Maria Betti

Determination of fission products and actinides in spent nuclear fuels by isotope dilution ion chromatography inductively coupled plasma mass spectrometry

An Elan 5000 inductively coupled plasma mass spectrometry (ICP-MS) instrument was modified for its installation in a glove-box for the analysis of radioactive materials. An ion chromatographic system was coupled to the ICP-MS instrument. The chromatographic pump was set outside the box while the injection valve and separation column were installed inside the box coupled directly to the cross-flow nebulizer. Performance characteristics of the modified ICP-MS system were evaluated regarding long-term stability, optimum plasma and ion lens conditions, sensitivity and detection limits, polyatomic ions, mass discrimination, detector dead time and uranium matrix interferences. Chromatographic methods were developed for the separation of fission Cs from Ba, for the lanthanide elements (La to Gd) and for the actinides (U to Cm) in order to eliminate isobaric interferences. Isotope dilution analysis was applied for the determination of selected fission products and actinides in spent nuclear fuels after ion chromatographic separation.

Determination of Neptunium and Plutonium in the Presence of High Concentrations of Uranium by Ion Chromatography Inductively Coupled Plasma Mass Spectrometry.

Ion chromatography (IC) coupled with ICP-MS was used to separate Np, Pu and U, overcoming the isobaric interferences present when the isotopic composition has to be determined and avoiding the influence of the tail of the 238 U peak on the 237 Np and 239 Pu peaks in samples with a high U content. The optimization of the parameters was carried out with a standard solution containing Np, U and Pu (ratio 1:1:1) at the 100 ng ml -1 concentration level. The precision and accuracy of the method were also evaluated using a sample containing 1 ng ml -1 of Np and Pu and 100 ng ml -1 of U. A 200 µl aliquot of the sample (previously treated with silver oxide in order to obtain the elements in a single oxidation state) was injected and, after passing through the separation column, the effluent was passed directly to the nebulizer. Different mobile phases and oxidizing/reducing agents were tested. The use of a high-capacity cation-exchange column (CS10), silver oxide as oxidizing agent and 40 mm 2,3-diaminopropionic acid monohydronitrate in 0.6 m HNO 3 as eluent in isocratic mode provided good resolution and recovery of the elements studied (96–98%). The precision of the method is 2.7, 1.1 and 1.7% for Np:U, Np:Pu and U:Pu, respectively, for a solution containing Np, Pu and U in a ratio of 1:1:1. Isotope dilution analysis applying IC separation was performed for the determination of Pu. The method of standard additions was used for the determination of Np. The agreement between the IC–ICP-MS results and the calculated values was within 15% for most isotopes.

Use of ion chromatography for the determination of fission products and actinides in nuclear applications

Abstract The application of ion chromatography (IC) for the determination of trace radioisotopes and ion impurities, as well as for the separation of fission products and actinides in applications of nuclear concern is reviewed. Particular attention is given to the on-line coupling of IC with nuclear and non-nuclear detection modes. Recent results obtained employing a coupled IC–inductively coupled plasma mass spectrometry (ICP-MS) for the characterization of the complete inventory of fission products and actinides in spent nuclear fuel and high-level liquid waste samples are discussed in terms of isobaric interference elimination and isotope determination.

Production of monodisperse uranium oxide particles and their characterization by scanning electron microscopy and secondary ion mass spectrometry

