Phenomenological uncertainties in the suspended radionuclide concentrations in containment during severe LWR accidents

CONTAIN, a code for integrated analysis of containment phenomenologies in complex LWR sever accident sequences, is being applied in a program for evaluating the uncertainties in USNRC-sponsored efforts to better define LWR accident source terms. The Surry TMLB sequence is studied in detail. Aerosol agglomeration uncertainties are found to contribute about an order of magnitude to the overall uncertainty in suspended radionuclides (almost entirely downward uncertainty; i.e., downward with respect to current base case estimates such as BMI-2104). Containment compartmentalization effects contribute substantial uncertainties in either direction, while effects due to complex multicomponent aerosol compositions contribute lesser, but still potentially significant uncertainties (mostly downward). Incomplete treatment of radionuclide decay chains can contribute factor-of-two upward uncertainties