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  • PNNL-23468 WTP-RPT-234 Rev. 0

    Chemical Disposition of Plutonium in Hanford Site Tank Wastes CH Delegard SA Jones February 2015

  • PNNL-23468 WTP-RPT-234 Rev. 0

    Chemical Disposition of Plutonium in Hanford Site Tank Wastes CH Delegard SA Jones February 2015 Prepared for the U.S. Department of Energy Under Contract DE-AC05-76RL01830 Pacific Northwest National Laboratory Richland, Washington 99352

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    Summary

    This report examines the chemical disposition of plutonium (Pu) in Hanford Site tank wastes, by itself and in its observed and potential interactions with the neutron absorbers aluminum (Al), cadmium (Cd), chromium (Cr), iron (Fe), manganese (Mn), nickel (Ni), and sodium (Na). Consideration also is given to the interactions of plutonium with uranium (U). No consideration of the disposition of uranium itself as an element with fissile isotopes is considered except tangentially with respect to its interaction as an absorber for plutonium.

    The report begins with a brief review of Hanford Site plutonium processes, examining the various means used to recover plutonium from irradiated fuel and from scrap, and also examines the intermediate processing of plutonium to prepare useful chemical forms. The paper provides an overview of Hanford tank defined-waste–type compositions and some calculations of the ratios of plutonium to absorber elements in these waste types and in individual waste analyses. These assessments are based on Hanford tank waste inventory data derived from separately published, expert assessments of tank disposal records, process flowsheets, and chemical/radiochemical analyses.

    This work also investigates the distribution and expected speciation of plutonium in tank waste solution and solid phases. For the solid phases, both pure plutonium compounds and plutonium interactions with absorber elements are considered. These assessments of plutonium chemistry are based largely on analyses of idealized or simulated tank waste or strongly alkaline systems. The very limited information available on plutonium behavior, disposition, and speciation in genuine tank waste also is discussed.

    The assessments show that plutonium coprecipitates strongly with chromium, iron, manganese and uranium absorbers. Plutonium’s chemical interactions with aluminum, nickel, and sodium are minimal to non-existent. Credit for neutronic interaction of plutonium with these absorbers occurs only if they are physically proximal in solution or the plutonium present in the solid phase is intimately mixed with compounds or solutions of these absorbers. No information on the potential chemical interaction of plutonium with cadmium was found in the technical literature. Definitive evidence of sorption or adsorption of plutonium onto various solid phases from strongly alkaline media is less clear-cut, perhaps owing to fewer studies and to some well-attributed tests run under conditions exceeding the very low solubility of plutonium. The several studies that are well-founded show that only about half of the plutonium is adsorbed from waste solutions onto sludge solid phases. The organic complexants found in many Hanford tank waste solutions seem to decrease plutonium uptake onto solids. A number of studies show plutonium sorbs effectively onto sodium titanate. Finally, this report presents findings describing the behavior of plutonium vis-à-vis other elements during sludge dissolution in nitric acid based on Hanford tank waste experience gained by lab-scale tests, chemical and radiochemical sample characterization, and full-scale processing in preparation for strontium-90 recovery from PUREX sludges.

    S.1 Objective

    The objective of this report is to summarize and evaluate the large amount of experimental and theoretical work and literature reports relating to the disposition of plutonium in tank waste, especially with respect to its interactions with compounds of the neutron-absorbing elements aluminum, cadmium, chromium, iron, manganese, nickel, sodium, and uranium.

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    Table S - 1 summarizes the objectives that apply to this task.

    Table S - 1: Summary of Work Objectives and Results

    Work Objective Objective

    Met? Discussion Review the known technical literature related to the disposition of plutonium in alkaline Hanford tank waste, including plutonium’s interactions with compounds of the neutron-absorbing elements aluminum, cadmium, chromium, iron, manganese, nickel, sodium, and uranium.

