Transport Of Plutonium Research Articles

Extension of the TRANSURANUS plutonium redistribution model for fast reactor performance analysis

Abstract The plutonium redistribution model (PUREDI) calculates the steady-state and transient radial plutonium concentration as a function of the radial temperature profile and the time for mixed oxide fuels (MOX). In the context of developing a TRANSURANUS version for Gen-IV fast reactor fuels, PUREDI has been modified and extended to include the effects of the local power density profile and the oxygen-to-metal ratio on plutonium transport. The model has been extensively verified by means of specific numerical tests, and after incorporation in the TRANSURANUS fuel performance code, has been assessed on the basis of post irradiation examinations of the SUPERFACT experiment, showing a good agreement with the experimental data.

Stabilization of Plutonium Nano-Colloids by Epitaxial Distortion on Mineral Surfaces

The subsurface migration of Pu may be enhanced by the presence of colloidal forms of Pu. Therefore, complete evaluation of the risk posed by subsurface Pu contamination needs to include a detailed physical/chemical understanding of Pu colloid formation and interactions of Pu colloids with environmentally relevant solid phases. Transmission electron microscopy (TEM) was used to characterize Pu nanocolloids and interactions of Pu nanocolloids with goethite and quartz. We report that intrinsic Pu nanocolloids generated in the absence of goethite or quartz were 2-5 nm in diameter, and both electron diffraction analysis and HRTEM confirm the expected Fm3m space group with the fcc, PuO2 structure. Plutonium nanocolloids formed on goethite have undergone a lattice distortion relative to the ideal fluorite-type structure, fcc, PuO2, resulting in the formation of a bcc, Pu4O7 structure. This structural distortion results from an epitaxial growth of the plutonium colloid on goethite, leading to stronger binding of plutonium to goethite compared with other minerals such as quartz, where the distortion was not observed. This finding provides new insight for understanding how molecular-scale behavior at the mineral-water interface may facilitate transport of plutonium at the field scale.

Soil–Root Interactions Controlling Upward Plutonium Transport in Variably Saturated Soils

Due to its high toxicity and a long half‐life, processes that may enhance Pu mobility in the environment and possible transport and exposure pathways need to be better understood and identified. The results of long‐term Pu field lysimeter experiments at the Savannah River Site showed anomalous distributions below the source, with significant upward migration above the source. A previously developed reactive transport model with an initial application of a steady downward velocity successfully simulated the below‐source distribution of the lysimeter data. Development and coupling of a transient flow model with root water uptake to the reactive transport model yielded a downward distribution fit almost identical to that from the steady‐state flow application. The model predicted very little upward migration, however. Additional evaluations done by testing several soil hydraulic‐ and chemistry‐related mechanisms that may enhance upward migration yielded no improvement. We developed an extension of the reactive transport model to include and test a new mechanism: root Pu uptake and xylem transport. The extended model produced simulations that capture the general behavior of the upward migration with no effect on the below‐source fit. These results, with the support of the additional finding that elevated Pu concentrations in the lysimeter surface sediment originated from the source used in the experiments, indicated that Pu root uptake and transport is a valid explanation for the observed upward migration and may play an important role in near‐surface Pu transport. Further research is needed to identify the uptake mechanisms and Pu behavior within plant systems, with special attention directed to the effect of Pu complexation with different chelating agents in soil and plants (siderophores, phytosiderophores, and others).

A Fully Transient Model for Long‐Term Plutonium Transport in the Savannah River Site Vadose Zone: Root Water Uptake

A Fully Transient Model for Long‐Term Plutonium Transport in the Savannah River Site Vadose Zone: Root Water Uptake

On radiocarbon and plutonium leakage to groundwater in the vicinity of a shallow-land radioactive waste repository

A shallow-land radioactive waste repository operated in boggy forest environment from 1963 to 1989. During the operation period, a considerable amount of technogenic radionuclides, in solidified state, was disposed into the vault established in the geological structure at the depth of up to 3 m. Environmental monitoring activities started after the closure of the repository in 1989. Recent investigations revealed transfer of radiocarbon and plutonium to the groundwater in the prevailing flow direction. Activity concentration of 239,240Pu in non-filtered fraction of the groundwater from observation well no. 4 determined by alpha-spectrometry was 6.4 × 10 −5 Bq l −1 in 2005, and 3.2 × 10 −4 Bq l −1 in 2006. Further analysis of colloid-facilitated transport of plutonium is planned. Variation of 14C activity concentration in the same well was monitored in 2006. It varied from 0.2 ± 0.1 Bq l −1 in October to 2.8 ± 0.6 Bq l −1 in June and July. Results imply further research into radiocarbon transfer to atmosphere and selected plant species.

