupled with sector field inductively coupled plasma-mass spectrometry to characterize nuclear samples.

High-pressure ion chromatography (HPIC) was coupled with sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS) to separate plutonium (Pu), uranium (U), neodymium (Nd) and gadolinium (Gd) nuclides from isobaric nuclides and to quantify them with high sensitivity. In this study, mixed bed ion exchange columns CG5A and CS5A were used, from which Pu and U were eluted first using 1 M nitric acid. The lanthanides were then separated using a gradient of 0.1-0.15 M oxalic acid with the pH adjusted to 4.5. The HPIC-SF-ICP-MS method was validated using different sample matrices, i.e. spent nuclear fuel and soil. The method was found to be repeatable and gave rise to transient signals suitable for quantification of nuclide-specific concentrations using external calibration. In terms of accuracy, the HPIC-SF-ICP-MS measurement results were in good agreement with those obtained using thermal ionization mass spectrometry (TIMS). Finally, the method provides an improvement in sample throughput (≤60 minutes per sample) and reduces exposure of the operator to radiation compared to off-line gravitational chromatography followed by TIMS.