Pu In Seawater Research Articles

Spatial distribution and modelling of 239+240Pu in the sediments and seawater columns of the South China Sea and Indian Ocean

In order to investigate the 239+240Pu potential influence in the ocean, and develop a new method for rapidly monitoring radioactive pollution, the 239+240Pu spatial distribution in the South China Sea (SCS) and the Indian Ocean (IND) sediments is analyzed by SF-ICP-MS (ELEMENT 2). The inventory-weighted mean activities of 239+240Pu were 0.413 ± 0.333 mBq/g, 0.128 ± 0.044 mBq/g, and 0.483 ± 0.606 mBq/g in the sediments of the SCS, eastern IND, and Arabian Sea, respectively. The 239+240Pu activity spatial distribution in the SCS sediments was influenced by the current, the vertical distribution of Pu in seawater, and the transport of particulate matter. The 239+240Pu activity spatial distribution in the IND sediments could be impacted by Antarctic Intermediate Water. The average of 240Pu/239Pu atomic ratios were 0.258 ± 0.034, 0.219 ± 0.031, and 0.212 ± 0.028 in the sediments of the SCS, eastern IND, and Arabian Sea, respectively. The 240Pu/239Pu atomic ratios in the SCS and IND indicate that Pu from the Pacific Proving Ground (PPG) is transported to the IND via the SCS internal current and transverse ocean currents within Indonesia. In addition, a seawater advection-dispersion equation (S-ADE) model is established based on the actual physical processes of radionuclides in the seawater column and well fitting results were obtained (R2 = 0.49 to 0.99). The 239+240Pu data and the geographic information from the sample site were used to correct the Pu distribution in the seawater. The calculated 239+240Pu mean concentrations in the surface seawater were 2.465 mBq/m3 and 2.205 mBq/m3 for the SCS and the eastern IND seawater, respectively, and the result is consistent with the previous measurements. Then, the 239+240Pu stored in the study area of SCS and eastern IND was estimated to be approximately 1.0–1.4% of the global ocean based on the model. This study provides a useful model for guiding and designing future monitoring of pollution by anthropogenic Pu and other isotopes.

Activity of radioactive isotopes in the offshore seawater at vicinity areas of Phu Quy, Phu Quoc and Bach Long Vy islands

In this work, activity of radioactive isotopes in some offshore seawater samples at vicinity areas of three islands has been investigated Phu Quy (Binh Thuan province), Phu Quoc (Kien Giang province), and Bach Long Vy (Hai Phong province). The ranges of radioactivity 226Ra, 238U, 137Cs, 90Sr, and 239,240Pu in seawater at three offshore islands are 2.09 ÷ 4.77 mBq/L, 2.33 ÷ 4.95 mBq/L, 0.98 ÷ 1.45 mBq/L, 1.22 ÷ 1.49 mBq/L, and 0.0045 ÷ 0.0066 mBq/L, respectively. These values show that the radioactivities of the above-mentioned radionuclides differ between monitoring periods and between three offshore islands of Vietnam, but which is equal to or lower than the corresponding value according to others seas in Vietnam and Asia – Pacific. The correlation between radioisotopes and properties of seawater (pH, conductance, and salinity) is also shown in this study to assess their impact on the fluctuations of the above radinuclides.

Plutonium and cesium baseline concentrations in seawater from northern Arabian Gulf

The Arabian Gulf is a semi-enclosed water body that has witnessed accelerated anthropogenic activity, in terms of commissioning of nuclear power plants, desalination facilities, oil refineries and extensive coastal development. Furthermore, three wars during the past three decades is a potential worry. This study presents the first plutonium baseline in seawater from the Northern Arabian Gulf. The 239+240Pu concentrations in seawater vary, between 2.9 and 4.9mBqm−3, a range that is comparable to other water masses at this latitude. The 238Pu ranged between 0.04 and 0.05mBqm−3 and the 137Cs concentration between 1.04 and 1.18Bqm−3. The ratio of 238Pu/239+240Pu at all eight sampling stations was 0.01, while the ratio of 239+240Pu/137Cs varied between 0.01 and 0.02. The presence of 137Cs and 239+240Pu in seawater from this region can mainly be attributed to the global atmospheric deposition and fluvial transport. The seawater concentration of 239+240Pu is five order of magnitude lower than bottom sediments in the area.

