Distribution Of Plutonium Research Articles

Migration of Plutonium, Micro- and Macroelements in the “Soil–Plant” System at Different Soil Moisture

In the vegetation experiment, the plutonium, micro- and macroelements migration in the “soil–agricultural plant” system depending on soil moisture in the range from 15 to 40٪ of absolute soil moisture were studied. The content of 239Pu was analyzed by α-spectrometry with preliminary radiochemical isolation. The elemental composition was analyzed by the ICP-MS and ICP-AES methods. Beans (Fabaceae) variety “Amber” were used as a test culture. The plutonium transfer factor obtained in the vegetation experiments are in the range of of 5.3×10–4–1.5×10–2, with an average value of 5.4×10–3 for the aboveground part of bean and range of 4.5×10–2–2.7×10–1, with an average of 1.6×10–1 for bean roots. It was determined that the distribution of plutonium, micro and macro elements in the vegetative organs of plants is not equally, the transfer factor of plutonium for the aboveground part of plants is lower than for the root part. It has been established that the accumulation of plutonium, micro- and macroelements, depending on soil moisture, is different for the organs of beans. The dependence of plutonium accumulation by plants on soil moisture is significantly higher than for other considered elements. A decrease in the coefficient of accumulation of plutonium in the aerial part of the beans is recorded with an increase in soil moisture up to two orders of magnitude. There is a trend towards a slight decrease in the accumulation coefficients of Fe, Mg, Mn, Cr, Mo, Ni, Co, Cu. For the root system of beans, a clear dependence of the accumulation of the considered elements on soil moisture is not observed.

Comparative sintering behaviour of MOX powders synthesized through the freeze granulation or dry-cogrinding routes

Two MOX powders containing 11 mol% Pu/(U+Pu) have been synthesized using the freeze granulation or dry-cogrinding routes. The sintering behaviour of green compacts has been investigated up to 1700 °C in an Ar/4.3 vol% H2 humidified with 1200 vpm H2O. The evolution of the sintering trajectory (grain size as a function of relative density) is identical up to approximately 94% relative density. Above this value, grain growth becomes significant in compacts made with the powder obtained by freeze granulation and densification becomes more modest. As for it, the sintering trajectory relating to the compacts shaped from the co-grinded powder continues up to approximately 97.5% relative density, without remarkable grain growth. Beyond this value, grain growth occurs and densification slows down. It has also been shown that the plutonium distribution is more homogeneous in the case of a sample sintered from the powder obtained by freeze-granulation (relative density around 97–99%).

Spatial distribution, source identification, and transportation paths of plutonium in the Beibu Gulf, South China Sea

To investigate the spatial distribution and source of plutonium isotopes in the Beibu Gulf, surface sediments were collected and analyzed using sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). The activities of 239+240Pu in surface sediments ranged from 0.012 to 0.451 mBq/g (mean: 0.171 ± 0.138 mBq/g, n = 36), indicating a decreasing trend in a counterclockwise direction from the southern bay mouth. The counterclockwise decreasing trend in the south of the bay mouth is similar to the current in the Beibu Gulf. The 240Pu/239Pu atom ratios in surface sediments ranged from 0.156 to 0.283 (mean: 0.236 ± 0.031, n = 36), slightly higher than that of the global fallout value of 0.18. This suggests that the Pu in the Beibu Gulf was a combination of global fallout and Pacific Proving Ground (PPG). The average contribution of the plutonium (Pu) derived from the PPG in the sediment was estimated to be 52 % ± 24 %.

