Thermodynamics of the conversion of calcium and magnesium fluorides to the parent metal oxides and hydrogen fluoride

The authors have used thermodynamic modeling to examine the reaction of calcium fluoride (CaF{sub 2}) and magnesium fluoride (MgF{sub 2}) with water (H{sub 2}O) at elevated temperatures. The calculated, equilibrium composition corresponds to the global free-energy minimum for the system. Optimum, predicted reaction temperatures and reactant mole ratios are reported for the recovery of hydrogen fluoride (HF), a valuable industrial feedstock. Complete conversion of MgF{sub 2} is found at 1,000 C and a ratio of 40 moles of H{sub 2}O per 1 mole of MgF{sub 2}. For CaF{sub 2}, temperatures as high as 1,400 C are required for complete conversion at a corresponding mole ratio of 40 moles of H{sub 2}O per 1 mole of CaF{sub 2}. The authors discuss the presence of minor chemical constituents as well as the stability of various potential container materials for the pyrohydrolysis reactions at elevated temperatures. CaF{sub 2} and MgF{sub 2} slags are available as wastes at former uranium production facilities within the Department of Energy Complex and other facilities regulated by the Nuclear Regulatory Commission. Recovery of HF from these wastes is an example of environmental remediation at such facilities

Study of the potential use of carburized niobium in plutonium processing

Carburized refractory metals, especially tantalum, have been shown to possess properties useful for application as hardware in the plutonium-processing environment. These applications are driven in part by a desire to minimize the production of radioactively contaminated waste. The current use of ceramics as containment materials for Pu processing are not ideal due to the short service life of the hardware, placing an additional burden on the contaminated waste stream. Carburized niobium has been examined for use as an improved hardware material. The Nb-C system is analogous to the previously studied Ta-C system. The low density of niobium relative to tantalum will improve the ergonomics of the glovebox environment. The choice of the Nb-C system will be supported by a thermodynamic and kinetic analysis. Preliminary results of the processing investigation also will be presented

High-temperature compatibility study of iridium (DOP-26 alloy) with graphite and plutonia

This report outlines the materials compatibility tests conducted on DOP-26 iridium alloy and carbon. The carbon used was in the form of woven graphite as present in the impact shell used to encase plutonia in nuclear heat sources. In addition, compatibility tests of the DOP-26 alloy with plutonia are described. The reactivity observed in both systems is discussed. 4 refs., 6 figs

Structural examination of iridium-based single-crystal preparations. [AlIr; IrSi]

A high-temperature crystal growth experiment produced discrete single-crystal products of AlIr and IrSi. The preparation and examination of these phases is described within. This project is part of a materials compatibility study relating to radioisotopic heat sources. These heat sources are comprised of a PuO/sub 2/ fuel pellet encapsulated in an Ir alloy containment shell. Th is introduced as an additive within the Ir to maintain ductility. Si and P are picked up inadvertently in the fuel processing. The compatibility of the heat sources with Al is of interest because of potential interactions with Al alloy hardware associated with the heat source environment

General-Purpose Heat Source development: Safety Verification Test Program. Bullet/fragment test series

The radioisotope thermoelectric generator (RTG) that will provide power for space missions contains 18 General-Purpose Heat Source (GPHS) modules. Each module contains four /sup 238/PuO/sub 2/-fueled clads and generates 250 W/sub (t)/. Because a launch-pad or post-launch explosion is always possible, we need to determine the ability of GPHS fueled clads within a module to survive fragment impact. The bullet/fragment test series, part of the Safety Verification Test Plan, was designed to provide information on clad response to impact by a compact, high-energy, aluminum-alloy fragment and to establish a threshold value of fragment energy required to breach the iridium cladding. Test results show that a velocity of 555 m/s (1820 ft/s) with an 18-g bullet is at or near the threshold value of fragment velocity that will cause a clad breach. Results also show that an exothermic Ir/Al reaction occurs if aluminum and hot iridium are in contact, a contact that is possible and most damaging to the clad within a narrow velocity range. The observed reactions between the iridium and the aluminum were studied in the laboratory and are reported in the Appendix

Martensitic nature of {delta} {yields} {gamma} allotropic transformation in plutonium

Isothermal and isoplethal studies using differential scanning calorimetry have been conducted to characterize the allotropic transformations of plutonium. The {delta}-{gamma} transformation (upon cooling) was observed to have a classic martensitic nature. The work described herein is the first quantitative study of this phenomena in plutonium

Solvent extraction of thorium from nitrate solutions by dibutyl butylphosphonate in Isopar H

Solvent extraction of thorium by 30 vol % dibutyl butylphosphonate-70 vol % Isopar H from salted and nonsalted nitric acid solutions was studied. Thorium distribution coefficients D/sub Th/'s were obtained for nitric acid solutions of approx. 0.3 to approx. 12 N and for solutions of 1 and 2 M NH/sub 4/NO/sub 3/ over the HNO/sub 3/ concentration range of approx. 0.5 to approx. 9 N. The nitric acid solution D/sub Th/'s varied from approx. 4.3 at the lowest acidity, increased to a maximum of approx. 40 at approx. 3-4 N H/sup +/, and then gradually decreased to approx. 18 at approx. 11.5 N H/sup +/. The solutions containing 1 and 2 M NH/sub 4/NO/sub 3/ gave definite salting-out effects with D/sub Th/'s of 79 to 90, respectively, at the lowest acidities; these values then decreased with acidity increases to those of the nonsalted acid solutions at approx. 5 N HNO/sub 3/ and paralleled the acid solution values up to approx. 12 N