[en] TRIMOVE is a numerical model for simulating both soil moisture flow and tritium transport through a column of unsaturated soil. The model, written by Y. Belot, is intended to describe the one-dimensional vertical movement of tritium in the soil-atmosphere continuum. Implied in the choice of the simulation method is the prospect of potential uses ranging from management to research. The main purpose is to study the effects of boundary and initial conditions, soil characteristics, and weather inputs on the vertical movement of water and tritium within and from a soil column, including the exchange of tritium between the soil surface and the atmosphere. The model deals with bare or vegetated soils considered as isothermal and homogeneous over the whole extent of the soil column. The model describes the transient transport of both ordinary water and tritiated water by means of two sub-models working in parallel at space and time scales that can be changed according to the problem and / or the process to be treated. Most of the model has taken advantage of process models developed by others. (author)

[en] TRIMASS1, is a code written in Fortran 77, that was developed at CEA by Y. Belot and G. Guinois for assessment of tritium atmospheric dispersion during routine operations. This is a multi-source, sector-averaged model, that requires the user to define as input data the source(s), and terrain characteristics and the weather annual-averaged conditions. The model is applicable to flat terrains and to a certain extent to rolling terrains showing small elevational differences (author)

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[en] Most of the deposition data that are available to assess the radiological consequences of an accident have been acquired for low-growing vegetation and are inadapted to forest areas. Consequently, a programme was undertaken to study the deposition of particles on components of different trees and extrapolate the experimental data so obtained to large-scale canopies. The experiments were performed in a wind tunnel allowing canopy components to be exposed to a flow of suspended fluorescent particles of reasonably uniform size. Emphasis was put on particles in the 0.3-1.2 μm subrange, because most of the radioactive particles sampled at long distance from sources are comprised in this size interval. The uptake rates were determined for bare and leaf bearing twigs of several evergreen species (Picea abies, Pinus sylvestris and Quercus ilex), as a function of wind speed and particle size. The deposition rates obtained for the tree components were then used as input to a model that describes the uptake of particles by a large-scale canopy under specified conditions of weather and canopy structure. The model accounts for the diffusion of particles between different strata of the canopy, as well as deposition of particles on the canopy components. It calculates the rates of particle deposition to the horizontal surface of the canopy, and the repartition of the deposited particles within the canopy. Increases in wind speed cause increased deposition, but the effect is less important that it would have been for larger particles. The deposition is relatively insensitive to the size of particles within the subrange considered in this study. 13 refs., 2 figs., 1 tab

[en] Field experiments were performed in Brittany to assess the washout coefficient Λ for molecular iodine. During each run, a few grams of nonradioactive iodine were released from a 12 meters telescopic mast, and the rain was sampled at a short distance downwind along complete transversal sections of the plume. The amount of iodine in each sample was determined by ionic chromatography to calculate the washout coefficient. In most cases, the results obtained (a few 10^-5 s^-1) are not so different as expected from the theoretical values assuming a complete solubility of iodine in rain water. 4 refs., 1 fig., 1 tab

[en] The present work has the objective to propose an adaptation of the Gaussian model to produce reasonable estimates of radon air concentration above or in the vicinity of well-characterized ground level area-sources. The FLURAD-AREA model developed in the present-work is basically similar to many other sector-averaged models. It consists of replacing each area-source by a set of equivalent point-sources and summing up the contributions of these points. The formula used to determine the average atmospheric concentrations due to an elementary point source is derived from the Gaussian plume formula, assuming that each direction in a wind sector cantered on the source is equally probable over a long period of time. But the new model differs from the previous ones in the treatment of the plume advective speed. In former models, the wind speed that appears in the dispersion formula is held constant throughout the computation and assumed to be equal to some reference wind speed (measured at a reference height of 10 m for instance). This seems quite unrealistic in case of a ground level source, since the average advective speed of the pollutant is obviously very low at small distances from the source and much greater at larger distances, due to the vertical extension of the plume. In the new model, this is taken into account by considering that, for each point-source, the average advective speed of the emitted pollutant increases with distance from the source. The new model is believed to give more realistic results that the former ones) particularly at short distances from the sources where the wind speed effect is of great importance. (author)

[en] In the event of a release of molecular tritium to atmosphere, some tritium can oxidized at soil surface and be gradually re-emitted to atmosphere as HTO. The two processes are characterized by a deposition velocity and an emission rate, which are commonly used in deposition/emission models designed to calculate the concentrations of HTO in atmosphere. A technique has been developed to determine the emission rate and its evolution, by covering a small area of undisturbed soil by a field chamber, exposing the enclosed soil to molecular tritium, then determining the changes in HTO vapour content of a measured air-stream passing through the chamber. The emission rate is derived by dividing the amount of HTO extracted from the chamber during a given period of time, by the average amount of HTO contained in the soil during the same period. First experiments have been done on bare and grass-covered soils. The data obtained from these small-scale field experiments are consistent with those obtained from a full-scale field study carried out at nearly the same place

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[en] During the last three years, current programme attention was focused on the behaviour of transuranics at the water-sediment and water-atmosphere interfaces. The objectives of this research were: (i) to learn more of the potential pathways back to man; (ii) to provide an input to the numerical models for estimating doses from short-term or long-term releases. This paper is a report of some of the most significant results and conclusions from the activities of the past three years