TRISO Fuel Performance Modelling with BISON

Modeling of tristructural isotropic (TRISO)-coated particle fuel is being refined in the fuel performance code BISON. New developments include the implementation of an updated set of material properties, TRISO failure mechanisms, fission product diffusion parameters, and the design of a Monte Carlo scheme that allows BISON to calculate the probability of fuel failure within a population of TRISO particles and the subsequent fractional release of key fission products.

New Fractional Release Factors, Ozone Depletion Potentials, and Lifetimes for Four Long-Lived CFCs: CFC-13, CFC-114, CFC-114a, and CFC-115

<p>Knowing the stratospheric lifetime of an Ozone Depleting Substance (ODS), and its potential depletion of ozone during that time, is vital to reliably monitor and control the use of ODSs. Here, we present improved policy-relevant parameters: Fractional Release Factors (FRFs), Ozone Depletion Potentials (ODPs), and stratospheric lifetimes, for four understudied long-lived CFCs: CFC-13 (CClF<sub>3</sub>), CFC-114 (CClF<sub>2</sub>CCCLF<sub>2</sub>), CFC-114a (CCl<sub>2</sub>FCF<sub>3</sub>), and CFC-115 (C<sub>2</sub>ClF<sub>5</sub>). Previously derived lifetime estimates for CFC-114 and CFC-115 have substantial uncertainties, while lifetime uncertainties for CFC-13 and CFC-114a are absent from the peer-reviewed literature (Carpenter & Danie <em>et al</em>, 2018).</p><p>This study used both observational and model data to investigate these compounds and this work derives, for the first time, observation-based lifetimes utilising measurements of air samples collected in the stratosphere. We also used a version of the NASA Goddard Space Flight Center (GSFC) 2-D atmospheric model driven by temperature and transport fields derived from MERRA/MERRA-2 reanalysis.</p><p>FRFs for these compounds, which had been lacking until now, were derived using stratospheric air samples collected from several research flights with the high-altitude aircraft M55-Geophysica, and the background trend from archived surface air samples from Cape Grim, Tasmania.</p><p> By using a previously-published correlation between lifetime and FRF for seven well-characterised compounds (CF<sub>4</sub>, C<sub>2</sub>F<sub>6</sub>, C<sub>3</sub>F<sub>8</sub>, CHF<sub>3</sub>, HFC-125, HFC-227ea and SF<sub>6</sub>), we were able to derive lifetimes for these four new species. Lifetime estimates for CFC-114a agreed within the uncertainties (agreement to one sigma) with the lifetime estimates compiled in Burkholder <em>et al</em>. (2018), while the one for CFC-114 agreed within 2 sigma (measurement-related uncertainties) with those cited in Burkholder <em>et al</em>. (2018). However, observation-based lifetimes for CFC-13 and CFC-115 only agreed with those in Burkholder <em>et al</em>. (2018) within 3 sigma. The lifetime uncertainties in this study were reduced compared to those in Carpenter & Danie <em>et al</em> (2018).</p><p>As our lifetime estimates for these latter two compounds are notably lower than previous estimates, this suggests that these two compounds may have had greater emissions than previously thought, in order to account for their abundance. It also implies that they will be removed from the atmosphere more quickly than previously thought.</p><p>New ODPs were derived for these compounds from their new lifetimes and FRFs. Since for two of these compounds (CFC-13 and CFC-114a), there is an absence of observation-derived ODPs in the peer-reviewed literature, this is new and relevant information. The ODPs for CFC-114 and CFC-115 are comparable with estimates from the most recent Scientific Assessment of Ozone Depletion (Burkholder <em>et al</em>., 2018). Providing new and updated lifetimes, FRFs and ODPs for these compounds will help improve future estimates of their tropospheric emissions and their resulting damage to the stratospheric ozone layer.</p><p>             </p><p><strong>References</strong></p><p>Burkholder <em>et al</em>. (2018). Appendix A, Table A-1 in <em>Scientific Assessment of Ozone Depletion: 2018, Global Ozone Research and Monitoring Project</em>, Report No. 58, World Meteorological Organization, Geneva, Switzerland,  http://ozone.unep.org/science/assessment/sap.</p><p>Carpenter, L.J., Danie, J.S.<em> et al </em>(2018). Scenarios and Information for Policymakers Chapter 6, Table 6-1 in <em>Scientific Assessment of Ozone Depletion: 2018, Global Ozone Research and Monitoring Project</em>, Report No. 58, World Meteorological Organization, Geneva, Switzerland.</p>

Magnetic Graphene Oxide Nanocarrier for Targeted Delivery of Cisplatin: A Perspective for Glioblastoma Treatment

Selective vectorization of Cisplatin (CisPt) to Glioblastoma U87 cells was exploited by the fabrication of a hybrid nanocarrier composed of magnetic γ-Fe2O3 nanoparticles and nanographene oxide (NGO). The magnetic component, obtained by annealing magnetite Fe3O4 and characterized by XRD measurements, was combined with NGO sheets prepared via a modified Hummer’s method. The morphological and thermogravimetric analysis proved the effective binding of γ-Fe2O3 nanoparticles onto NGO layers. The magnetization measured under magnetic fields up to 7 Tesla at room temperature revealed superparamagnetic-like behavior with a maximum value of MS = 15 emu/g and coercivity HC ≈ 0 Oe within experimental error. The nanohybrid was found to possess high affinity towards CisPt, and a rather slow fractional release profile of 80% after 250 h. Negligible toxicity was observed for empty nanoparticles, while the retainment of CisPt anticancer activity upon loading into the carrier was observed, together with the possibility to spatially control the drug delivery at a target site.

