Investigation of Zircaloy-4 Doped with Metallic Burnable Poisons

Burnable poisons are used in all commercial reactors to level the power distribution and to reduce the requirements for an excessively large control system. It has been proposed that metallic rare earth elements, serving as burnable poisons, might be alloyed with the fuel cladding rather than mixed with fuel in the form of compounds. This research project studies the effect of such additions on the ductility.and the corrosion resistance of three such alloys.

Alloys of Zircaloy-4 with 0.5 % Gd, 2.0 % Dy, and 2.0 % Er, chosen to represent the maximum likely concentrations of the absorbing elements to be used in a nuclear reactor, were melted and rolled into sheet. Tensile tests were conducted to obtain a quantitative measure of ductility. In addition, coupons were exposed to superheated steam in an autoclave to test the corrosion resistance of the alloys. Only the Gd alloy survived the test. Scanning electron microscopy and energy dispersive x-ray analysis were conducted to investigate the possibility of second phase formation and segregation of the rare earth elements in an attempt to elucidate the mechanism of failure of the alloys.