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All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Detecting Clandestine Reprocessing Activities in the Middle East

Nuclear reprocessing plants release krypton-85 that can be detected in the atmospheric air downwind from the facility. Atmospheric transport modelling is applied to determine the area over which krypton-85 emissions from undeclared reprocessing activities in the Middle East would still be detectable against the background. This is used to assess the feasibility of monitoring known reprocessing plants and detecting unknown reprocessing plants. The annual wind flow over Dimona is analyzed and it is concluded that a known reprocessing plant could be monitored with one or a few fixed monitoring stations. Unknown reprocessing plants are more difficult to detect due to the high background levels of krypton-85 and fixed stations would not be feasible. Instead, the number of air samples that have to be taken at random locations for a successful detection is calculated. Taking random air samples can present a logistical effort but can yield reliable and timely detection of clandestine reprocessing plants. This could be used for verification of an international treaty that prohibits the separation of plutonium in the Middle East.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2020

Integrating Data Sources for Improved Safeguards and Accountancy of Electrochemical Fuel Reprocessing Systems. Final Report

Electrochemical reprocessing (also commonly known as “pyroprocessing”) of used nuclear fuel is an alternative to aqueous reprocessing that confers a number of advantages, including the ability to process more recently-discharged fuel, smaller resultant waste volumes, and the lack of isolation of plutonium in the product stream. While electrochemical reprocessing systems have seen a significant research and development effort, nuclear safeguards and security of these systems remains under-developed, particularly given the significant differences in operating environment and process flowsheet compared with established aqueous methods. Objective 4 of DOE’s nuclear energy research and development activities in Nuclear Energy Research and Development Roadmap is: “Understand and minimize the risks of nuclear proliferation and terrorism.” Material Control & Accountancy (MC&A) programs at nuclear processing plants deter and detect theft and diversion of nuclear material by both outside and inside adversaries. Empirical modeling and data analytics of online measurements and state indicators can improve the timeliness of detection and reduce the uncertainty in accountancy measures. To support the development and demonstration of such methods, data are needed that capture expected measurement values collected throughout electrochemical reprocessing facilities. A review of the available literature of current research in measurements for electrochemical reprocessing systems identified twenty-two candidate measurement methodologies, which characterize fuel/salt composition, concentrations of various isotopes and elements, and operational parameters throughout the reprocessing facility. Four primary measurement methodologies have been simulated based on either physical simulations or empirical correlations: gamma emissions, neutron emissions, hybrid k-edge densitometry (HKED), and cyclic voltammetry. Initial investigation into the use of these measures for process monitoring and detection suggests the approach is viable and worthy of further investigation. This report summarizes efforts to generate signatures of key measurements during operation of electrochemical reprocessing facilities and initial investigation of data analytics to support process monitoring, diversion detection, and accountancy.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Tritium Management Requirements and Approaches for UNF Reprocessing

Four radionuclides have been identified as being sufficiently volatile in reprocessing of nuclear fuel that their release to the environment needs to be controlled to meet U.S. regulatory requirements. These radionuclides are {sup 3}H, {sup 14}C, {sup 85}Kr, and {sup 129}I. While iodine has been the focus of a number of studies due to the high decontamination factor (DF) requirements on multiple escape pathways, it is clear from prior studies that the control of tritium will also be a significant issue for future reprocessing plants, especially if processing relatively short-cooled fuels (<10 yr post-reactor discharge). Tritium contained in a used nuclear fuel (UNF) matrix will be released into the liquid and off-gas streams during fuel reprocessing. The amounts released into the process streams are a function of the type and burnup of the fuel processed and the chemical processes employed within the reprocessing plant. Previous studies have examined the tritium capture requirements for the reprocessing facility assuming that all of the tritium contained in the fuel matrix is volatilized in the head-end operations; i.e., tritium pretreatment is employed and tritium is completely released from the cladding. This scenario tends to limit the release pathway to the headend off-gas stream. Previous studies by Jubin and Spencer examined the accumulation and distribution of tritium in an aqueous-based reprocessing plant.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Nuclear Fuels and Reprocessing Technologies: A U.S. Perspective