Artificial radionuclides in the atmosphere over Lithuania

Measurements of airborne radioactive aerosol concentration were carried out on the basis of 1–3 days samples after the Chernobyl disaster and during the period of 1992–2003. Transport of “hot” particles of different composition resulted in the high activity concentrations of 137Cs, 238Pu, 239,240Pu and 241Am in the atmosphere in Vilnius at the end of April 1986. The 240Pu/ 239Pu atom ratio showed clear evidence of non-global plutonium originating from the Chernobyl accident in the atmosphere over Lithuania. The 240Pu/ 239Pu atom ratio ranged from 0.14 to 0.40 in monthly samples in Vilnius in 1995–2003. An increase in activity concentration of 137Cs by a factor of 100 (up to 300 μBq/m 3) was found following forest fires in the Ukraine and Belarus. However, no transport of the Chernobyl plutonium was observed and the 240Pu/ 239Pu atom ratio in samples collected during the forest fires was found to be 0.229 and 0.185, respectively. The exponential decrease in the 240Pu/ 239Pu atom ratio from 0.30 to 0.19 (mean values) was observed in 1995–2003.

Diffusive transport of neptunium and plutonium through compacted sand-bentonite mixtures under anaerobic conditions

Diffusive transport of neptunium, plutonium, tritiated water (HTO), Cs+and I-in compacted sand-bentonite mixtures was studied by a through-diffusion method. Experiments for Np were performed in the presence of carbonate where Np is stable as NpIV(CO3)2(OH)22-and those for Pu in the presence of fulvic acid where the Pu is stable as fulvic complexes. These experiments were performed under Ar (pO2< 10-6atm). Effective diffusivity (De) values of (1.81 ± 0.03) × 10-10, (1.8 ± 0.8) × 10-10, (5.1 ± 0.8) × 10-11and (9.0 ± 4.1) × 10-11m2s-1were obtained for HTO, Cs+, I-and Np(CO3)2(OH)22-, respectively. The ratio of theDeto the diffusivity in bulk of the water was around 0.1 for Np(CO3)2(OH)22-, HTO and Cs+, which is consistent with the pore diffusion model. Observed diffusive transport of Pu was much smaller than those of HTO, Cs+, I-and Np(CO3)2(OH)22-probably because Pu was present as colloidal forms and that confined pore space in the compacted sand-bentonite mixtures does not allow diffusive transport of colloidal plutonium.

Colloid Transport of Plutonium in the Far-Field of the Mayak Production Association, Russia

Sorption of actinides, particularly plutonium, onto submicrometer-sized colloids increases their mobility, but these plutonium colloids are difficult to detect in the far-field. We identified actinides on colloids in the groundwater from the Mayak Production Association, Urals, Russia; at the source, the plutonium activity is approximately 1000 becquerels per liter. Plutonium activities are still 0.16 becquerels per liter at a distance of 3 kilometers, where 70 to 90 mole percent of the plutonium is sorbed onto colloids, confirming that colloids are responsible for the long-distance transport of plutonium. Nano-secondary ion mass spectrometry elemental maps reveal that amorphous iron oxide colloids adsorb Pu(IV) hydroxides or carbonates along with uranium carbonates.

