During the past few decades, there has been a renewed interest in advanced reactor concepts, especially the high-temperature gas-cooled and the molten salt-cooled technologies for energy production as well as hydrogen or process heat generation. Tri-structural isotropic fuel is intended to be used in some of these emerging reactor technologies. The fuel bearing TRISO particles are encapsulated in graphite, which acts in the capacity of a moderator. TRISO based fuels can be fabricated in the form of spherical pebbles or cylindrical compacts, the latter of which are then loaded into prismatic graphite blocks.

The work described in this report has evaluated the technical feasibility of maturing the pulsed current technology and its full-scale application to processing TRISO used nuclear fuel. No insurmountable technological or safety barriers were identified to successfully maturing the technology to the fourth TRL, which was considered appropriate for a DOE-NE program. The authors recommend DOE-NE’s Nuclear Fuel Cycle and Supply Chain Office should pursue the technology on that basis. In the immediate future, the authors recommend DOE-NE’s Nuclear Fuel Cycle and Supply Chain Office should acquire non-radioactive surrogate and natural uranium TRISO compacts and pebbles as they become available from commercial vendors. These surrogates could then be used to mature the pulsed current technology.

Abstract This Plan demonstrates the availability of technologies for processing TRISO used nuclear fuel for waste management and actinide recovery purposes. These technologies are judged to be at a very low level of technology readiness and as such they constitute a fertile research area for the DOE-NE’s Office of Materials and Chemical Technologies. Strategies to mature the technologies to a point where they can reasonably be considered in engineering alternatives analyses typically involve laboratory-scale tests using fuel simulant to characterize process streams and demonstrate key engineering features. Several criteria are available to help selecting candidate technologies for further maturation. also applicable to processing unirradiated TRISO fuel to recover High Assay Low Enriched Uranium, for example, from fresh fuel that has failed quality requirements. appropriate material, forms and fabrication techniques. Laboratory-scale studies can be performed with simulants and unirradiated fuel and then verified with irradiated fuel. A source of irradiated fuel to be identified but fuel may not have to be irradiated in a reactor to induce the key irradiation effects For large scale tests of a technology’s simulants used understanding laboratory-scale.

This study explores the potential benefit to flowsheets for recovering actinides from used nuclear fuel of a process simplification in the head-end portion. The process simplification replaces acid dissolution of used nuclear fuel with dissolution in the tri-butyl phosphate solvent used in the industrially mature Plutonium Uranium Reduction Extraction flowsheet. Though characterized by considerable uncertainty, simplified flowsheets appear feasible and potentially offer significant reductions in process complexity, nitrate inventory, secondary liquid effluent generation, and plant footprint.

This study explores the potential benefit to the used nuclear fuel actinide recovery flowsheet of a process simplification and establish the experimental work needed to develop the simplified flowsheet. The simplification is based on replacing acid dissolution of used nuclear fuel with dissolution in the tri-butyl phosphate solvent used in the industrially mature Plutonium Uranium Reduction Extraction flowsheet. Though characterized by considerable uncertainty, simplified flowsheets appear feasible and potentially offer significant reductions in process complexity, nitrate inventory, secondary liquid effluent generation and plant footprint. Initial development of the technology should focus on key fission product and actinide dissolution as a function of process conditions and understanding the fundamental chemistry of tri-butyl phosphate solvent chemistry. Development of ancillary technologies for minor actinide separations and fuel pretreatment for tritium management is also recommended.

ii Abstract The study described in this report was initiated to evaluate the status of waste management practices associated with fast spectrum molten salt reactors (FS-MSRs). Waste streams specific to variable spectrum MSRs are also considered. Waste management practices for MSRs are fundamentally different from those of their solid-fueled counterparts. To best advance MSR concepts to implementation, these differences warrant fresh thinking on a variety of subject areas, rather than adapting techniques established for solid-fueled reactors. A number of areas are recommended for focused technological research and development. While not exclusive, these target areas are considered to provide the most impact to advancing FS-MSR waste management practice: • Specific to variable spectrum MSRs, neutron moderator(s) that are tolerant to radiation and high temperatures (alternative to graphite) • New concepts for remote, long-handled tooling and radiation-resistant electronics • Salt dehalogenation processes (primarily for fluorides as chlorides have demonstrated options) • Phosphate and silicate waste form evaluations for dehalogenated salt streams • Integration of lithium-7 and chlorine-37 recovery and recycle into waste treatment approaches • Strategies for chlorine-37 isotopic enrichment • Integrated capture and storage of fission product noble gases (e.g., radiation-tolerant sorbents)

