The sensitivity and reproducibility of high-temperature, high-pressure steam tests for Zircaloy nodular corrosion were studied as a function of test parameters, such as temperature, pressure, test duration, and flow rate, using a recirculating autoclave loop. Other variables, such as heat-up rate and oxygen and hydrogen gas contents, were also studied.

The effects of the test variables and gaseous species on test reproducibility are minimized by the addition of a prefilming step at 410°C for 4 to 8 h before exposing the test samples to a higher nodule-forming temperature. The prefilming treatment reduces the degree of nodular corrosion, but the reduced nodule sensitivity can be regained by controlling the second-step test temperature. A test involving a prefilming step at 410°C/1500 psig (102 bars) for 8 h and a nodule sensitivity step at 510°C/1500 psig (102 bars) for 16 h has been found to be capable of reproducibly discriminating Zircaloy cladding source materials into a broad spectrum of nodular corrosion susceptibility. Good reproducibility of the 410/510°C two-step test was demonstrated over 40 test runs using control samples. The two-step test was calibrated to in-reactor corrosion performance using pretested samples and irradiated plenum samples removed from fuel rods.