Safety of ocean shipments of plutonium between Europe and Japan

Sandia National Laboratories (SNL) has conducted an extensive study of emergency response planning applicable to sea transport of plutonium for the Japan Nuclear Cycle Development Institute (JNC). This work covered four separate areas to better define the accident environment for long range sea transport of nuclear materials. A probabilistic safety analysis evaluated technical issues for the transport of plutonium between Europe and Japan. An engine room fire aboard a purpose built ship was used to analyse the vulnerability of plutonium packaging designed to International Atomic Energy Agency (IAEA) standards. A comprehensive corrosion study estimated the time required for sea water to breach a containment boundary in submerged generic plutonium packaging. A survey of worldwide commercial recovery capabilities provided a compilation of information on the capabilities of salvaging high value cargo from sunken ships. This paper addresses salvage modes from harbour depths to the deepest ocean trenches. Previous studies (J. L. Sprung et al., SNL reports SAND98-1171/1 and SAND98-1171/2, May 1998) included a probabilistic risk assessment of the overall safety, source term evaluations and finite element structural dynamics calculations to determine the effects of ship to ship collisions on nuclear material containers and the effects of ship fires on transport packaging as determined by actual fire experiments conducted on board a test ship. The previous studies, together with this work, form a comprehensive technical basis that encompasses the overall safety of sea transport of plutonium between Europe and Japan. Based on these technical analyses, transport of nuclear materials by sea in Type B packaging, approved in accordance with US Nuclear Regulatory Commission (NRC) and IAEA regulations, and carried in purpose built ships with adequate surveillance, has a very high degree of safety for the failure modes studied. Non-purpose built ships do not have the redundancy in safety features provided by the newer purpose built ships. However, SNL studies on non-purpose built ships have shown accident environments to be within NRC and IAEA regulatory assumptions for Type B packaging. These studies were carried out for both structural ship to ship collisions and engine room fires by analysis (for the collisions) and direct experimentation and analysis (for the fires). Thus, land transport mode regulations are applicable for sea transport accident conditions.

UNCERTAINTIES ANALYSIS OF DOSES RESULTING FROM CHRONIC INHALATION OF PLUTONIUM AT THE MAYAK PRODUCTION ASSOCIATION

A method is presented to determine the uncertainties in the reported dose due to incorporated plutonium for the Mayak Worker Cohort. The methodology includes errors generated by both detection methods and modeling methods. To accomplish the task, the method includes classical statistics, Monte Carlo, perturbation, and reliability groupings. Uncertainties are reported in percent of reported dose as a function of total body burden. The cohort was initially sorted into six reliability groups, with "A" being the data set that the investigators are most confident is correct and "G" being the data set with the most ambiguous data. Categories were adjusted based on preliminary calculation of uncertainties using the sorting criteria. Specifically, the impact of transportability (the parameter used to describe the transport of plutonium from the lung to systemic organs) was underestimated, and the structure of the sort was reorganized to reflect the impact of transportability. The finalized categories are designated with Roman numerals I through V, with "I" being the most reliable. Excluding Category V (neither bioassay nor autopsy), the highest uncertainty in lung doses is for individuals from Category IV-which ranged from 90-375% for total body burdens greater than 10 Bq, along with work histories that indicated exposure to more than one transportability class. The smallest estimated uncertainties for lung doses were determined by autopsy. Category I has a 32-38% uncertainty in the lung dose for total body burdens greater than 1 Bq. First, these results provide a further definition and characterization of the cohort and, second, they provide uncertainty estimates for these plutonium exposure categories.

Parameter and model sensitivities for colloid‐facilitated radionuclide transport on the field scale

We investigate the potential effects of inorganic colloids on radionuclide transport in groundwater using generic sensitivity studies and an example based on the alluvial aquifer near Yucca Mountain, Nevada. Our emphasis is on kinetically controlled sorption of radionuclides on mobile and immobile colloids. Three kinetic sorption models are considered for the sensitivity analysis: bilinear, Langmuir, and linear. Plutonium is assumed to be injected into the Yucca Mountain alluvial aquifer at a constant rate and follows a random stream tube to a monitoring boundary. The linear sorption model provides a reasonable upper bound on colloid‐facilitated plutonium transport for the site‐specific conditions. In the absence of colloid filtration and retardation, colloids enhance the plutonium discharge by a large factor over the situation without colloids. Exchange of plutonium between solution and reversibly attached colloids makes colloid retardation relatively ineffective at reducing colloid‐facilitated transport except when the retardation factor is large. Irreversible removal of colloids (filtration) is more effective than retardation at reducing colloid‐facilitated transport. For fixed filtration rate the degree of attenuation depends sensitively and nonmonotonically on the rate of plutonium desorption from colloids. These results emphasize the need for accurate measurements of rates of desorption from colloids as well as in situ studies of filtration of naturally occurring colloids.

