PC-CREAM 08®; is a complex model that is divided into several parts for ease of use. The main division of the program is into 'Models' and 'ASSESSOR'.
The Models part includes a series of mathematical models that predict the transfer of radionuclides through the environment and provide estimates of activity concentrations in various environmental media following a continuous release. The output of these models is then used as input to the dose assessment part of the program ASSESSOR.
An overview of each of the models included within PC-CREAM 08®; and the dose assessment part of the program is given in the following sections. Further details of the models and data are given in the accompanying methodology report (Smith, 2009).
PLUME is the atmospheric dispersion model used within PC-CREAM 08®;. It is a Gaussian plume model (Clarke, 1979; Smith, 2009) which takes into account the meteorological conditions during the release, the roughness of the land surface and the physical characteristics of the radionuclides being released.
The model calculates activity concentrations in air, deposition rates and external gamma dose rates from radionuclides in the cloud (cloud gamma) at various distances downwind of the release point. The output from the model can be used as input to ASSESSOR which combines these results with site specific meteorological data and actual release rates to calculate actual activity concentrations in air, deposition rates and cloud gamma dose rates downwind of the release point.
The deposition rates from PLUME are used to scale the results from the other models, namely RESUS, GRANIS and FARMLAND, to estimate doses from various exposure routes arising from the discharge of radionuclides to the atmosphere.
RESUS can be used to estimate activity concentrations in air arising from the resuspension of previously deposited radionuclides. It uses a formula derived by Garland (Smith, 2009) which is independent of the radionuclide considered with the exception that differences in radioactive decay are taken into account.
The activity concentrations, which are calculated for a unit deposition rate, are input to ASSESSOR which scales them by the actual deposition rate at various locations downwind of the discharge point and combines them with habit data to calculate doses from inhalation of resuspended material.
External exposure to gamma radiation from radionuclides deposited on the ground is calculated using the GRANIS model (Smith, 2009). GRANIS models the transfer of radionuclides through the soil and takes into account the shielding properties of the soil when estimating doses one metre above the soil surface.
The doses are calculated based on a unit deposition rate. The GRANIS model includes some organ doses as well as effective dose. Effective doses are input to ASSESSOR which scales them by the actual deposition rate at various locations downwind of the discharge point and combines them with habit data to estimate actual exposures.
FARMLAND (Smith, 2009) is a suite of models that can be used to predict the transfer of radionuclides into terrestrial foods following deposition onto the ground. The food categories considered are those that are most important in the human diet, namely, green vegetables, root vegetables, fruit, grain, cow milk, cow milk products, cow meat, cow liver, sheep meat, and sheep liver.
Activity concentrations in each food are calculated for a unit deposition rate. These activity concentrations are input to ASSESSOR which scales them by the actual deposition rate at various locations downwind of the discharge point and combines them with habit data to calculate ingestion doses.
The marine dispersion model used in PC-CREAM 08®; is based closely on the MARINA II model (Smith, 2009; EC, 2003). The model can be used to predict the activity concentrations in sea water, sediments and marine biota for user-defined discharge rates.
These activity concentrations are input to ASSESSOR which scales them by the actual discharge rate and combines them with habit data to calculate doses from ingestion of marine foods, external exposure to beach sediments and inhalation of sea spra
PC-CREAM 08®; includes two models for calculating the dispersion of radionuclides released to rivers (Smith, 2009). The 'Screening' model is a simple dilution model which assumes instantaneous equilibrium between the water and river sediments and should be used as a screening tool. It can be used in three modes depending on the amount of input data available.
For more detailed assessments the Dynamic model can be used. This is a time dependent compartment model and requires a greater amount of input data to run.
Clarke RH (1979). The first report of a Working Group on Atmospheric Dispersion: A model for short and medium range dispersion of radionuclides released to the atmosphere. Chilton, NRPB-R91.
EC (2003). MARINA II. Update of the MARINA project on the radiological exposure of the European Community from radioactivity in North European marine waters. Radiation Protection 132. EC, Luxembourg.
Smith JG and Simmonds JR (Editors) (2009) The methodology for assessing the radiological consequences of routine releases of radionuclides to the environment used in PC-CREAM 08®;.