Validation of the cloud radiation calculation in the scope of the nuclear power plant monitoring system in Baden-Wuerttemberg

Within the dispersion model (ABR) used in the scope of the nuclear power plant monitoring system of Baden-Wuerttemberg (KFUe) the calculation of the cloud radiation is based on the method of adjoint fluxes taking into account 30 energy groups of the gamma energy spectrum. This allows an efficient calculation of the cloud radiation during normal and emergency operating conditions. To validate this model comparison calculations have been performed using the Monte Carlo code MCNP. The approach for the MCNP calculation can be described as follows. Starting from an emission point photons for each of the 30 energy groups have been emitted in an isotropic manner taking into account the scattering processes in the air and on the ground until the photons reach the detector. By means of the detector the flux density spectrum can be calculated and from there on the dose can be obtained using a dose/flux relation.