Evaluation of a conceptual model for the subsurface transport of plutonium involving surface mediated reduction of Pu(V) to Pu(IV)

A conceptual model is proposed to explain the transport behavior of plutonium in laboratory columns packed with a sandy coastal soil from the U.S. Department of Energy (DOE)'s Savannah River Site. The column transport experiments involved the introduction of a finite step input of plutonium, predominately in the +5 oxidation state, into the columns followed by elution with a low-carbonate solution of 0.02 M NaClO 4 at pH 3, 5, and 8. Total plutonium concentrations were measured in the effluent as a function of time. These elution profiles suggest at least two distinct physical/chemical forms of plutonium, each with a different mobility. To explain the observed behavior, the following conceptual model was evaluated: [1] equilibrium partitioning of plutonium (V) and plutonium (IV) between the aqueous and sorbed phases as defined by pH-dependent, oxidation-state specific distribution coefficients and [2] kinetic reduction of plutonium (V) to plutonium (IV) in the sorbed phase. The conceptual model was applied to the column experiments through a one-dimensional advective/dispersive mathematical model, and predictions of the mathematical model were compared with the experimental data. Overall, the model was successful in predicting some of the major features observed in the experiments. It also yielded quantitative estimates of the rate constant for surface mediated reduction of plutonium (V) to plutonium (IV) that were of the same order (10 −4 to 10 −5 s −1) as those calculated from batch data both for this soil and for goethite.

Transport of plutonium ( 239/240Pu) and caesium ( 137Cs) in the Irish Sea: comparison between observations and results from sediment and contaminant transport modelling

A model for radionuclide transport in the marine environment is described and applied, in the Irish Sea, to the movement of caesium ( 137Cs) and plutonium ( 239/240Pu) discharged from Sellafield. The model resolves processes operating on tidal time scales, whilst being simple enough to run over decadal time periods. Modelled processes include transport in the water column, exchange of contaminants between dissolved and particulate phases, wave–current sediment resuspension, sediment transport and mixing of material within the seabed. Transport in the water column is by a combination of tide, wind and density-driven flows. Sediment transport is based on the erosion, advection and deposition of three sediment classes representing sand, flocculated mud/silt and fine background components. Transfer of radionuclides between the dissolved and sediment phases is implemented using rate equations. A layered seabed is incorporated with transfers between layers representing biological and physical mixing processes. We demonstrate that the model is able to reproduce observed concentrations of 137Cs and 239/240Pu in the water column, the build-up of 239/240Pu in the seabed over a 30-year time span, including recent changes in seabed inventory distributions. The model is used to identify and quantify the mechanisms responsible for this recent redistribution of 239/240Pu in the region. The results suggest that whilst sediment transport plays a role in redistributing contaminated sediment in the eastern Irish Sea, desorption, followed by transport in the dissolved phase and reabsorption onto particulate material, is the primary mechanism for redistribution of 239/240Pu.

Transport of plutonium in surface and sub-surface waters from the Arctic shelf to the North Pole via the Lomonosov Ridge

New data on the levels and long-range transport of plutonium in the Arctic Ocean, recorded in the course of two expeditions to this zone in 1994 and 1996, are discussed in this paper. Specifically, approximately 100 plutonium measurements in surface and sub-surface water sampled at 58 separate stations throughout the Kara, Laptev and East Siberian Seas, as well as along latitudinal transects across the Lomonosov Ridge, are reported and interpreted in terms of the circulation pathways responsible for the transport of this element from the North Atlantic to the Arctic Shelf and into the Arctic interior. In addition, the behaviour of plutonium in its transit through the vast Arctic shelf seas to open waters under extreme environmental conditions is discussed in terms of the partitioning of plutonium between filtered (<0.45 μm) seawater and suspended particulate, and its association with colloidal matter. Finally, limited evidence of the presence of a colloidal plutonium component in Arctic waters subject to direct riverine input is adduced.

