RIMPUFF : : Users guide. Version 30 (PC version)

The mesoscale dispersion model RIMPUFF is a fast and operational computer code suitable for real-time simulation of hazards from radioactivity released to the atmosphere. The model (using output from the LINC2W program) applies to non-homogeneous terrain and moderate topography on a horizontal scale of 0 to 50 km, and responds to changing (in-stationary) meteorological conditions.

The Lagrangian puff-model simulates time-changing continuous releases by sequentially relasing a series of Gaussian shaped puffs at a fixed release rate on a specified grid. The amount of radioactive material allocated to individual puffs equals the release rate times the elapsed time between puff releases.

RIMPUFF is equipped with computer-time effective features for terrain and stability-dependent dispersion parameterization, plume rise formulas, inversionand ground-level reflection capabilities and wet/dry (source) depletion. In addition, the code optionally provides local relative diffusion parametrization and a scheme for horizontal/vertical shear diffusion.

It can treat plume bifurcation in complex terrain by using a puff-splitting scheme. When applied to orographically influenced dispersion scenarious, RIMPUFF can be interfaced with a flow-model, allowing the flow-model to compute the larger scale (e.g. beyond 500 m grid resolution) mean windfield. In diagnostic mode and for complex terrain with stationary meteorological conditions, radioactive exposure is well assessed via the release of a single initial puff.

With optimization, processing time for a +2 Hour forecast with RIMPUFF would be on the order of 2 CPU minutes or less on a 286 PC-system. (AB) 38 refs..