Plutonium Accumulation by Vegetation on Different Soils

The high variability of the plutonium transfer factors presented in the literature makes it relevant to study the mechanisms that affect its migration ability and its availability for vegetation. The variability of transfer factors is explained by different properties of soils, since the redox potential and soil acidity can significantly affect the mobility of plutonium. In the vegetation experiment, the migration of plutonium in the “soil-agricultural plant” system was studied for different types of soils. The content of 239 + 240Pu was analyzed by alpha spectrometry with preliminary radiochemical isolation. Plutonium migration parameters were determined using barley (Hordeum) and beans (Fabaceae) as test cultures. The plutonium accumulation coefficients obtained in the course of vegetation experiments are in the range of 3.1 × 10–4–6.8 × 10–3, with an average value of 3.8 × 10–3 for the aboveground part of barley and 9.2 × 10–3–7.6 × 10–2, with an average value of 3.8 × 10–2 – for the root system of barley. The transfer factor range was 1.5 × 10–3–5.7 × 10–3 with an average value of 3.7 × 10–3 and 5.8 × 10–2–6.5 × 10–2 with an average value of 6.2 × 10–2 for the aboveground part and the root system of the beans, respectively. It has been determined that the nature of the plutonium distribution over the vegetative organs of the crops under consideration is non-uniform. On average, the plutonium transfer factor for the aboveground part of plants is lower than for the root part by more than 40 times. It has been determined that the accumulation of plutonium in the aboveground parts of plants growing on different types of soil is not the same for individual species/organs of agricultural plants. For the aboveground part of the agricultural crops under consideration, the transfer factors differ up to several orders of magnitude. In general, the accumulation of plutonium by vegetation growing on different soils types is arranged in the following row: soddy-podzolic (Retisol) and gray forest soil (Phaeozem) lowland peat-bog (Histosol) \( \gg \) typical chernozem (Chernozem). The smallest accumulation of plutonium by vegetation is observed in soils with a high content of organic matter. For the root system of plants, the dependence of the plutonium accumulation coefficients on the soil type is uncertain.

First application of plutonium in soil erosion research on terraces

The spatial distributions of 239+240Pu and 137Cs in soils from Longji Rice Terraces were investigated to evaluate soil erosion. The activity concentrations of 239+240Pu and 137Cs in the surface soils of the paddy fields were in the range of 0.089–0.734 and 1.80–7.88 mBq/g, respectively. The activities of 239+240Pu and 137Cs showed very similar distribution trends, first increasing and then decreasing with increasing elevation. The 240Pu/239Pu atom ratios in the surface soils ranged from 0.162 to 0.232. The activities of 239+240Pu and 137Cs in the soil cores tended to be uniformly distributed within the plowed layer and declined exponentially below this depth. The mean soil erosion rates of Longji Rice Terraces estimated by 239+240Pu and 137Cs tracer methods were 5.44 t/(ha·a) and 5.16 t/(ha·a), respectively, which demonstrated that plutonium can replace 137Cs as an ideal tracer for soil erosion research in the future. Landform features are the main factors affecting the distribution of plutonium and 137Cs as well as soil erosion in the Longji Rice Terraces.

Vertical distribution of plutonium isotopes from the floodplain and lacustrine sediments in Poyang Lake, China

Anthropogenic radionuclides deposited in sediments have been used for environmental radiation risk valuation as well as source identification. In this study, we investigated the vertical distribution of plutonium (Pu) isotopes and 240Pu/239Pu atom ratios in both floodplain and lacustrine sediments in Poyang Lake. The 239+240Pu activity concentrations in floodplain sediment cores were found to range from 0.002 to 0.085 Bq kg−1, with a maximum value at the subsurface layer. The activity in lacustrine sediment cores was from 0.062 to 0.351 Bq kg−1 with a mean of 0.138 ± 0.053 Bq kg−1. The inventory of 43.15 Bq m−2 in lacustrine sediment core is comparable to the average value of global fallout expected at the same latitude. The average 240Pu/239Pu atomic ratios (0.183 ± 0.032) for sediment cores indicated that the global fallout is the major source of Pu in the studied region. The results are of great significance to the further understanding of sources, records, and environmental impacts of regional nuclear activities in the environment.

DISTRIBUTION OF RADIOACTIVE ELEMENTS DURING SLAG REMELTING OF STRUCTURAL MATERIALS OF VVER FUEL ELEMENT SHELLS

At the radiochemical plant of FSUE “PO “Mayak” in the process of processing spent nuclear fuel (SNF), about 170 tons/year of metal radioactive waste (MRW) are formed, mainly represented by fuel element shells structural materials (SM) containing residual amounts of radionuclides after fuel dissolution, and spent fuel assemblies (SFAS) sent to storage. It is possible to achieve compaction and decontamination of MRW by a method based on slag remelting in an induction furnace with a cold crucible. In order to establish the distribution of actinides and fission products (FP), thermodynamic slag remelting process modeling of the VVER-1000 reactor plant SM fuel rods shells and SFAS, experimental data obtained verification were carried out. The most probable distribution of actinides and FP by melting products is shown. Most of the curium and americium are concentrated in the metal – 99 and 94 wt %, respectively. The maximum extraction of uranium into the slag phase in the form of UO2 dioxide is up to 40 wt %. The distribution of plutonium in the temperature range of 1500–2000°C over the slag (in the form of PuO and PuO1.61 oxides) and metal phases occurs in almost equal proportions. It has been established that up to 99.78 wt % cesium, the content of europium and americium is 0.05 and 0.17 wt %, respectively.

