ABSTRACT

The Effluent Treatment Facility (ETF) at the Hanford nuclear-waste storage site is a waste treatment facility that removes radioactive and hazardous contaminants from various sources. The facility processes substantially more dilute waste that has lower pH values than the waste found in the tank farms. The Secondary Waste Receiving Tank B (SWRT-B) at the ETF exhibited corrosion attack on the tank ceiling and upper wall during recent inspections and this paper presents the results of laboratory investigations performed to evaluate whether the in-tank additions of sulfuric acid that are made to adjust waste pH are a possible cause for the corrosion attack. Laboratory testing was conducted to evaluate the susceptibility of 304H stainless steel (UNS S30409), including in the sensitized condition to investigate microstructural differences in welded regions, to H2SO4 vapor corrosion or splash-back corrosion. The results of electrochemical testing indicate that as-received 304H showed no susceptibility to corrosion in 4% H2SO4 even when anodically polarized while sensitized 304H exhibited corrosion at open circuit conditions. A kettle test designed to simulate the addition of H2SO4 to the SWRT-B to investigate acid vapor and splash-back corrosion was unable to replicate the corrosion observed in the tank.

INTRODUCTION

The Effluent Treatment Facility (ETF) at the Hanford nuclear-waste storage facility is a waste treatment facility permitted under the Resource Conservation and Recovery Act of 1976 (RCRA). The facility 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. The waste processed by the ETF is substantially more dilute than the waste stored in the tanks. It has been operational since December 1995 and will reach its original 30-year design life in 2025.

The facility accepts low-level, mixed wastewaters for treatment. It has received a variety of mixed wastes from other areas of the Hanford facility, and because of this, the fluids in tanks, piping, and other process vessels in the ETF have a wide range of chemistries. There are 17 major tanks and process vessels, and associated piping in the ETF. The waste streams processed in the ETF are different from tank-farm wastes in that the ETF wastes can contain higher chloride and sulfate concentrations and lower nitrate and nitrite concentrations. The pH values of most of the ETF wastes are also lower than found in the tank farm. This necessitates the use of stainless steels or Ni-base alloys in the main and secondary treatment trains of the ETF.

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