NKS ICP User 2017 Seminar Proceedings

The ICP User seminar was held at Risø, Denmark, during 25-27 September 2017. The seminar consisted of 2-day lectures given by six invited professionals and thirteen seminar participants, as well as 1-day lab training by invited expert. The lectures covered different topics including theoretical principles of ICP, methodology development and application of ICP techniques for different isotopes/isotopic ratios, recent development of new ICP technology and its application, etc. The results obtained from the inter-comparison exercise 2016 were presented and discussed. The lab training covered demonstration of the operation of ICP-MS, software and technical instructions. The seminar was attended by 51 individuals from 26 organisations

Studies of Long-lived Radionuclides in the Environment - with Emphasis on 99Tc, 237Np and Pu Isotopes

Studies of the long-lived anthropogenic radionuclides 99Tc, 237Np, 239Pu and 240Pu were performed in marine and terrestrial areas contaminated by different accidental and controlled releases of radioactive materials. The three main sources discussed in this thesis are nuclear weapons tests, nuclear reprocessing plants and the Chernobyl accident. Results are mainly based on measurements of environmental samples collected in different parts of Sweden. An analytical method for trace analysis of plutonium and neptunium in environmental samples using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) is described, and the results compared with those from conventional alpha spectrometry. The use of activated carbon filters for the separation of 99Tc from marine waters, with an adsorption efficiency in the range of 70%, is described. During 1991, 1995 and 2001 brown seaweed samples were collected at several stations along the Swedish west coast. In addition to these locations, a well-defined site (Särdal; 56.76 °N, 12.63 °E) was included from which 99Tc data were collected from 1967 to 2000. The effect of discharges from the Sellafield EARP (Enhanced Actinide Removal Plant) from 1995-1996 was observed in brown seaweed from the Swedish west coast 4-5 years later, with a ten-fold increase in 99Tc activity concentration. An inverse correlation between 99Tc and 137Cs concentrations in seaweed was observed due to continuous mixing of high-Tc-low-Cs (Atlantic Sea) and low-Tc-high-Cs (Baltic Sea) waters. Radioactive materials from the Chernobyl accident contaminated various part of Sweden and by analysing lichen samples from different areas an estimate of the deposited 237Np density could be made. Through the determination of 240Pu/239Pu and 237Np/239Pu atomic ratios, source identification could be made in Swedish lichen samples. In the areas most contaminated by the Chernobyl accident in Sweden, the Chernobyl-derived 237Np contribution was up to 30% of the total concentration. However, the plutonium contributions from Chernobyl in the same samples were as high as 85%. Sellafield-derived 237Np was found in brown seaweed samples from the Swedish west coast, indicating greater mobility in the marine environment than that of Pu

Development of Gd-148 analysis method using stable Gd

The analytical method of Gd determination was developed with the aim to analyse Gd-148 in environmental and bioassay samples. It involves the use of anion exchange resin, extraction chromatography, and cation exchange resin. Alkaline fusion and calcium oxalate co-precipitation are used for solid samples dissolution and liquid samples preconcentration, respectively. Total method recovery was tested with natural Gd (Gd-157) using ICP-QQQ-MS. A maximum total recovery of 75 % was obtained

