AN ASSESSMENT OF THE UNCERTAINTY IN THE WASTE VOLUME OF THE HANFORD SITE SINGLE-SHELL AND DOUBLE-SHELL TANKS By:

This paper presents a study to determine the uncertainty in the volume estimates of the Hanford Site single-shell and double-shell tanks. Through a detailed analysis of the standard method for estimating waste volume from surface level measurements, a number of systematic biases were identified as well as the five main sources of uncertainty. As a result of systematic biases, the current volume estimates may overstate the total tank waste volume by as much as 460,000 gallons. The surface level measurements for all 177 tanks were analyzed between January 1, 1990 and January 7, 1999. The surface level data was investigated using several analysis of variance (ANOVA) models to estimate the main parameters of volume uncertainty for each of 177 tanks. This paper also presents a new finite element-based approach, called the voxel method, that was developed to estimate Hanford tank waste volumes. The new method accurately reflects the different shape of each type of tank, eliminates the systematic biases, and accounts for the sources of uncertainty. Using a Monte Carlo simulation model based on the voxel approach, this study generated a volume probability distribution for each of the 177 tanks. The volume distributions were combined with probability distributions of waste density an