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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Analysis of fission gas release kinetics by on-line mass spectrometry

The release of fission gas (Xe and Kr) and helium out of nuclear fuel materials in normal operation of a nuclear power reactor can constitute a strong limitation of the fuel lifetime. Moreover, radioactive isotopes of Xe and Kr contribute significantly to the global radiological source term released in the primary coolant circuit in case of accidental situations accompanied by fuel rod loss of integrity. As a consequence, fission gas release investigation is of prime importance for the nuclear fuel cycle economy, and is the driven force of numerous R and D programs. In this domain, for solving current fuel behavior understanding issues, preparing the development of new fuels (e.g. for Gen IV power systems) and for improving the modeling prediction capability, there is a marked need for innovations in the instrumentation field, mainly for: . Quantification of very low fission gas concentrations, released from fuel sample and routed in sweeping lines. Monitoring of quick gas release variations by quantification of elementary release during a short period of time. Detection of a large range of atomic masses (e.g. H{sub 2}, HT, He, CO, CO{sub 2}, Ne, Ar, Kr, Xe), together with a performing separation of isotopes for Xe and Kr elements. Coupling measurement of stable and radioactive gas isotopes, by using in parallel mass spectrometry and gamma spectrometry techniques. To fulfill these challenging needs, a common strategy for analysis equipment implementation has been set up thanks to a recently launched collaboration between the CEA and the Univ. of Provence, with the technological support of the Liverpool Univ.. It aims at developing a chronological series of mass spectrometer devices based upon mass filter and 2D/3D ion traps with Fourier transform operating mode and having increasing levels of performances to match the previous challenges for out-of pile and in-pile experiments. The final objective is to install a high performance online mass spectrometer coupled to a gamma spectrometer in the fission product laboratory of the future Jules Horowitz Material Test Reactor. An intermediate step will consist of testing first equipment on an existing experimental facility in the LECA-STAR Hot Cell Laboratory of the CEA Cadarache. This paper presents the scientific and operational stakes linked to fission gas issues, resumes the current state of art for analyzing them in nuclear facilities, then presents the skills gathered through this collaboration to overcome technological bottlenecks. Finally it describes the implementation strategy in nuclear research facilities of the CEA Cadarache. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2019

Measurements of fission gas release from nuclear fuel in support of BISON fuel performance analysis

This project established a fuel irradiation and fission gas release (FGR) loop that has been designed for implementation at the PULSTAR reactor of North Carolina State University (NCSU). The FGR loop is capable of analyzing various types of fuel samples including, e.g., uranium dioxide fuel (UO 2 ) and uranium silicide (U 3 Si 2 ) samples. The fuel samples were produced and characterized at Idaho National Laboratory (INL) and shipped NCSU. The samples are ready for irradiation in the FGR loop to a given total thermal neutron fluence and under controlled temperature conditions. An innovative high resolution gamma-ray spectrometry approach and instrumentation have been established to monitor the loop’s sweep gas and perform high accuracy measurements of the gas release rates relative to predicted birth rates to establish the release-to-birth ratio (R/B) for a given radionuclide. In addition, uncertainty minimization is achieved through the formulation of the measurement observables into relative release-to-birth indicators for selected radionuclides. The experimental findings will be utilized to enhance and validate the fission gas release models that are currently implemented in the BISON fuel performance code. The experimentally deduced physical parameters will be incorporated in BISON’s fission gas release models. Atomistic simulations of fuel behavior have been performed to investigate the mechanisms of fission gas migration in the fuel. At this stage, performance of the fuel irradiation experiments awaits licensing approval by the US NRC.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Experimental Technetium Release from Simulated Salt-stone Cementitious Waste Form - 18419

