Current proposed regulatory agreements (Consent Decree) at the Hanford Site call for closure of the Single-Shell Tank (SST) Waste Management Area (WMA) C in the year 2019. WMA C is part of the SST system in 200 East area ofthe Hanford Site and is one of the first tank farm areas built in mid-1940s. In order to close WMA C, both tank and facility closure activities and corrective actions associated with existing soil and groundwater contamination must be performed. Remedial activities for WMA C and corrective actions for soils and groundwater within that system will be supported by various types of risk assessments and interim performance assessments (PA). The U.S. Department of Energy, Office of River Protection (DOE-ORP) and the State ofWashington Department of Ecology (Ecology) are sponsoring a series of working sessions with regulators and stakeholders to solicit input and to obtain a common understanding concerning the scope, methods, and data to be used in the planned risk assessments and PAs to support closure of WMA C. In addition to DOE-ORP and Ecology staff and contractors, working session members include representatives from the U.S. Enviromnental Protection Agency, the U.S. Nuclear Regulatory Commission (NRC), interested tribal nations, other stakeholders groups, and members of the interested public. NRC staff involvement in the working sessions is as a technical resource to assess whether required waste determinations by DOE for waste incidental to reprocessing are based on sound technical assumptions, analyses, and conclusions relative to applicable incidental waste criteria.

The Hanford Site, managed by the U.S. Department of Energy (DOE), is undergoing the world's largest environmental cleanup. Sixty percent of the nation's chemically toxic, highly radioactive wastes are stored in 177 deteriorating underground storage tanks. In 2018, waste retrieval was completed for sixteen tanks in Waste Management Area (WMA) C. WMA C will be the first to undergo closure and set precedence for future closures. This dissertation presents three crucial studies that contribute to resolve key data and knowledge gaps for advancing closure, a unique and challenging venture. For "closure," tanks will be removed from service and WMA C placed in a condition protective of human health and the environment. To date, DOE has not specified WMA C closure engineering tasks and field actions for their regulatory framework. Therefore, policy indecisions and data gaps remain, confusing regulators and stakeholders, resulting in extended schedules and increased costs. I conducted a high-level Systems Engineering analysis to identify short- and long-term closure engineering functions and performance requirements, determine preliminary engineering tasks and field actions, and develop recommendations to optimize this "first-of-its-kind" effort.Residual wastes within WMA C tanks and ancillary equipment pose a threat to the Columbia River, the lifeblood of the interior Pacific Northwest. Residual wastes must be physically stabilized to prevent subsidence, solidified, and encapsulated to meet regulatory requirements. In the second study, I developed cementitious flowable-fills through formulation, laboratory assessment, and field testing. For flowable, self-leveling structural and non-structural fills, slump flow, bleed water, and shrinkage measurements guided reformulation efforts. I ultimately identified self-consolidating grouts, which met WMA C closure engineering performance requirements.WMA C closure will include placement of a landfill cover once the tank system is filled with desired grout(s). The cover must isolate and contain the waste, minimize its leaching, and limit it from reaching the deeper vadose-zone and groundwater. I performed Hydrus-1D modeling to determine the thickness of a viable cover and assess placement scenarios for an evapotranspiration cover. Potential and actual evaporation, precipitation leakage through the cover, and recharge of wastewater to groundwater were estimated and contrasted to determine favorable placement.

At the Department of Energy's (DOE) Hanford Site in south central Washington State, there are 177 large underground tanks with associated facilities that are used to store radioactive hazardous waste. Some of these tanks have leaked, with the result that there is tank waste in the Site's groundwater. DOE's Office of River Protection (ORP) plans to remediate these storage facilities (WP-13678, ''Integrated Mission Acceleration Plan'') by retrieving waste from the tanks, performing facility stabilization, and implementing soil cleanup. Before such work can be performed, performance analyses of various options must be performed for OW, DOE Headquarters, and the Washington State Department of Ecology (Ecology). Because of the large number of performance analyses for each tank and the large number of tanks, performance analyses for the different agencies will be integrated to the maximum extent possible. This document focuses on the requirements for performance analyses used to satisfy Ecology requirements. There are three types of large underground tanks at Hanford: single-shell tanks (SST), double-shell tanks (DST), and miscellaneous underground storage tanks (MUST). The SSTs have a storage capacity ranging from 50,000 to 1,000,000 gallons. Although waste is still present, they do not meet current regulatory requirements for the addition of waste. The DSTs have a storage capacity ranging from 500,000 to 1,160,000 gallons and are expected to meet current regulatory requirements. The SSTs are grouped into twelve tank farms (A, AX, B, BX, BY, C, S, SX, T, TX, TY, and U). For regulatory purposes, the twelve tank farms are grouped into seven waste management areas (WMA) (MAX, BBXIBY, C, S/SX, T, TWTY, and U), although the T and TWTY WMAs are often treated as a unit. The DSTs are grouped only into tank farms (AN, AP, AW, AX, AY, AZ, and SY). MUSTS are smaller tanks (maximum size of 50,000 gallons) that are scattered in various farms. Section 2.0 provides an overview and summary of this document. Section 3.0 describes the requirements of performance analyses. Section 4 provides the contents of the master performance assessment.

DOE Tank Waste: How clean is clean enough? The U.S. Congress asked the National Academies to evaluate the Department of Energy's (DOE's) plans for cleaning up defense-related radioactive wastes stored in underground tanks at three sites: the Hanford Site in Washington State, the Savannah River Site in South Carolina, and the Idaho National Laboratory. DOE plans to remove the waste from the tanks, separate out high-level radioactive waste to be shipped to an off-site geological repository, and dispose of the remaining lower-activity waste onsite. The report concludes that DOE's overall plan is workable, but some important challenges must be overcomeâ€"including the removal of residual waste from some tanks, especially at Hanford and Savannah River. The report recommends that DOE pursue a more risk-informed, consistent, participatory, and transparent for making decisions about how much waste to retrieve from tanks and how much to dispose of onsite. The report offers several other detailed recommendations to improve the technical soundness of DOE's tank cleanup plans.

This mission analysis report for the Hanford Tanks Initiative (HTI) supports the Hanford Site's Single-Shell Tank (SST) Waste Retrieval Program in its commitment to remove waste from the SSTs for treatment and final closure of the tanks. The results of the HTI will support the US Department of Energy's (DOE) privatization of retrieval efforts. This report addresses the HTI problem statement: Alternative technologies to past practice sluicing (PPS) have not yet been demonstrated to remove the hard heel from a sluiced tank or to remove waste from a leaking SST. Nor have performance-based criteria for cleanout and closure been demonstrated to the degree necessary to validate them as technically and economically achievable. This report also defines the mission statement and mission boundaries; the known interfaces, both programmatic and project; the mission level requirements; the test and evaluation methodology; and measures of success.