Effects of Globally Waste-Disturbing Activities on Gas Generation, Retention, and Release in Hanford Waste Tanks

Abstract

Various operations are authorized in Hanford single-and double-shell tanks that disturb all or a large fraction of the waste. These globally waste-disturbing activities have the potential to release a large fraction of the retained flammable gas and to affect future gas generation, retention, and release behavior. This report presents analyses of the expected flammable gas release mechanisms and the potential release rates and volumes resulting from these activities. The background of the flammable gas safety issue at Hanford is summarized, as is the current understanding of gas generation, retention, and release phenomena. Considerations for gas monitoring and assessment of the potential for changes in tank classification and steady-state flammability are given. v Summary This report presents an assessment of the effects of globally waste-disturbing activities on flammable gas generation, retention, and release. The assessment includes the potential for hazardous flammable gas releases, considerations for determining the frequency of gas monitoring during the disturbance, and the potential for long-term changes in tank classification and gas generation rate resulting from the disturbance. Global waste disturbances are those that affect all or a large fraction of the waste in a tank. The disturbance may involve draining the supernate or interstitial liquid, dissolving solids, or mobilizing the settled sediment. Nine specific activities that occur or are approved in Hanford double-shell (DST) and single-shell (SST) waste tanks are considered in this report. While many of these operations could be performed in both SSTs and DSTs, all but one are considered specific to one type. The nine globally waste-disturbing activities are the following: Waste removal-pumping supernate or slurry out of a DST Waste addition-pumping liquid or slurry into a DST Saltwell pumping-removing interstitial liquid from SSTs Saltcake dissolution-adding water to dissolve soluble solids in an SST while pumping out the resulting brine Water addition-adding water to a DST or SST without concurrent brine removal Mixer pump operation-mobilizing sediment in DSTs by the hydraulic jet forces of a mixer pump Airlift circulator operation-mobilizing sediment by airlift pumping in several DSTs Chemical addition-adding sodium hydroxide or nitrite solution to DSTs to prevent corrosion Evaporation-gradually concentrating supernate in DSTs by evaporating water from the waste surface.

Estimate of the Distribution of Solids Within Mixed Hanford Double-Shell Tank AZ-101: Implications for AY-102

“…Aside from multi-instrument trees, etc., the internal tank structures with the most potential to impact UDS mobilization and suspension during mixer pump operation are the 22 airlift circulators (ALCs) that were intended to mix the waste by introducing a stream of air bubbles into 30-inch-diameter cylindrical tubes with a bottom elevation 30 inches above the tank bottom (Stewart et al 2005). Fifteen of the ALCs extend to 294 inches above the tank bottom, and the remainder to 234 inches.…”

Overview of Hanford Site High-Level Waste Tank Gas and Vapor Dynamics

“…GREs can be spontaneous, as when the inventory of trapped gases exceeds the capacity of the waste to trap it, or induced, as when waste-disturbing activities cause a portion of trapped gas to be released. The most significant GREs are those caused by rapid buoyant displacement of a portion of a bulk solids layer under a deep layer of supernate (Stewart et al 2003). Some episodic GREs in DSTs release enough gas to cause a detectable drop in the waste surface level.…”

“…Operational activities such as waste retrievals, supernatant and interstitial liquid pumping, core sampling, and water lancing are known to enhance gas and vapor releases. The mechanisms that affect releases can be broadly described as follows (Stewart et al 2003).…”

Review of the Technical Basis of the Hydrogen Control Limit for Operations in Hanford Tank Farms

“…(c) The 241-prefix for tank identifiers is not used in this report. Stewart et al (2002) have evaluated the gas release behavior of nine authorized global wastedisturbing activities in Hanford waste storage tanks: waste removal from DSTs, waste addition to DSTs, saltwell pumping from single-shell tanks (SSTs), saltcake dissolution in and pumping from SSTs, water addition to DSTs or SSTs, mixer pump operation in DSTs, airlift circulator operation in DSTs, chemical addition in DSTs, and evaporation of water from supernatant liquid in DSTs. Gas release mechanisms occurring in these activities that have been observed to cause significant releases are summarized here.…”