Readiness evaluation for sustained operations is a continuous function that progresses from overseeing establishment of five key programmatic elements during design and construction phases to monitoring the output of those elements performing during commissioning and operations. Continuously assessing readiness for sustained operations becomes an important business function for the U.S. Department of Energy’s Office of River Protection as competition for federal funds increases with increasing waste treatment operations throughout the Office of Environmental Management complex. The five key programmatic elements are as follows: Risk management – Risks and opportunities should prioritize continuous improvement initiatives and be informed by the design and technical authorities and stakeholder monitors. Continuous improvement – All levels of the project organization should exhibit commitment to continuous improvement and learning. Continuity of design and technical authorities – The authorities are responsible for managing knowledge for its effective use in the other elements. Stakeholder monitoring – Active and deliberate monitoring of stakeholder relationships. Sustained operations integrated business planning – Integrated business planning in a federal environment competitive for congressional funding.

This report evaluates best practices for flowsheet and technology (F&T) management and makes recommendations for Hanford tank waste treatment operations initially for Direct Feed Low Activity Waste (DFLAW). Establishing practicing F&T management operations prior to hot commissioning the Hanford Waste Treatment Plant is desirable to ensure focused F&T leadership and F&T capabilities and competencies are immediately ready to sustain DFLAW production operations. Management of F&T is characterized by the five programmatic elements important to sustained operations and leads to recommendations for Hanford tank waste treatment operations:

Almost every facet of chemical engineering is impacted when processing material with radioactive and fissile properties. Different containment concepts, passive or secure cells and canyons, have evolved in Europe and the USA, respectively, and have profoundly impacted equipment and processing concepts. The special features associated with filtration, ion exchange and solvent extraction processes and equipment are aimed at reducing maintenance requirements, simplifying operations and reducing plant footprint and height. Equipment materials considerations include corrosion resistance and special measures required to control criticality and radiation damage. Process intensification and transportable equipment and processes are the two important trends associated with chemical engineering for advanced aqueous radioactive material separations.

The efficacy of a new spherically engineered form of resorcinol-formaldehyde (RF) resin was tested for cesium removal on two actual Hanford tank wastes. Small-scale processing was conducted according to the River Protection Project-Waste Treatment and Immobilization Plant flowsheet in a lead-lag column format. The RF resin processed 95 bed volumes (BVs) of high potassium-bearing waste (AP-101) and >200BVs of a high complexant-bearing waste (AN-102) before reaching 50% cesium breakthrough. Elution with 0.5M nitric acid was effective and complete after processing 16 BVs. Cesium and other analyte fractionations to the process stream effluent and eluate were evaluated. The RF resin resulted in very little metal and radionuclide fractionation, other than cesium, to the eluate. The spent resins were measured for most analytes relevant to land-disposal requirements. The actinide concentrations on the spent resins were <3% of the transuranic waste limit; the residual cesium concentrations were <4mCi/kg; chromium was the only metal, regulated by the Resource Conservation Recovery Act, that was measured in quantities significant to land-disposal regulations.

Pacific Northwest National Laboratory has been tasked by Bechtel National Inc. (BNI) on the River Protection Project-Waste Treatment Plant (RPP-WTP) project to perform research and development activities. The Pretreatment Engineering Platform (PEP) is being designed and constructed as part of a plan to respond to an issue raised by the WTP External Flowsheet Review Team (EFRT) entitled “Undemonstrated Leaching Processes” and numbered M12. The PEP replicates the WTP leaching process using prototypic equipment and control strategies. The approach for scaling PEP performance data to predict WTP performance is critical to the successful resolution of the EFRT issue. This report describes the recommended PEP scaling approach, PEP data interpretation and provides recommendations on test conduct and data requirements.

The U.S. Department of Energy (DOE) Office of River Protection’s Waste Treatment Plant (WTP) will process and treat radioactive waste that is stored in tanks at the Hanford Site. The waste treatment process in the pretreatment facility will mix both Newtonian and non-Newtonian slurries in large process tanks. Process vessels mixing non-Newtonian slurries will use pulse jet mixers (PJMs), air sparging, and recirculation pumps. An anti-foam agent (AFA) will be added to the process streams to prevent surface foaming, but may also increase gas holdup and retention within the slurry. The work described in this report addresses gas retention and release in simulants with AFA through testing and analytical studies. Gas holdup and release tests were conducted in a 1/4-scale replica of the lag storage vessel operated in the Pacific Northwest National Laboratory (PNNL) Applied Process Engineering Laboratory using a kaolin/bentonite clay and AZ-101 HLW chemical simulant with non-Newtonian rheological properties representative of actual waste slurries. Additional tests were performed in a small-scale mixing vessel in the PNNL Physical Sciences Building using liquids and slurries representing major components of typical WTP waste streams. Analytical studies were directed at discovering how the effect of AFA might depend on gas composition and predicting the effect of AFA on gas retention and release in the full-scale plant, including the effects of mass transfer to the sparge air. The work at PNNL was part of a larger program that included tests conducted at Savannah River National Laboratory (SRNL) that is being reported separately. SRNL conducted gas holdup tests in a small-scale mixing vessel using the AZ-101 high-level waste (HLW) chemical simulant to investigate the effects of different AFAs, their components, and of adding noble metals. Full-scale, single-sparger mass transfer tests were also conducted at SRNL in water and AZ-101 HLW simulant to provide data for PNNL’s WTP gas retention and release modeling.

