ABSTRACT
Due to its long radioactive half-life, iodine-129 is considered to be an important radionuclide in the context of underground radioactive waste disposal safety assessment. Iodine speciates as iodide (I-) in reducing conditions and iodate (IO3-) in oxidizing conditions. As iodate is more reactive, it is much less mobile than iodide. Consequently, in considering vertically upward transport within a soil profile, iodine will tend to accumulate at the top of the capillary fringe. In this paper, a model of iodine transport across a capillary fringe is developed by coupling equations for variably saturated flow, oxygen dynamics and rate-limited sorption. Model parameters are obtained by consideration of literature values, calibration on soil column data and other supporting laboratory experiments. The results demonstrate the importance of rate kinetics on the migration and bioavailability of radioiodine in the near-surface environment.
Subject(s)
Environmental Monitoring/methods , Radiation Monitoring/methods , Soil Pollutants, Radioactive/analysis , Biological Transport , Calibration , Equipment Design , Hydrogen-Ion Concentration , Iodides/analysis , Iodine/chemistry , Iodine Radioisotopes/chemistry , Kinetics , Models, Theoretical , Oxidation-Reduction , Oxygen/chemistry , Water MovementsABSTRACT
This paper discusses whether flood hazard in the UK is increasing and considers issues of flood risk management. Urban development is known to increase fluvial flood frequency, hence design measures are routinely implemented to minimize the impact. Studies suggest that historical effects, while potentially large at small scale, are not significant for large river basins. Storm water flooding within the urban environment is an area where flood hazard is inadequately defined; new methods are needed to assess and manage flood risk. Development on flood plains has led to major capital expenditure on flood protection, but government is attempting to strengthen the planning role of the environmental regulator to prevent this. Rural land use management has intensified significantly over the past 30 years, leading to concerns that flood risk has increased, at least at local scale; the implications for catchment-scale flooding are unclear. New research is addressing this issue, and more broadly, the role of land management in reducing flood risk. Climate change impacts on flooding and current guidelines for UK practice are reviewed. Large uncertainties remain, not least for the occurrence of extreme precipitation, but precautionary guidance is in place. Finally, current levels of flood protection are discussed. Reassessment of flood hazard has led to targets for increased flood protection, but despite important developments to communicate flood risk to the public, much remains to be done to increase public awareness of flood hazard.