Plutonium Signatures in a Dated Sediment Core as a Tool to Reveal Nuclear Sources in the Baltic Sea.

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvären bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, 240Pu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 ± 0.31)·10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 ± 0.11)·10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958).

Temporal evolution of plutonium concentrations and isotopic ratios in the Ukedo - Takase Rivers draining the Difficult-To-Return zone in Fukushima, Japan (2013–2020)

In 2011, the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) accident released significant quantities of radionuclides into the environment. Japanese authorities decided to progressively reopen the Difficult-To-Return Zone after the decontamination of priority reconstruction zones. These areas include parts of the initially highly contaminated municipalities located to the north of the FDNPP, including Namie Town, an area drained by the Ukedo and Takase Rivers. Eleven years after the accident, research focused on the spatial distribution of plutonium (Pu) and radiocesium (Cs) isotopes at contrasted individual locations. To complement previous results, the current research was conducted on flood sediment deposits collected at the same locations after major flooding events during eleven fieldwork campaigns organised between 2013 and 2020 at the outlet of the Ukedo and Takase Rivers (n = 22).The results highlighted a global decrease of the Pu and 137Cs contents in sediment with time during the abandonment phase in the region, from 2013 (238.20 fg g−1) to 2020 (4.28 fg g−1). Furthermore, based on the analysis of the 240Pu/239Pu isotopic ratios, the plutonium transiting these rivers (range: 0.166 – 0.220) essentially originated from the global fallout (0.180 ± 0.014 (Kelley et al., 1999)). Sediment showed contrasted properties in the two investigated rivers, which is likely mainly the result of the occurrence of Ogaki Dam on upper sections of the Ukedo River as it strongly impacts the material supply from this river to the Pacific Ocean. A statistical analysis highlighted the strong correlation between Pu activity concentrations and 137Cs activities in both rivers, confirming that both radionuclides are transported with a similar pathway. Despite it was detected early after the accident (2011–2013), the current research demonstrates that plutonium originating from FDNPP is no longer detected in these rivers draining the Difficult-To-Return Zone at the onset of the reopening of the area to its former inhabitants.

Distributions of Radiocesium and Plutonium in the Korean Seas and North Pacific after the Fukushima Accident, 2011–2014

The distributions of artificial radionuclides, radiocesium (134Cs and 137Cs) and plutonium isotopes (238Pu and 239+240Pu), in the surface water around the Korean seas (East/Japan Sea and Yellow Sea) in 2011–2012 and in three sections in the North Pacific between 2011 and 2014 were examined. The 137Cs activities in the surface water in the Korean seas in 2011 (immediately after the Fukushima nuclear power plant (NPP) accident on 17 March 2011) were comparable or not significantly different relative to those in 2010 and 2012. However, 134Cs, which had been not detected in the study area before the Fukushima accident (under the detection limit of 0.1 mBq kg−1 level), were detected rapidly in 2011 after the accident (in about 60% of the 72 samples) and gradually disappeared due to their short half-life (t1/2 = 2.06 years) in 2012 (detected in about 16% of the 24 samples). In addition, the highest activities of radiocesium and Pu isotopes appeared locally in some stations of the Korean Strait region (located between Korea and Japan) within 1–2 months immediately after the accident. This suggests that the radioactive nuclides released immediately after the Fukushima accident were significantly introduced through the atmosphere, based on recent studies conducted in neighboring areas. We also showed that the spatial distribution of radiocesium in the North Pacific moved eastward from 2012 to 2014, and we attempted to quantify the residence time of radiocesium (137Cs) in the Korean seas based on the long-term (tens of years scale) temporal trends of 137Cs activity data, which have been collected since the 1960s and 1970s. The estimated retention time of 137Cs in the East/Japan Sea and Yellow Sea were 25 ± 0.6 and 8.0 ± 0.1 years, respectively. These results are expected to be used as a preliminary study for a potential future event of a marine radioactive accident (which, of course, cannot be predicted) and as basic data for predicting the influences of radionuclide releases in the ocean.