Analytical method for the determination of Np and Pu in sea water by AMS with respect to the Fukushima accident

A chemical separation procedure for plutonium (Pu) and neptunium (Np) was developed using extraction chromatography, mass spectrometry and radiometric analysis to determine their concentrations and isotopic ratios in sea water. 241Am, which causes isobaric background to 241Pu in mass spectrometric measurements, was successfully separated from the Pu fraction by this method. Water samples which were spiked with 242Pu and 237Np or 239Np, respectively, were used for chemical yield determination. The chemical yields of Pu and Np, which were determined by alpha and gamma spectrometry at the Radiochemie München (RCM), of more than 85% were obtained. The developed method was applied to analyze the concentration of Pu and Np in the certified reference material, IAEA-443, by Accelerator Mass Spectrometry (AMS) at the Maier–Leibnitz-Laboratory (MLL) to check the applicability of the method to sea water samples. The concentrations of 240Pu, 241Pu and 237Np obtained in this study are in agreement with the certified and literature values within the uncertainties. Due to strong isotopic interference of 239Pu with 238U, it was not possible to analyze the concentration of 239Pu. Some modifications of the chemical separation method to suppress the uranium (U) fraction are under consideration. This method can be used for the analysis of Pu and Np in Pacific Ocean water samples collected after the Fukushima accident.

Distributions of Pu isotopes in seawater and bottom sediments in the coast of the Japanese archipelago before and soon after the Fukushima Dai-ichi Nuclear Power Station accident

A radioactivity measurement survey was carried out from 24 April 2008 to 3 June 2011 to determine the levels of plutonium isotopes and 240Pu/239Pu atom ratios in the marine environments off the sites of commercial nuclear power stations around the Japanese islands; the sampling period extended to two months after the Fukushima Dai-ichi Nuclear Power Station accident. In our previous study (Oikawa et al., 2015), data on Pu isotopes and 241Am in sediments have already been reported. In this study, we report those on Pu isotopes in seawater as well as sediments, and the characteristics of sediments in addition (e.g., ignition loss and biogenic opals). Concentrations of 239+240Pu in seawater and bottom sediments remained nearly constant at all sampling locations during the survey period. In addition, no regional differences were observed in the 239+240Pu concentrations in surface waters. Higher 239+240Pu concentrations were found in bottom waters at deeper sampling locations, but the 240Pu/239Pu atom ratios were nearly constant regardless of the water depth. Higher 239+240Pu concentrations were also found in bottom sediments at deeper sampling locations, but vice versa for 240Pu/239Pu atom ratios as reported in the previous report. The sediments samples from deeper locations showed the higher percentage of ignition loss as well as the higher content of biogenic opal. There was likely to be some driving force participating in the transfer of Pu isotopes associated with biogenic substances to the deeper seabed. The present survey showed that the accident at the Fukushima Dai-ichi Nuclear Power Station did not contribute much to the inventory of Pu isotopes in the adjacent sea area.

Life time prediction of polymer used as thermal insulation in offshore oil production conditions: Ageing on real structure and reliability of prediction

Polymers are widely used for passive thermal insulation coatings on steel pipe in offshore oil and gas production. In this industry, structures used in deep sea have to be reliable as they are in service for more than 20 years in a very severe environment: sea water, hydrostatic pressure, temperature. One of the main questions is how to test and predict the lifetime of such structures in the laboratory. This study presents one approach that has been developed to characterize and predict the degradation of polyurethanes used as thermal insulation materials.Based on results obtained during accelerated ageing of the PU in sea water, a prediction of degradation through the thickness has been set up taking into account the temperature profile in the coating, water absorption and hydrolysis. Validity of this model has been investigated by comparing predictions with experimental data obtained on a real structure that has been aged for more than a year with an internal temperature up to 125 °C in water under hydrostatic pressure. Using this prediction, the effect of different parameters (such as coating thickness, internal and external temperature) on the degradation level of a structure has been examined.