Reprocessing and/or waste management issues are of concern to the “back end” of the nuclear fuel cycle. Of course, there are a great many “nuclear fuel cycle” scenarios to consider; if not in practice, then at least in theory. The simplest conceptually is the “once through” fuel cycle in which the spent fuel is discarded. The more complex fuel cycle scenarios involve reprocessing spent nuclear fuels and a family of nuclear reactor technologies to accommodate burning and breeding for various military and commercial needs. Therefore, the selection of a specific “fuel cycle” is what ultimately imposes the engineering requirements of the reprocessing and waste management technologies. No one part is independent of the other parts in a fuel cycle flowsheet; all parts are fully integrated. This paper presents a summary of radiochemical processes, nuclear reactor technologies, nuclear fuel types, and the reprocessing technologies that serve the different nuclear fuel types. Comprehending how this series of topics are related to each other is a prerequisite to understanding the requirements of any reprocessing strategy. The summary materials presented here are selective, as opposed to comprehensive. More detailed information on any one subject can be found in the reference materials.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Green Catalysts for Reprocessing Thermoset Polyurethanes

Polyurethane (PU) thermosets are usually landfilled at the end of their service lifetimes and cannot be recycled through conventional means. Although dibutyltin dilaurate (DBTDL) is an effective catalyst for reprocessing PU thermosets, organotins are immunotoxic and teratogenic, which is concerning for catalysts embedded within covalent adaptable networks (CANs). Here, we identify Zr(acac) 4 and Zr(tmhd) 4 as catalysts to reprocess PU CANs more sustainably. Thermoset PU foams containing Zr-based catalysts exhibit characteristic stress relaxation times between 6 and 200 s, similar or faster than DBTDL. These catalysts are capable of reprocessing a PU foam for four or five cycles. Dynamic mechanical thermal analysis indicates that zirconium-based catalysts preserve glass transition temperature and crosslink density between cycles and are promising catalysts for bulk reprocessing of thermoset PUs. Here, a solvent-free reprocessing method was developed by co-milling the PU foam and the Zr catalyst. Ultimately, these reprocessing methods using Zr-based catalysts will impart greater sustainability and circularity to PU plastics.

Catalysts↗
DOE OSTI2016

Impacts of Tritium Management Approaches on Tritium Distribution and Capture Requirements for UNF Reprocessing

Four radionuclides have been identified as being sufficiently volatile in reprocessing of nuclear fuel that their gaseous release needs to be controlled to meet U.S. regulatory requirements. These radionuclides are {sup 3}H, {sup 14}C, {sup 85}Kr, and {sup 129}I. Although iodine has been the focus of a number of studies due to the high decontamination factor (DF) requirements on multiple escape pathways, it is clear from prior studies that the control of tritium will also be a significant issue for future reprocessing plants, especially if processing relatively short-cooled fuels (<10 yr post reactor discharge). Tritium contained in a used nuclear fuel (UNF) matrix will be released into the liquid and off-gas streams during fuel reprocessing. The amounts released into the process streams are a function of the type and burnup of the fuel processed, and the chemical processes employed within the reprocessing plant. Previous studies have examined the tritium capture requirements for the reprocessing facility assuming that all of the tritium is volatilized in the head-end operations; i.e., tritium pretreatment is employed and tritium is completely released from the cladding. This scenario tends to limit the release pathway to the head-end off-gas stream. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Enhancements to a dissolver burn up credit safety case to reduce further GD use in the thermal oxide reprocessing plant (THORP), Sellafield - 14229

THORP reprocesses fuel from Britain's Advanced Gas-cooled Reactors (AGRs) and fuel from Light Water Reactors (LWRs). The THORP dissolvers use nitric acid poisoned with Gadolinium (Gd) to ensure criticality safety. The dissolver criticality safety case uses a burnup credit approach to determine a minimum required Gd concentration. The burn up credit approach followed originates from a time when fuel receipts for THORP were ongoing and hence models a deliberately conservative and artificial fuel type to cover all potential fuel receipts. External fuel receipts have now ceased and detailed information on post irradiation U and Pu isotopics is available for all fuel scheduled for reprocessing. Work has therefore been undertaken to determine whether the burn up credit safety case could be revised to be more representative of the fuel actually remaining for reprocessing and hence to reduce further the required Gd concentration for the dissolvers. This would ultimately reduce the quantity of high active liquid waste requiring treatment and storage. The great majority of fuel remaining for reprocessing in THORP is AGR fuel, for which the typical burnup is known to be much higher than was previously assumed in the safety case. Pu and U isotopics for irradiated AGR fuel were examined with the fuel inventory code FISPIN. Modelling with the code MONK then showed that the Gd requirement for irradiated AGR fuel of a given burnup was much lower than in the previous safety case due to the change in Pu:U ratio and Pu{sup 240} in Pu for AGR fuel compared with the previous conservative assumptions. The burnup of all remaining LWR fuel was found to be high and hence lower dissolver Gd concentrations could also be tolerated for reprocessing this fuel. The work has concluded that the THORP dissolver Gd concentration can be halved for all remaining LWR and AGR fuel campaigns with a consequent cost saving of ∼ UK pound 4 m in Gd and high active waste processing time. Implementation of this improvement is currently ongoing on the plant. (author)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Nuclear criticality safety standard for a fuel reprocessing plant assuming burnup credit published by the atomic energy society of Japan - 14591

