NORWEGIAN-METEOROLOGICAL-INSTITUTE REAL-TIME DISPERSION MODEL SNAP (SEVERE NUCLEAR ACCIDENT PROGRAM) - RUNS FOR ETEX AND ATMES II EXPERIMENTS WITH DIFFERENT METEOROLOGICAL INPUT

The Norwegian Meteorological Institute (DNMI) has developed and implem ented for opera tional use a real-time dispersion model-Severe Nuclear Accident Program (SNAP)-with capability for predicting concentrations and depositions of the radioactive debris from large accidental relea ses. SNAP has been closely linked to DNMI's operational numerical weat her prediction (NWP) models. How good are these predictions? Participa tion in ETEX has partly answered this question. DNMI used SNAP-with LA M50S giving meteorological input for these real-time dispersion calcul ations. LAM50S-Limited Area Model with 50 km grid squares-was DNMI's o perational NWP model in 1994 when ETEX took place. In this article we report on how SNAP performed in the first of the ETEX releases-in near -real-time mode, using LAM50S-and in hindcast mode for ATMES II, using ''ECMWF 1995: ETEX Data set (ATMES II)''-as meteorological input data . These two input data sets came from NWP models with quite different characteristics-but with similar resolution in time and space. The res ults from these dispersion simulations matched closely. Deviations ear ly in the simulation period shrank to insignificant differences later on. Since both input data sets were based on ''weather analysis'' and had similar resolution in space and time, SNAP described the dispersio n of the released material very similar in these two simulations. (C) 1998 Elsevier Science Ltd. All rights reserved.