Experiments are being conducted to evaluate the early release of technetium (Tc) from fresh salt-stone waste forms using dynamic flow-through tests. Salt-stone is a chemically reducing, grout-based waste form used by the U.S. Department of Energy (DOE) to dispose of low-activity salt solutions arising from high-level radioactive waste tank closure activities at the Savannah River Site (SRS). A key safety function of salt-stone is maintaining a low-flow, chemically reducing environment that will attenuate the release of redox-sensitive radioelements such as Tc. Salt-stone also provides a physical barrier due to its low intrinsic permeability, which limits both water and oxygen ingress. These release experiments, conducted to support the U.S. Nuclear Regulatory Commission's monitoring role during tank closure, are designed to provide independent information on how well salt-stone will perform its safety function. The dynamic leach tests were conducted in a Hassler-type core-holder permeameter system that allows an accelerated flow rate of simulated SRS groundwater through an intact cylinder of salt-stone spiked with Tc-99 at a concentration of approximately 2,100 Bq/g (3 ppm). The first salt-stone specimen to be tested (Specimen 2) was prepared with Grade 100 ground granulated blast-furnace slag and aged for 119 days in a temperature-controlled, low-oxygen, high-humidity environment. Before test completion, 9.5 pore volumes (PV) of simulated SRS groundwater were passed through the salt-stone cylinder. After a few PV, apparent saturated hydraulic conductivity (K{sub sat}) values calculated from flow data reached a steady-state value of approximately 1.0 x 10{sup -9} cm/s, which is within the range of previously reported data. Tc-99 concentrations in leachate peaked early during the leach test at 2.0 x 10{sup -7} M and then declined to approximately 4 x 10{sup -8} M after 9.5 PV. The leachate Tc-99 concentration after elution of 9.5 PV is broadly consistent with a Tc solution concentration controlled by the solubility of reduced Tc solids. The range of Tc-99 concentrations is similar to the range reported for a column test that was sponsored by DOE, but the time pattern of release differs. The second salt-stone specimen tested (Specimen 3) was aged for 372 days and it further differed from the first specimen in that its Grade 100 slag component had been finely ground using a mortar and pestle in an attempt to make it more reactive. This second test yielded Tc release behavior broadly similar to that observed during the first test, except that the early Tc peak (at 1.2 x 10{sup -6} M) was six times higher and the concentration after 6.7 PV (8.8 x 10{sup -8} M) was approximately two times higher than in the first test. In addition, the steady-state K{sub sat} was an order of magnitude lower than that of the first specimen. During the second test, the injection pump was intentionally turned off for a period of 11 days (i.e., approximate residence time for 1 PV) and a Tc spike was observed when pumping resumed, suggesting that longer residence times may promote higher Tc effluent concentrations. During a second intentional shut-down of the pump for 25 days (approximate residence time for 2 PV), another Tc spike was observed. An unplanned excursion to higher confining pressure physically affected the specimen, temporarily lowering the apparent K{sub sat} followed by a subsequent increase in both K{sub sat} and Tc effluent concentration. One hypothesis is that the transient spike in confining pressure and resulting salt-stone compression and later decompression may have induced Tc release from otherwise inactive pores. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Analysis of a Loop for Fission Gas Release and Monitoring at the PULSTAR Reactor

Modern nuclear fuel performance analysis tools aim at establishing a predictive approach for examining macroscopic fuel behavior due to fuel gaseous swelling and the associated pellet cladding mechanical interaction (PCMI). In general, the macroscopic behavior is highly sensitive to understanding microscopically driven phenomena, which in this case is the release of fission gas (i.e., Kr and Xe) from the fuel. Previous studies identified the uncertainties associated with the intra-granular fission gas diffusion coefficient as most limiting for the accuracy of fission gas release calculations. In particular, it was concluded that, in order to improve fission gas release as well as gaseous swelling predictions using fuel performance codes, a better characterization of the diffusion coefficient is needed. This work explores the implementation of an on-line fission gas release and measurement loop at the North Carolina State University (NCSU) PULSTAR reactor. A unique characteristic of this loop is the ability to control the temperature of the fuel samples during irradiation to establish a more accurate correlation between the irradiation conditions and an observable such as the intragranular gas diffusion coefficient. Analysis was performed of an 'in-pile' fission gas release experiment that is currently under implementation at the NCSU PULSTAR reactor. Using MCNP6 calculations and COMSOL simulations the fission rate density and temperature distributions in UO{sub 2} microspheres were estimated. To explore the feasibility of detecting fission gas isotopes, estimates of R/B for {sup 138}Xe were obtained using the equivalent sphere model and combined with MCNP6 predicted B estimates to obtain R. Assuming detection in a typical gamma-ray spectrometry HPGe system, it was conclude that reasonable count rates will be achieved to allow extraction of release information. At this stage, accurate assessment is underway of the performance of various loop components to set the final design criteria in support of loop fabrication. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Stimulation of synaptoneurosome glutamate release by monomeric and fibrillated α-synuclein

