CORROSION BEHAVIOR OF ALLOY 22 IN CONCENTRATED NITRATE AND CHLORIDE SALT ENVIRONMENTS AT ELEVATED TEMPERATURES

摘要

The possible waste package design at the potential repository at Yucca Mountain, Nevada, may consist of an outer container made of Alloy 22. Under the repository conditions, hygroscopic salts may deposit on the waste package surfaces and sorb moisture from the atmosphere when the relative humidity is near or above their deliquescence relative humidity, causing aqueous corrosion of the waste package.The corrosion rates of Alloy 22 in the liquid and vapor phases in a system containing an equimolar NaCl-NaNO3-KNO3 mixture were measured at temperatures ranging from 150 to 180 °C [302 to 356 °F]. Also, polarization curves and open-circuit potentials were obtained in the liquid phase. To simulate the potential Yucca Mountain emplacement drift condition, the experiments were conducted under ambient pressure, and the test system was not deaerated. No significant localized corrosion was observed, and general corrosion was found to be the primary mode of attack. The general corrosion rates measured in the liquid phase from mostly thermally-aged specimens in preliminary short-term tests were from 1 to 10 :m/yr [0.04 to 0.4 mil/yr]–significantly higher than the rates obtained under autoclave conditions and reported in the literature. Further experiments are underway to verify these preliminary results.