High stack-level modeling

Because of extreme venting conditions assumed, effective stack heights and resultant plumes from both 3- and 5-minute discharge conditions attain heights beyond the micro-meteorological conditions assumed in accepted computation models. It is therefore highly probable there will be considerably further atmospheric dispersion and diffusion of the VCM than predicted in the results shown. That is, the ground level concentration can be expected to be considerably lower than the values shown in Table 6. 

Since the above-core calculations represented an infinite array of fuel channels, they did not include those parts of the pressure vessel in the vicinity of the hot gas duct penetration and therefore no account was taken in the above-core calculation of the neutrons wMch scatter around the top comer of the graphite stack and enter the hot gas duct penetration area. The neutron fluxes in the vicinity of the hot duct entrances were therefore takai to be equal to the fluxes calculated for the side shield model with a contribution added to account for the top-core leakage component. This component was scaled fi om the sub-core results and is considered to probably result in pessimistically high flux values for the hot gas duct pen ration since the neutron flux levels below the core are generally higher than those above. 

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