A Monte Carlo program to calculate the exposure rate from airborne radioactive gases inside a nuclear reactor containment building

A program was developed to calculate the exposure rate resulting from airborne gases inside a reactor containment building. The calculations were performed for the location of a wall-mounted area radiation monitor. The program uses Monte Carlo techniques and accounts for both the direct and scattered components of the radiation field at the detector. The scattered component was found to contribute about 30% of the total exposure rate at 50 keV and dropped to about 7% at 2,000 keV.; The results of the calculations were normalized to unit activity per unit volume or air in the containment building. This allows the exposure rate readings of the area monitor to be used to estimate the airborne activity in the containment building in the early phases of an accident. Such estimates, coupled with containment leak age rates, determine the estimated release rate for use in offsite dose projection calculations.