Technical Basis for Chemistry Control Program

This report documents the evaluations was undertaken to establish the sampling and analysis requirements, for the Double-Shell Tank (DST) waste based on a review of the chemical composition of the waste mechanisms for chemistry change, and operations and waste transfers in the tanks. A sampling schedule, for the DST waste has been established previously and is documented in the Technical sampling Basis-Waste Information Requirements Document (TSB-WIRD). However, the TSB-WIRD was based on programmatic drivers for the collection of waste samples rather than on the specific needs of a chemistry control program. The focus of this evaluation is to ensure that the sampling requirements of the TSB-WIRD meet the needs of the DST chemistry control program defined in Tank Farms Technical Safety Requirements (TSR) Administrative Control (AC) 5.15, and to provide adjustments, if necessary, to those sampling requirements to account for known mechanisms for changes in chemistry of the tanks. DST waste composition data for nitrite, nitrate, and hydroxide was compiled from sample data and best basis liquid composition data extracted from the Tank Waste Information Network System (TWINS) database. Operations in the tanks up to January 1, 2001, were reviewed. Three free hydroxide depletion models were used to predict the future tank liquid hydroxide concentration over the next five year period and trend historical sample results where possible. This data was used as the method to provide priority to the sampling requirements provided in the TSB-WIRD. The effort looked at identifying those tanks that could become caustic deficient prior to the next scheduled tank specific sampling event, and recommended appropriate actions for those tanks that may not comply with the waste chemistry limits defined in AC 5.15