Abstract Secondary ion mass spectrometry (SIMS) can be confidently used to measure uranium isotopic ratios in single particles. Dense particles of known isotopic composition and size allow the precision and the accuracy of the applied procedure to be estimated. These particles can be obtained by dissolving standard reference uranium materials, nebulizing the solution in droplets of proper diameter and collecting the particles after the desolvation and calcination of the droplets. A new instrumental set up, based on a commercial vibrating orifice aerosol generator to generate monodisperse droplets of the solutions from four uranium oxide reference materials, is described. The droplets were dried and calcined in a sequence of three furnaces. The morphology of the monodisperse uranium oxide particles was studied by scanning electron microscopy. It was observed that the particles were nearly spherical and consisted of dense material. Their diameter distribution evidenced the presence of two populations mainly, the first showing a narrow distribution with a maximum centered at approximately 1 μm. The first statistical moment ratios between the two populations remained practically constant at 1.24±0.01. This demonstrated that the second population was due to the formation of one particle from two droplets of solution (theoretical double mass≡diameter ratio of 2 3 =1.26). Secondary ion mass spectrometry was used to verify the isotopic composition of the produced particles. Typical accuracies of better than 0.4% for 235U/238U and a few percent for the minor isotopes have been achieved. For the determination of the 236U content, the signal at mass M=239 (due to 238UH+) was used to correct the 235UH+ contribution to 236U at mass M=236, greatly improving the accuracy of the 236/238 ratio with increasing enrichment of the 235U isotope.

Civil use of depleted uranium

In this paper the civilian exploitation of depleted uranium is briefly reviewed. Different scenarios relevant to its use are discussed in terms of radiation exposure for workers and the general public. The case of the aircraft accident which occurred in Amsterdam in 1992 involving a fire, is discussed in terms of the radiological exposure to bystanders. All information given has been obtained on the basis of an extensive literature search and are not based on measurements performed at the Institute for Transuranium Elements.

Studies on simultaneous separation and determination of lanthanides and actinides by ion chromatography inductively coupled plasma mass spectrometry combined with isotope dilution mass spectrometry

A procedure for the simultaneous separation and determination of fission products (lanthanides) and actinides (Pu, Np, U, Am and Cm) is described. The method is based on the use of an anionic/cationic mixed bed chromatographic column (CS5A, Dionex), coupled on-line to an ICP-MS detector. Optimisation of the parameters was carried out with standard solutions containing actinides and lanthanides at the 50 ng ml−1 concentration level. The effects of different oxidising/reducing agents as well as different mobile phases on the intensity and position of the chromatographic peaks were investigated. The analytical procedure was validated by the use of certified materials as well as by other independent techniques. Analytical figures of merit resulting from the procedure were compared with those obtained using other commercially available ion-exchange stationary phases. The procedure developed was applied to the inventory of spent nuclear fuel samples. Detection limits of 0.25 ng ml−1 and 0.45 ng ml−1 were obtained for lanthanides and actinides, respectively. Analytical precision was typical better than 5% over seven repeated measurements.

Determination of caesium and its isotopic composition in nuclear samples using isotope dilution-ion chromatography-inductively coupled plasma mass spectrometry

As the natural isotopes of Ba give isobaric interferences on the radioactive isotopes of Cs at nominal masses of 134, 135 and 137, a chemical separation of Cs from Ba has been necessary for the determination of the isotopic composition of Cs by mass spectrometric techniques in highly active nuclear wastes (HAW), dissolved spent nuclear fuels or radioactively contaminated environmental samples. Ion chromatography (IC), which allows Cs and Ba to be chemically separated according to their different cationic charge, was coupled to an ICP-MS instrument and the chemical separation was performed on-line and followed directly by mass spectrometry. Three separation schemes were compared with respect to chromatographic resolution, accuracy and precision in irradiated spent fuel samples. The mass discrimination factors for the radioactive Cs isotopes were calculated by using a solution of natural Ba for the different chromatographic processes. They were found to be less than –2.5%. The results obtained by IC-ICP-MS were compared with those obtained by γ-spectrometry and with simulation calculations based on the KORIGEN code. The method using a CS5 cation-exchanger column and 1 M HNO 3 as eluent gave a detection limit of 16 pg g –1 for total Cs with a precision of 2.5% at a concentration level of 100 ppb (n=7). Under the same chromatographic conditions, the accuracy of the ratio 134 Cs/ 137 Cs, calculated considering the γ-spectrometry measurements, was 2.5%.

Deposition and distribution of Chernobyl fallout fission products and actinides in a Russian soil profile.