In this paper an outline of the standard published in April 2015 by the Atomic Energy Society of Japan (AESJ) is presented. The standard gives basis of nuclear safety management of a spent fuel reprocessing plant that assumed burnup credit in nuclear criticality safety evaluation. Ten years ago the AESJ published Basic Items of Criticality Safety Control: 2004, AESJ-SC-F004:2004, which prescribed basic ideas, requirements and methods on nuclear criticality safety controls of facilities handling with nuclear fuel materials in general for preventing a nuclear criticality accident. However, it did not include any specific procedures for adopting burnup credit. Therefore, a new standard was envisaged as the first Standard for fuel reprocessing plants, which clarified the specific procedures to apply burnup credit to designers, operators, maintenance persons and administrators. The Standard, Procedures for Applying Burnup Credit to Criticality Safety Control of a Reprocessing Facility: 2014, AESJ-SC-F025: 2014, was developed by the AESJ after vital discussions of the Working Group on Nuclear Criticality Safety Control, which were followed by critical reviews of the Special Committee on Nuclear Fuel Cycle and those of the Standard Committee, where both committees were established under the AESJ. The followings are some features of the standard: 1. In many countries, application of burnup credit has been considered especially in transportation and storage of spent fuel. The standard applies to a reprocessing plant, especially to the Rokkasho Reprocessing Plant in Japan. The present edition of the Standard assumes the first phase of burnup credit, i.e., burnup credit considering reduction in {sup 235}U, production of {sup 239}Pu and changes in other actinides, but not considering neutron absorption effect of fission products. 2. This standard covers nuclear criticality safety management including safety design and safety control stages. It prescribes each procedure of nuclear safety management with emphasis on its necessity rather in detail. Attached to the standard are seven appendices, which give reference to it, and explanations, which provide supplemental information to the readers. Future needs of AESJ standards in the field of nuclear criticality safety will be discussed in the presentation. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Multiple Reprocessing Cycles of Corn Starch-Based Biocomposites Reinforced with Curauá Fiber

Biocomposites with a corn starch-based biodegradable polymer as matrix and 10 wt% vegetable curauá fiber were processed by injection molding and were submitted to reprocessing up to ten cycles with or without 3 wt% of maleic anhydride grafted polypropylene as coupling agent. The effect of reprocessing on hardness, impact and tensile properties as well as on the morphology, thermal properties, chemical structure and soil degradation behaviour of the matrix and biocomposites was evaluated. Curauá fibers have increased hardness, impact and tensile strengths as well as increased tensile modulus and decreased elongation at break of the biocomposites with respect to starch-based matrix and these properties slightly decreased or no considerable changes were observed with the reprocessing cycle increase. The addition of coupling agent promoted an increase in all properties and they remained almost constant with the reprocessing cycle increase. Thus, the incorporation of curauá fiber within starch-based matrix can improve the mechanical properties of the biocomposites which showed potential to be recycled despite the weight loss in soil degradation tests reached around 10 wt% after 230 days for biocomposites reprocessed ten cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Present and future potential of krypton-85 for the detection of clandestine reprocessing plants for treaty verification