U, Pu, and Am nuclear signatures of the Thule hydrogen bomb debris

This study concerns an arctic marine environment that was contaminated by actinide elements after a nuclear accident in 1968, the so-called Thule accident. In this study we have analyzed five isolated hot particles as well as sediment samples containing particles from the weapon material for the determination of the nuclear fingerprint of the accident. We report that the fissile material in the hydrogen weapons involved in the Thule accident was a mixture of highly enriched uranium and weapon-grade plutonium and that the main fissile material was U-235 (about 4 times more than the mass of Pu-239). In the five hot particles examined, the measured uranium atomic ratio was U-235/U-238 = 1.02 +/- 0.16 and the Pu-isotopic ratios were as follows: Pu-240/Pu-239 0.0551 +/- 0.0008 (atom ratio), Pu-238/Pu239+240 = 0.0161 +/- 0.0005 (activity ratio), Pu-241/Pu239+240 = 0.87 +/- 0.12 (activity ratio), and Am-241/Pu239+240 = 0.169 +/- 0.005 (activity ratio) (reference date 2001-10-01). From the activity ratios of Pu-241/Am-241, we estimated the time of production of this weapon material to be from the late 1950s to the early 1960s. The results from reanalyzed bulk sediment samples showed the presence of more than one Pu source involved in the accident, confirming earlier studies. The Pu-238/Pu239+240 activity ratio and the Pu-240/Pu-239 atomic ratio were divided into at least two Pu-isotopic ratio groups. For both Pu-isotopic ratios, one ratio group had identical ratios as the five hot particles described above and for the other groups the Pu isotopic ratios were lower (Pu-238/Pu239+240 activity ratio similar to 0.01 and the Pu-240/Pu-239 atomic ratio 0.03). On the studied particles we observed that the U/Pu ratio decreased as a function of the time these particles were present in the sediment. We hypothesis that the decrease in the ratio is due to a preferential leaching of U relative to Pu from the particle matrix

Particle Size-dependent Dissolution of Uranium Aerosols in Simulated Lung Fluid : A Case Study in a Nuclear Fuel Fabrication Plant

Inhalation exposure to uranium aerosols can be a concern in nuclear fuel fabrication. The ICRP provides default absorption parameters for various uranium compounds but also recommends determination of material-specific absorption parameters to improve dose calculations for individuals exposed to airborne radioactivity. Aerosol particle size influences internal dosimetry calculations in two potentially significant ways: the efficiency of particle deposition in the various regions of the respiratory tract is dependent on aerodynamic particle size, and the dissolution rate of deposited materials can vary according to particle size, shape, and porosity because smaller particles tend to have higher surface-to-volume ratios than larger particles. However, the ICRP model assumes that deposited particles of a given material dissolve at the same rate regardless of size and that uptake to blood of dissolved material normally occurs instantaneously in all parts of the lung (except the anterior portion of the nasal region, where zero absorption is assumed). In the present work, the effect of particle size on dissolution in simulated lung fluid was studied for uranium aerosols collected at the plant, and its influence on internal dosimetry calculations was evaluated. Size fractionated uranium aerosols were sampled at a nuclear fuel fabrication plant using portable cascade impactors. Absorption parameters, describing dissolution of material according to the ICRP Human Respiratory Tract Model, were determined in vitro for different size fractions using simulated lung fluid. Samples were collected at 16 time-points over a 100-d period. Uranium content of samples was determined using inductively coupled plasma mass spectrometry and alpha spectrometry. In addition, supplementary experiments to study the effect of pH drift and uranium adsorption on filter holders were conducted as they could potentially influence the derived absorption parameters. The undissolved fraction over time was observed to vary with impaction stage cut-point at the four main workshops at the plant. A larger fraction of the particle activity tended to dissolve for small cut-points, but exceptions were noted. Absorption parameters (rapid fraction, rapid rate, and slow rate), derived from the undissolved fraction over time, were generally in fair agreement with the ICRP default recommendations for uranium compounds. Differences in absorption parameters were noted across the four main workshops at the plant (i.e., where the aerosol characteristics are expected to vary). The pelletizing workshop was associated with the most insoluble material and the conversion workshop with the most soluble material. The correlation between derived lung absorption parameters and aerodynamic particle size (impactor stage cut-point) was weak. For example, the mean absorption parameters derived from impaction stages with low (taken to be &amp;lt;5 mu m) and large (&amp;gt;= 5 mu m) cut-points did not differ significantly. Drift of pH and adsorption on filter holders appeared to be of secondary importance, but it was found that particle leakage can occur. Undissolved fractions and to some degree derived lung absorption parameters were observed to vary depending on the aerodynamic size fraction studied, suggesting that size fractionation (e.g., using cascade impactors) is appropriate prior to conducting in vitro dissolution rate experiments. The 0.01-0.02 mu m and 1-2 mu m size ranges are of particular interest as they correspond to alveolar deposition maxima in the Human Respiratory Tract Model (HRTM). In the present work, however, the dependency on aerodynamic size appeared to be of minor importance, but it cannot be ruled out that particle bounce obscured the results for late impaction stages. In addition, it was noted that the time over which simulated lung fluid samples are collected (100 d in our case) influences the curve-fitting procedure used to determine the lung absorption parameters, in particular the slow rate that increased if fewer samples were considered.Funding Agencies|Swedish Radiation Safety Authority [SSM2016-589-2]; Westinghouse Electric Sweden AB</p

