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Abstract: 241Pu was determined in slurry samples from a nuclear reactor decommissioning project at the Paul Scherrer Institute (Switzerland). To validate the results, the 241Pu activities of five samples were determined by LSC (TriCarb and Quantulus) and ICP-MS, with each instrument at a different laboratory. In lack of certified reference materials for 241Pu, the methods were further validated using the 241Pu information values of two reference sediments (IAEA-300 and IAEA-384). Excellent agreement with the results was found between LSC and ICP-MS in the nuclear waste slurries and the reference sediments. [Copyright &y& Elsevier]

Abstract: A method to analyse Pu and Np was optimised to achieve low detection limits and high sample throughput. Soil and sediment samples were ashed and digested with a borate fusion. After dissolving the melt in nitric acid, Pu and Np were separated on a TEVA extraction chromatopraphy column. It was measured with a sector field ICP-MS. Detection limits in soils and sediments as low as 1×10−15 g/g for Pu and Np were achieved. The method was applied to reference materials, soil profiles from Switzerland and sediment samples from the river Yenisei (RU), where radioactive nuclides have been discharged. [Copyright &y& Elsevier]

We present plutonium (Pu) and uranium (U) isotopic fingerprints (or signatures) in environmental samples collected at Bikar Atoll. Bikar is the second –most northern atoll of the Republic of the Marshall Islands, and therefore an important reference point to evaluate the extension of the regional fallout from the Pacific Proving Grounds (PPG) in Bikini and Enewetak Atolls. Previous studies have shown that regional fallout from atmospheric nuclear weapon testing (NWT) in Bikini and Enewetak has resulted in elevated levels of fallout radionuclides in this atoll. In order to optimally interpret the isotopic fingerprints, we compare our results with data obtained in eleven certified reference materials, representing different contamination sources. As well as 238Pu, 239Pu, 240Pu, 241Pu, 238U and 235U, this study also encompasses less commonly reported radionuclides such as 242Pu, 244Pu and 236U. We show the importance of combining numerous fingerprints for improved assessment of the source of a nuclear contamination. In samples from Bikar, Pu and U isotope ratios were found to vary within narrow ranges. Pu and U fingerprints suggest that regional fallout from the Castle Bravo test in March 1954 was the main source of the contamination. This was further confirmed by two different age dating approaches that estimated 1954 as the year of the contamination. We demonstrate that use of an exponential function to approximate the yield of heavy radionuclides in thermonuclear explosions with increasing mass is a valid approach for estimating the age of a contamination. We show that, if sufficient radionuclide activity concentration measurement results with low uncertainties are available, this method is robust. • Isotopic signatures of Pu and U at Bikar Atoll, Marshall Islands. • 242Pu/239Pu, 244Pu/239Pu and 236U/239Pu ratios in environmental samples and certified reference materials. • Determination of contamination age from 241Am/241Pu activity ratio. • Determination of contamination age based solely on Pu isotopic ratios. [ABSTRACT FROM AUTHOR]

In general, restarting the generalized minimum residual method (GMRES) slows down the convergence speed. There exist a number of methods that improve the convergence of restarted GMRES. One of them is GMRES with deflated restarting [SIAM J. Sci. Comput., 24 (2002), pp. 20-37] introduced by Morgan. This method retains a number of harmonic Ritz vectors at each restart to mitigate convergence slowdown. We investigate the accuracy of this method and propose a slight modification of it that is mathematically equivalent. We show that the new implementation has better numerical properties, especially if high accuracy of the solution is required. Numerical results are presented that confirm our theoretical results. [ABSTRACT FROM AUTHOR]

We present the validation of a radiochemical procedure for the determination of 55Fe and 63Ni in water and steel samples from nuclear decommissioning activities. The in-house validation was an essential requirement of the accreditation to ISO/IEC 17025. A combination of co-precipitation, anion chromatography and extraction chromatography steps was used for separating and purifying both radionuclides. The activities were measured by liquid scintillation counting. Due to the lack of reference materials, the method was validated by analysing simulated samples and by the standard addition technique. The parameters precision/accuracy, repeatability/linearity, selectivity/specificity, decision threshold, detection limit and uncertainty of the method were evaluated. [ABSTRACT FROM AUTHOR]

