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

摘要

This paper presents a study to determine the uncertainty in the volume estimates of the HanfordSite single-shell and double-shell tanks. Through a detailed analysis of the standard method forestimating waste volume from surface level measurements, a number of systematic biases wereidentified as well as the five main sources of uncertainty. As a result of systematic biases, thecurrent volume estimates may overstate the total tank waste volume by as much as 460,000gallons. 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 ofvariance (ANOVA) models to estimate the main parameters of volume uncertainty for each of177 tanks. This paper also presents a new finite element-based approach, called the voxelmethod, that was developed to estimate Hanford tank waste volumes. The new methodaccurately reflects the different shape of each type of tank, eliminates the systematic biases, andaccounts for the sources of uncertainty. Using a Monte Carlo simulation model based on thevoxel 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 andanalyte concentration to derive overall inventory distributions for 73 analytes in 177 tanks.