SummaryThis report describes the equipment, techniques, and results of lateral earth pressure at rest and shear modulus measurements on kaolin clay as well as two chemical sludge simulants. The testing was performed in support of the problem of hydrogen gas retention and release encountered in the doubleshell tanks (DSTs) at the Hanford Site near Richland, Washington. Wastes from single-shell tanks (SSTs) are being transferred to double-shell tanks (DSTs) for safety reasons (some SSTs are leaking or are in danger of leaking), but the available DST space is limited.The current System Plan for the Hanford Tank Farms (Rev. 4, Certa and Wells 2009) uses relaxed buoyant displacement gas release event (BDGRE) controls for deep sludge (i.e., high-level waste [HLW]) tanks, which allows the tank farms to use more storage space in some of the DSTs. The relaxed BDGRE controls are based on preliminary analysis of a gas release model from van Kessel and van Kesteren (2002). Applying the van Kessel and van Kesteren model requires parametric information for the sediment, including the lateral earth pressure at rest and shear modulus.A device to concurrently measure the lateral earth pressure at rest (k 0 ) and shear modulus (G max ), the "k 0 consolidometer," was designed and produced. Independent measurements taken with reproductions of this device using kaolin clay slurries over a shear-strength range similar to that of Hanford sludge are shown to be in agreement with the literature. No measurements of the lateral earth pressure at rest and shear modulus are currently available for actual Hanford sludge. Thus, it is not possible to establish that the lateral earth pressure at rest and shear modulus measured on the chemical simulants and the relationship to shear strength described by these iv measurements represent these parameters for actual Hanford sludge. Further, although the simulants are unique with respect to each other, they do not represent the possible range of actual Hanford sludge.Recommendations are made addressing the enhancement and expansion of the simulant data set, the analysis of existing and future actual Hanford waste characterization data for insight into the shear modulus, and hot-cell testing of actual waste samples.v Acronyms and Abbreviations IntroductionRadioactive wastes composed of liquid (water and dissolved solids) and settled undissolved solids (UDS) are stored in 177 large underground storage tanks on the Hanford Site. The 177 storage tanks include 149 single shell tanks (SSTs) and 28 double shell tanks (DSTs). Waste will be retrieved from the SSTs to interim storage in the DSTs. Certa and Wells (2009) (System Plan, Rev. 4) report that the Baseline Case, which, in part, describes how the River Protection Project (RPP) mission ( a ) could be achieved given an underlying set of assumptions, shows that there is adequate DST space to meet the near-term success criteria for specific SST retrieval. Subsequently, however, there will be minimal DST space available to proceed with additional SST...

 What is an appropriate mixing metric/requirement that corresponds to adequate gas release and can this requirement be used as an alternative to conducting gas release testing? Do the simulants used in previous gas release testing adequately represent actual waste at plant conditions and what is the most suitable simulant for any planned gas release testing? What is the quantity of hydrogen that could be retained and released during normal, abnormal, and post-design-basis event operations for a range of imperfect mixing conditions (i.e., how much margin is allowed in targeting complete bottom clearing and complete vessel motion)? What is the quantity of hydrogen that can be retained and released in low-solids vessels? What is the margin in the current hydrogen generation rate estimates?Specific test and analysis objectives were identified for each of these questions and subsequently documented in a test plan; however, no technical activities were completed under the test plan for addressing these technical questions. iv S.2 Results and Performance Against Success CriteriaSuccess criteria were developed for each testing and analysis objective and documented in the project test plan; however, no technical activities were completed on the objectives under the test plan. Accordingly, no results are available to compare against the success criteria.

Gas generation in Hanford's underground waste storage tanks may, under certain conditions, lead to gas accumulation within the layer of settled solids (sludge) at the tank bottom. The gas, which typically has hydrogen as the major component together with other flammable species, is formed principally by radiation-driven chemical reactions. Accumulation of these gases within the sludge in a waste tank is undesirable and limits the amount of tank volume for waste storage. Further, accumulation of large amounts of gas in the sludge may potentially result in an unacceptable release of the accumulated gas if the sludge-layer density is reduced to less than that of the overlying sludge or that of the supernatant liquid. Rapid release of large amounts of flammable gases could endanger personnel and equipment near the tank. For this reason, a thorough understanding of the circumstances that can lead to a potentially problematic gas accumulation in sludge layers is needed. To respond to this need, the Deep Sludge Gas Release Event Project (DSGREP) was commissioned to examine gas release behavior in sludges.

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