The in-reactor corrosion and hydrogen pickup of Zircaloy-2 and Zr-2.5Nb pressure tube materials are being studied in two test loops: a light water loop in the NRU research reactor, and a new heavy water loop in the Halden reactor. The complimentary test programs examine the corrosion behavior of small specimens as a function of fast neutron flux and fluence, temperature, water chemistry, and specimen pre-oxidation.

In NRU tests conducted over a range of reducing conditions (20 to 60 cm³ H² · kg^-1) at 568 K, Zr-2.5Nb specimens bearing “thin” prefilm oxides (⩽6 ηm) experience a reduction in oxidation rate influx. However, samples with thick prefilm oxides exhibit higher rates, suggesting that, like Zircaloy-2, rates for Zr-2.5Nb may increase as the oxide film continues to thicken.

Initial results from the Halden program (5 to 7 cm³ D² · kg^-1) show that prefilmed specimens from tubes made of β-quenched material exhibit lower oxidation and deuterium pickup rates than tubes made from non-β-quenched materials. Prefilmed tubes made from β-quenched material also pickup a lower percentage of the D generated by the corrosion reaction. At high flux levels, prefilmed specimens from tube made of both materials exhibit a narrow range of percentage pickup values (4 to 5%), irrespective of temperature. A preliminary examination of activation energies over the range 523 to 598 K suggests significant differences in the temperature dependencies for oxidation and deuterium pickup of prefilmed specimens of tubes made from β and non-β-quenched Zr-2.5Nb. The differences are correlated with fast flux level.