In this paper the most important problems in dating lake sediments with unsupported 210 Pb are summarized and the progress in gamma-spectrometry of the unsupported 210 Pb is discussed. The main topics of these studies concern sediment samples preparation for gamma-spectrometry, measurement techniques and data analysis, as well as understanding of accumulation and sedimentation processes in lakes. The vertical distributions of artificial ( 137 Cs, 241 Am, 239 Pu) and natural radionuclides ( 40 K, 210,214 Pb, 214 Bi) as well as stable trace elements (Fe, Mn, Pb) in sediment cores from four Swiss lakes were used as examples for the interpretation, inter-comparison and validation of depth–age relations established by three 210 Pb-based models (CF-CSR, CRS and SIT). The identification of turbidite layers and the influence of the turbidity flows on the accuracy of sediment dating is demonstrated. Time-dependent mass sedimentation rates in lakes Brienz, Thun, Biel and Lucerne are discussed and compared with published data. [ABSTRACT FROM AUTHOR]

We present the radioanalytical strategies used for the determination of strontium radioisotopes in routine and emergency samples. While in routine monitoring, the main goal is to achieve limits of detection as low as possible. In emergency, priority is given to the rapid procurement of data about a contamination. The parameters accuracy, precision and detection limit of the radiochemical methods are shown. We present the results obtained over the past 22 years in proficiency tests and in the analysis of reference materials. • Determination of Sr radioisotopes in routine monitoring program. • Determination of Sr radioisotopes in nuclear or radiological emergency. • Validation of radiochemical methods. • Extension of validity period of certified reference materials. [ABSTRACT FROM AUTHOR]

We applied three techniques (DF-ICP-MS, PERALS and alpha-spectrometry) for the determination of minor actinides at environmental levels. For each method the limit of detection and the resolution were estimated in order to study the content and isotopic composition of the actinides. Two international reference materials, IAEA-135 (Irish Sea Sediment) and IAEA-300 (Baltic Sea sediment) were analyzed for activity concentrations of 238Pu, 239Pu, 240Pu, 241Pu and 241Am. The sensitivities of the three determination techniques were compared. [ABSTRACT FROM AUTHOR]

The Aare-Rhine river system with its four nuclear power plants on the banks of these rivers and with its intermediate lakes and reservoirs provide the unique chance to analyze the input of radioactivity into the system thereby furnishing information on the sources, to analyze the transport within the sediment and along the rivers, and to refine unsupported 210Pb dating validated by known discharge maxima. At three locations (Lake Biel, Klingnau Reservoir, old branch of the Rhine) in the Aare and Rhine rivers system downstream of the older nuclear power plants (NPPs) Mühleberg and Beznau, the vertical distributions of 137Cs, 210Pb, 214Pb, 214Bi, 40K, 7Be, 239Pu, 240Pu, 241Am, and 237Np in sediment cores were determined. Depth-age relations using the excess 210 Pb were established with the raw and with the piecewise Constant Rate Supply (CRS) models. A comparison of the piecewise CRS method with the imprints of known discharges showed differences of up to two years. Besides typical 137Cs signals (about 100 Bq∙kg−1) from the atmospheric nuclear weapons testing (NWT) and the Chernobyl fallouts, imprints of known 137Cs discharges (10–70 Bq∙kg−1) from the NPPs were found in the sediments. The 237Np distributions (6–10 Bq∙kg−1) essentially follow the 137Cs NWT distributions. In the sediment downstream the NPP Mühleberg (Lake Biel) a239Pu distribution (<3 Bq∙kg−1) was found, which was solely due to the NWT fallout. Downstream the NPP Beznau (Klingnau Reservoir and an old branch of the Rhine), besides the NWT distribution, also imprints of 239Pu discharges (up to 7 Bq∙kg−1) were found within the time interval 1963 to 1986.240Pu/239Pu ratios revealed that the burn-up times of the nuclear fuel in the NPP (235U enrichment of 3.5%), from which the discharges stem, should be about 1 year or less. A comparison between the calculated and the measured 137Cs/239Pu ratio revealed no large discrepancies for the Lake Biel and Rhine positions, but in the Klingnau distribution, the calculated 137Cs/239Pu ratio is one order of magnitude larger than the measured one. The reason could be either a natural uranium research reactor as the source, or strong, short-range 239Pu precipitation after the discharge from the Beznau NPP. The largest 239Pu peak in the Rhine sediment (1968/70) corresponds to no major peak in the Klingnau sediment. For the NPP Mühleberg discharge of 1982 the ratio of the 137Cs deposition in sediments from Lake Biel, Klingnau Reservoir and the Rhine river is about 1 : 0.5 : 2.9. For the 1977/78 239Pu deposition the ratio is 1 : 0.02, for the Klingnau Reservoir and the Rhine sediments, respectively. These numbers indicate a long-range transport of Cs and a rather short-range transport of Pu. • Unique study area: sediments downstream NPPs in a single river system. • Piecewise CRS depth-age relations verified (Δt < ±2 years) by known NPP discharges. • Several trans-uranium distributions measured; 237Np established as proxy for NWT activity. • Nuclide activity ratios distinguish between NWT, Chernobyl and reactor activity. • Long-range Cs and short-range Pu transport along the river system recognized. [ABSTRACT FROM AUTHOR]