The α-synuclein protein exists in vivo in a variety of covalently modified and aggregated forms associated with Parkinson's disease (PD) pathology. However, the specific proteoform structures involved with neuropathological disease mechanisms are not clearly defined. Since α-synuclein plays a role in presynaptic neurotransmitter release, an in vitro enzyme-based assay was developed to measure glutamate release from mouse forebrain synaptoneurosomes (SNs) enriched in synaptic endings. Glutamate measurements utilizing SNs from various mouse genotypes (WT, over-expressers, knock-outs) suggested a concentration dependence of α-synuclein on calcium/depolarization-dependent presynaptic glutamate release from forebrain terminals. In vitro reconstitution experiments with recombinant human α-synuclein proteoforms including monomers and aggregated forms (fibrils, oligomers) produced further evidence of this functional impact. Notably, brief exogenous applications of fibrillated forms of α-synuclein enhanced SN glutamate release but monomeric forms did not, suggesting preferential membrane penetration and toxicity by the aggregated forms. However, when applied to brain tissue sections just prior to homogenization, both monomeric and fibrillated forms stimulated glutamate release. Immuno-gold and transmission electron microscopy (TEM) detected exogenous fibrillated α-synuclein associated with numerous SN membranous structures including synaptic terminals. Western blots and immuno-gold TEM were consistent with SN internalization of α-synuclein. Additional studies revealed no evidence of gross disruption of SN membrane integrity or glutamate transporter function by exogenous α-synuclein. Finally, overall excitotoxicity, due to enhanced glutamate release in the face of either overexpressed monomeric α-synuclein or extrasynaptic exposure to fibrillated α-synuclein, should be considered as a potential neuropathological pathway during the progression of PD and other synucleinopathies.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Controlled release of losartan from acid- and heat-treated halloysite nanotubes

In this work, a simple method was used to sustained release of losartan (LOS) as a high blood pressure-controller drug using halloysites (HNT) as a carrier. The present work can be considered as an effective method because of using HNT as a natural source, which is available, inexpensive, safe with specific structure that led to release of drug, gradually. This carrier was improved by calcination and etching processes and their effect was investigated on loading amount and in vitro release of drug from HNT. The products were characterized by various analyses such as: BET (Brunauer–Emmett–Teller), TG (thermal gravimetry), TEM (transmission electron microscopy), and XRD (X-ray powder diffraction). According to the studies, two processes improving had no effect on structure and morphology of HNT and only increased the lumen size of them. It should be noted, removal water molecules through calcination had binary effect on halloysites: enlargement of lumen and decreasing the drug loading. Besides, release rate was investigated and it showed that maximum and minimum release rate of LOS are assigned to simple HNT and etched-HNT (EHNT), respectively. Kinetics studies confirmed that releasing the LOS molecules from HNT followed by diffusion process that is identified as Fickian diffusion.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Development of Novel Biodegradable Enrofloxacin–Silica Composite for In Vitro Drug Release Kinetic Studies

A sustained drug delivery system is developed by using nonionic polymer to formulate drug release rate from silica capsules. To serve this purpose, silica capsules filled with poly(ethylene glycol) (PEG) were incorporated with a veterinary antibiotic drug enrofloxacin (ENF); as a model hydrophobic drug by using a general and facile sol–gel route. The physicochemical properties of the prepared drug-loaded composites were investigated by scanning electron microscope (SEM), nitrogen adsorption, Fourier transform infrared spectroscopy and thermal analysis (TGA). The impact of the media’s ionic strength on the drug release was evaluated over a range of 0–0.4 M to simulate the gastrointestinal feed in two physiological pH conditions. Sodium chloride was applied for ionic concentration adjustment due to its ability to salt out polymers in the midrange of the lyotropic series. Simultaneously, the drug release kinetics was evaluated by fitting experimental data to common empirical (zero-order, first order and Higuchi) and semi-empirical (Ritger–Peppas and Sahlin–Peppas) models. The drug release kinetics from capsules revealed a non-Fickian diffusion and pure relaxation-controlled release. Of these models, Sahlin–Peppas equation best fit the release data of ENF. To determine the best model, non-linear regressions were carried out.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Transient receptor potential ankyrin 1 channels are involved in spontaneous peptide hormone release from astrocytes

