Independent Assessment of Science and Technology for the Department of Energy's Defense Environmental Cleanup Program (2019) / Chapter Skim
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3 Review and Assessment of Technologies and Alternative Approaches
3 Review and Assessment of Technologies and Alternative Approaches
Pages 47-74
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From page 47... ...
Mitigate uncertainties, vulnerabilities, or risks, or otherwise significantly improve the cleanup program. As noted in Chapter 1, this study charge calls for a future-focused r eview and assessment of technologies and alternative approaches that have the potential to substantially reduce cleanup program costs, schedules, and risks or uncertainties.
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From page 48... ...
They are intended to be broadly illustrative of the types of S&T development opportunities and are not intended to be definitive. Section 3.2 illustrates, again by example, how these technologies and alternative approaches could be applied to some key DOE-EM cleanup challenges to reduce long-term costs; accelerate schedules; mitigate uncertainties, vulnerabilities, or risks; or otherwise significantly improve the cleanup program.
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From page 49... ...
3.1.1 Change Chemistry at Bulk and Interfacial Scales DOE-EM waste streams contain hazardous and/or radioactive elements in specific chemical forms, referred to as chemical species. The form of a species -- for example, whether it is contained in a solid or aqueous phase -- can greatly affect the ease with which that species can be removed from the waste stream for treatment and disposal.
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Some examples of potential future treatment technologies and approaches include • Electrochemistry to modify chemical conditions, ranging from oxi dation state changes of elements that are contaminants to in situ electrodeposition or vitrification; • Interfacial control of reactivity leading to improved separations and/or sequestration; • Understanding interfacial surface chemistries between suspended particulates to enable better rheology control in complex waste streams; and • Use of biological processes to achieve oxidation state con trol of redox-sensitive contaminant species and to drive in situ sequestration. 3.1.2 Change Nuclear Properties Much of the hazard associated with radioactive waste is derived from its elemental composition, isotopic composition, and molecular speciation.
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From page 51... ...
A building information model -- a three-dimensional view of a structure or facility to show all systems as installed -- is an example of a VR environment. 3.1.4 Change Interrogation Approaches Interrogation approaches are means for remotely characterizing important properties of waste streams and/or contaminated facilities without 2 For example, lasers are being investigated for use in making medical isotopes through trans mutation reactions (see MIT Technology Review, 2011)
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From page 52... ...
They could also be used to characterize the interiors of underground waste tanks and their contents without having to retrieve and analyze physical samples. Such approaches could transform the DOE-EM cleanup program through betterinformed cleanup decisions, reduced worker risks, and reduced cleanup times and costs.
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From page 53... ...
Other examples relevant to decision making are provided in Section 3.1.7. 3.1.6 Change Disposal Pathways DOE-EM's cleanup activities are generating thousands of radioactive and hazardous waste streams.
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From page 54... ...
There may be new disposal pathways for DOE-EM waste streams that are protective of human health and the environment but faster and less costly to achieve than current pathways. Some examples include • Near-surface storage vaults to allow time for decay of waste streams containing short-lived radioactive constituents; • Boreholes and deep-injection wells for disposal of short-lived, high activity radioactive wastes; • Pretreatment of waste streams to remove long-lived and/or envi ronmentally mobile radioactive constituents that prevent disposal in near-surface engineered facilities; • Low-temperature waste forms such as geopolymers, room- temperature ceramics, and composite cements to serve as durable alternatives to high-temperature waste forms such as glass and reduce volatilization of radioactive and hazardous constituents during processing; and • New waste forms for stabilization of wastes that are mobile in the environment.
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4. Develop real-time capabilities for in situ analysis and modification of waste streams and processing approaches to reduce the need for batching and batch storage.
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The first five cleanup challenges focus on remediation of radioactive wastes stored in underground tanks at the Hanford and Savannah River Sites (see Figure 3.1 and Sidebar 3.1)
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This process is costly and time intensive. Retrieval of the waste stored in underground tanks at Hanford and Savannah River is also challenging because
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. The group of tanks is referred to as a "tank farm." SOURCE: Department of Energy.