This paper presents the results of 137Cs and 210Pb dating of sediments from the northern and western basins of Lago Maggiore and the southern basin of Lago di Lugano. Vertical distributions of 137Cs in sediment cores taken in 2017/18 were compared to those of the sediment cores taken almost two decades ago at the same positions. This comparison showed that 137Cs peaks do not alter their shape significantly over time and 137Cs remains a reliable time-marker for many decades. 210Pb dating using for the first time the piecewise "constant rate supply" (CRS PW) model constrained with 137Cs time-markers is performed for sediment cores of Lago Maggiore and Lago di Lugano. "Event-linked" mass accumulation rates (MARs) were derived from the CRS PW model. In combination with the dry bulk density, organic matter content, 40K and 210Pb activity concentrations, these "event-linked" MARs were used for the identification of one or more event layers (turbidites, detrital layers) in 1-cm thick sediment samples. "Continuous" mean MARs which are independent of the event layers were estimated: in Lago Maggiore sediment cores they are 0.066–0.090 g cm−2 yr−1; in Lago di Lugano they vary in the range of 0.032–0.057 g cm−2 yr−1 with higher values in the time interval 1963–1986 as compared to 1986–present. • 137Cs remains a reliable time-marker in lake sediments for the next decades. • Necessity of using piecewise constant rate supply 210Pb model constrained with 137Cs. • Event-linked mass accumulation rates (MARs) as indicators for event layers. • Estimation of continuous MARs which are independent of event layers. [ABSTRACT FROM AUTHOR]

We present long-term records of the 137 Cs and 90 Sr activity concentrations in soil, grass and milk from two lowland and two alpine pastures of Switzerland. The data is used for better understanding the long-term behavior of these radionuclides in the environment. Transfer factors between compartments are used as qualitative indicators of the magnitude of transfer and as a way to compare different elements (e.g. Cs and Sr) in similar conditions. The long-term behavior was quantified by means of the effective half-life which integrates all processes that cause a decrease of activity in a given medium such as leaching, fixation, erosion and radioactive decay. Our study shows that 90 Sr is more likely transferred from alpine soil to grass than 137 Cs. This is explained by a stronger fixation of Cs in the soils. We observed higher transfers of 90 Sr to grass in soils with lower Ca concentrations, and vice versa. In contrast, the transfer of 137 Cs to grass was not affected by the variations of the K content in the soil. We provide evidence that shows that 137 Cs, after intake by dairy cattle, is more likely transferred to milk than 90 Sr. However, as the 90 Sr and Ca transfers to milk are influenced by parameters/processes that were not taken into account in our study, our result cannot be entirely validated. The effective half-lives of 137 Cs and 90 Sr in soil, grass and milk corresponded with previous estimates in alpine soils. We have found that processes other than radioactive decay are responsible for a major decrease of the 90 Sr activity in soil. For 137 Cs, on the other hand, radioactive decay is among the most relevant process. Our data shows to be of interest in studying the trends of behavior of radionuclides in alpine regions. [ABSTRACT FROM AUTHOR]