Radiochemistry laboratory waste management

As part of the Oak Ridge Dose Reconstruction, a detailed assessment of 131I releases from radioactive lanthanum (RaLa) processing is being conducted. From 1944 through 1956, fuel slugs from Oak Ridge (X-10) and Hanford reactors were dissolved and processed at Oak Ridge to separate 140La for Los Alamos weapons development. Fuel cooling times were as short as several hours, and dissolver off-gas passed through a caustic scrubber. In an earlier feasibility study, simple screening analyses identified RaLa processing as one of the largest potential contributors to off-site risk from the three Oak Ridge plants, with releases over 3.7 PBq (100,000 Ci) considered likely. With the close proximity of surrounding populations and potential 1311 releases comparable to those established in the Hanford dose reconstruction, a detailed investigation was initiated. Inventories of 131I and 140Ba in X-10 slugs were calculated using the ORIGEN 2.1 code, detailed slug exposure records, and neutron flux distributions determined in the X-10 reactor in 1945. Informal expert elicitation was used to estimate a 131I release fraction for use in the initial iteration of the assessment. For later iterations, a simple numerical model of iodine distribution in RaLa chemical processing was prepared to predict releases from the dissolver and waste neutralizer tank based on five mass-balance equations. The critical caustic scrubber was then modeled with a kinetic-based model of iodine mass transfer. Separate analyses of release fractions are necessary for a number of off-normal conditions and accidents. The models were integrated for estimation of time histories of 131I release, interfacing with calculations of environmental transport, off-site exposure, and ranges of historical doses and health risks in a manner that reflects the uncertainty of all components