<title>Uncertainty estimation of Hanford tank chemical and radionuclide inventories and concentrations</title>

Abstract

The exact physical and chemical nature of 55 million gallons of radioactive toxic waste held in 177 underground waste tanks at the Hanford Site is not known with sufficient detail to support the safety, retrieval, and immobilization missions presented to Hanford. The purpose of this study is to estimate probability distributions for the inventory of each of 72 analytes in each of 177 tanks. This will enable uncertainty intervals to be calculated for inventories and should facilitate the safety, retrieval, and immobilization missions.The methodology presented in this paper is based on scientific principles, sound technical knowledge of the realities associated with the Hanford waste tanks, chemical analysis of samples from the tanks, historical data and other Hanford research. As a result of the processing histories, waste storage practices and historical records, some of the waste can be partitioned into more homogeneous subsets that can be identified to tanks and locations within tanks. Therefore, by using this we can maximize the information extracted from the relatively few samples we have for each tank, combining sample data information from similar tanks to generate a sample based estimate of the chemical and radionuclide concentrations of each of the many waste subsets. Then by multiplying the concentrations for a specific analyte (micrograms of the analyte per gram of waste, or microCuries of the analyte per gram of waste) by the density (grams per liter) by the volume in a tank (liters), we can get an estimate of the mass of a particular analyte (or radionuclide contribution) in each tank. This methodology does this in a probabilistic framework; thus using and generating probability distributions instead of single point estimate numbers.

Statistical Methods for Estimating the Uncertainty in the Best Basis Inventories

“…Uncertainty estimates were previously determined for all of the Best-Basis tank inventories (Ferryman et al 1998 Best-Basis inventory estimates are sample-based, engineering-based, or model-based. Although uncertainty estimates were previously determined for sample-, engineering-, and model-based data, it was determined that sufficient information would be provided and resources better utilized by updating only sample-based uncertainty estimates for the current effort.…”