Many alloying additions have been attempted for improving mechanical properties and corrosion resistance of thorium. Only few elements (like zirconium and

a) Note that the materials were in variously processed initial conditions before tensile testing at room temperature.

hafnium) allow extensive solid solubility. However, many reactive elements form intermetallic compounds instead of forming solid solutions. Addition of two known alloying elements, namely, uranium and indium, to thorium improves the mechanical strength of thorium, whereas three elements, namely, zirconium, tita­nium, and niobium, improve corrosion resistance. Thorium-uranium and tho­rium-plutonium alloys provide opportunities for combining fertile and fissile materials to develop potential thorium-based fuel cycles. Table 7.4 summarizes ten­sile properties of Th-U alloys as a function of uranium content. It clearly shows that uranium addition to thorium increases the yield strength and tensile strength; however, it decreases ductility. Thorium-uranium alloys in excess of 50 wt% U can be readily melted and cast. Powder metallurgy techniques can also be used.

The creep data of Th-9wt% U alloy are shown in Figure 7.17. The plot shows retention of strengthening due to the mechanical effect at 600 °C.