Evolution of Solution Chemistry through Interactions with Waste Package Internal Structural Components
- PDF / 88,385 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 42 Downloads / 203 Views
Evolution of Solution Chemistry through Interactions with Waste Package Internal Structural Components Y.-M. Pan, C.S. Brossia, G.A. Cragnolino, D.S. Dunn, V. Jain, and N. Sridhar Center for Nuclear Waste Regulatory Analyses (CNWRA) Southwest Research Institute 6220 Culebra Road, San Antonio, TX 78238-5166, USA ABSTRACT The chemistry of the aqueous environment inside any breached waste packages is critical to the release of radionuclides from the waste packages for high-level waste disposal. A corrosion test cell that simulates some aspects of the internal geometry of the waste packages has been designed to investigate changes in the in-package solution chemistry. A series of tests was conducted to evaluate solution chemistry variations as a function of applied potential and temperature using a specimen of Type 316L stainless steel with a predrilled hole as a simulated pit. A micro-syringe was used to extract solutions from inside and outside the pit. The solutions were analyzed for cation concentrations using capillary electrophoresis, and the pH was measured using a micro-electrode. Preliminary measurements showed substantially high cation concentrations inside the pit due to anodic dissolution of Type 316L stainless steel. The solution pH became considerably acidic, reaching a value of 2.6. These results suggest that interactions of waste package internal structural components with incoming water may have significant influence on the evolution of water chemistry and the subsequent corrosion of waste forms such as spent nuclear fuel. INTRODUCTION The composition of the groundwater entering breached waste packages can be influenced and modified by natural processes such as evaporation, reactions with host rock, and reactions with components of the engineered barriers such as drip shield and waste package materials. Variables such as pH, carbonate concentration, and redox potential would be influenced by interactions of groundwater with engineered barriers in any repository and could have a substantial effect on waste package and waste form corrosion. The U.S. Department of Energy (DOE) evaluation of the potential evolution of the in-package chemistry is based on calculations performed with a numerical code, EQ 3/6, that simulates the reaction of fluids with waste forms and waste package internal components after the occurrence of the thermal pulse [1]. The DOE analysis showed that the corrosion of inner waste package materials could result in relatively large changes in the fluid chemistry, and relatively low pH values can be expected as a result of corrosion of stainless steel structural components, specifically because of chromium oxidation to Cr6+ species. One of the main concerns in evaluating the DOE analysis is the spatial variation in chemistry that is likely to occur inside waste packages and result in local pH values considerably more acidic than those calculated based on a volume averaged mass. Pitting and crevice corrosion are localized forms of attack that result from the breakdown of passive film cause
Data Loading...
