Dose projection using dispersion models

Byline: Borut Breznik, Marija Zlata Boznar, Primoz Mlakar, Gianni Tinarelli Dose projection is a tool for decision making in the case of a nuclear emergency situation. In this work the dose projection software developed for the Krsko NPP located in Slovenia is described. This software can be used for a quick emergency evaluation in the case of a hypothetical pressurised water reactor accident, and for emergency exercises. The software was developed to estimate reactor core damage, the status of fission product barriers, potential releases, atmospheric dispersion and finally the dose calculation. The intention was to use all the available automatic on-line measurements of the radiological monitors in the NPP, meteorological monitors in the surroundings and a modern atmospheric dispersion model capable of accurate calculations in the complex orography which is characteristic of the plant location. It is also important that the software is written in a user-friendly way, automated as highly as possible and executed on a widely used Windows platform for PCs. Details are given in the paragraphs Measurements and software modules and Air pollution dispersion calculation module. The program should provide a dose projection at an early stage of the accident (first hours) for distances of a few kilometres from the NPP. The results are available for a 25 km by 25 km area that includes the Krsko basin and some nearby hills and valleys. The results should support the decision of the emergency team in the NPP about evacuation or sheltering in the environment in the early phase of the accident. In the past the software used only a simple Gaussian air pollution dispersion model. Recently it was replaced with a numerical Lagrangean model called 'Spray'. Since the software was intended to be used for severe accident scenarios, it was also expected that the on-line meteorological and radiological parameters would not be completely available at all possible stages. For the case of missing radiological data, alternative possibilities were included, that require fewer or no measurements. The selection of this alternative is based on the operator's judgement according to the latest available data. Reduction of information certainly decreases the accuracy of the result. The final paragraphs explain the procedures for core status estimation, source term determination and dose projection.