Highlights: • TRPA1 regulates spontaneous calcium signals in astrocytes. • Astrocytes spontaneously release gliotransmitters. • Spontaneous gliotransmitter release is modulated by TRPA1 channels. Astrocytes, a large population of glial cells, detect neurotransmitters and respond by increasing intracellular Ca{sup 2+} concentration ([Ca{sup 2+}]{sub i}) and releasing chemical molecules called gliotransmitters. Recently discovered Ca{sup 2+} influx through transient receptor potential ankyrin 1 (TRPA1) channels is reported to cause spontaneous [Ca{sup 2+}]{sub i} increase in astrocytes. While several physiological functions of TRPA1-mediated spontaneous Ca{sup 2+} signal have been revealed, relation with gliotransmitter release, especially peptide hormone exocytosis is largely unknown. We therefore explored the [Ca{sup 2+}]{sub i} and exocytosis dynamics in rat astrocyte cell line C6 cells and primary astrocytes. TRPA1-mediated spontaneous [Ca{sup 2+}]{sub i} transients were observed in both C6 cells and primary astrocytes. Total internal reflection fluorescence microscopy revealed that Venus-tagged brain-derived neurotrophic factor and neuropeptide Y were released spontaneously from astrocytes. Activation of TRPA1 channels enhanced the frequency of peptide hormone exocytosis, and inhibition of TRPA1 channels decreased the number of peptide hormone exocytosis. These results suggest that TRPA1-mediated spontaneous [Ca{sup 2+}]{sub i} increase modulates the spontaneous release of peptide hormones from astrocytes.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Noble and Major Gases Released from Rock Core Materials as Intrinsic Tracers for Detecting Carbon Dioxide Leakage – Laboratory Evaluation

The elemental and isotopic compositions of noble gases constitute a set of non-reactive geochemical tracers. Noble gases released from geological formations in contact with pore water acidified by leaked carbon dioxide (CO2) can potentially be employed as tracers for detection of CO2 leakage from storage reservoirs in carbon sequestration sites. In a set of laboratory tests, core materials from a stratigraphic borehole at the proposed FutureGen 2.0 carbon storage site (Jacksonville, IL, USA) were reacted with an aqueous acid to simulate contact with aqueous CO2 and the gas released from the reaction was collected. The major gas components, the noble gas concentrations and isotopic ratios were determined to evaluate the feasibility of using the released noble gases as tracers for crustal water-rock interactions. Experiments yielded several promising tracer candidates for intrinsic monitoring of CO2 leakage at the proposed FutureGen 2.0 site. The most robust signals stem from CH4 and 4He released by carbonates associated with dolomite and shale formations from the primary containment zone. No useful signal was obtained from the sandstone formation due to its very low yield of gas when acidified. Xenon released from the primary-containment zone also showed promise as a tracer, but a more robust analysis requires a different experimental set up. A general enrichment of CH4, N2 and light noble gas isotopes with respect to Ar abundance was observed and is consistent with the addition of major gases (CO2, CH4, and to a lesser extent N2) released by a combination of the decomposition of carbonate mineral phases and/or organic matter in the dolomite and shale formations. The enrichment of these major gases leads to enhanced signals from heterogeneous molecular and isotopic ratios including 3He/4He, 4He/22Ne, 20Ne/22Ne, 21Ne*/22Ne, 20Ne/36Ar, 84Kr/36Ar, 132Xe/36Ar, and 132Xe/84Kr, amongst others.

noble gases, tracers, carbon sequestration, CO2, i↗
DOE OSTI2015

Release and control of hydrogen sulfide during sludge thermal drying

The release of hydrogen sulfide (H2S) during sludge drying is a major environmental problem because of its toxicity to human health. A series of experiments were performed to investigate the mechanisms and factors controlling the H2S release. Results of this study show that: 1) the biomass and activity of sulfate-reducing bacteria (SRB) in sludge were the major factors controlling the amount of H2S release, 2) the sludge drying temperature had an important effect on both the extent and the timing of H2S release from the sludge, and 3) decreasing sludge pH increased the H2S release. Based on the findings from this study, a new system that integrates sludge drying and H2S gas treatment was developed to reduce the amount of H2S released from sludge treatments.

