Corrosion Product Identification and Relative Rates of Corrosion of Candidate Metals in an Irradiated Air-Steam Environm
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CORROSION
IDENTIFICATION AND RELATIVE RATES OF CANDIDATE METALS IN AN IRRADIATED AIR-STEAM ENVIRONMENT
PRODUCT
DONALD T. REED*, V. SWAYAMBUNATHAN*, RICHARD A. VAN KONYNENBURG**
B.
S.
TANI*
OF
CORROSION
AND
Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Il 60439 ** Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550 *
ABSTRACT Previously reported work by others indicates that dicopper trihydroxide nitrate, Cu2NO3(OH)3, forms on copper and copper alloys subjected to irradiated moist air near room temperature. We have performed experiments over a range of temperature and humidity, and have found that this species is formed at temperatures up to at least 150 0 C if low to intermediate relative humidities are present. At 150*C and 100% relative humidity, only Cu20 and CuO were observed. The relative general corrosion rates of the copper materials tested in 1-month experiments at dose rates of 0.7 and 2.0 kGy/h were Cu > 70/30 Cu-Ni > Al-bronze. High-nickel alloy 825 showed no observable corrosion. INTRODUCTION The U.S. Department of Energy, through its Office of Civilian Radioactive Waste Management, is conducting the Yucca Mountain Project. The purpose of this project is to determine the suitability of Yucca Mountain, in southern Nevada, as a location for a high level nuclear waste repository. Lawrence Livermore National Laboratory (LLNL) is concerned with evaluating waste package performance for the proposed repository, and Argonne National Laboratory is under subcontract to LLNL to perform experimental work. In order to give "reasonable assurance" of "substantially complete" containment for 300 to 1000 years, as required in federal regulation 10CFR Part 60, we need to develop a rather complete understanding of the oxidation and corrosion behavior of the waste package material in the expected environment over long time periods. This understanding is needed both for selection of the container material and for assessment of waste package performance. The expected environment in the unsaturated zone proposed for the repository is moist air. The temperatures of the packages are expected to rise initially because of nuclear decay heat and then to drop slowly over long times. The highest temperature expected at a container surface is about 200 to 250*C. For many packages the surface temperature will be maintained above the local boiling point (96 0 C) throughout the containment period, preventing the existence of more than a few molecular layers of liquid water on the container surface. After the temperature drops below the boiling point, the packages are still expected to remain dry, because the vadose water is expected to be confined to pores in the rock and to undergo matrix flow under the influence of capillary forces and gravity. In addition, since each package will always be at a higher surface-averaged temperature than the nearby rock wall, any liquid water on a package would
Mat. Res. Soc. Symp. Proc. Vol. 176. @1990 Materials Research Society
518
tend to undergo n
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