Modeling colloid transport for performance assessment

The natural system is expected to contribute to isolation at the proposed high-level nuclear waste (HLW) geologic repository at Yucca Mountain, NV (YM). In developing performance assessment (PA) computer models to simulate long-term behavior at YM, colloidal transport of radionuclides has been proposed as a critical factor because of the possible reduced interaction with the geologic media. Site-specific information on the chemistry and natural colloid concentration of saturated zone groundwaters in the vicinity of YM is combined with a surface complexation sorption model to evaluate the impact of natural colloids on calculated retardation factors ( R F) for several radioelements of concern in PA. Inclusion of colloids into the conceptual model can reduce the calculated effective retardation significantly. Strongly sorbed radionuclides such as americium and thorium are most affected by pseudocolloid formation and transport, with a potential reduction in R F of several orders of magnitude. Radioelements that are less strongly sorbed under YM conditions, such as uranium and neptunium, are not affected significantly by colloid transport, and transport of plutonium in the +5 valence state is only moderately enhanced. Model results showed no increase in the peak mean annual total effective dose equivalent (TEDE) within a compliance period of 10,000 years, although this is strongly dependent on container life in the base case scenario. At longer times, simulated container failures increase and the TEDE from the colloidal models increased by a factor of 60 from the base case. By using mechanistic models and sensitivity analyses to determine what parameters and transport processes affect the TEDE, colloidal transport in future versions of the TPA code can be represented more accurately.

Colloid-facilitated tracer transport by steady random ground-water flow

We study the transport of reactive solute in a three-phase system (water–solid matrix-colloids) in natural porous media. Semianalytical (integral) solutions are derived for the first time, which can be used for computing expected concentration, mass flux, or discharge for the dissolved as well as for colloid-bounded tracer. The results are based on a few simplifying assumptions: advection-dominated transport, linear mass transfer reactions, and steady-state colloidal concentration. Derived semianalytical expressions capture the main features of colloid-facilitated transport (the reversible-equilibrium and irreversible-kinetic sorption of tracers on colloids), and are applicable for the general class of linear sorption processes on the porous matrix. Derived solutions account for spatial variability of flow and sorption parameters, which is relevant for field-scale applications. We apply the theoretical results to the transport of neptunium and plutonium, using flow and transport data from the alluvial aquifer near Yucca Mountain, Nevada. Based on the zeroth and first temporal moment, dimensionless indicators are proposed for assessing the potential impact of colloid-facilitated tracer transport in aquifers. Generic sensitivity curves show the importance of tracer-colloid kinetic rates. Even very low irreversible rates (which will generally be difficult to determine in the laboratory) may yield observable effects for sufficiently long transport times. The obtained results can be used for assessing the significance of colloid-facilitated tracer transport under field conditions, as well as for setting further constraints on relevant parameters which need to be estimated in the field.

Using Plutonium Excretion Data to Predict Dose from Chronic and Acute Exposures

Using fission track analysis (FTA) in conjunction with a composite theoretical model of the transport of plutonium (Pu) in the human body creates a new opportunity to estimate the exposure and dose to the general population due to plutonium in the environment. For the purposes of this study, data derived from FTA performed at the University of Utah's Center for Excellence in Nuclear Technology, Engineering and Research (CENTER) has been used to predict doses for two populations. Both population groups have no known history of plutonium exposures. Therefore, two exposure scenarios (acute and chronic) were assumed to provide boundaries for dose estimates. Dose predictions focus on equivalent dose to lung, liver, and skeletal systems and range from 0.01 mSv to 560 mSv as a function of organ, sample collection interval and exposure type. Additionally, these reconstructions demonstrate the sensitivity of dose calculations to time of sample collection and duration of exposure. As anticipated for a class Y particle, the predicted average equivalent tissue dose to the lungs represents the highest dose to the evaluated compartments. Furthermore, the data imply that the general population receives a dose one order of magnitude lower than a radiation worker with no history of exposure for the equivalent exposure scenario.

