Performance Analysis of Copper Canister Corrosion Under Oxidizing or Reducing Conditions
- PDF / 581,294 Bytes
- 8 Pages / 414.72 x 648 pts Page_size
- 38 Downloads / 191 Views
PERFORMANCE ANALYSIS OF COPPER CANISTER CORROSION UNDER OXIDIZING OR REDUCING CONDITIONS KAREN WORGAN*, MICHAEL APTED* AND ROLF SJOBLOM** * Intera Information Technologies, Inc., Denver, Colorado 80235 ** Swedish Nuclear Power Inspectorate, Stockholm, Sweden ABSTRACT The finite-difference CAMEO code for modeling general corrosion of copper canisters is described. CAMEO represents the engineered barrier system and surrounding fractured host rock in 3-dimensional cylindrical coordinates. The time of containment failure is evaluated using CAMEO, as constrained by transport rates of corrodants to the canister or by transport rates of corrodant products away from the canister. Additional chemical processes explicitly modeled in CAMEO include 1) copper corrosion, and 2) kinetics of Cu(I) oxidation to Cu(II), both as a function of near-field pore water chemistry, specifically pH, Eh, and chloride concentration. The diffusional transport and sorption behavior of Cu(I) and Cu(Il) are also separately incorporated. INTRODUCTION Copper is considered for a long-term canister material because 1) copper displays an extensive range of thermodynamic stability over mildly reducing, mildly alkaline conditions expected in a deep, crystalline-rock repository, and 2) for redox conditions outside of this range of stability, the rate of formation of more stable copper solids can be constrained by rate of diffusive mass-transport of reactants (or products) through the compacted bentonite buffer. Diffusive transport rates are highly predictable compared to other long-term processes that may affect near-field performance, and can be used to set upper limits on the rates of general corrosion of metallic copper canisters [1]. CAMEO is a performance assessment code developed to evaluate the rate of general corrosion of copper canisters constrained by diffusive mass-transport, and to estimate containment failure times over a wide range of postulated repository conditions. CAMEO is modified from the CALIBRE code, previously developed for and tested by the Swedish Nuclear Power Inspectorate (SKI) for source-term analysis of radionuclide release from the engineered barriers. The computational structure and capabilities of CAMEO are presented. Note, that while general corrosion is often postulated to control the long-term performance of copper canisters [1], potential localized corrosion mechanisms must also be considered in a complete assessment. MASS-TRANSFER LIMITS TO GENERAL CORROSION The near field of a deep geological repository for spent nuclear fuel is illustrated in Figure 1. The spent fuel is shown as contained within a copper canister located within an excavation hole or drift. This waste package is surrounded by a low permeability buffer material, typically compacted bentonite or bentonite-sand mixture. The low permeability of the buffer prevents advective flow of water through it, effectively decoupling the waste package from the hydrology of the site. The migration of reactants and products across this buffer are constrained by diffusi
Data Loading...