A conceptual counter-current process flowsheet was developed for sodium hydroxide recovery from alkaline solutions via pseudohydroxide extraction (PHE). PHE relies on a simple sodium ion/proton exchange mechanism at elevated pH using a weak organic acid extractant. The contact of the sodium-loaded organic phase with water results in the reconstitution of the extractant in the organic phase and sodium hydroxide in the aqueous phase. In this work, the 3,5-di-tert-butylphenol (35-DTBP) cation exchanger was used in the Isopar (R) L diluent modified with isooctyl alcohol Exxal (R) 8. Equilibrium isotherms determined for PHE from pure sodium hydroxide solutions and simulated radioactive waste leachate were used to develop a semi-empirical model that could be used for designing PHE process flow-sheets. Using this model, a conceptual PHE flowsheet was developed for recovering NaOH from solutions generated by caustic leaching of radioactive tank sludges. The flowsheet consists of the extraction, scrub, and strip processes, each employing four equilibrium stages. The modeling of this flowsheet indicates 97% recovery of the sodium hydroxide from the waste leachate feed solution. An experimental demonstration, performed with a simulated radioactive waste leachate using batch contacts in a co-current analog of the counter-current flowsheet, confirmed the potential for practical application of PHE technology.

Bechtel National, Inc. (BNI) is evaluating the alternate Cs ion exchanger, spherical resorcinol-formaldehyde (RF), for use in the River Protection Project-Waste Treatment Plant (RPP-WTP).( ) Previous test activities with spherical RF indicate that it has adequate capacity, selectivity, and kinetics to perform in the plant according to the flowsheet needs. It appears to have better elution and hydraulic properties than the existing alternatives: ground-gel RF and SuperLig® 644 (SL 644).( ) To date, the spherical RF performance testing has been conducted on freshly manufactured resin (within ~2 months of manufacture). The ion exchange resins will be manufactured and shipped to the WTP up to 1 year before being used in the plant. Changes in the resin properties during storage could reduce the capacity of the resin to remove Cs from low-activity waste solutions. Active sites on organic SL-644 resin have been shown to degrade during storage (Arm et al. 2004). Additional testing was needed to study the effects of storage conditions and aging on spherical RF ion exchange performance. Variables that could have a significant impact on ion exchange resins during storage include storage temperature, medium, and time. Battelle—Pacific Northwest Division (PNWD) was contracted to test the effects of variousmore » storage conditions on spherical RF resin. Data obtained from the testing will be used by the WTP operations to provide direction for suitable storage conditions and manage the spherical RF resin stock. Storage test conditions included wet and dry resin configurations under nitrogen at three temperatures. Work was initially conducted under contract number 24590-101-TSA-W000-00004 satisfying the needs defined in Appendix C of the Research and Technology Plan( ) TSS A-219 to evaluate the impact of storage conditions on RF resin performance. In February 2007, the contract mechanism was switched to Pacific Northwest National Laboratory (PNNL) Operating Contract DE-AC05-76RL01830.« less

Aqueous haze formation and behavior was studied in the liquid-liquid system tri-n-butyl phosphate in odorless kerosene and 3M nitric acid with uranyl nitrate and cesium nitrate representing the major solute and an impurity, respectively. A pulsed column, mixer-settler and centrifugal contactor were chosen to investigate the effect of different turbulence characteristics on the manifestation of haze since these contactors exhibit distinct mixing phenomena. The dispersive processes of drop coalescence and breakage, and water precipitation in the organic phase were observed to lead to the formation of haze drops of similar to 1 mu m in diameter. The interaction between the haze and primary drops of the dispersion was critical to the separation efficiency of the liquid-liquid extraction equipment. Conditions of high power input and spatially homogeneous mixing enabled the haze drops to become rapidly assimilated within the dispersion to maximize the scrub performance and separation efficiency of the equipment. (c) 2006 American Chemical Society.