Burnup calculations are applied to determine the amount of krypton-85 that is produced during the irradiation of nuclear fuel. Since krypton-85 is most likely released into the atmosphere during reprocessing to separate plutonium, atmospheric transport modeling is used to calculate the worldwide distribution of krypton-85 concentrations stemming from emissions from declared reprocessing plants. Our results are the basis for scenarios in which emissions from clandestine reprocessing facilities have to be detected against various background levels. We conclude that today’s background imposes heavily on the ability to detect small and medium plutonium separation rates; only high separation rates of 1 SQ per week and higher have a chance to be detected with feasible outlay. A fixed network of monitoring stations seems too costly; instead the high number of samples that are required rather calls for mobile sampling procedures, where air samples are collected at random locations over the world and are analyzed in regional laboratories for their krypton-85 concentration. Furthermore, it is argued that krypton-85 emissions from declared reprocessing activities have to be significantly lowered to enable a worldwide verification of the absence of even smaller clandestine reprocessing. For each scenario the number of samples that have to be taken for probable detection is calculated.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Reprocessing Models for the Optical Light Curves of Hypervariable Quasars from the Sloan Digital Sky Survey Reverberation Mapping Project

We explore reprocessing models for a sample of 17 hypervariable quasars, taken from the Sloan Digital Sky Survey Reverberation Mapping project, which all show coordinated optical luminosity hypervariability with amplitudes of factors ≳2 between 2014 and 2020. We develop and apply reprocessing models for quasar light curves in simple geometries that are likely to be representative of quasar inner environments. In addition to the commonly investigated thin-disk model, we include the thick-disk and hemisphere geometries. The thick-disk geometry could, for instance, represent a magnetically elevated disk, whereas the hemisphere model can be interpreted as a first-order approximation for any optically thick out-of-plane material caused by outflows/winds, warped/tilted disks, and so on. Of the 17 quasars in our sample, 11 are best-fitted by a hemisphere geometry, five are classified as thick disks, and both models fail for just one object. We highlight the successes and shortcomings of our thermal reprocessing models in case studies of four quasars that are representative of the sample. While reprocessing is unlikely to explain all of the variability that we observe in quasars, we present our classification scheme as a starting point for revealing the likely geometries of reprocessing for quasars in our sample and hypervariable quasars in general.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Spent Fuel Reprocessing Development and Usage of Fission Products as Starting Precursor for Ceramic Waste-Forms - 16498

The principal purpose of spent fuel reprocessing consists in the recovery of the uranium and plutonium and the separation of fission products so as to allow re-use of fissile isotopes and waste preparing for disposal. Reprocessing is a series of chemical operations that separates plutonium and uranium from other constituents in nuclear waste. Indeed, the plutonium separated can be used to fuel reactors, but also to make nuclear weapons. Since reprocessing operations are far more expensive than using uranium fuel and disposing of the spent fuel directly, this process is not readily considered. Without doubts the reprocessing price of $1000 per kilogram of heavy metal (kgHM), like uranium must be less by at least 2-3 times compared to directly deposing the spent fuel. And some more simple technology (in comparison with PUREX process) must be developed, for example, technology based on precipitation processes. One of the options to change reprocessing technology is the idea to use certain fission products occurring in spent fuel in considerable amount and capable to form insoluble substances as suitable materials for long-term storage or final disposal of radioactive wastes. The development of new materials for HLW immobilization are intended to reduce disposal cost. The present work was aimed at the search for the simple engineering decisions that would provide opportunity of fission products usage as starting precursor for ceramic waste-forms. The results of experiments on synthesis of Pd-based metallo-ceramic compositions are presented in this paper. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Circular Reprocessing of Thermoset Polyurethane Foams

Thermoset polyurethane (PU) foams are widely used in industrial applications, but they cannot be recycled by conventional melt reprocessing because of their cross-linked structures. The introduction of carbamate exchange catalysts converts thermoset PU into covalent adaptable networks (CANs), which are amenable to reprocessing at elevated temperatures. However, this approach has produced solid PU films, which have fewer uses and lower commercial demand. In this work, simultaneous reprocessing and refoaming of thermoset PU foams is demonstrated by leveraging the melt-processability of PU CANs and allowing cell growth by gas generation in a twin-screw extruder. The optimal operating temperature of the refoaming process is determined through chemical, thermal, and structural analysis of PU foam extrudates. The foam-to-foam extrusion process produces controllable, continuous, and uniform foam structures, as characterized by cell diameter and cell number density. Low-density PU foams are obtained through a process simulating injection molding. The compression properties of reprocessed PU foam are compared with as-synthesized PU foam to demonstrate efficacy of the refoaming processes. These results demonstrate that PU foams can be prepared through recycling while maintaining microstructural and chemical integrity. In the future, this strategy may be applied to thermoset PU foams of various chemical compositions and shows promise for scalability.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evaluation of the Waste Streams from Management of Reprocessing Off-Gas Streams - 18483