Distribution and migration of 239,240Pu in soil profiles in North China

The source, vertical distribution and migration behavior of plutonium in five soil profiles (from forest, grassland and desert areas) in northern China were investigated. The average 240Pu/239Pu atomic ratio of 0.184 ± 0.022 observed in these samples is in good agreement with the reported value of global fallout, suggesting that the global fallout is the major source of plutonium in northern China. The 239,240Pu inventories in five soil profiles ranges from 43.3 Bq/m2 to 175 Bq/m2, lying in the reported range for global fallout in the similar latitude band. The effective convection velocity (0.04–0.16 cm/y) and effective dispersion coefficient (0.13–0.41cm2/y) of plutonium in different soil profiles derived using the CDE model varies significantly, attributed to multi-factors including location, topography, climate and soil types. The results showed that the migration of plutonium in grassland soil is significantly slow compared to other type of soil, especially desert soil.

Plutonium Systemic Biokinetic Model for Rats

A baseline compartmental model (relative to modeling decorporation) of the distribution and retention of plutonium (Pu) in the rat for a systemic intake is derived. The model is derived from data obtained from a study designed to evaluate the behavior of plutonium in the first 28 days after incorporation. The model is based on a recently published model of americium (Am) in rats, which incorporated a pharmacokinetic (PK)-front-end modeling approach, which was used to specify transfer to and from the extracellular fluids (ECF) in the various tissues in terms of vascular flow and volumes of ECF. In the americium model, the approach was "cell-membrane limited," meaning that rapid diffusion of americium occurred throughout all the extracellular fluids (i.e., the blood plasma and interstitial fluids), while back-end rates representing transport into and out of the cells were determined empirically. However, this approach was inconsistent with the plutonium dataset. A good fit to the data is obtained by incorporating aspects of the Durbin et al. model structure, with plutonium in plasma separated into "free" and "bound" components. Free plutonium uses a cell-membrane-limited front end as for americium. Bound plutonium uses a capillary-wall-limited front end, where transfer rates from blood plasma into the interstitial fluids are relatively slow, and must be determined either empirically or from a priori knowledge. As in the Durbin et al. model, both free and bound plutonium are available for deposition in bone. In addition, our model has some bound plutonium associated with uptake to the gastrointestinal (GI) tract. Uncertainties in transfer rates were investigated using Markov Chain Monte Carlo (MCMC). It is anticipated that this model structure of plutonium will also be useful in interpreting comparable data from decorporation studies done in experimental animals.

Characterization by electron probe microanalysis, Raman spectroscopy and transmission electron microscopy of a MOX fuel sintered from a freeze-granulated powder

The microstructure of a 98.7 % dense U0.856Pu0.144O1.993 sintered sample (average grain size around 1.5 µm) has been characterized by electron probe microanalysis, Raman spectroscopy and transmission electron microscopy. Raman spectroscopy gives results comparable to electron probe microanalysis in terms of studying the spatial distribution of plutonium in a homogeneous sintered MOX fuel. The use of transmission electron microscopy allows additional characterizations of great interest for investigating the chemical homogeneity of sintered MOX fuels. At the scale of the elementary grains constituting the sintered polycrystal, a variation in the Pu/(U+Pu) content has been observed which can change typically from 0 to about 40 at% over a short distance (from 100 to 150 nm). Thereby, the thorough characterization of the microstructure of MOX fuels by transmission electron microscopy is a critical step to understand their genesis and to apprehend their dissolution properties with a view to their reprocessing.

Plutonium distribution in sequentially extracted phases of arable and uncultivated soils

The aim of this study was to determine the distribution of alpha-emitting plutonium isotopes from arable and uncultivated soils. The effect of soils cultivation on plutonium fractionation and mobility was studied using the sequential extraction technique (modified Tessier’s method). Soil samples were collected from the surface layer in the selected points. By means of reagents with increasing leaching power, the fractions were separated: readily available, carbonate bound, sesquioxide (Fe/Mn) bound and organically bound as well as residual. The content of 239+240Pu in the fractions was determined by alpha spectrometry. The sequential analysis showed that in the case of uncultivated soils, 67% of Pu was combined with organic matter, 15% was permanently bound to the matrix, but only 4% was associated with the available fraction, and 2% with the carbonate one. Arable soils revealed a different distribution: 36% of Pu was combined with the organic fraction, only 7% was bound permanently but as much as 9% was bound with the available fraction, and 11% with the carbonate one. It was proved that plutonium is bound mostly by organic matter (67% Pu—uncultivated and 36%—arable soils), however, the amounts of Pu combined with the labile fractions (ion-exchange and carbonate) are approximately 4 times higher for the arable soils than for uncultivated ones. This proves that soil cultivation can lead to the launch of plutonium in soil and its transition to more accessible forms which can cause a radiological risk.