sludge, H2S, treatment, drying, control↗
DOE OSTI2024

Impact of temperature variations on BISON predictions of Ag release in AGR-1 and AGR-2 experiments

Understanding and quantifying the release of fission products like silver (Ag) from TRistructural ISOtropic (TRISO) fuel particles is important to assess the safe operation of advanced high temperature reactors. Although the silicon carbide (SiC) layer of TRISO particles is effective as the main fission product barrier, Ag can be released from intact TRISO particles. A mechanistic model for the effective Ag diffusivity, D eff , was previously developed as a function of temperature and microstructure variables informed by atomistic modeling of Ag diffusivity on the mesoscale. Here in this study, we use this model to explore how experimental temperature uncertainties impact the overall predicted Ag release. This analysis shows that temperature uncertainties have a significant impact on the overall Ag release predictions. Furthermore, we show that the time average volume average temperature (TAVA) temperature is not an appropriate proxy for temperature histories to predict fission product release. We attribute this to the Arrhenius dependence of Ag diffusivity with respect to temperature. The detailed temperature histories, therefore, provide the most accurate results are are of most importance for modeling efforts. Overall, this work shows the importance of considering the experimental uncertainty of the temperature on computational predictions of fission product transport and release and the need for more accurate temperature histories from future experiments.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

Controlled release of ibuprofen by meso–macroporous silica

Structured meso–macroporous silica was successfully synthesized from an O/W emulsion using decane as a dispersed phase. Sodium silicate solution, which acts as a silica source and a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (EO{sub 19}PO{sub 39}EO{sub 19}) denoted as P84 was used in order to stabilize the emulsion and as a mesopore template. The materials obtained were characterized through transmission electron microscopy (TEM), scanning electron microscopy (SEM), small-angle X-ray diffraction scattering (SAXS) and nitrogen adsorption–desorption isotherms. Ibuprofen (IBU) was selected as the model drug and loaded into ordered meso–macroporous materials. The effect of the materials’ properties on IBU drug loading and release was studied. The results showed that the loading of IBU increases as the macropore presence in the material is increased. The IBU adsorption process followed the Langmuir adsorption isotherm. A two-step release process, consisting of an initial fast release and then a slower release was observed. Macropores enhanced the adsorption capacity of the material; this was probably due to the fact that they allowed the drug to access internal pores. When only mesopores were present, ibuprofen was probably adsorbed on the mesopores close to the surface. Moreover, the more macropore present in the material, the slower the release behaviour observed, as the ibuprofen adsorbed in the internal pores had to diffuse along the macropore channels up to the surface of the material. The material obtained from a highly concentrated emulsion was functionalized with amino groups using two methods, the post-grafting mechanism and the co-condensation mechanism. Both routes improve IBU adsorption in the material and show good behaviour as a controlled drug delivery system. - Graphical abstract: Ibuprofen release profiles for the materials obtained from samples P84{sub m}eso (black diamonds), P84{sub 2}0% (white squares), P84{sub 5}0% (black triangles), P84{sub 7}5% (white diamonds), P84{sub 7}5% functionalized by grafting (black squares) and P84{sub 7}5% functionalized by co-condensation method (white triangles). Display Omitted - Highlights: • Ordered meso–macroporous material is used as a controlled delivery system for ibuprofen. • Incorporation of macropores in mesoporous silica improves ibuprofen adsorption. • Meso–macroporous structures provide a lower delivery than mesoporous silica. • APTES functionalization in meso–macroporous materials improves ibuprofen adsorption and delivery behaviour.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Light-stimulated cargo release from a core–shell structured nanocomposite for site-specific delivery