Nuclear fuel reprocessing is being considered in the United States as part of an effort to help meet US energy needs and as a means to improve waste management. During the chemical processing of UNF to recover the valuable components for reuse, a number of volatile radionuclides will be released into the off-gas streams of the reprocessing plant. These volatile radionuclides include H-3, C-14, Kr-85, and I-129. Off-gas abatement systems for the volatile radionuclides will be required to ensure that air emissions from a UNF reprocessing facility can meet or exceed emission requirements set forth by the US Environmental Protection Agency and the US Nuclear Regulatory Commission. An initial engineering evaluation of offgas abatement systems was completed recently. The evaluation addressed the designs of the head-end offgas treatment system, which typically includes both the shear off-gas and the dissolver off-gas and vessel off-gas treatment system. Based on this study, the waste volumes for each of the four primary volatile radionuclides (H-3, C-14, Kr-85, and I-129) were estimated. Included in these estimates were the nonradioactive isotopes and the 'tramp' elements found in air (e.g., Kr and C-12 as CO{sub 2}) and process chemicals (e.g., I and Cl). Because the final waste form for these radionuclides has not been selected, estimated volumes were calculated for various alternative waste forms as appropriate. The resulting waste volume for I was found to be highly dependent on the final waste form selected and increased by a factor of 2 to 4 by tramp halogens that would be released into the off-gas stream from the process chemicals. The volume of tritiated water from the fuel was quite small, but the estimated volume of the final waste form depended on the tritium management approach employed within the reprocessing plant. The Kr waste volume was calculated assuming pure Kr (i.e., assuming complete separation of Xe and Ar). For the case of no Xe separation, the estimated waste volume increased by factor of ∼10. Argon from the air, if not removed, increased the estimated volume by a factor of 425. The estimated volume of C-14 waste was dominated by the CO{sub 2} from the air leaking into the processing cell. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Safeguards Lessons Learned from the Rokkasho Reprocessing Plant - 19502

Once operational, the Rokkasho Reprocessing Plant (RRP) will have an operating throughput of 800 MT of uranium in irradiated LWR fuel per year. In order to establish effective and efficient safeguards at RRP, the safeguards discussion with the IAEA was initiated in 1988. However, at that time there were no available models or guidelines that could be used as a reference and multiple difficulties were recognized for the implementation of safeguards into a large scale reprocessing plant. Therefore, from 1988 to 1992, a multinational forum, referred to as LASCAR (Large Scale Reprocessing Plant Safeguards) [1], provided the recommendations on how an effective safeguards approach could be implemented into a large scale reprocessing plant while efficiently using existing resources. During the course of safeguards discussions between the IAEA, the State, and JNFL, the use of operator's equipment and measurement systems (by signal splitting with authentication) for inspections was studied. JNFL also examined incorporating inspection requirements into the process design: to reduce the costs associated with system installation and future system maintenance and to ensure effective, efficient, and credible safeguards implementation into the RRP (this approach has essentially become the 'Safeguards by Design (SBD)' process). From these studies and JNFL's experience of implementing safeguards into a new plant [2], JNFL established and applied signal splitting from operator's equipment as a means for providing inspectors required safeguards information. In addition, the LASCAR findings were utilized to establish the safeguards implemented into the RRP. Safeguards implementation into RRP commenced March 31, 2006. On June 4, 2008, the IAEA approved the 'integrated safeguards approach' for RRP. This paper provides a high level overview of the major safeguards implemented at RRP and the lessons learned from this implementation that can be applied to existing or future similar facilities. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Dioctyl ether radiolysis under used nuclear fuel reprocessing conditions: Foundational knowledge for the development of sacrificial ligand grafts

