Current Work Programme

Chlorine-36 Accumulation in Soil and Crop Uptake

The current project on chlorine-36 extends the work previously undertaken on the behaviour of Cl-36 in soils and uptake into plants [Limer et al, 2008] to include dose assessment and takes into account not only root uptake but also contamination of crops by direct interception of irrigation water. This is so that the relative significance of direct deposition and root uptake can be understood. Special consideration has been given to the assessment of uncertainties, with a clear separation of the contribution to uncertainties arising from:

  • the assessment of Cl-36 concentrations in crops,
  • the assumptions for the potential exposure groups or representative persons, and
  • the dose per unit intake.

This work programme has now been completed and the report is available to download.

Review of models for Carbon 14 Dose Assessment

Interest in improved dose assessment methods for long-term releases of C-14 to the biosphere gave rise to a model review within the BIOPROTA programme [BIOPROTA, 2005]. This qualitative review of models concluded that the major difficulty surrounding the conceptual model for C-14 concerns identifying the conditions under which mixing and isotopic equilibrium may reasonably be assumed. Such system understanding needs to take account of the temporal and spatial scale of the assessment, including the nature of the release from the geosphere. A key issue is the decision as to whether kinetic models are useful and/or necessary, compared with an equilibrium approach. It was also argued that more data are needed for gaseous exchange from surface waters and soils to the atmosphere and how this affects the specific activity in the water and soil compartments, as well as uptake into plants.

The overall objective of the current project is to improve confidence in dose assessments for long-term releases into the biosphere of C-14 disposed in radioactive waste repositories, focussing upon the soil and plant components of the biosphere. This project compares quantitative estimates of soil, plant and canopy atmosphere C-14 concentrations arising from a scenario with unit C-14 activity in groundwater that is used to irrigate the crops.

The comparison of results for the different models, including uncertainty estimates, will be used to indentify:

  • the implications of adopting different modelling approaches,
  • the relevant processes, and
  • the site specific information necessary for applying different models.

This work programme has now been completed and the report is available to download.

Environmental Behaviour of Se-79

An international workshop on the environmental behaviour of Se-79, a radionuclide of importance for intermediate and low-level waste, took place in May 2008, hosted by Nagra, Switzerland. As a result of this workshop, a work programme was established. The current work programme aims to develop a better understanding of the processes affecting Se-79 accumulation in soils and uptake into plants. The work programme includes:

  • A review of the current knowledge (and new research) on Se-79 behaviour in the soil-plant system; Consideration of the Features, Events and Processes (FEPs) of potential relevance to the assessment of doses to hypothetical critical groups arising in the long term due to releases to the terrestrial biosphere from a repository for radioactive waste disposal;
  • Development of an interaction matrix which shows how the FEPs can be combined to create a conceptual assessment model. The intention is to provide a transparent and traceable record of how information has been included, or indeed, excluded, with recorded justification, from the assessment model; and,
  • Identification of data which need to be determined site specifically, as opposed to reliance upon site generic sources.

It is intended that the output be used as the basis for the development of improved assessment models or to provide a better basis for selection of parameters for existing models.

This work programme has now been completed and the report is available to download.

Non-human biota dose assessment: Sensitivity analysis and knowledge quality assessment

The focus of this project is on those aspects of biota dose assessment that are specific to the consideration of potential impacts of long-term releases from geological waste repositories. The aim is to evaluate the robustness of (generic) biota dose assessment data in relation to the key long-lived radionuclides applicable to deep geological disposal facilities and to identify important data gaps and uncertainties. A sensitivity analysis will be performed and knowledge quality assessment undertaken. It is intended that the project will help identify where further modelling or experimental work is required in order to reduce assessment uncertainties. The project is due to complete in December 2009.

Site Characterisation

The links between site characterisation and the biosphere component of the assessment, including guidance on protocols for obtaining data, have been considered in the Theme 3: Site Characterisation, Experiments and Monitoring report. Experience with characterisation at particular sites is now being gathered from those who have done the work, in terms of recognition of difficult areas as well as successes. It is hoped that this can be useful to others. The next step being considered is to share information on how the obtained data is presented and interpreted, for the purpose of demonstrating an understanding of the site, and for use in developing scenarios for possible site evolution, and for evaluation of these scenarios via conceptual and mathematical models for site behaviour. These models can then be used to justify assumptions for assessment models which address radionuclide migration and accumulation in the biosphere and radiation exposure of humans and other biota. The site characterisation work may also directly supply data for input to existing models for assessing particular scenarios. Following the flow of information and the management of data in the entire process is all part of the challenge, especially if it can be intelligently linked to characterisation for operational phase environmental impact assessments. The experience gained and shared is intended to help make continued site investigation work as effective and efficient as possible. For further information, please contact: lara.duro[at]amphos21.com, jorge.molinero[at]amphos21.com or gmsabingdon[at]btinternet.com

In situ Study of the Long Term Sorption of Iodine onto Organic Matter

Iodine is generally present in environments as an anion (either iodide or iodate) and is therefore soluble in groundwater and migrates relatively quickly through rock and overburden to low-lying landscape positions such as wetlands where it can be retained by the organic matter of soils (iodine can only be retained in its oxidised form. This reaction with phenols, for example, is well known for I2 or I3-; the question is what controls the oxidation. Organic matter and bacterial activity seem to play an important role). Peat bogs are often located at low-lying landscape positions and are very rich in organic matter and therefore iodine is likely to "accumulate" in peat bogs.

An 18 month experimental study has been initiated, which aims to increase understanding of the mechanisms that govern the mobility and transport of iodine in peat bogs, and to acquire values for assessment models such as soil Kd and plant CR (concentration ratio). The study will focus on:

  • the biogeochemical cycle of iodine in the peat bog including:
    • the transfer of iodine along the carbon cycle in the peat bog (plant uptake, speciation of iodine in the plant, consequences of the biodegradation of the plant material on the availability of iodine in the peat); and, - the role of the redox potential on the migration and the speciation of iodine in the peat bog.
  • the retention of iodine onto the peat; and
  • the relation between the chemistry of organic matter and the retention of iodine.

Such an understanding of the mechanisms that govern the fate of iodine in peat bogs will form the basis for a better model of the transfers of this element in these types of ecosystems.

BIOPROTA database

A web-based version of the BIOPROTA database is currently under development. The intention is to make available the information gathered under previous database projects in a web-access system to which sponsors may add additional data in individual project folders. Further information on the BIOPROTA database is available here.