Inhibiting pitting corrosion in carbon steel exposed to dilute radioactive waste slurries Page: 2 of 17
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Paper No.
98
CORROSIONQ7
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The NACE Annual Conference and Corrosion Show
INHIBITING PITTING CORROSION IN CARBON STEEL
EXPOSED TO DILUTE RADIOACTIVE WASTE SLURRIES
Philip E. Zapp and David T. Hobbs
Westinghouse Savannah River Co.
Savannah River Laboratory
Aiken SC 29808
AbSTRACT
Dilute caustic high-level radioactive waste slurries can induce pitting corrosion in carbon steel. Cyclic
potentiodynamic polarization tests were conducted in simulated and actual waste solutions to determine
minimum concentrations of sodium nitrite which inhibit pitting in ASTM A537 class 1 steel exposed to these
solutions. Susceptibility to pitting was assessed through microscopic inspection of specimens and inspection of
polarization scans. Long-term coupon immersion tests were conducted to verify the nitrite concentrations
established by the cyclic potentiodynamic polarization tests. The minimum effective nitrite concentration is
expressed as a function of the waste nitrate concentration and temperature.
Keywords: High-level radioactive waste, nitrite, hydroxide
INTRODUCTION
High-level radioactive wastes are stored in large underground carbon steel tanks at the U.S. Department
of Energy's Savannah River Site near Aiken, SC. The wastes result from the nitric acid dissolution of nuclear
fuel and target components performed in the course of nuclear materials production for national defense and
space programs. All waste is neutralized with sodium hydroxide prior to transfer to the tanks. Because of the
high pH, the waste consists of two phases: a liquid phase or supernatant liquid, comprised of water soluble
salts, and a solid phase or sludge, comprised of hydrous oxides of various metal ions. The sludge, which is
suspended in a salt solution, contains most of the radioactivity; radioactive cesium and strontium are water
soluble and thus reside in the supernatant liquid. The supernatant liquid and the liquid phase of the sludge
suspension contain high concentrations of nitrate.1 The high free hydroxide concentration in the liquid
inhibits both nitrate stress corrosion cracking and general corrosion of the carbon steel.
Publication Right ^
Copyright by NAr-F~~NWAE._has hnan given first rights of publication of this manuscript. Request for permission to publish thisjT&ouseiTpfinany form in part or in whole,
must be made in writing to NACE, Products DivliiofT;T^r^*ia34Q,±tguston, Texas 77218. TJiainamjeeftpHTasrnoryeTbeen reviewed by NACE, and accordingly,
the material presented and the views expressed are solely those of thaautteffsfanaareT^ endorsed by the Association. Printed in the U.S.A.
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Zapp, P. E. & Hobbs, D. T. Inhibiting pitting corrosion in carbon steel exposed to dilute radioactive waste slurries, article, January 1, 1991; Aiken, South Carolina. (https://digital.library.unt.edu/ark:/67531/metadc1070289/m1/2/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.