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The HARP system is the application part of a grant project No. 102/07/1596 supported by the Grant Agency of the Czech Republic (period 2007 - 2009), which was solved in the Institute of Information Theory and Automation of the ASCR. The innovated version of the product is a complex software tool for purposes of modelling radiological consequences of radionuclide releases due to the normal and emergency operation of a nuclear facility. Aerial transport of discharged radionuclides is studied up to the 100km from a source of pollution. Dispersion, deposition and successive radioactivity migration towards the human body is simultaneously modelled. As the system contains a database of demographical data on the area of interest, it can evaluate the major radiological quantities and a radiological burden of population due to different pathways of irradiation in both the early and the late phases of a radiation accident.

The core of the system is an atmospheric dispersion model. Generally, the modular architecture of the system enables for insertion of an arbitrary dispersion model. The default is segmented Gaussian plume model. Even simple, the Gaussian model is consistent with the random nature of atmospheric turbulence and it is an approximative solution of the Fickian diffusion equation. Proved semi-empirical formulas are available for approximation of important effects like interaction of the plume with near-standing buildings, momentum and buoyant plume rise during release, power-law formula for estimation of wind speed changes with height, depletion of the plume activity due to the removal processes of dry and wet depositions, radioactive decay and creation of daughter products, dependency on physical-chemical forms of admixtures and land-use characteristics, plume lofting above inversion layer, etc.

A special emphasis is laid on the proper treatment of types of input parameters fluctuations in sense of differentiation between variability and uncertainty. Some model uncertainties arising from the conceptual limitations can be roughly estimated on the basis of ensemble-based approach with alternative parametrization of physical effects taking place in the atmospheric dispersion. The system offers extensive interactive graphical user interface for presentation of wide range of outputs important for decision makers. Thus, the system also comprises a simulation and training tool enabling responsible staff to improve their knowledge and perception of the problem details. The HARP code has proved useful in the fields of evaluation of environmental impact assessment (EIA) and probability safety assessment (PSA) studies, where the influence of operation of a nuclear facility on the surrounding environment is appraised.

Advanced data assimilation methods based on Bayesian filtering developed within the grant project are incorporated into the assimilation subsystem. It means, that the system offers a framework for embodiment of relevant information from different sources, such as measurements and expert judgements, in a statistically optimal way. Provided that the system is connected to a monitoring network, it can be run in the on-line regime, where the subjectively chosen parameters regarding the release scenario (magnitude of release etc.) are iteratively re-estimated upon measurements. This assimilation methodology can be also used as a tool for testing of different topologies of a monitoring network and selection of the best one with regards to its functionality and economical and other constraints.

The HARP system is tuned and tested in cooperation with National Radiation Protection Institute of the Czech Republic in Prague, where the product is connected to a database server providing up to date short term meteorological forecasts on a three dimensional grid.