Detection of Fission Coincidences With Plastic Scintillators for the Characterization of Radioactive Waste Drums

This work addresses the use of plastic scintillators as an alternative to ³He neutron detectors for radioactive waste drum characterization. The time response of scintillators is three orders of magnitude faster than that of gas proportional counters, and they offer similar neutron detection efficiency at lower cost. However, they are sensitive to gamma rays and the neutron-gamma pulse shape discrimination (PSD) is not possible with standard PVT scintillators. The proposed approach uses the neutron and gamma times of flight in triple coincidences recorded with ²⁵²Cf, AmBe, and ⁶⁰Co sources. A 2-D histogram of time delays between the second and first detected pulses, on the <inline-formula> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula>-axis, and between the third and second pulses, on the <inline-formula> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula>-axis, evidences a specific region of interest for spontaneous fission coincidences. MCNPX-PoliMi simulations are performed, which are in good agreement with previous experiments and allow for investigating the types of coincidences (<inline-formula> <tex-math notation="LaTeX">$\gamma \gamma \gamma $ </tex-math></inline-formula>, nnn, <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>nn, <inline-formula> <tex-math notation="LaTeX">$\gamma \gamma \text{n}$ </tex-math></inline-formula>) and optimizing the rejection of neutron and gamma scattering crosstalk. The method was also experimentally tested with a 118-L mock-up drum filled with a metallic or an organic matrix, showing a correct estimation of the net fission signal up to an &#x201C;alpha ratio&#x201D; of 12 between fission and (<inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>,n) neutron emissions. Matrix and localization effects were also measured, showing a sensitivity (useful signal per gram of ²⁴⁰Pu_eq) for a homogeneous distribution of plutonium in the iron matrix about three times larger than in the wood matrix, due to neutron slowing-down in the latter. This difference can be taken into account by the prior knowledge of the matrix characteristics or by neutron and gamma attenuation measurements. In contrast, in case of a point source with an unknown position in the matrix, the relative localization uncertainty is 26% for the metallic drum, and 41% for the organic one.

Vertical and spatial distribution of plutonium and radio-cesium in lake sediment of China

Anthropogenic radionuclides of plutonium and 137Cs in the environment were usually applied for tracing the environmental impact of nuclear activities as well as establishing the chronology of recent lake sediment. In this study, the vertical distribution and spatial differentiation of plutonium and 137Cs in lake sediments of China were systematically contrastive analyzed to elucidate the regional influence by the local fallout from Chinese nuclear tests. The results demonstrated that the inventory of 137Cs and 239,240Pu, and their isotopic composition in lake sediments in northwestern China were obviously different from other regions, indicating that a portion of radionuclides in lakes in northwest China were originated from the Chinese Lop Nor Nuclear Test site (CNTs), and radionuclides in lakes of other regions may be completely originated from global fallout. Usually, the anthropogenic radionuclides recorded in lake sediments showed a single peak corresponding to the maximum deposition of 1964. However, two or three accumulation peaks of radionuclides were also observed in a few lakes. For the application of radionuclides on the dating of recent sediment, the accumulative peak of 239,240Pu and 137Cs signed to the period of 1963–1964 is the only practicable time marker for lake sediments in other regions of China. Isotopic information, such as 240Pu/239Pu ratio and 239,240Pu/137Cs activity ratio, may be useful for accurate sediment chronology, as well as used as a fingerprint to identify the source of the associated radioactive substance in the environment.

Distribution and source of plutonium in sediments from the southern Gulf of Mexico

