ABSTRACT

The Effluent Treatment Facility (ETF) at the Hanford site is a multi-waste treatment facility that accepts a variety of mixed wastes from other areas of the Hanford site. Visual inspections of the ETF components have revealed pitting below the water line in the secondary waste receiving tanks and concentrate tanks, which are constructed of stainless steels (SS). The exact cause of the pitting is still uncertain given the variety of waste sources and range of processing strategies in the ETF. One possible cause of the pitting relates to the use of hydrogen peroxide (H2O2), which is added to the waste stream to assist in decomposition of organic constituents in the wastewater. The H2O2 injected in the system may not be completely consumed in the process, which could lead to residual H2O2 levels of up to 10 ppm and a resultant increase in corrosion potential. Electrochemical evaluations were initially performed in a simple chloride solution (0.5 M NaCl), which demonstrated that H2O2 levels as low as 10 ppm can cause localized corrosion of Type 304 SS. It was also found that low H2O2 levels (≤ 20 ppm) can produce localized corrosion on Type 304 SS in an ETF waste simulant containing 0.035 M NaCl as well as oxyanions such as nitrate and sulfate.

INTRODUCTION

The Effluent Treatment Facility (ETF) at the Hanford Nuclear Reservation site is a multi-waste treatment facility that removes radioactive and hazardous contaminants from various sources such as condensate wastewater generated by 242-A Evaporator campaigns, groundwater projects, solid waste disposal facilities, and other Hanford clean-up activities. It has been operational since December 1995 and will reach its original 30-year design life in 2025.

The waste streams processed in the ETF are different from Hanford tank-farm wastes, in that the ETF wastes range to relatively higher chloride and sulfate concentrations, and lower nitrate and nitrite concentrations. The pH values of the ETF wastes can approach pH 5, which is much lower than those found in the tank farm. Additionally, the redox potential of ETF waste may increase when residual oxidizing agents such as hydrogen peroxide (H2O2) are present in the waste stream.

This content is only available via PDF.
You can access this article if you purchase or spend a download.