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We review the development of a disaster health care response system in Mississippi aimed at improving disaster response efforts. Large-scale disasters generate many injured and ill patients, which causes a significant utilization of emergency health care services and often requires external support to meet clinical needs. Disaster health care services require a solid infrastructure of coordination and collaboration to be effective. Following Hurricane Katrina, the state of Mississippi implemented best practices from around the nation to establish a disaster health care response system. The State Medical Response System of Mississippi provides an all-hazards system designed to support local response efforts at the time, scope, and scale required to successfully manage the incident. Components of this disaster health care response system can be replicated or adapted to meet the dynamic landscape of health care delivery following disasters. (Disaster Med Public Health Preparedness. 2017;11:600–604)
Nd-bearing zirconolite was leached at 90°C for 157 days in 0.001M citric acid under single-pass-flow-through conditions (modified MCC-4 protocol). Three different flow rates were used, ranging in an order of magnitude from 10 mL per day to 100 mL per day, to determine the effect of the rate of leachant replenishment on the durability of the zirconolite. Results of previous studies on the role of complexing agents on the leaching behaviour of single-phase zirconolite have been included in the discussion.
The pH of the citric acid solution was adjusted to 5 using KOH, mimicking that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.
Simulated groundwater containing 0.001M citric acid at 90°C led to congruency in elemental releases and a diminution of release rate with time of about an order of magnitude, reaching virtual constancy after about 50 to 60 days to a level of about 10−5 g m−2 day−1. The most significant finding was that the elemental release rates of Nd, Ti and Zr (and Ca and Al where detected) were similar for all flow rates. Clearly, varying flow rate by up to an order of magnitude had no effect on elemental releases i.e. there is no solubility limit control on releases at 0.001M citric acid concentration.
An important finding of previous studies using identical leaching protocols with 0.001M citric acid, and inferred in our latest investigations reported here, was that there is no secondary layer development at the surface of the zirconolite to affect leach rates. In contrast, parallel tests carried out in deionised water instead of citric acid showed that hydroxides form in situ on the zirconolite surface, effectively forming hydrolysed zirconolite. This controls further dissolution of the zirconolite matrix due to the solubility limit being reached with respect to the hydrolysed phases rather than with zirconolite. Complexation by citrate ions prevents such control by hydrolysed species on zirconolite solubility.
Even under the more aggressive conditions imposed in these studies (0.001M citric acid), and regardless of flow rate of the leachant, elemental releases from zirconolite are very low for a candidate wasteform and demonstrate its attributes as a ceramic-based wasteform for the containment of actinides.
We have studied the aqueous durability of pyrochlore-structured yttrium-titanate (Y2Ti2O7) and Nd/Al-bearing zirconolite [(Ca0.8Nd0.2)Zr(Ti1.8Al0.2)O7] in both neutral and acidic solutions, with and without the presence of 0.001 M of NaF. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) were used to characterize the composition, structure and morphology of the pyrochlore (Y2Ti2O7) and zirconolite surfaces, both before and after static dissolution testing at 90 and 150°C for four weeks. The leachates were also analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to estimate the individual elemental releases. The results show that the presence of F- ions only has a significant effect in acidic media on the dissolution behavior of pyrochlore and zirconolite. This detrimental effect is more pronounced for pyrochlore than zirconolite; the Y2Ti2O7 surface was replaced completely by alteration products after dissolution testing at 150°C for 4 weeks in acidic media with 0.001 M fluoride ions.
Nd-bearing zirconolite was leached at 90°C for 6 months in 0.001M citric acid, and also in deionised water, to determine the effect of organic-bearing solutions on durability. The pH of the citric acid solution was adjusted to 5 using KOH, approximating that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.
Releases were incongruent in the tests carried out in water. Release rates of Ti, Zr and Nd were comparatively very low (commonly too low to be measured) over the first 80 days of leaching. Rates for Ca and Al were 2 to 4 orders of magnitude higher than Ti, Zr and Nd over this same period. At about 80 days, there was an anomalous decrease in pH from 6 to 4 which enhanced release rates of Ti and Nd in particular. There was development of titania crystals, and the suggestion of hydrolysed titania, on the surface after 6 months. Thermodynamic equilibrium between the leachates and hydrolysed species on the surface of the zirconolite may be the key to apparent cessation of alteration, at least during thefirst 80 days of leaching.
By contrast, zirconolite leached in 0.001M citric acid maintained release rates of Ti, Zr and Nd 2 to 4 orders of magnitude greater than those in water for the first 80 days, values sustained, within an order of magnitude, for the remainder of the leach tests. Releases were congruent. The surface of the zirconolite showed no signs of secondary phase development. This suggests complexation by citrate ions prevented control by hydrolysed species on zirconolite solubility.
In the early 1980s a synroc variant, SYNROC-D, was developed for immobilisation of high-level defence waste stored at the Savannah River Plant, USA. A key phase in the immobilisation matrix was spinel, used to immobilise the large proportion of iron and alumina in the waste. Here we examine the feasibility of this approach for other alumina-rich wastes, not necessarily containing iron, derived from the dissolution of aluminium fuel cladding. The advantages of using a magnesia spinel, as opposed to hercynite (FeAl2O4), as the primary alumina-bearing phase are discussed in terms of an increase in waste loading and process flexibility. Two options for sodium incorporation, glass and the titanate phase freudenbergite, are considered.
Polished tiles (7×7×2 mm3) of Nd-bearing zirconolite were fabricated and then some were irradiated on both large faces with 3 MeV or 2 MeV Au2+ ions (total fluence of ≥ 1 × 1015 ions/cm2) in order to render the zirconolite amorphous and so simulate displacement damage caused by alpha decay. Both the irradiated and non-irradiated tiles were then subjected to static dissolution tests in 0.01M nitric solution (pH2) at 90 C, for periods of 0–1, 1–7, 7–14 and 14–28 days. It was found that radiation damage did not affect the dissolution rate of zirconolite as indicated by the elemental leach rates of Nd, Ti, Ca and Al. The results of solution analyses are consistent with those obtained from X-ray Photoelectron Spectroscopy (XPS) in that the Ca, Nd, Ti and Al concentrations in the top surface layer (< 5 nm) all decreased with respect to that of Zr after dissolution testing, and the leached surface composition of the non-irradiated zirconolite is very similar to that of the two irradiated specimens. The implications of these results are discussed in the context of previous work.
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