Here, we report on new data (75 analyses) of plutonium (Pu) isotopes to elucidate activity concentrations, inventories, sources, and their transport from the ocean surface to the seafloor from a collection of six deep-sea sediment cores (depths ranging from 257 to 3739 m) in the southern Gulf of Mexico. Sediment cores collected from the continental shelf and upper slope region of the Gulf of Mexico showed 240Pu/239Pu ratios of 0.15 to 0.26, and 239+240Pu-inventories ranging from 14.7 to 33.0 Bq m−2. Inventories and ratios are consistent with global fallout Pu for this tropical region. In contrast, sediment cores collected from the lower slope region and abyssal plain showed low 240Pu/239Pu ratios of 0.07 to 0.13 and much lower 239+240Pu inventories below 6.8 Bq m−2. This implies that only a small fraction of the expected global fallout Pu has reached the deep-sea sediments. The low 240Pu/239Pu isotope ratios indicate that fallout from the Nevada testing site was an important source of Pu in deep-sea sediments, and that this Pu was likely more efficiently scavenged from the water column than Pu from global fallout. We estimated that up to 44% of the total inventory of 239+240Pu in deep-sea sediments is due to the Nevada source. Low values and a progressive decrease of 240Pu/239Pu ratios and 239+240Pu inventories with increasing water depth have been previously reported for the Gulf of Mexico. Analysis of Pu isotopes in two sediment traps from the upper slope regions shows 240Pu/239Pu ratios comparable to those observed in global fallout. These results indicate that global fallout Pu is currently the main source of Pu in sinking particles in the water column. Therefore, a significant fraction of global fallout Pu must still be present, either in a dissolved phase, or as biologically recycled material in the water column, or scavenged on the shelf and shelf break. Our results bring to light important questions on the application of Pu isotopes to establish sediment chronologies in deep-sea sediments, since global fallout features such as the 1963 maximum are not available.

Оценка содержания изотопов плутония в почве в районе размещения хранилища радиоактивных отходов в городе Обнинске

One of the sources of radionuclides released into the environment are radioactive waste storage. The plutonium isotopes concentration in the soils of the territory adjacent to the former radioactive waste storage facility in Obninsk was estimated. The cause of pollution was the depressurization of one of the storage tanks and the release of radionuclides due to its overflow with surface and ground waters in the period from 1998 to 1999. Samples were analyzed by alpha spectrometry with preliminary radiochemical isolation with complete decomposition of soil samples. The Pu-239+240 content range in the surface soil layer was 3.7-9.6 Bq/kg, with an average value of 6.7 Bq/kg, which is an order of magnitude higher than the level of its global fallout. In some samples, significant amounts of Pu-238 are observed, the relative content of which is 10-50% of Pu-239+240, that exceeds the its relative content due to the global fallout which is 2-5%. The depth distribution of plutonium isotopes has been studied. It has been established those significant concentrations of plutonium are observed to the depth of 95 cm for this territory. There is no definite dependence of the distribution of plutonium isotopes along the vertical soil profile. The random distribution of plutonium to the soil depth indicates that the source of Pu-239+240 are groundwater. Elevated concentrations of plutonium isotopes in the soil surface of the territory under consideration, its significant concentrations at soil depth indicates that the contamination is a consequence of the leakage of plutonium isotopes from the radioactive waste storage facility in Obninsk. The same concentrations can be expected in the lowland of the adjacent territory.

Level, distribution and sources of plutonium in the northeast and north China

Concentrations of 239Pu and 240Pu in 163 surface soil samples and five soil cores collected from the northeast and north China were analyzed using the radiochemical separation combined with inductively coupled plasma mass spectrometry measurement. The average 240Pu/239Pu atomic ratios (0.185 ± 0.018) for all surface soil samples indicated that the global fallout is the major source of plutonium in the studied region. The 239,240Pu concentrations of the surface soil ranged from 0.002 mBq/g to 4.82 mBq/g, lying in the range of the reported results in the areas with similar latitude, except for a few samples. The distribution of 239,240Pu in this region is controlled by the deposition of plutonium in the atmosphere and its preservation in the soil, which were affects by multi-factors such as topography, climate, utilization of the land and vegetation coverage. The analytical results could be used as the baseline data for the assessment of the impact of nuclear activities in the past and the future.

Influence of the PuO2 content on the sintering behaviour of UO2-PuO2 freeze-granulated powders under reducing conditions

The sintering behaviour of freeze-granulated UO2-PuO2 powders containing 33 and 15 mol% Pu/(U + Pu) was investigated under reducing conditions up to 1700 °C. For both compositions, the “grain size versus relative density” trajectory was constructed. All the experimental points form a single trajectory meaning that a relative density/grain size pair obtained after sintering seems independent of the thermal path (heating rate, soak time, soak temperature) and of the Pu content. Exploiting the “grain size versus relative density trajectory” enabled also to propose that densification was controlled by grain boundary diffusion and grain growth by the grain boundaries whatever the Pu content. An activation energy around 510 kJ/mol was obtained for densification, which was close to the value reported for the grain boundary diffusion of plutonium cations in U1-xPuxO2 polycrystals. Whatever the Pu/(U + Pu) content, the sintered microstructure of 98 % dense samples possesses a homogeneous distribution of plutonium and uranium cations.