This paper reported a core–shell structured site-specific delivery system with a light switch triggered by low energy light (λ=510 nm). Its core was composed of supermagnetic Fe{sub 3}O{sub 4} nanoparticles for magnetic guiding and targeting. Its outer shell consisted of mesoporous silica molecular sieve MCM-41 which offered highly ordered hexagonal tunnels for cargo capacity. A light switch N1-(4aH-cyclopenta[1,2-b:5,4-b′]dipyridin-5(5aH)-ylidene)benzene-1, 4-diamine (CBD) was covalently grafted into these hexagonal tunnels, serving as light stimuli acceptor with loading content of 1.1 μM/g. This composite was fully characterized and confirmed by SEM, TEM, XRD patterns, N{sub 2} adsorption/desorption, thermogravimetric analysis, IR, UV–vis absorption and emission spectra. Experimental data suggested that this composite had a core as wide as 150 nm and could be magnetically guided to specific sites. Its hexagonal tunnels were as long as 180 nm. Upon light stimuli of “on” and “off” states, controllable release was observed with short release time of ~900 s (90% capacity). - Graphical abstract: A core–shell structured site-specific delivery system with a light switch triggered by yellow light was constructed. Controllable release was observed with short release time of ~900 s (90% capacity). - Highlights: • A core–shell structured site-specific delivery system was constructed. • It consisted of Fe{sub 3}O{sub 4} core and MCM-41 shell grafted with light switch. • This delivery system was triggered by low energy light. • Controllable release was observed with short release time of ~900 s.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Synthesis, characterization, and controlled release antibacterial behavior of antibiotic intercalated Mg–Al layered double hydroxides

Graphical abstract: The antibiotic anion released from Mg–Al LDHs provides a controlled release antibacterial activity against the growth of Micrococcus lysodeikticus in 3.5% NaCl solution. Highlights: ► Antibiotic anion intercalated LDHs were synthesized and characterized. ► The ion-exchange one is responsible for the release process. ► The diffusion through particle is the release rate limiting step. ► LDHs loaded with antibiotic anion have high antibacterial capabilities. -- Abstract: Antibiotic–inorganic clay composites including four antibiotic anions, namely, benzoate (BZ), succinate (SU), benzylpenicillin (BP), and ticarcillin (TC) anions, intercalated Mg–Al layered double hydroxides (LDHs) were synthesized via ion-exchange. Powder X-ray diffraction and Fourier transform infrared spectrum analyses showed the successful intercalation of antibiotic anion into the LDH interlayer. BZ and BP anions were accommodated in the interlayer region as a bilayer, whereas SU and TC anions were intercalated in a monolayer arrangement. Kinetic simulation of the release data indicated that ion-exchange was responsible for the release process, and the diffusion through the particles was the rate-limiting step. The antibacterial capabilities of LDHs loaded with antibiotic anion toward Micrococcus lysodeikticus growth were analyzed using a turbidimetric method. Significant high inhibition rate was observed when LDH nanohybrid was introduced in 3.5% NaCl solution. Therefore, this hybrid material may be applied as nanocontainer in active antifouling coating for marine equipment.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Multiphysics simulation of TRISO fuel compacts and the effects of homogenization on silver release predictions

This work studies the impact of explicit and homogenized modeling approaches on the multiphysics simulation of TRistructural ISOtropic (TRISO) fuel compacts in prismatic High Temperature Gas Reactors (HTGRs) and the silver release predictions. TRISO fuel compacts exhibit complex double heterogeneity that significantly affects heat conduction, neutron transport, and fission products release. In this work, we use Cardinal, a multiphysics tool based on the Multiphysics Object-Oriented Simulation Environment (MOOSE) framework, to couple neutron transport and heat conduction. OpenMC is used for neutron transport and the MOOSE heat transfer module is used for the heat conduction. Then, we use BISON for the silver release predictions. Two different modeling approaches—explicit modeling of individual TRISO particles and homogenized representation using effective thermal properties—are compared at high TRISO packing fractions (20% and 40%) across varying power densities. Results demonstrate that homogenization significantly under-predicts peak temperatures, for the case of high power/TRISO, there is a difference of 83.73 K in the maximum temperature. Additionally, homogenization underestimates the silver release predictions compared to explicit modeling. Specifically, the temperature and power density differences lead to significant differences in silver release predictions. This work demonstrates the importance of accurately modeling heterogeneity of the TRISO particles to reliably predict fission product release and assess reactor safety margins.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Fast Surface Oxygen Release Kinetics Accelerate Nanoparticle Exsolution in Perovskite Oxides