Plutonium as a chronomarker in Australian and New Zealand sediments: a comparison with 137Cs

The construction of high resolution chronologies of sediment profiles corresponding to the last 50–100 years usually entails the measurement of fallout radionuclides 210Pb and 137Cs. The anthropogenic radionuclide, 137Cs, originating from atmospheric nuclear weapons testing can provide an important “first appearance” horizon of known age (1954–1955), providing much-needed validation for the sometimes uncertain interpretations associated with 210Pb geochronology. However, while 137Cs usually provides a strong signal in sediment in the northern hemisphere, total fallout of 137Cs in the southern hemisphere was only 25% that of the north and the low activities of 137Cs seen in Australian and New Zealand sediments can make its horizon of first appearance somewhat arguable. Low 137Cs fallout also limited the size of the 1963–1964 fallout peak, a peak that is usually seen in northern hemisphere sediment profiles but is often difficult to discern south of the equator. This paper shows examples of the use of nuclear weapons fallout Pu as a chronomarker in sediment cores from Australia (3 sites) and New Zealand (1 site). The Pu profiles of five cores are examined and compared with the corresponding 137Cs profiles and 210Pb geochronologies. We find that Pu has significant advantages over 137Cs, including greater measurement sensitivity using alpha spectrometry and mass spectrometric techniques compared to 137Cs measurements by gamma spectrometry. Moreover, Pu provides additional chronomarkers associated with changes in the Pu isotopic composition of fallout during the 1950s and 1960s. In particular, the 238Pu/ 239+240Pu activity ratio shows distinct shifts in the early 1950s and the mid to late 1960s, providing important known-age horizons in southern hemisphere sediments. For estuarine and near-shore sediments Pu sometimes has another significant advantage over 137Cs due to its enrichment in bottom sediment relative to 137Cs resulting from the more efficient scavenging of dissolved Pu in seawater by sediment particles.

Distribution of plutonium and americium in the marginal seas of the northwest Pacific Ocean

Plutonium isotopes and 241Am were studied in seawater and sediment from the East China Sea, the Yellow Sea, the East Sea/Sea of Japan, the Sea of Okhotsk, and the northwest Pacific Ocean, collected between 1993 and 1996 with the aim to contribute to better understanding the behaviour of plutonium and americium in the marine environment. 239,240Pu concentrations in surface water varied from 2.3 to 13μBql−1 in the East China Sea and from 3.5 to 9.4μBql−1 in the East Sea. The 239,240Pu vertical profiles in water showed a broad subsurface maximum between 500 and 1000m with a range of 30–40μBql−1, and gradually decreased from 1000m depth down to the seafloor. 241Am concentrations in surface water showed values from 1.1 to 2.2μBql−1 in the East Sea, from 1.0 to 3.1μBql−1 in the Sea of Okhotsk, and from 0.68 to 12.0μBql−1 in the northwest Pacific Ocean. The activity ratios of 241Am/239,240Pu in seawater showed values similar to the global fallout ratio, which suggests that the source of these radionuclides in the northwest Pacific Ocean is global fallout. However, the 241Am/239,240Pu activity ratios in sediment were found to be much higher (1.0–1.9) than the global fallout ratio (0.37), confirming that 241Am is scavenged from the water column more rapidly than 239,240Pu. The 239,240Pu inventories in the water column of the East Sea were from 0.98 to 93Bqm−2 depending on water depth and sedimentation rates. The 241Am inventory in the water column east of Kamchatka was 6.3±1.0Bqm−2 and the sediment inventory in the Sea of Okhotsk was 16±2Bqm−2. 239,240Pu concentrations in sinking particles in the southwest Japan Basin were from 3.7 to 5.2Bqkg−1 (dry weight) with fluxes of 0.19–4.50mBqm−2d−1 and at the Ulleung Basin from 2.4 to 3.7Bqkg−1 (dry weight) with fluxes of 0.77–1.10mBqm−2d−1. The mean residence time of 239,240Pu in the water column of the East Sea derived from sediment trap data was 140±20 years, 2–3 times less than in the Atlantic and Pacific oceans.