    Yes The report provides an overview of Hanford Site plutonium processes, describes the Hanford Defined Waste properties with respect to plutonium and neutron absorber relative concentrations, and lists absorber element compounds observed and postulated to be present in Hanford tank waste sludges, the primary locus of plutonium in the tank waste. It then presents an extensive review of plutonium chemistry in Hanford tank waste and in alkaline systems as gleaned from the technical literature dating from the time of the Manhattan Project. The report further describes the disposition of plutonium sent to the tank waste as both solution and as solids. A discussion of plutonium’s interactions with compounds of the neutron absorber elements aluminum, cadmium, chromium, iron, manganese, nickel, and uranium through coprecipitation and sorption follows. Because of the high solubilities of most sodium salts, chemical interactions of plutonium are expected to be minimal except in the event of precipitation of lower-solubility salts such as sodium diuranate and that of the co-location of soluble sodium salts with less soluble sludge phases. Finally, the report summarizes the behavior of plutonium in the dissolution of genuine Hanford tank waste sludges by treatment with nitric acid.

    S.2 Work Exceptions

    No work exceptions are applicable to this report.

    S.3 Results and Performance against Success Criteria

    Table S - 2 presents research and technology (R&T) success criterion for achieving the work objective.

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    Table S - 2: The Success Criterion for the Plutonium Disposition Review Task

    Success Criterion How Work Did or Did Not Meet the Success Criterion Review the known technical literature related to the disposition of plutonium in alkaline Hanford tank waste including plutonium’s interactions with compounds of neutron absorber elements aluminum, cadmium, chromium, iron, manganese, nickel, sodium, and uranium.

    This success criterion was met. The report summarizes over 100 technical publications found in journals, from the Hanford, Savannah River, and other US-DOE Sites, and international sources related to the chemistry of plutonium, absorber elements, and their joint interactions in Hanford tank waste and in related alkaline systems akin to Hanford tank waste.

    S.4 Quality Requirements

    The PNNL Quality Assurance (QA) Program is based upon the requirements defined in DOE Order 414.1D, Quality Assurance, and Title 10 of the Code of Federal Regulations Part 830, Energy/Nuclear Safety Management, and Subpart A—Quality Assurance Requirements (a.k.a. the Quality Rule). PNNL has chosen to implement the following consensus standards in a graded approach:

     ASME NQA-1-2000, Quality Assurance Requirements for Nuclear Facility Applications, Part 1, Requirements for Quality Assurance Programs for Nuclear Facilities.

     ASME NQA-1-2000, Part II, Subpart 2.7, Quality Assurance Requirements for Computer Software for Nuclear Facility Applications.

     ASME NQA-1-2000, Part IV, Subpart 4.2, Graded Approach Application of Quality Assurance Requirements for Research and Development.

    The procedures necessary to implement the requirements are documented through PNNL’s “How Do I…?” (HDI1).

    The Waste Treatment Plant Support Project (WTPSP) implements an NQA-1-2000 QA Program, graded on the approach presented in NQA-1-2000, Part IV, Subpart 4.2. The WTPSP Quality Assurance Manual (QA-WTPSP-0002) describes the technology life cycle stages under the WTPSP Quality Assurance Plan (QA-WTPSP-0001). The technology life cycle includes the progression of technology development, commercialization, and retirement in process phases of basic and applied research and development (R&D), engineering and production, and operation until process completion. The life cycle is characterized by flexible and informal QA activities in basic research, which become more structured and formalized through the applied R&D stages.

    The work described in this report has been completed under the QA technology level of basic research. WTPSP addresses internal verification and validation activities by conducting an independent technical review of the final data report in accordance with WTPSP procedure QA-WTPSP-601, Document Preparation and Change. This review verifies that the reported results are traceable, that inferences and conclusions are soundly based, and that the reported work satisfies the test plan objectives.

    1 System for managing the delivery of PNNL policies, requirements, and procedures

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    S.5 R&T Test Conditions

    This report summarizes historical literature and government-sponsored reports that describe the chemistry of Hanford Site tank waste and plutonium and neutron absorber elements. No experimental testing was required to complet

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