DISCLAIMER'letter reporting refinement of flammable gas generatiodretention models using void meter and retained gas sampling data."The data obtained from operating the void fraction instrument 0 (Stewart et al. 1996a), and retained gas sampler (RGS) (Shekarriz et al. 1997) have determined the amount and composition of gas retained in the wastes in the six double-shell tanks on the Flammable Gas Watch List (Johnson et al: 1997). The interpretation of those data and the models for gas retention and release developed or improved as a result represent significant progress toward an adequate understanding of the mechanisms of gas generation, retention, and release. This report summarizes the VFI and RGS data and presents the models these data have enabled us to develop.. iii AbstractThis report describes the current understanding of flammable gas retention and release in Hanford double-shell waste tanks AN-103, AN-104, AN-105 The applicable data available from the void fraction instrument, retained gas sampler, ball rheometer, tank characterization, and field monitoring are summarized. Retained gas volumes and void fractions are updated with these new data -Using the retained gas compositions from the retained gas sampler, peak dome pressures during a gas burn are calculated as a function of the fraction of retained gas hypothetically released instantaneously into the tank head space. Models and criteria are given for gas generation, initiation of buoyant displacement, and resulting gas release; and predictions are compared with observed tank behavior. V Summary .The gas retention and release behaviors of Hanford double-shell tanks (DSTs) on the Hammable Gas Watch List (FGWL), were characterized in detail using the ball rheometer and void fraction instrument 0 from December 1994 to May 1996. These are reported in Stewart et al. (1996a). Additional data on gas .composition and void fraction have since become available on four of these tanks (AW-101, AN-103, AN-104, and AN-105) using the retained gas sampler (RGS) from March through September 1996 and are described in Shekarriz et al. (1997).The main objective of the work presented in this report is improving the models for gas retention and release based on these data and updating the original gas retention and release calculations with the new RGS and core sample data-Because of this extensive characterization effort, we have a better knowledge and understanding of these DSTs than of any other Hanford tanks. We include models that help explain current gas retention and release behavior and examine the potential for other tanks to exhibit hazardous episodic gas releases. The models developed for gas generation based on waste sample testing are also summarized. While none of these models have been formally ve$i,ed and validated for safety analysis, they are consistent with the extant body of data and observations. The updates to earlier calculations and improvements to gas generation, retention, and release models are summarized below. G a s Generation Models and ...

No abstract

Portions of this document may be Uegible in electronic image products. Images are produced from the best available original document.

Mitigation of episodic flammable gas releases from Hanford Waste Tank 241-SY-101 was accomplished in July 1993 with the installation of a mixer pump that prevents gas retention. But it has not been possible until recently to measure the effects of mixing on the waste or how much gas remains and where it is located. Direct measurements of the void fraction and rheology of the mixed waste by the void fraction instrument provide estimates of the location, quantity, and behavior of undissolved gas in the tank. This report documents the compilation and integration of the information that enables this understanding. * and ball rheometer along with previous data iii V possible to measure properties in situ at specific points by using the ball rheometer and the VFI. When integrated, this information provides a framework from which the quantity and distribution of retained (undissolved) gas in Tank 241-SY-101 can be estimated. The results of this analysis, summarized in Table 4.4 of the report, indicate that the tank currently contains approximately 5,700 ft3 of gas in situ (3.8% average void), or about 7,800 ft3 when expanded to atmospheric pressure. In addition to the "best" estimate derived from in-tank temperature and property measurements, two other estimation methods were considered in this report. The first of these correlates atmospheric pressure and waste surface level to determine the waste compressibility. This compressibility, along with an assumed gas elevation, yields an estimate of the gas volume that is consistent with the best estimate described above, provided that the gas elevation is defmed properly. The second method, developed in support of the current mixer pump safety assessment, uses an extrapolation of retained gas estimates from historical data prior to pump installation to determine a gas-free waste level. The current gas inventory is interpolated between the gas-free state and that just prior to a large gas release event using waste surface level measurements. As proposed, this method gives significantly larger volumes than the best estimate, but it can be made consistent by correcting some of its assumptions. Direct measurements, similar to those of the VFI, are difficult, expensive, and available. from only a few locations in the tank. But indirect measurements, such as the response of the tank waste level to barometric pressure changes, provide little information about the distribution of the gas and, in fact, require some knowledge of the distribution of the gas in order to provide an estimate of retained gas quantity. To help address this problem, a set of dynamic bubble/particle models has been developed that provide insight into the state, amount, and distribution of retained gas in Tank 241-SY-101 as it responds to the mixer pump and barometric pressure variations. The models predict average amounts of retained gas in various layers of the tank-crust, convective layer, and loosely-settled layer that are compared with the VFI measurements to calibrate the model. While the models have no...

Executive SummaryThis report presents the rationale for adopting a recommended characterization strategy that uses a risk-based decision-making eamework for managing the Tank Waste Characterization Program at Hanford. The risk-managemendvalue-of-information (VOI) strategy that is illustrated explicitly links each information-gathering activity to its cost and provides a mechanism to ensure that characterization funds are spent where they can produce the largest reduction in risk. The approach was developed by tailoring well-known decision analysis techniques to specific tank waste characterization applications. 'This report illustrates how VOI calculations are performed and demonstrates that the VOI approach can definitely be used for real Tank Waste Remediation System (TWRS) characterization problems.The goal of a characterization strategy is to provide timely information to support decisions. Information has value if it leads to better decisions, which are those with better expected consequences. Thus the VOI should be gauged by the expected increase in the value of decisions. Frequently, information will reduce uncertainty about consequences. Idormation will also often lead to decisions that involve reduced risks.Qualitatively speaking, a source of information (e.g., a tank waste sample) is valuable if it has the potential for changing subsequent decisions, such as whether to keep transuranic (TRU) waste separate from high-level waste (HLW). For a source of information to be valuable, two conditions must be met:1. The decision alternatives must have uncertain consequences (otherwise, there is nothing to be learned from the information).2. Depending on the information obtained, different decisions may be best (otherwise, the information would not have any impact).VOI decision analysis techniques are used for determining risk-based characterization requirements.This approach provides an understandable technical basis that explicitly links sampling, analysis, physicalchemical modeling, and other "learning" activities to risk reduction. Furthermore, VOI analysis provides a clear measure of completion because additional characterization activities are not justified when the costs exceed the calculated risk reduction value.Risk-based requirements defined in terms of the VOI become a defensible basis for integration and prioritization of needs across tanks and program elements requiring information about waste composition, phenomenology, and performance. Knowing the value of obtaining specific information will provide an explicit basis for investments in research and/or technology development to reduce costs and technical uncertainty. This approach will also provide a defensible basis for budgeting and scheduling decisions by providing the means for selecting the most impactfid characterization work for funding each year. This integration, coupled with statistically and technically sound sampling and analysis, monitoring, and laboratow methods, will result in an implementation plan that provides the most cost-effect...