Selection of biosphere transfer parameter values for radioactive waste disposal impact assessments, a site specific approach

In order to perform radiological impact assessments of radioactive waste disposals, a compartmental model taking into account generic data for biosphere transfer parameters values is usually used. To improve its performance assessments calculations, Andra (French national radioactive waste management agency) decided to adapt this type of biosphere model to its sites conditions. On one hand, specific models have been developed such as model for 36Cl based on isotopic dilution and on local stable chlorine contents. On the other hand, biosphere transfer factors values are issued from experimental studies adapted to Andra context: soil characteristics, climate, agricultural habits and species. These specific data are useful only if main factors controlling mobility have been determined previously for each radionuclide, which implicates good knowledge of environmental radionuclides behaviour. This site-specific approach allows to reduce uncertainty and range of variation of impact calculations and ensure a consistent model. It helps also to achieve scientific community approval by showing mastery of radionuclides environmental processes and public understanding by focusing demonstration on real local conditions. The methodology is fully presented. Two examples for uranium and chlorine and the limits of this approach are given

Relative contributions of soil chemistry, plant physiology and rhizosphere induced changes in speciation on Ni accumulation in plant shoots

40 ref.International audienc

Phytoavailability of zirconium in relation to its initial added form and soil characteristics

International audienc

Effect of selenite additions on microbial activity and dynamics in three soils incubated under aerobic conditions

International audienc

Using stable elements and soil properties to access the fate of radionuclide in the soil-plant system

International audienc

Effect of sterilization and experimental conditions on the isotopic exchange of nickel in two contrasting soils

International audienc

Effect of aeration on mobility of selenium in columns of aggregated soil as influenced by straw amendment and tomato plant growth

International audienceSelenium is an essential nutrient that is potentially toxic: one of its radio-elements is also a component of long-lived radioactive waste for which long-term deep geological storage is envisaged. The chemistry of Se in soils is complex and very sensitive to redox potential and microbial activity which largely determine its oxidation state and chemical form. The dynamics of Se have been extensively studied in soils where it is deficient, and even more so when concentrations are potentially toxic. In contrast, relatively little information is available on the fate of Se in soils at intermediate concentrations (1–5 mg kg− 1). Some chemical reactions and biological processes that influence Se dynamics may be strongly concentration dependent. We have followed microbial activity by monitoring soil gas composition and Se volatilization and measured changes in Se fractionation using chemical extractions in a column of aggregated soil. A small proportion of soil Se was accumulated in the leaves, stems and fruits of tomato plants. Net Se volatilization losses were small (0.12% in a two-month period). There was a considerable upward movement of freshly added Se, but not of native soil Se. This vertical mobility was greater than that predicted from solute movement driven by evaporation. Selenium was strongly immobilized at the water-saturated, anoxic base of the soil columns. Straw amendment and the growth of a tomato plant did not lead to stronger association with soil organic matter. It was not possible to correlate changes in fractionation of Se between treatments and along a soil profile with the calculated fraction of anoxia, except in the completely anoxic zone

Transport and retention of aged anthropogenic iodine in a boreal peat bog

Iodine-129 is a radionuclide of major concern in the international safety assessments for deep geological storage and disposal of nuclear waste because it migrates quickly through the geosphere to the biosphere and then from the soil to humans through the food-chain. However, in organic soils the 129I may be immobilized over a long time period, and so these soils represent a potential accumulation point in the biosphere. Effects of long residence times of iodine in soils are scarce. The present paper gives some insight on the aging of stable iodine under natural conditions. Stable iodine was introduced as KI in 1987 at the base of a sphagnum bog to simulate arrival of iodine via a groundwater discharge from the geosphere. Fifteen years later, the groundwater, the soil and the vegetation have been sampled and analysed for iodine. The results we present give insight on the mobility of “aged" iodine, the retention properties of the peat, and provide iodine transfer factors for native boreal plant species. This study demonstrates bogs present good sinks for iodine and limit the transfer of iodine to some of the “wildlife" food-chains

Responses of anaerobic bacteria to soil amendment with selenite

Soil (Haplic Luvisol) was incubated in anaerobic microcosms with and without addition of a small amount of selenite (2 mg Se kg(-1)) and straw, and changes in both bacterial populations (fermentative and selenite-respiring) and selenium fractionation were assessed. Selenite caused an initial decrease in CO2 emission (-98% alone and -60% with straw) but this effect decreased with time. Selenite and straw additions enhanced the dynamics of fermentative and selenite-respiring bacteria but their effect was not cumulative. Selenium became less easily extractable during incubation: the non-extractable fraction of added selenium increased from 22% to 68% (73% with straw)