Tom Wiencek

Development of very-high-density low-enriched-uranium fuels

The RERTR program has recently begun an aggressive effort to develop dispersion fuels for research and test reactors with uranium densities of 8 to 9 g U/cm{sup 3}, based on the use of {gamma}-stabilized uranium alloys. Fabrication development teams and facilities are being put into place and preparations for the first irradiation test are in progress. The first screening irradiations are expected to begin in late April 1997 and first results should be available by end of 1997. Discussions with potential international partners in fabrication development and irradiation testing have begun.

Low-temperature irradiation behavior of uranium-molybdenum alloy dispersion fuel

Abstract Irradiation tests have been conducted to evaluate the performance of a series of high-density uranium–molybdenum (U–Mo) alloy, aluminum matrix dispersion fuels. Fuel plates incorporating alloys with molybdenum content in the range of 4–10 wt% were tested. Two irradiation test vehicles were used to irradiate low-enrichment fuels to approximately 40 and 70 at.% 235 U burnup in the advanced test reactor at fuel temperatures of approximately 65 °C. The fuel particles used to fabricate dispersion specimens for most of the test were produced by generating filings from a cast rod. In general, fuels with molybdenum contents of 6 wt% or more showed stable in-reactor fission gas behavior, exhibiting a distribution of small, stable gas bubbles. Fuel particle swelling was moderate and decreased with increasing alloy content. Fuel particles with a molybdenum content of 4 wt% performed poorly, exhibiting extensive fuel–matrix interaction and the growth of relatively large fission gas bubbles. Fuel particles with 4 or 6 wt% molybdenum reacted more rapidly with the aluminum matrix than those with higher-alloy content. Fuel particles produced by an atomization process were also included in the test to determine the effect of fuel particle morphology and microstructure on fuel performance for the U–10Mo composition. Both of the U–10Mo fuel particle types exhibited good irradiation performance, but showed visible differences in fission gas bubble nucleation and growth behavior.

Irradiation behavior of U-Nb-Zr alloy dispersed in aluminum

Abstract Three U–Nb–Zr alloys (U–5Nb–3Zr, U–6Nb–4Zr, and U–9Nb–3Zr) were included in a screening irradiation test of low-enrichment aluminum matrix dispersion fuels. Fuel particles made from these alloys reacted readily with aluminum during fuel fabrication and post-fabrication annealing, resulting in large fuel plate thickness increases. Under irradiation, the behavior of U–5Nb–3Zr (wt%) alloy based fuel was poor at 41 at.% 235U burnup, showing indications of incipient breakaway swelling. The post-irradiation microstructural characteristics of U–6Nb–4Zr based fuel were somewhat better than those of U–5Nb–3Zr, but is marginal at 70 at.% burnup. U–Mo based fuels generally show less reaction on fabrication and better fuel performance characteristics during irradiation.

Irradiation behavior of U6Mn–Al dispersion fuel elements

Irradiation testing of U6Mn–Al dispersion fuel miniplates was conducted in the Oak Ridge Research Reactor (ORR). Post-irradiation examination showed that U6Mn in an unrestrained plate configuration performs similarly to U6Fe under irradiation, forming extensive and interlinked fission gas bubbles at a fission density of approximately 3×1027m−3. Fuel plate failure occurs by fission gas pressure driven `pillowing’ on continued irradiation.

Magnetohydrodynamic stability in the electromagnetic levitation of horizontal molten‐metal sheets

High‐frequency electromagnetic (EM) fields are investigated for the levitation of thin horizontal sheets of liquid metal. A magnetic configuration is analyzed in which inductance stabilization provides global stability and magnetic flux compression provides local stability. Stability analysis indicates that frequencies greater than about 24 kHz are desirable to stably levitate 6 mm thick steel. For stability in systems without active feedback, a conducting screen is required below the metal, with a gap between the screen and the molten metal of no more than twice the metal thickness. Experiments in which 10 kHz EM fields were used to statically levitate sheets of molten tin indicate that dominant magnetohydrodynamic instabilities are of the Rayleigh–Taylor type and correspond to theory.