Exsolution is a recent advancement for fabricating oxide-supported metal nanoparticle catalysts via phase precipitation out of a host oxide. A fundamental understanding and control of the exsolution kinetics are needed to engineer exsolved nanoparticles to obtain higher catalytic activity toward clean energy and fuel conversion. Since oxygen release via oxygen vacancy formation in the host oxide is behind oxide reduction and metal exsolution, we hypothesize that the kinetics of metal exsolution should depend on the kinetics of oxygen release, in addition to the kinetics of metal cation diffusion. In this report we probe the surface exsolution kinetics both experimentally and theoretically using thin-film perovskite SrTi 0.65 Fe 0.35 O 3 (STF) as a model system. We quantitatively demonstrated that in this system the surface oxygen release governs the metal nanoparticle exsolution kinetics. As a result, by increasing the oxygen release rate in STF, either by reducing the sample thickness or by increasing the surface reactivity, one can effectively accelerate the Fe 0 exsolution kinetics. Fast oxygen release kinetics in STF not only shortened the prereduction time prior to the exsolution onset, but also increased the total quantity of exsolved Fe 0 over time, which agrees well with the predictions from our analytical kinetic modeling. The consistency between the results obtained from in situ experiments and analytical modeling provides a predictive capability for tailoring exsolution, and highlights the importance of engineering host oxide surface oxygen release kinetics in designing exsolved nanocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Release dynamics of nanodiamonds created by laser-driven shock-compression of polyethylene terephthalate

Laser-driven dynamic compression experiments of plastic materials have found surprisingly fast formation of nanodiamonds (ND) via X-ray probing. This mechanism is relevant for planetary models, but could also open efficient synthesis routes for tailored NDs. We investigate the release mechanics of compressed NDs by molecular dynamics simulation of the isotropic expansion of finite size diamond from different P-T states. Analysing the structural integrity along different release paths via molecular dynamic simulations, we found substantial disintegration rates upon shock release, increasing with the on-Hugnoiot shock temperature. We also find that recrystallization can occur after the expansion and hence during the release, depending on subsequent cooling mechanisms. Our study suggests higher ND recovery rates from off-Hugoniot states, e.g., via double-shocks, due to faster cooling. Laser-driven shock compression experiments of polyethylene terephthalate (PET) samples with in situ X-ray probing at the simulated conditions found diamond signal that persists up to 11 ns after breakout. In the diffraction pattern, we observed peak shifts, which we attribute to thermal expansion of the NDs and thus a total release of pressure, which indicates the stability of the released NDs.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Controlled release of cortisone drugs from block copolymers synthetized by ATRP

Diseases affecting posterior eye segment, like macular edema, infection and neovascularization, may cause visual impairment. Traditional treatments, such as steroidal-drugs intravitreal injections, involve chronic course of therapy usually over a period of years. Moreover, they can require frequent administrations of drug in order to have an adequately disease control. This dramatically reduce patient’s compliance. Efforts have been made to develop implantable devices that offer an alternative therapeutic approach to bypass many challenges of conventional type of therapy. Implantable drug delivery systems (DDS) have been developed to optimize therapeutic properties of drugs and ensure their slow release in the specific site. Polymeric materials can play an essential role in modulating drug delivery and their use in such field has become indispensable. During last decades, acrylic polymers have obtained growing interest. Biocompatibility and chemical properties make them extremely versatile, allowing their use in many field such as biomedical. In particular, block methacrylate copolymer with a balance of hydrophilic and hydrophobic properties can be suitable for prolonged DDS in biomedical devices. In this work, we focused on the realization of a system for controlled and long term release of betamethasone 17,21-dipropionate (BDP), a cortisone drug, from methacrylic block copolymers, to be tested in the treatment of the posterior eye’s diseases. Different series of methyl methacrylate/hydroxyethyl methacrylate (MMA/HEMA) block and random copolymers, with different monomer compositions (10–60% HEMA), were synthetized by Atom Transfer Radical Polymerization (ATRP) to find the best hydrophilic/hydrophobic ratio, able to ensure optimal kinetic release. Copolymer samples were characterized by NMR spectroscopy ({sup 1}H-NMR, {sup 13}C-NMR, CosY), SEC, TGA and DSC. Monitoring of drug release from films loaded with BDP was carried out by HPLC analysis. Evaluation of different kinetic models allowed to deduce that release of BDP is controlled over time from PMMA-b-PHEMA 53/47. In particular, PMMA-b-PHEMA 53/47 showed the best release profile to achieve the therapeutic reference dose of 3 µg/die, employed in treatment of posterior eye disease, up to four months. Accordingly, PMMA-b-PHEMA 53/47 has been tested to prepare ocular inserts. Ocular inserts with different shape and the same area of polymer films have been obtained using silicon moulds made by a 3D printer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