From 1988 to 1993, the Nuclear Safety and Protection Institute (Institut de Protection et de Sûreté Nucléaire--IPSN) conducted experimental programs focused on transfers to vegetation following accidental localized deposits of radioactive aerosols. In relation to vegetable crops (fruit, leaves, and root vegetables) and meadow grass these experiments have enabled a determination of the factors involved in the transfer of cesium, strontium, and ruthenium at successive harvests, or cuttings, in respect of various time lags after contamination. The dynamic modeling given by these results allows an evaluation of changes in the mass activity of vegetables and grass during the months following deposit. It constitutes part of the ASTRAL post-accident radioecology model.
It was apparent that the cesium migrates horizontally in greater proportions than the strontium that pooly fixes on the particles and infiltrates into the first centimeter of the soil. One parameter to take into account would appear to be the initial humidity of the soil. The sedimentary crust favours the exportation of cesium and strontium by preventing its infiltration, while at the same time trapping part of the contamination on its immobile particles. In the case of wet discharge, the contamination of cesium tends to disperse. It is now necessary to extend the domain of study of our factors for completing results. Dry periods in structural history and organic contents appeared to be most important.
RÉSUMÉUn accident sur un réacteur nucléaire avec dépôt de radionucléides sur des surfaces urbaines pourrait présenter un danger d'irradiation externe pour les populations.Aiïn d'appréhender ce risque, et compte tenu du peu de données disponibles dans la littérature, il nous est apparu opportun de tester en laboratoire l'efficacité de techniques de décontamination sur des surfaces urbaines judicieusement choisies avant d'envisager une étude de faisabilité à plus grande échelle. L'originalité de ce travail a consisté à évaluer, par le biais d'expérimentations en milieu contrôlé, l'efficacité d'une pluie et de lavages avec des solutions agressives sur des tuiles en argiie et du béton contaminés avec des aérosols de césium et de strontium. L'eau de pluie s'est révélée peu efficace pour éliminer les radionucléides, son action est d'autant plus faible que l'intensité de la pluie est élevée. Une plus grande efficacité a été obtenue après 2 h 30 de lavage avec la solution NH,CI (0,l mol 1") appliquée directement après la contamination. L'activité résiduelle est alors de 90 % sur les tuiles et de 40 % sur le béton. Les résultats obtenus sont moyens pour le béton mais peu satisfaisants pour les tuiles et confirment, dans des conditions de dépôt accidentel, la dficulté de déplacer une telle contamination.ABSTRACT Washing processes impact on the deconîamination of tiles and concrete contaminate by radioactive cesium and strontium.An accident on a nuclear reactor with a radionuclide deposition on urban surfaces could present a danger of external of irradiation for the populace. In order to evaluate this risk, and taking into account the few available data in the literature, it appeared essential to us to test in the laboratory the efficacy of decontamination techniques on judiciously selected urban surfaces before considering a feasihility study on a large scale. The originality of this work consisted in evaluating hy the means of experiments in controlled environment the decontaminating efficiency of a rain event and washings with agressive solutions on Clay tiles and concrete contaminated with strontium and cesium aerosols. The rainwater proved not to be very to be effective in eliminating the radionuclides, the weaker its effect the higher its intensiîy. A greater efficiency was obtained after 2h30 of washing with the NH,CI 0,l mol 1-' solution applied directly after the Contamination. The residual activity then amounts to 90% on the tiles and 40% on the concrete. The results obtained are average for the concrete but not very satisfactory for the tiies and confirm, under conditions of accidental deposit, the difficulty in moving such a contamination.
In this article two methods are exposed -with its practica1 application in the school-in order to discover whether the golden crown of King Hieron 111 from Siracusa (111 c. bC) was totally made of gold or, on the contrary, the goldsmith who had made it, changed by silver part of the gold given by rhe King.
The decrease of radioactivity for 134 Cs, ^Sr, 106 Ru, 57 Co, UOm^g during food processing was measured. Washing and bleaching vegetables directly contaminated by a single aerosol deposit led to a radioactivity decrease (depending on the vegetable, the radionuclide and the time of deposition) up to 90% for caesium. The efficiency of these processes was less important when the vegetables were contaminated by root transfer, except for peeling of root vegetables. Canning of vegetables undirectly contamined by caesium, strontium, cobalt and ruthenium, after paring and bleaching, was rather interesting with residual radioactivity varying from 30 to 50% for green beans and from 5 to 20% for carrots. Measurements of stable caesium and strontium in cereals before and after industrial processing showed an important activity decrease; retention factors varied from 0.1 to 0.2 for wheat milling and 0.1 to 0.4 for rice processing.
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