The Thermal Stability of Al-USiAl Dispersion Fuels and Al-U Alloys

The stability of Al-USiAl dispersion fuels and Al-U alloys was examined at temperatures between 200 and 400°C for times up to 93 days. The Al-U alloys, which contained 21 to 37 wt% uranium, did not show any dimensional or metallurgical changes after 93 days at 400°C. After being heated at 200°C, the Al-USiAl fuel showed no dimensional or metallurgical changes. However, between 250 and 400°C, the USiAl particles reacted with the aluminum matrix to form UAl₃ and UAl₄. The amount of reaction increased with temperature and time. The aluminum diffuses into the USiAl particles along grain boundaries to form the new Al-U compounds. Although the Al-USiAl fuel showed thermal instability at 250°C and above, the in-reactor behavior under normal operation is expected to be satisfactory since fuel temperatures will generally be <200°C.