This report is Revision 2 of PNNL-14271. Revision 1 expanded the analysis of interstitial liquid drainage-induced gas releases to address a general retrieval scenario (the previous version of this report assumed a center-out retrieval approach and conditions). Tank waste conditions (waste volumes, interstitial liquid levels, temperatures, retained gas void fractions, etc.) were also updated in Revision 1. Revision 2 extends the analysis to address water addition rates of 110 gpm and brine pump-out rates of 110 gpm.

It is possible to retrieve a large fraction of soluble waste from the Hanford single-shell waste tanks (SSTs) by dissolving it with water. This retrieval method will be demonstrated in Tanks U-107 and S-112 in the next few years. If saltcake dissolution proves practical and effective, many of the saltcake SSTs may be retrieved by this method. Many of the SSTs retain flammable gas that will be released into the tank headspace as the waste dissolves. This report describes the physical processes that control dissolution and gas release. Calculation results are shown and describe how the headspace hydrogen concentration evolves during dissolution. The observed spontaneous and induced gas releases from SSTs are summarized, and the dissolution of the crust layer in SY-101 is discussed as a recent example of full-scale dissolution of saltcake containing a large volume of retained gas. The report concludes that the dissolution rate is self-limiting and that gas release rates are relatively low.

It is possible to retrieve a large fraction of soluble waste from the Hanford single-shell waste tanks (SST) by dissolving it with water. This retrieval method will be demonstrated in U-107 and S-112 in the next few years. If saltcake dissolution proves practical and effective, many of the saltcake SSTs may be retrieved by this method. Many of the SSTs retain a large volume of flammable gas that will be released into the tank headspace as the waste dissolves. This report describes the physical processes that control dissolution and gas release. Calculation results are shown describing the headspace hydrogen concentration transient during dissolution. The observed spontaneous and induced gas releases from SSTs is summarized and the dissolution of the crust layer in SY-101 is discussed as a recent example of full-scale dissolution of saltcake containing a very large volume of retained gas. The report concludes that the dissolution rate is self limiting and gas release rates are relatively low.

The Hanford Federal Facility Agreement and Consent Order (Tri-Party Agreement) (Ecology et al. 1994), requires the retrieval of 99 percent of the Hanford Site single-shell tank (SST) waste. Retrieval of the waste requires the completion of saltwell pumping and then the sluicing of all 149 tanks, at a cost of over $3 billion. The retrieved waste is to be processed and vitrified for ultimate disposal as glass. This document shows that the intent of the Tri-Party Agreement can be met by sluicing the waste from only 86 tanks, after the completion of saltwell pumping. This partial retrieval option will result in a cost savings of over $600 million in construction and operation alone, and will significantly reduce the volume of glass requiring disposal.