On the Use of Mercury as a Means of Locating Background Sources in Ultra Low Background HPGe-Detector Systems

In low-level gamma-ray spectrometry, it is common to measure large samples in order to obtain low detection limits for the massic activity (in mBq/kg). These samples have significant shielding effects. In order to study whether the background sources in three ultra low background HPGe detectors were located in the detector or in the shield, Marinelli beakers filled with hyperpure mercury were measured. Although the measurements were hampered by the presence of cosmogenically produced 194Hg, information regarding the major background location of 40K, 60Co, 137Cs, 210Pb, 226Ra, 228Ra and 228Th could be obtained.JRC.D.4-Isotope measurement

Particle Size Dependent Dissolution of Uranium Aerosols in Simulated Gastrointestinal Fluids

Uranium aerosol exposure can be a health risk factor for workers in the nuclear fuel industry. Good knowledge about aerosol dissolution and absorption characteristics in the gastrointestinal tract is imperative for solid dose assessments and risk management. In this study, an in vitro dissolution model of the GI tract was used to experimentally study solubility of size-fractionated aerosols. The aerosols were collected from four major workshops in a nuclear fuel fabrication plant where uranium compounds such as uranium hexafluoride (UF6), uranium dioxide (UO2), ammonium uranyl carbonate, AUC [UO2CO3 center dot 2(NH4)(2)CO3] and triuranium octoxide (U3O8) are present. The alimentary tract transfer factor, f(A), was estimated for the aerosols sampled in the study. The transfer factor was derived from the dissolution in the small intestine in combination with data on absorption of soluble uranium. Results from the conversion workshop indicated a f(A) in line with what is recommended (0.004) by the ICRP for inhalation exposure to Type M materials. Obtained transfer factors, f(A), for the powder preparation and pelletizing workshops where UO2 and U3O8 are handled are lower for inhalation and much lower for ingestion than those recommended by the ICRP for Type M/S materials f(A) = 0.00029 and 0.00016 vs. 0.0006 and 0.002, respectively. The results for ingestion and inhalation f(A) indicate that ICRPs conservative recommendation of f(A) for inhalation exposure is applicable to both ingestion and inhalation of insoluble material in this study. The dissolution- and subsequent absorption-dependence on particle size showed correlation only for one of the workshops (pelletizing). The absence of correlation at the other workshops may be an effect of multiple chemical compounds with different size distribution and/or the reported presence of agglomerated particles at higher cut points having more impact on the dissolution than particle size. The impact on dose coefficients [committed effective dose (CED) per Bq] of using experimental f(A) vs. using default f(A) recommended by the ICRP for the uranium compounds of interest for inhalation exposure was not significant for any of the workshops. However, a significant impact on CED for ingestion exposure was observed for all workshops when comparing with CED estimated for insoluble material using ICRP default f(A). This indicates that the use of experimentally derived site-specific f(A) can improve dose assessments. It is essential to acquire site-specific estimates of the dissolution and absorption of uranium aerosols as this provides more realistic and accurate dose- and risk-estimates of worker exposure. In this study, the results indicate that ICRPs recommendations for ingestion of insoluble material might overestimate absorption and that the lower f(A) found for inhalation could be more realistic for both inhalation and ingestion of insoluble material.Funding Agencies|Swedish Radiation Safety Authority [SSM2016-589-2]; Westinghouse Electric Sweden AB</p