Thermal Stabilization of {sup 233}UO{sub 2}, {sup 233}UO{sub 3}, and {sup 233}U{sub 3}O{sub 8}

Abstract

This report identifies an appropriate thermal stabilization temperature for 233 U oxides. The temperature is chosen principally on the basis of eliminating moisture and other residual volatiles. This report supports the U. S. Department of Energy (DOE) Standard for safe storage of 233 U (DOE 2000), written as part of the response to Recommendation 97-1 of the Defense Nuclear Facilities Safety Board (DNFSB), addressing safe storage of 233 U.The primary goals in choosing a stabilization temperature are (1) to ensure that the residual volatiles content is less than 0.5 wt % including moisture, which might produce pressurizing gases via radiolysis during long-term sealed storage; (2) to minimize potential for water readsorption above the 0.5 wt % threshold; and (3) to eliminate reactive uranium species. The secondary goals are (1) to reduce potential future chemical reactivity and (2) to increase the particle size thereby reducing the potential airborne release fraction (ARF) under postulated accident scenarios.

Oxygen Isotopic Composition of U3O8 Synthesized From U Metal, Uranyl Nitrate Hydrate, and UO3 as a Signature for Nuclear Forensics

“…On the other hand, all of the resulting U 3 O 8 samples were identical, consisting of a single-phase α-U 3 O 8 , irrespective of the UNH or UO 3 phase from which it had been prepared. The range of temperatures in which U 3 O 8 samples were synthesized by both routes, UNH or UO 3 , ensured a complete conversion of the starting materials into a single phase of U 3 O 8 . This result is in good agreement with a previous study that examined the morphological changes in α-U 3 O 8 synthesized from amorphous-UO 3 , under four calcination temperatures 650, 700, 750, and 800 °C under purified air.…”

“…A similar 18 O enrichment was reported by Klosterman et al for the difference between samples prepared at 600–700 and 800 °C. We attribute this change to the preferential loss of the lighter oxygen isotope from the U 3 O 8 lattice, which starts above 750 °C, and to the change in cooling rates, as discussed in Section .…”

“…The production processes of uranium fuel pellets (UO 2 ) consist of several stages, starting with milled uranium ore to produce intermediate products, mainly uranyl nitrate hydrate (UNH), ammonium diuranate (ADU), and uranium peroxide. − Uranium oxides such as UO 3 , U 3 O 8 , and UO 2 , in the form of powders, are intermediate compounds within uranium ore processing and nuclear fuel production cycle, regardless of the above-mentioned starting materials. − U 3 O 8 is almost ever present in the production cycle of nuclear fuel. Furthermore, U 3 O 8 is a major compound in nuclear waste management due to its thermal and chemical stability. − All production processes of U 3 O 8 compounds in the nuclear industry involve three major parameters: calcination temperature, calcination time, and the cooling rate of the products …”

Quantifying Morphological Features of α-U3O8 with Image Analysis for Nuclear Forensics

“…A synthesis temperature for α-U 3 O 8 of 600 °C was chosen based on previous research by Hoekstra et al , They stated that UO 3 will begin conversion to U 3 O 8 at temperatures as low as 450–470 °C but complete conversion only occurs as the temperature reaches 650 °C. A temperature of 600 °C was chosen as the lower boundary to reflect this transition zone.…”

Thermodynamics of Fluorite-Structured Oxides Relevant to Nuclear Energy: A Review

“…Uranium dioxide, the most common nuclear fuel, has a high melting point (around 2800 °C) and high thermal conductivity compared to other uranium oxides. , When the oxygen partial pressure increases, extra oxygen is introduced into the interstitial sites. This distorts the anion sites in the fluorite structure, forming stabilizing cuboctahedra in oxides with composition U 3 O 7 to U 4 O 9 .…”