Concentration of particulate plutonium in surface and deep-water samples collected during the IAEA’97 expedition

Abstract Concentrations of particulate plutonium together with dissolved plutonium and the biogenic unique organic ligand (SOL) in particulate matter (PM) in surface and deep waters were determined in samples collected during the IAEA’97 cruise to the Pacific Ocean. Concentrations of particulate 239,240Pu in the water column ranged from 0.04 to 0.28 mBq m−3. The percentage of particulate 239,240Pu to total 239,240Pu in seawater was less than 10% in surface waters and less than 2% in deep waters. In order to characterize particulate 239,240Pu in seawater, the relationship between particulate 239,240Pu, dissolved 239,240Pu and SOL concentrations in surface PM was examined. The results reveal that particulate 239,240Pu in surface waters was linearly related to SOL concentration and independent of dissolved 239,240Pu concentrations. On the other hand, particulate 239,240Pu in deep waters does not seem to be related to the SOL concentration alone. pH values are discussed as another factor controlling particulate 239,240Pu in deep waters. The results suggest that the dominant chemical form of 239,240Pu in surface and deep PM, which may exist as Pu(IV), is a complex of SOL onto PM.

Vertical profiles of 239+240Pu in seawater from the East China Sea

Seawater samples were collected from the East China Sea continental shelf and analyzed for 239+240Pu activities. The vertical profiles of 239+240Pu had a similarity for all three stations in the East China Sea. 239+240Pu concentrations were low in the surface layer (3-4 mBq/m3) and increased gradually with depth to become high in the near-bottom layer (7-10 mBq/m3). 239+240Pu concentrations in seawater and the concentrations of suspended particles showed almost the same vertical profiles in the East China Sea continental shelf. The maximum value of 239+240Pu found in the near-bottom layer may be due to the contribution of Pu-rich suspended particles.

Numerical simulation of 137Cs and 239,240Pu concentrations by an ocean general circulation model

We simulated the spatial distributions and the temporal variations of 137Cs and 239,240Pu concentrations in the ocean by using the ocean general circulation model which was developed by National Center of Atmospheric Research. These nuclides are introduced into seawaters from global fallout due to atmospheric nuclear weapons tests. The distribution of radioactive deposition on the world ocean is estimated from global precipitation data and observed values of annual deposition of radionuclides at the Meteorological Research Institute in Japan and several observed points in New Zealand. Radionuclides from global fallout have been transported by advection, diffusion and scavenging, and this concentration reduces by radioactive decay in the ocean. We verified the results of the model calculations by comparing simulated values of 137Cs and 239,240Pu in seawater with the observed values included in the Historical Artificial Radionuclides in the HAM database, which has been constructed by the Meteorological Research Institute. The vertical distributions of the calculated 137Cs concentrations were in good agreement and are in good agreement with the observed profiles in the 1960s up to 250 m, in the 1970s up to 500 m, in the 1980s up to 750 m and in the 1990s up to 750 m. However, the calculated 137Cs concentrations were underestimated compared with the observed 137Cs at the deeper layer. This may suggest other transport processes of 137Cs to deep waters. The horizontal distributions of 137Cs concentrations in surface water could be simulated. A numerical tracer release experiment was performed to explain the horizontal distribution pattern. A maximum 239,240Pu concentration layer occurs at an intermediate depth for both observed and calculated values, which is formed by particle scavenging. The horizontal distributions of the calculated 239,240Pu concentrations in surface water could be simulated by considering the scavenging effect.

