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The Impact of Vapor Phase Species on the Corrosion Potential of Hanford Double Shell Tanks.


EMSL Project ID
37302

Abstract

The goal of the proposed project is to develop a sound technical basis for control of corrosion in the vapor space and the liquid/air interface (VS/LAI) in the Hanford Double Shell Tanks. Specifically, this proposal will focus on the impact on the VS/LAI corrosion potential of DST tank steels in response to changes in chemistry that can occur as waste tank supernatants dry and exchange atmospheric gases (e.g. CO2 and NH3). The specific tanks targeted in this study have highly variable CO2 and NH3 contents in the vapor space as a result of tank ventilation and the radiolysis of nitrogen containing organic compounds present in tank supernatants. Evaluation of the impact of supernatant drying is important since the supernatant level in the HLW tanks can change a result of ventilation, chemical additions, transfers, or waste retrieval. Our initial studies will focus on five double shell tanks (AN-107, AN-102, AY-101, AY-102, and SY-102). With the exception of SY-102 all of these tanks have previously required adjustment of the supernatant composition to remain within corrosion guidance. SY-102 was chosen because of the large range in nitrate/nitrite ratio observed in this tank (which could lead to stress corrosion cracking) and the potential high chloride content. Characterization of the steel surface before and after the corrosion experiments will be conducted at the EMSL to determine the oxide composition and structure including identification of the unreacted steel surface, an intermediate region comprised of Fe(II)/Fe(III) oxides, and a immediate surface region comprised of Fe(III) oxides. The changes in the structure and composition of the oxide surface coatings with changes in solution composition are the key to providing the molecular level basis for predicting VS/LAI tank corrosion.

Project Details

Project type
Exploratory Research
Start Date
2010-05-25
End Date
2011-05-29
Status
Closed

Team

Principal Investigator

Andrew Felmy
Institution
Washington State University

Team Members

Elizabeth Hoffman
Institution
Savannah River National Laboratory

Odeta Qafoku
Institution
Environmental Molecular Sciences Laboratory