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These include, for example (see Table 3.1) , • Approaches for modifying tank waste chemistry to improve the ease and efficiency of retrieval and also to reduce water use during retrieval operations;
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• Robotics and human–machine interfaces to reduce the need for direct human involvement in waste retrieval operations; and • Interrogation approaches for in situ characterization of the physi cal, chemical, and radiological properties of tank waste and for in situ characterization of tank interiors after retrieval operations are completed. 3.2.2 Stabilize Residual Tank Waste and Underground Tanks in Place DOE-EM plans to close the underground waste tanks6 at the Hanford and Savannah River Sites in place after waste retrieval operations are completed (see Sidebar 3.2)
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underground tanks at the Hanford Site have been closed as of late 2018. Once all of the tanks have been closed, the tank farms may be covered with engineered caps to reduce water ingress and inhibit physical access.
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3.2.3 Improve the Efficiency and Effectiveness of In Situ Monitoring of Physical and Chemical Conditions Within and Beneath Underground Tanks DOE-EM monitors the conditions of its underground tanks through a number of means, including • In situ measurements of tank waste temperatures, • In situ measurements of tank liquid levels, • In situ examinations of tank-wall and -floor conditions, • Laboratory analyses of tank corrosion conditions using coupons of tank shell materials removed from the tanks at periodic intervals, • Laboratory analyses of tank headspace gases to detect the products of chemical reactions in stored waste, and • Laboratory analyses of soil samples collected from beneath tanks obtained by drilling (see Figure 3.3) .7 The technologies and alternative approaches described in Section 3.1 can be used to improve capabilities to monitor the long-term effectiveness of tank closures.
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• Models that integrate the data collected from the instruments and sensors above to analyze the performance of operating tanks and tank closures with little or no operator intervention. 3.2.4 Develop Real-Time Capabilities for In Situ Analysis and Modification of Waste Streams During Processing to Reduce the Need for Batching and Batch Storage The current flowsheets for processing tank wastes at the Hanford and Savannah River Sites are based on batch processing principles.
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3.2.5 Separate Long-Lived and Environmentally Mobile Radioactive Constituents from Waste Streams Some DOE-EM waste streams contain long-lived and/or environmentally mobile radioactive constituents that are difficult to remove by current waste processing approaches and may preclude their disposal in near-surface engineered facilities. Three such constituents are tritium (hydrogen-3)
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From page 65... ...
Tc-99 and I-129, along with other fission products and transuranic isotopes, are present in tank wastes at Hanford and Savannah River. These wastes are being processed to produce two waste streams, a high-level radioactive waste stream and a low-activity radioactive waste stream.
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Those activities included • Stabilizing and shipping residual plutonium to Savannah River; • Removing contaminated equipment, including process tanks, glove boxes, and various machinery, from the buildings; and • Demolishing facilities to slab-on-grade. Decontamination and demolition (D&D)
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, • Smart autonomous robots to reduce and/or eliminate the need for manual labor in facility D&D; • Technologies for rapid in situ characterization of radioactive and chemical hazards in equipment and facilities; and • Technologies for removing contamination from equipment and facilities to minimize radioactive and hazardous waste volumes and allow recycling or productive reuse of building equipment and materials. 3.2.7 Characterize and Stabilize and/or Retrieve Contamination in the Vadose Zone The vadose zone comprises the unsaturated portion of the soil column between the ground surface and groundwater table.
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From page 68... ...
Characterizing and modeling this heterogeneity to predict contaminant distributions has met with limited success. Moreover, even when contaminant distributions in the vadose zone are known, recovering contaminants, or stabilizing them in situ by modifying subsurface hydrological or geochemical properties, is challenging, particularly for metals and radioisotopes that are distributed in large subsurface volumes.
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From page 69... ...
of the site contain carbon tetrachloride, chromium, iodine, nitrate, technetium, t ritium, and uranium. Plumes originating along the Columbia River corridor contain chromium, strontium, and uranium.
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DOE is building near-surface waste cells at all of its large sites (and at many smaller sites) to dispose of cleanup-related materials -- including, for example, contaminated soil, contaminated equipment, facility demolition debris, and waste streams that have been treated for near-surface onsite disposal.
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. • Prototype Hanford Barrier was constructed over a crib (i.e., an under A ground structure that was used to dispose of liquids to the subsurface from a nearby tank farm)
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Decision tools to monitor sensor outputs and provide predictions of functional losses. These sensors must be cost effective, self-calibrating, and have long operational lives or be easily replaceable.
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These include, for example (see Table 3.1) , • Smart sensors for autonomous, continuous, and centralized in situ monitoring of locations and movements of contaminant plumes -- and that reduce the need for direct human involvement in monitor ing processes.
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