Near-field corrosion interactions between glass and corrosion resistant alloys

Xiaolei Guo,Gerald S Frankel,Dien Ngo,Joseph V Ryan,Stephane Gin,Hongshen Liu,John D Vienna,Chandi Mohanty,Jiawei Luo,Seong H Kim

doi:10.1038/s41529-020-0114-1

Abstract

This study explores the corrosion interactions between model nuclear waste glass materials and corrosion resistant alloys, under accelerated conditions that simulate the near field of a nuclear waste repository. The interactions between the corrosion of stainless steel (SS) 316, alloy G30, or alloy 625, and international simple glass or soda-lime silica glass are systematically studied. The dissimilar materials were exposed in close proximity to each other in different electrolytes at 90 °C. After exposure, the glass surface exposed near metals showed different regimes of corrosion, with distinct surface morphologies and chemistries that were likely affected by the local environment created by the localized corrosion of metals. Surface and solution analyses showed that the corrosion rate of glass was enhanced by the presence of metals. Infrared spectroscopy data suggested the local build-up of stresses in the contact area of glass, which may lead to the mechanical instability of the glass alteration layer. On the other hand, the effect of glass on metal corrosion is strongly dependent on the leaching solution. In electrolytes containing abundant aggressive anions such as Cl−, glass seems to suppress the localized corrosion of SS by the precipitation of a Si-rich surface film that protects the SS substrate from solutions. However, in less aggressive electrolytes, the corrosion rate of SS was increased by the presence of glass corrosion products. Overall, our study showed that the hidden and localized damage on glass in contact with metals may enhance the release rate of glass components compared to typical uniform glass corrosion.

Highlights

The high-level nuclear waste (HLW) existing as the legacy of defense applications and other by-products of spent nuclear fuel reprocessing will be melted into borosilicate glass, and cast into stainless steel (SS) canisters[1]
The initial ionic strength may be lower in the actual repository conditions, Cl− and Na+ ions are likely to be enriched at the material interface during corrosion[16]
Recent studies showed that this statement is still valid when the glass corrosion reaches a steady state regime where the solution is saturated with silica, the rate-limiting mechanisms are likely not the same for the two regimes[24]

Summary

Introduction

The high-level nuclear waste (HLW) existing as the legacy of defense applications and other by-products of spent nuclear fuel reprocessing will be melted into borosilicate glass, and cast into stainless steel (SS) canisters[1]. These canisters will be enclosed within waste packages and emplaced in a mined underground geologic repository, which is the approach planned by most countries with such waste[2]. Alloy 22 is an extremely corrosion resistant metal alloy, so any environment that could corrode Alloy 22 would penetrate the SS structures within the canister and allow the corrosive environments to attack the encapsulated glass waste forms, leading to the release of radionuclides. Crevice corrosion[6,7,8] may be triggered once aqueous environment exists at the interface between the SS canister and the nuclear waste glass, which may create a series of issues

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Conclusion