A Calorimetric Investigation of Zirconium, Titanium, and Zirconium Alloys from 60 to 960°C

Structural materials for nuclear reactors must meet three stringent conditions: they must have adequate mechanical properties at the operating temperature, they must be corrosion resistant to the heat transfer medium (air, water, or alkali metals), and they must not absorb neutrons excessively. This last requirement is a particularly stringent one, for it is met by only four accessible metals: aluminum, magnesium, beryllium, and zirconium, as Table I shows.

For reactors which operate at low temperatures, aluminum serves as an excellent constructional material, but it cannot be used for more efficient high-temperature reactors, because of its low elevated temperature strength associated with its low melting point of 660 °C. Although magnesium has a lower absorption cross section than aluminum, it has a lower melting point (650 °C) and poorer corrosion resistance, thus offering no particular advantages over aluminum. The use of beryllium is impractical except for very special applications, because of its extreme brittleness and the relative scarcity of its ores. In contrast, zirconium ores are abundant; the metal is fairly easily produced; it has satisfactory mechanical properties and excellent corrosion resistance at temperatures above the practical operating range for aluminum; and techniques of fabrication are now well developed. Thus zirconium comes at once to the foreground as a structural material for the construction of nuclear reactors.