A re-evaluation of the 131I atmospheric releases from the Hanford site

The atmospheric release of I-131 from the Hanford site for the 1950's and 1960's, focused on the period of releases after the year 1950, has been re-evaluated using processing plant stack monitoring data to address a series of questions and concerns that have arisen related to the the source term. Historical stack monitoring data have been used to re-assess the releases by creating either a release factor to use with the calculated plant throughput or using the stack monitoring results as the basic estimate, and the results have been verified using historical atmospheric monitoring data from a location;several kilometers distant. Uncertainties in all of the historical data have been addressed in the re-assessment. Compared to the original estimate between 1950 and 1971 of 2.46 +/- 0.71 PBq, the stack monitoring results show a release of I-131 to the atmosphere of 1.55 +/- 0.23 PBq. The concurrent atmospheric monitoring results imply a release of 1.75 +/- 0.11 PBq over the same period, but this result is inflated by inclusion of global fallout. The total effective dose estimated to a full-time, nearby adult resident from I-131 using the Heeb source term from 1950 through 1972, is 0.73 mSv; using the source term based on stack monitoring data in the Hanford Environmental Dose Reconstruction project models, it is 0.51 mSv.