Corrosion interactions between stainless steel and lead vanado-iodoapatite nuclear waste form part II

Tiankai Yao,Jie Lian,Yachun Wang,Gerald S Frankel,Penghui Lei,Xiaolei Guo

doi:10.1038/s41529-020-0119-9

Abstract

This paper studied the release of iodine from lead vanado-iodoapatite (I-APT, Pb9.85(VO4)6I1.7), a potential nuclear waste form for the radioactive waste element of I-129, which can be enhanced when crevice corrosion of stainless steel (SS) occurring nearby. Reference corrosion studies of I-APT were performed in different bulk solutions including DI water, 0.6 M and 6 M NaCl, and 0.1 M HNO3 without metal crevice corrosion interactions. The localized enrichment of Cl−, one of the major consequences of SS crevice corrosion, was found to be the decisive factor that led to the enhanced release of iodine. A surface alteration layer consisting of a mixture of nanocrystalline I-APT and Cl-rich apatite (Cl-APT) formed on I-APT surface. Meanwhile, large Cl-APT crystals formed at the crevice mouth on the I-APT surface. This study reveals a new near-field corrosion mechanism for ceramic waste forms when they are exposed to aggressive local corrosive conditions created by the electrochemical reactions of nearby metals. The insight gained in this study could be beneficial for a more accurate prediction of waste form degradation.

Highlights

Crystalline ceramics are important host materials for long-term immobilization of long-lived radioactive wastes such as actinides[1] and volatile iodine[2,3]
To better understand the formation mechanism of the band pattern, the rectangular-shaped I-APT sample corroded in close this paper underscore the possible occurrence of degraded iodine proximity to stainless steel (SS) in 0.6 M NaCl solution for 28 days at 90 °C was retention capability of I-APT waste form due to the initiation and cross-sectioned and the microstructure/morphology were proceeding of crevice corrosion from tight contact with canister observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS)
Since the SS and I-APT specimens were in direct contact with each other, and no external load was applied, the gap of the crevice was governed by the roughness of the samples

Summary

INTRODUCTION

Crystalline ceramics are important host materials for long-term immobilization of long-lived radioactive wastes such as actinides[1] and volatile iodine[2,3]. Benchmarking experiments using HNO3 and different concentrations of NaCl as solvents indicate that the ion exchange between I of the I-APT and Cl− in the solution is the governing mechanism for the the different sample geometry that may affect the distance for diffusion of ion species Both factors could influence the mass transport inside the crevice, and eventually the corrosion morphologies. To better understand the formation mechanism of the band pattern, the rectangular-shaped I-APT sample corroded in close this paper underscore the possible occurrence of degraded iodine proximity to SS in 0.6 M NaCl solution for 28 days at 90 °C was retention capability of I-APT waste form due to the initiation and cross-sectioned and the microstructure/morphology were proceeding of crevice corrosion from tight contact with canister observed by SEM and energy dispersive spectroscopy (EDS).

RESULTS

DISCUSSION

Crevice corrosion experiment

Microstructure characterization