Corrosion of Glass-Bonded Sodalite and Its Components as a Function of pH and Temperature
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CORROSION OF GLASS-BONDED SODALITE AND ITS COMPONENTS AS A FUNCTION OF pH AND TEMPERATURE Seung-Young Jeong, Lester. R. Morss, and William. L. Ebert Chemical Technology Division, Argonne National Laboratory, Argonne, IL 60439 ABSTRACT A glass-bonded sodalite ceramic waste form (CWF) has been developed to immobilize electrorefiner salt wastes from electrometallurgical treatment of spent sodium-bonded reactor fuel for disposal. A degradation model is being developed to support qualification of the CWF for disposal in the federal high-level waste disposal system. The parameter values in the waste form degradation model were previously determined from the dissolution rates measured in MCC-1 tests conducted at 40, 70, and 90°C. The results of several series of tests that were conducted to confirm the applicability of the dissolution rate model and model parameters are presented in this paper: (1) Series of MCC-1 tests were conducted in five dilute buffer solutions in the pH range of 4.8 – 9.8 at 20°C with hot isostatic pressing (HIP) sodalite, HIP glass, and HIP CWF. The results show that the model adequately predicts the dissolution rate of these materials at 20°C. (2) Tests at 20 and 70°C with CWF made by pressureless-consolidation (PC) indicate that the model parameters extracted from the results of tests with HIP CWF can be applied to PC CWF. (3) The dissolution rates of a glass made with a composition corresponding to 80 wt. % glass and 20 wt. % sodalite were measured at 70°C to evaluate the sensitivity of the rate to the composition of binder glass in the CWF. The dissolution rates of the modified binder glass were indistinguishable from the rates of the binder glass. INTRODUCTION Spent sodium-bonded nuclear fuel is being conditioned for disposal by using an electrometallurgical technique developed at Argonne National Laboratory (ANL). A glassbonded sodalite ceramic waste form (CWF) was developed for disposition of radioactive salt recovered from the electorefiner during conditioning [1]. The CWF is prepared by first mixing zeolite 4A with waste salts at ~500°C to occlude the waste-loaded salt within cages of the zeolite structure. The salt-loaded zeolite is then mixed with commercial borosilicate glass frit (75 wt. % salt-loaded zeolite and 25 wt. % glass) and vitrified at ~915°C. When heated, the salt-loaded zeolite transforms to sodalite, Na8(AlSiO4)6Cl2, and the glass frit melts to encapsulate the sodalite. The resulting waste form consists of sodalite inclusions fixed in a glass matrix. The CWF can be made using either hot isostatic pressing (HIP) or pressureless-consolidation (PC) processes. The PC process has been selected for immobilizing EBR II fuel. The dissolution behavior of the CWF has been modeled with the expression [2] (η • pH)
rate = k 0 ×10
×e
(-E a /RT)
×(1- Q/K)
where rate is the dissolution rate of the CWF, k0 is the intrinsic rate constant, η is the pH dependence coefficient, Ea is the activation energy, Q is the ion activity product, and K is apparent solubility product of the CWF. Serie
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