Static leach tests with the EBR-II metallic waste form.

Abstract

A metallic waste form (MWF) will be used to immobilize contaminated cladding hulls recovered after electrometallurgical treatment of spent sodium-bonded nuclear fuel from the Experimental Breeder Reactor-II (EBR-II). Tests were conducted to determine if the high-level waste (HLW) glass degradation model developed for total system performance assessment (TSPA) calculations for the Yucca Mountain repository system can be used to represent the degradation of disposed MWF. Static tests were conducted at 50, 70, and 90 C with monolithic samples of MWF in pH buffer solutions spiked with NaCl at a MWF surface-to-solution volume ratio of about 200 m{sup -1}. Test specimens were prepared from a surrogate MWF ingot containing about 10 mass% U. Solutions were exchanged after 14, 28, and 70 days. The cumulative amount of U released into solution through 70 days was used to calculate the MWF degradation rate for each test condition. The rate was independent of temperature. The rate was highest in acidic solutions, lowest in neutral solutions, and intermediate in alkaline solutions. The uranium release rate from a breached canister, which is the product of the MWF degradation rate and the surface area of two MWF ingots in a canister, was compared with the release rate calculated with the HLW glass degradation model for a glass log at the same temperature and pH values. The uranium release rates measured for MWF are less than the degradation rates calculated for HLW glass (compared on a mass per time basis).