Radiation-induced ligand destruction and concomitant degradation product formation is unavoidable under envisioned used nuclear fuel reprocessing conditions, and ultimately limits the recyclability of a given solvent system formulation. With this in mind, a novel approach to ligand innovation for advanced separations processes is in the design of tailored “protomolecules,” which when exposed to ionizing radiation undergo desired chemical transformations, thereby allowing for a reprocessing solvent system to advantageously evolve with absorbed radiation dose. Here we provide foundational knowledge for the time-resolved (electron pulse) and steady-state (cobalt-60 gamma) radiolytic behavior of dioctyl ether, a protomolecule grafting surrogate. Gamma irradiation of single-phase solutions of dioctyl ether (5–100 vol.%) in n-dodecane resulted in the loss of dioctyl ether (G = -0.72 µmol J –1 ) and the formation of octane (G = 0.11 µmol J –1 ) and octanol (G = 0.15 µmol J –1 ) degradation products, the latter of which is a known reprocessing phase modifier and radioprotectant. Further, these radiation-induced changes were attributed to direct radiation effects, for more concentrated dioctyl ether solutions, and indirect radiation effects, predominantly driven by the reaction of dioctyl ether with the dodecane radical cation, for which we report a second-order rate coefficient of k = (1.53 ± 0.05) × 10 10 L mol –1 s –1 . Under typical biphasic extraction (4.0 mol L –1 HNO 3 ) and strip (0.1 mol L –1 HNO 3 ) reprocessing conditions, gamma irradiation of 5 vol.% dioctyl ether solvent systems afforded negligible change in the rate of parent molecule destruction but promoted significant differences in the radiolytic behavior of its degradation products. These differences are attributed to their respective interactions with [dioctyl ether/HNO 3 /H 2 O] and [octanol/HNO 3 /H 2 O] adducts extracted into the organic phase. Overall, these results support the grafting of ether linkages to advanced separations ligands (e.g., modified diglycolamides).

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Cost-Benefit Assessment of Krypton and Xenon Recovery from Aqueous Reprocessing

The purpose of this paper is to provide an understanding of the cost-benefit of capturing Kr and Xe from the existing process of aqueous reprocessing of UNF. The study accomplishes this with a market assessment of Xe prices and volumes today, coupled with a cost estimate of Kr and Xe capture out of cryogenic distillation within aqueous reprocessing. The market assessment shows that the average price of Xe is about $\$ $60/L while the average price of Kr is about $\$ $1/L. The assessment also shows that the market structure for Xe is one of oligopoly, in other words, very few suppliers to the Xe market. The assessment shows growing demand for Xe, particularly in medical applications like anesthesia. The cost assessment finds the unit cost of Xe to range from $\$ $71.50/L to $\$ $131.13/L. This range is only slightly above the current range of market prices today, and with growing demand for Xe, prices could reach the range it would take to support extraction of Xe from aqueous reprocessing. On the other hand, the estimated cost range for Kr is $\$ $830.15/L up to $\$ $1,522.52/L, which far exceeds the range of market prices for Kr. However, as the text notes, Kr capture is already part of aqueous reprocessing so these costs are sunk costs (already incurred) whereas the cost estimates for Xe are marginal cost (if Xe is desired, then the cost estimate would result from the Xe capture).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Reprocessable polyhydroxyurethane networks reinforced with reactive polyhedral oligomeric silsesquioxanes (POSS) and exhibiting excellent elevated temperature creep resistance

The rapid development of covalent adaptable networks or vitrimers shows promise for addressing the long-standing recycling issues associated with conventional, permanently cross-linked thermosets. At the same time, it is important to demonstrate that properties of reprocessable polymer networks can be optimized to meet the ongoing demand for high-performance materials. We have fabricated reprocessable polyhydroxyurethane (PHU) network composites reinforced with reactive polyhedral oligomeric silsesquioxanes (POSS). With functionalized POSS serving as a fraction of the cross-linkers, the PHU–POSS network nanocomposites exhibit significantly enhanced storage modulus at the rubbery plateau region relative to the neat PHU network. With up to 10 wt% POSS loading, these network composites can undergo melt-state reprocessing at 140 °C with 100% property recovery associated with cross-link density. We also show that hydroxyurethane dynamic chemistry leads to excellent creep resistance at elevated temperature up to 90 °C and is unaffected by reactive incorporation of POSS. In conclusion, this study demonstrates the effectiveness of POSS as nanofillers for designing high-performance, organic-inorganic dynamic PHU networks with excellent reprocessability.

42 ENGINEERING↗