Formula omitted] transport into the Arctic Ocean from underwater nuclear tests in Chernaya Bay, Novaya Zemlya

Radionuclide measurements have been conducted on sediment, seawater and biota samples collected in Chernaya Bay, on the southern coast of Novaya Zemlya, the site of two underwater nuclear tests conducted in the 1950s. 239,240 Pu levels in sediments from the central region of Chernaya Bay exceed concentrations of 15,000 Bq/kg, and are among the highest ever reported for the marine environment. It is estimated that approximately 11 TBq of 239,240 Pu from the tests has been retained in the sediments of Chernaya Bay. Plutonium from Chernaya Bay is distinguished by 240 Pu/ 239 Pu atom ratios of 0.03 that are much lower than ratios of 0.18 typical of global fallout. High levels of 137 Cs (Bq/kg) and 60 Co (Bq/kg) were also measured in surface sediments in the central regions of Chernaya Bay near the presumed epicentre of the explosions. Applications of a biodiffusion model to excess 210 Pb sediment depth profiles indicate that the distribution of 239,240 Pu is governed mainly by sediment mixing in this low sedimentation rate (<0.1 cm/yr) regime and, as a result, most of the 239,240 Pu has been retained in the upper 20 cm of the sediment column. Elevated levels of 239,240 Pu measured in Macoma (104 Bq/kg), Fucus (15 Bq/kg) and polychaete (1292 Bq/kg) from Chernaya Bay, indicate that 239,240 Pu levels in the benthos are comparatively high and that significant uptake has occurred in the food chain. Although levels of 239,240 Pu in bottom water from Chernaya Bay are high (4.2 Bq/m 3), restricted exchange over the fjord sill limits the present rates of 239,240 Pu transport from contaminated sites in Chernaya Bay into the eastern Barents Sea. However, low 240 Pu/ 239 Pu atom ratios measured in sediment cores collected throughout the eastern Barents Sea indicate that significant offshore transport of plutonium from Chernaya Bay has occurred in the past, probably at the time of the original nuclear tests. The large difference in end member 240 Pu/ 239 Pu atom ratios for Chernaya Bay fallout (0.03) and atmospheric fallout (0.18) has been exploited to estimate that 2 TBq of 239,240 Pu in Barents Sea sediments was originally derived from Chernaya Bay. Further, a plume of low 240 Pu/ 239 Pu ratio plutonium, distributed in a northwestward direction, is evident in sediments along the southern coastline of Novaya Zemlya, indicating that an additional quantity of Chernaya Bay plutonium may have been transported into the Arctic Ocean.

Study of the Accident Environment During Sea Transport of Nuclear Material: Probabilistic Safety Analysis of Plutonium Transport from Europe to Japan

AbstractThis study describes and analyses the safety of a large number of plutonium transport operations for the international transport of plutonium by maritime cargo vessels for selected routes. The analysis centres on conventional cargo vessels and their accident history in order to provide an estimate of the probability of accident occurrences for such vessels. This is an ultraconservative study since the radioactive materials described in this study will, in all likelihood, be transported in purpose-built ships that incorporate many safety features not found in regular cargo vessels. Follow-on studies can use the information developed in this study in order to estimate the probability of accident occurrences involving purpose-built ships. The accident probabilities developed in this study, for conventional cargo vessels, provide a conservative bounding estimate of the probabilities for accidents involving purpose-built ships. This study estimates the safety of transporting plutonium from Europe to Ja...

Study of the Accident Environment During Sea Transport of Nuclear Material: Analysis of An Engine-Room Fire on a Purpose-Built Ship

The programme goal was to show that the IAEA safe transport regulations adequately cover the thermal effects of an engine-room fire on plutonium transport packages stowed aboard a purpose-built ship. The packages are stored in transport containers located in a cargo hold of the ship. For this study, it was assumed that the packages in No 5 Hold, adjacent to an engine-room, could be subject to heating due to a fire in the engine-room. The No 5 hold and the engine-room are separated by a water-filled bulkhead. This study addressed the heat transfer from an engine-room fire that could heat and evaporate water out of the water-filled bulkhead and the resulting temperature conditions around the packages and inside the packages near their elastomeric seals.