A Method for Calculating Doses to the Population from 133Xe Releases During the Three Mile Island Accident

Abstract

On 28 March 1979, a series of events occurred at Three Mile Island, Unit 2, which subsequently resulted in the release of noble gases into the atmosphere. The primary source of these gases was the Makeup and Purification System which carries primary system water into the auxiliary building. Degassing of this water, in concert with leakage out of the waste gas handling system, allowed radioactive gas to enter and pass through the building air filters to the atmosphere. The resulting offsite radiation levels at several locations were much greater than those due to routine operation.Doses received by the population were mainly due to '33Xe. The health and safety consequences of these releases were analyzed and found to be minimal in an Ad Hoc Interagency Report published by NRC, HEW and EPA in May 1979. In that report, the dose to the general population is estimated by two different methods, both of which rely on offsite TLD measurements. This article describes in detail one of the calculational methods that was used in the report. This method utilizes the topological time-averaged meteorological dispersion factors derived from meteorological data obtained during the accident as well as TLD data from the site environs.The dose to the population residing within 50 miles of the accident was estimated to be about 3400 person-rem by this method.