Atmospheric dispersion models (ADM) are important radiation protection tools for modelling the public consequences of a radiological release. Conventional ADM approaches, like Gaussian plume models, have known limitations, and so much active research goes into improved flow modelling. However, in the radiological and nuclear field it is also important to be able to calculate the external doses. Conventional external dose models often break apart as well in the near range, because of heterogeneity of the plumes and deposition fields. In this work, we present an improved external dose modelling technique for use in ADM based on three-dimensional (3D) finite cloud modelling.For this, we adapted the Atmospheric Dispersion and Dose Equivalent Rates (ADDER) model by (I) including a puff algorithm alongside the existing plume algorithm, (II) implementing the Briggs’ rural dispersion parameterisation and (III) implementing a bespoke RDD puff rise algorithm that builds on previous work by Sharon et al. (2012). We benchmark our model on results from the Suffield Full-Scale Radiological Dispersal Device (FSRDD) Field Trials, which involved the detonation of three explosives labelled with lanthanum-140, and monitoring of their dispersion in the near range. We report the correspondence between deposition, ground shine and cloud shine model predictions and measurements. For the ground shine measurements, we quantitatively compare a direct dose conversion model with our finite ground algorithm. For 2/3 trials, we report FAC2>0.5, NAD<0.5, MG≤1.33 and VG≤2.0 for the ground shine computed with our finite algorithm. While previous studies of the FSRDD Field Trials only looked at time-integrated metrics, here, we also report continuous-in-time model predictions and measurements. We see future potential in coupling our external dose model to a more detailed Computational Fluid Dynamics (CFD) dispersion model.
Mechanistic models of iodine dry deposition have been developed to describe the transfer of radioiodine from the atmosphere to vegetation, but their applicability to long-term environmental exposure conditions remains poorly documented. This study evaluates the applicability of a dry deposition model under long-term environmental conditions using 129I measurements collected near the Orano La Hague reprocessing plant (France) between October 2018 and December 2019. Atmospheric gaseous and particulate 129I were monitored, and atmospheric activities were reconstructed at a 30-min time resolution using simultaneously measured 85Kr as a tracer of plant releases. Dry deposition to grass was simulated using mechanistic deposition models for gaseous and particulate iodine and compared with monthly 129I measurements in rain-protected grass. Approximately 90% of atmospheric 129I was present as gaseous I2, which accounted for more than 95% of the modelled deposition to grass. The original deposition model overestimated measured 129I inventories by approximately a factor of three. Introducing an effective post-deposition elimination term with half-lives of 7.7-8.5 days substantially improved the agreement between modelled and measured inventories. These results indicate that initial dry deposition alone is insufficient to describe 129I inventories in vegetation over long-term exposure periods and that post-deposition losses need to be considered when extending mechanistic I2 deposition models to environmental conditions.
36Cl is a naturally occurring radionuclide produced mainly in the atmosphere. In addition to its natural production, 36Cl has been introduced in significant quantities by humans into the environment because of nuclear bomb tests or nuclear accidents. Natural inputs, together with anthropogenic inputs, contribute to an ambient background activity of 36Cl in the environment. In addition to these inputs, other potential future inputs associated to civil nuclear activities (decommissioning of nuclear power plants, waste disposals) should be anticipated. A good understanding of sources of 36Cl in the environment, including an assessment of their variability, accumulation in soil, and fate in environmental media and at interfaces, is therefore necessary in the context of nuclear activities assessment. Considering this background, we propose here a review of knowledge relating to the sources, exchanges, accumulation, and fate of 36Cl in the environment. It addresses: (i) the identification and quantification of natural and anthropogenic sources and fallout of 36Cl in the environment, and the factors of spatial and temporal variability, including solar cycles and events, latitudinal geomagnetic effect, latitudinal differences in Stratosphere-Troposphere Exchange, distance from the sea, and local precipitation; (ii) the assessment of the exchange processes at the interface between atmosphere and soils, i.e. dry and wet deposition; (iii) the assessment of 36Cl accumulation, fate and speciation in soils and the factors of variability, in particular chlorination/dechlorination processes; (iv) the bioaccumulation processes of 36Cl in plants, i.e. root uptake, foliar absorption and translocation.
Microbial biofilms are increasingly recognised as chemically active interfaces that determine whether radionuclides remain dissolved, accumulate in sediments or enter secondary transport pathways. Their extracellular polymeric substances (EPS) supply diverse binding ligands, create steep microenvironmental gradients and retain redox-active cofactors, thereby coupling sorption to metabolic and mineral-mediated transformations. Yet these same properties complicate claims of durable immobilisation: adsorbed radionuclides may desorb, biomass-associated reduced species may be less persistent than crystalline minerals, and detachment can convert a local sink into a mobile carrier. This review critically examines the interaction of microbial biofilms with uranium, technetium, neptunium, plutonium, caesium, strontium and selected redox-sensitive co-contaminants in contaminated soils, groundwater and surface-water sediments. Particular attention is given to molecular EPS composition, coordination chemistry, extracellular electron transfer, U(IV) product identity, Fe–Mn–S coupling, phosphate mineralisation and redox reversal. Recent evidence from contaminated-aquifer biofilms, field bioaugmentation, flow-through reactors and molecular spectroscopy is assessed by distinguishing instantaneous removal, retained inventory, mineralogical persistence and cumulative contaminant export. A mechanistic risk framework is proposed in which long-term performance depends on the evolving relationship among biofilm physiology, aqueous ligands, oxidant fluxes, hydraulic connectivity and particle mobilisation. The central implication is that biofilm-enhanced sequestration should be judged by radionuclide mass balance and post-disturbance stability rather than by short-term decreases in dissolved concentration alone.
More than a decade after the 2011 Fukushima Daiichi Nuclear Power Plant accident, the internal redistribution of 137Cs within Japanese cedar (Cryptomeria japonica) wood remains an important unresolved question for timber safety and radiological forest management. This study provides the first post-2020, compartment-level, multi-height 137Cs dataset for Japanese cedar at the Yamakiya Experimental Forest (Kawamata Town, Fukushima Prefecture; ∼1000 – 3000 kBq m−2 deposition). In 2024, wood cores were extracted at tree-base (∼0.4 m), breast height (1.3 m), and upper-trunk (10 m) from three model trees using a 12-mm increment borer, divided into the three youngest sapwood annual rings (SW1-3) and consequent 5 annual rings samples of bulk sapwood (SW) and heartwood (HW), and measured for 137Cs activity by a high-purity Ge-detector. A water-leaching fractionation protocol (distilled water, 20:1 water-to-fresh-mass ratio, 24 h orbital shaking) was applied to each sample to resolve 137Cs into a leachable fraction and a residual matrix-bound fraction. The heartwood-to-sapwood (HW/SW) 137Cs concentration ratio averaged approximately 2.0 across the three trees by 2024 confirming continued heartwood enrichment beyond the system-level quasi-equilibrium reached around 2020. Vertical 137Cs distributions were broadly uniform across all three sampling heights, contrasting with the height-dependent gradients of the early post-accident period. The leachable fraction was dominant in both sapwood and heartwood, with total concentrations strongly correlated with leached (R2 = 0.4–0.9) but not matrix-bound concentrations, indicating that 137Cs in cedar wood is predominantly present in a hydrated, water-soluble ionic form. Proportion of the leached 137Cs activity averaged 0.57 ± 0.15 for sapwood and 0.51 ± 0.14 for heartwood. The study significantly contributes to understanding of 137Cs distribution and cycling in Japanese cedar.
