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Title: Modelling the Dispersion of Radionuclides Following Short Duration Releases to Rivers
Author: J T Smith
Author: M Bowes
Author: F H Denison
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1096, Representation ID: 346, Object ID: 2365
This project develops a model for assessing short duration liquid discharges of radionuclides to rivers. The assessment of doses arising from discharges to rivers is normally carried out by considering annual average discharge rates. Actual authorised discharges, however, may occur unevenly during the year or relatively high short-term discharges could occur in the unlikely event of an incident. Short term radionuclide releases could potentially result in temporary increases in radionuclide activity concentrations in water and fish which are greater than those resulting from a continuous discharge. The purpose of this project is to develop a model to assess short term releases from these sites, and where possible develop generic methods of assessing short term releases. An advection-dispersion model was developed to predict the concentrations of radionuclides in the river environment, ie in river water, river bed sediment and in predatory fish. Uptake of radionuclides to fish was modelled by estimating rates of uptake of radionuclides via the aquatic food chain or across the gill, as appropriate. The model was used to predict the concentrations of the radionuclides in the river Thames and its tributaries as a result of short duration discharges into stretches of the Thames and River Colne. Model output is given as a series of graphs of activity concentration and time integrated activity concentration resulting from a 1 MBq discharge for the following release durations: 5 minutes, 1 h, 3 h, 12 h and 24 h. The five locations for which predictions are given were 100 m, 300 m, 1000 m, 3000 m and 10000 m downstream. - The river volumetric flow rate was shown to be the most important environmental variable determining activity concentrations in water, fish and sediments following a release. - The duration of release significantly influences peak radioactivity concentrations in water. Duration of release does not influence the maximum activity concentrations in fish and sediments, nor does it influence the estimates of time integrated activity concentrations in water, fish and sediments. - The fraction of radioactivity sorbed to suspended particulates can significantly affect radioactivity concentrations in water (dissolved phase), fish, and bed sediments. - The water temperature significantly influences the maximum activity concentration in fish, because fish feeding rates are much lower at lower water temperatures.
Publisher: Environment Agency
Subject Keywords: RiversRadioactivityWater pollutionRadioactive contaminationSediment pollutionFreshwater fishesWater temperatureModellingFreshwater ecology
Extent: 124
Total file downloads: 20

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