An Assessment of Initial Leaching Characteristics of Alkali-Borosilicate Glasses for Nuclear Waste Immobilization

Initial leaching characteristics of simulated nuclear waste immobilized in three alkali- borosilicate glasses (ABS-waste) were studied. The effects of matrix composition on the containment performance and degradation resistance measures were evaluated. Normalized release rates are in conformance with data reported in the literature. High Li and Mg loadings lead to the highest initial de-polymerization of sample ABS-waste (17) and contributed to its thermodynamic instability. Ca stabilizes non-bridging oxygen (NBO) and reduces the thermodynamic instability of the modified matrix. An exponential temporal change in the alteration thickness was noted for samples ABS-waste (17) and Modified Alkali-Borosilicate (MABS)-waste (20), whereas a linear temporal change was noted for sample ABS-waste (25). Leaching processes that contribute to the fractional release of all studied elements within the initial stage of glass corrosion were quantified and the main controlling leach process for each element was identified. As the waste loading increases, the contribution of the dissolution process to the overall fractional release of structural elements decreases by 43.44, 5.05, 38.07, and 52.99% for Si, B, Na, and Li respectively, and the presence of modifiers reduces this contribution for all the studied metalloids. The dissolution process plays an important role in controlling the release of Li and Cs, and this role is reduced by increasing the waste loading.

Evaluation of stratospheric age of air from CF₄, C₂F₆, C₃F₈, CHF₃, HFC-125, HFC-227ea and SF₆; implications for the calculations of halocarbon lifetimes, fractional release factors and ozone depletion potentials

In a changing climate, potential stratospheric circulation changes require long-term monitoring. Stratospheric trace gas measurements are often used as a proxy for stratospheric circulation changes via the mean age of air values derived from them. In this study, we investigated five potential age of air tracers – the perfluorocarbons CF4, C2F6 and C3F8 and the hydrofluorocarbons CHF3 (HFC-23) and HFC-125 – and compare them to the traditional tracer SF6 and a (relatively) shorter-lived species, HFC-227ea. A detailed uncertainty analysis was performed on mean ages derived from these new tracers to allow us to confidently compare their efficacy as age tracers to the existing tracer, SF6. Our results showed that uncertainties associated with the mean age derived from these new age tracers are similar to those derived from SF6, suggesting that these alternative compounds are suitable in this respect for use as age tracers. Independent verification of the suitability of these age tracers is provided by a comparison between samples analysed at the University of East Anglia and the Scripps Institution of Oceanography. All five tracers give younger mean ages than SF6, a discrepancy that increases with increasing mean age. Our findings qualitatively support recent work that suggests that the stratospheric lifetime of SF6 is significantly less than the previous estimate of 3200 years. The impact of these younger mean ages on three policy-relevant parameters – stratospheric lifetimes, fractional release factors (FRFs) and ozone depletion potentials – is investigated in combination with a recently improved methodology to calculate FRFs. Updates to previous estimations for these parameters are provided.

Evaluation of stratospheric age-of-air from CF₄, C₂F₆, C₃F₈, CHF₃, HFC-125, HFC-227ea and SF₆; implications for the calculations of halocarbon lifetimes, fractional release factors and ozone depletion potentials

In a changing climate, potential stratospheric circulation changes require long-term monitoring. Stratospheric trace gas measurements are often used as a proxy for stratospheric circulation changes via the mean age of air values derived from them. In this study, we investigated five potential age of air tracers – the perfluorocarbons CF4, C2F6 and C3F8 and the hydrofluorocarbons CHF3 (HFC-23) and HFC-125 – and compare them to the traditional tracer SF6 and a (relatively) shorter-lived species, HFC-227ea. A detailed uncertainty analysis was performed on mean ages derived from these new tracers to allow us to confidently compare their efficacy as age tracers to the existing tracer, SF6. Our results showed that uncertainties associated with the mean age derived from these new age tracers are similar to those derived from SF6, suggesting these alternative compounds are suitable, in this respect, for use as age tracers. Independent verification of the suitability of these age tracers is provided by a comparison between samples analysed at the University of East Anglia and the Scripps Institution of Oceanography. All five tracers give younger mean ages than SF6, a discrepancy that increases with increasing mean age. Our findings qualitatively support recent work that suggests the stratospheric lifetime of SF6 is significantly less than the previous estimate of 3200 years. The impact of these younger mean ages on three policy-relevant parameters – stratospheric lifetimes, Fractional Release Factors (FRFs), and Ozone Depletion Potentials – is investigated in combination with a recently improved methodology to calculate FRFs. Updates to previous estimations for these parameters are provided.

A new time-independent formulation of fractional release

The fractional release factor (FRF) gives information on the amount of a halocarbon that is released at some point into the stratosphere from its source form to the inorganic form, which can harm the ozone layer through catalytic reactions. The quantity is of major importance because it directly affects the calculation of the ozone depletion potential (ODP). In this context time-independent values are needed which, in particular, should be independent of the trends in the tropospheric mixing ratios (tropospheric trends) of the respective halogenated trace gases. For a given atmospheric situation, such FRF values would represent a molecular property.We analysed the temporal evolution of FRF from ECHAM/MESSy Atmospheric Chemistry (EMAC) model simulations for several halocarbons and nitrous oxide between 1965 and 2011 on different mean age levels and found that the widely used formulation of FRF yields highly time-dependent values. We show that this is caused by the way that the tropospheric trend is handled in the widely used calculation method of FRF.Taking into account chemical loss in the calculation of stratospheric mixing ratios reduces the time dependence in FRFs. Therefore we implemented a loss term in the formulation of the FRF and applied the parameterization of a mean arrival time to our data set.We find that the time dependence in the FRF can almost be compensated for by applying a new trend correction in the calculation of the FRF. We suggest that this new method should be used to calculate time-independent FRFs, which can then be used e.g. for the calculation of ODP.