Chemical speciation of plutonium in seawater.

Concentrations of particulate and dissolved plutonium in seawater were determined together with strong organic ligands (SOL) in particulate matter (PM). The concentration of particulate 239,240Pu in surface waters of the Western North Pacific ranged from 0.03 to 0.3 mBq m(-3) during the period from 1987 to 1997. The percentage of particulate Pu to total Pu in seawater was less than 10% in surface waters, whereas its portions were less than 1% in deep waters. In order to characterize particulate Pu in seawater, the relationships between particulate Pu, dissolved Pu and SOL concentrations in surface PM were examined. The result reveals that particulate Pu was linearly related to the SOL concentration independent of dissolved Pu concentration. Mass balance analysis suggests that a dominant chemical form of Pu in surface PM, which may exist as Pu(IV), is a complex with strong organic ligands in PM.

Determination of plutonium in seawater using co-precipitation and inductively coupled plasma mass spectrometry with ultrasonic nebulisation

A flow injection–inductively coupled plasma–mass spectrometric (FI–ICP–MS) procedure, utilising ultrasonic nebulisation with membrane desolvation (USN/MD), has been developed for the determination of plutonium (Pu) in seawater at fg l −1 concentration levels. Seawater samples (1 l), after filtration, were subjected to co-precipitation with NdF 3, followed by ion exchange to enrich Pu and to reject seawater matrix ions and co-existing uranium. The seawater concentrate (1.0 ml) was then analysed by FI–ICP–MS. The limit of detection for 239 Pu in seawater based on an enrichment factor of 1000 was 5 fg l −1, and precision at the 0.80 pg l −1 level was 12% RSD. Accuracy was verified via recovery experiments, and by comparing survey data for the Irish Sea with that derived by standard methodology based on co-precipitation and α-spectrometry. Concentrations for dissolved 239 Pu and 240 Pu in the Irish Sea were in the range of 0.267–0.941 pg l −1 (0.614–2.164 mBq l −1) and 0.051–0.196 pg l −1 (0.428–1.646 mBq l −1), respectively.

Concentration levels and behavior of transuranium nuclides in Japanese coastal marine environment

The concentration of239,240Pu and241Am in different samples collected from the coastal marine environment of Ibaraki Prefecture, Japan facing the Pacific Ocean have been studied. Seawater samples have been collected since 1975 and sea-biota since 1981. The mean concentration levels of239,240Pu and241Am were 0.51, 0.20 for anchovy, 0.22, 0.11 for flounder, 4.9, 0.77 for brown algae, 2.0, 2.4 for shellfish, and 0.022, 0.0028 for seawater (in mBq/kl), respectively. The chronological change of239,240Pu in seawater was influence by fallout amounts. The activity ratio between the nuclides showed steady levels after two years from the end of atmospheric nuclear explosion tests. Activity levels and the ratios for each type of sample are briefly discussed.

Determination of 239,240Pu in seawater

In order to be able to predict the fate and pathways of plutonium dispersed on the ocean, the concentration of 239,240 Pu in surface and deep seawaters collected during cruises from 1976 to 1982 in areas suchas the Pacific Ocean were determined by the Japanese reference procedure. 236 Pu and 242 Pu, calibrated by reference to a standardized 241 Am solution, were used as yield tracers and in view of the correction necessary for 236 Pu decay, the half-life of 236 Pu was redetermined by preparing synthetic mixtures such as 236Pu + 239, 240Pu and measuring the decrease in the 236Pu/ 239,240Pu alpha-activity ratio by alpha-spectrometry. The concentration of 239, 240Pu in seawaters studied in this work were in range from 2 to 37 μBq1 −1, and from the secular change in the concentration and in 239, 240Pu profile, it is suggested that plutonium in the ocean is resistant to scavenging and renoval by settling matter. The 236Pu half-life va;ue obtained in this work, (1046.9 ± 3.1) days, compared well with the value reported in 1957.