In this article the distribution of fission products and actinides in a soil profile from Novo Bobovicky in Russia, which was contaminated due to the Chernobyl nuclear power plant accident, is described. The ground deposition of long-lived fission products determined by gamma-spectrometry was (recalculated to 26 April 1986) 1600 kBq (137)Cs/m(2), 900 kBq (134)Cs/m(2) and 60 kBq (125)Sb/m(2). Of these radionuclides (137)Cs shows the dominating activity at the present time. After 6.5 years 90% of the Cs and Sb activity was contained in the upper 4 cm. A (239,240)Pu ground deposition of 77.4+/-8.0 Bq/m(2) was determined by alpha-spectrometry. The (238)Pu/(239,240)Pu activity ratio of 0.30+/-0.03 and (241)Pu/(239,240)Pu activity ratio of 115+/-14 (in 1986) measured in the soil profile, indicates that the analysed Pu originates mainly from the Chernobyl accident. The average (234)U/(238)U activity ratio of 1.06+/-0.29 indicates that the uranium in this soil is dominated by naturally occurring uranium. The alpha- and beta-autoradiography revealed that the activity is mainly present in particulate form. It could further be observed that the spots containing alpha- or beta-activity originated from different particles. A comparison of alpha-autoradiography with the bulk Pu and Am activity showed that 92% of the alpha-activity was present as clearly detectable alpha-spots. The beta-active particles, located by beta-autoradiography were correlated with gamma-spectrometric measurements and contained only (137)Cs. These hot spots ranged from 0.02 to 0.15 Bq.It could be concluded that the vertical transport of (137)Cs and fuel fragments occurs mainly by movement of particles through the soil. It could also be concluded that the fuel fragments found, in this soil were depleted in respect to Cs, Sb and Eu. Comparison of the analysed (238)Pu/(239,240)Pu, (241)Pu/(239,240)Pu and (241)Am/(239,240)Pu ratios with the ratios calculated with ORIGEN-S code gave an estimate of the average burn-up of the fuel particles to be in the range of 11-12 GWd/tU. The results presented in this article are valid for this single soil profile and should not be generalised unless validated in a more rigorous study of a larger number of soil profiles.

Characterisation of Radioactive Particles by SIMS

Abstract. Secondary ion mass spectrometry (SIMS) was optimised for characterisation of uranium- and plutonium-containing particles in soils, swipes and forensic samples. This was done by analysing in-house produced spherical UO2-particles. Screening techniques as α-autoradiography together with SIMS analysis were employed to detect UO2-particles in a soil sample from Chernobyl.The use of SIMS was exploited for the identification of uranium- and plutonium-containing particles and for the determination of their isotopic composition. The particles collected on swipe samples were transferred to a special adhesive support for the analysis by SIMS. Particles containing highly enriched uranium with diameters up to 10 μm were also detected in a forensic sample. For the measurements of the isotopic ratios a mass resolution of 1000 was used. At this resolution flat-top peaks were obtained which greatly improve the accuracy of the measurement. The isotopic composition of the particles was measured with a typical accuracy and precision of 0.5%. Statistically meaningful results can be obtained, for instance, from a specimen containing as few as 1010 atoms/μm3 of uranium in particles of UO2 weighing a few picograms.

Neptunium determination by dc glow discharge mass spectrometry (dc-GDMS) in Irish Sea sediment samples

Direct current glow discharge mass spectrometry (dc-GDMS) has been applied for the direct analysis of 237Np in marine sediment samples from the Irish Sea. The secondary cathode technique was exploited to promote the sputtering of the sediment samples once compacted into a pellet. A certified marine sediment doped with a certified 237Np solution was used for obtaining matrix-matching samples for calibration purposes. Acquiring 100 points over an integration time of 300 ms a detection limit down to 80 pg g−1 was obtained. Results on 237Np were in agreement with those obtained by the determination of 233Pa by γ-spectrometry.