Kaiser Aluminum and Chemical Company
Thorium Remediation Project
May 2004 - June 2006
SRA is subcontracted by RECON (A&E prime to Kaiser) to provide the SMCM radiation monitoring system for use with RECON's material handling system. The SMCM system and an innovative dig face characterization measurement system deployed on an excavator were the subject of a poster by SRA at the 2004 Annual Health Physics Society Meeting in Washington, D.C. (link to SRA web site for HPS Poster for more info and photos). This work involves sorting of an estimated 240,000 tons of thorium bearing material with concentrations up to 200 pCi/g into onsite and offsite categories, and also ensuring that the offsite material meets the waste site waste acceptance criteria. All reporting including waste manifest forms are based on SMCM data. The comparisons of SMCM reported values by a verification contractor of onsite materials that have been placed were good. The major requirement to complete sorting 240,000 tons in less than a year was the capability of sorting soil at rates up to 300 tons per hour. This is critical to completion of the project at the lowest possible cost. This survey represented the second major deployment of the SMCM system based on a conveyor, and had more process functions automated (e.g. spectrometer controls such as gain). The system is operating at up to 250 tons per hour, and that rate is limited by the overall material handling process, not SMCM. SRA believes that this is a record production rate, with many previous systems operated at less than 5 tons per hour. Measurements are taken for each 63 Kg mass, and an average of one ton is used for reporting purposes, with diversion of quantities as small as 63 Kg that are out of specification. This technique avoids errors associated with sampling especially when the material is not well mixed. It also can significantly reduce the material shipped offsite for burial.
