Abstract
High Cr2O3 containing Monofrax™ K‐3 is a robust refractory that is used in the fiberglass industry and used in radioactive waste glass melters worldwide. Monofrax™ K‐3 is tolerant of transition metal oxides but contains highly reduced solid solutions of spinels, that is, (Mg,Fe2+)(Al,Cr)2O3. Conversely, many of the waste feeds being processed are highly oxidizing. The K‐3 refractory corrosion was tested in sealed crucibles starting with slurried melter feed instead of prereacted glass called for by ASTM C621. Testing the refractory coupon during the feed‐to‐glass conversion exposes the refractory to the oxidizing and reducing species being released during vitrification, for example, NO3−, NO2−, CO2, CO, O2. Corrosion rates measured in highly oxidizing (high nitrate) feeds were ~1.8–2.8 times higher than those determined using prereacted glass or reduced feeds. Confirmatory corrosion rates were measured on Monofrax™ K‐3 coupons immersed in oxidizing feed in a 1/100th‐scale HLW pilot‐scale melter. Corrosion is heterogeneous or incongruent as Ni and Fe in the waste glass exchange with Mg and Al in the refractory. An insoluble NiFe2O4 spinel corrosion product is formed that can build up a protective layer along the refractory walls or spall and settle to the melter floor depending on melt pool convection/agitation.
Highlights
High Cr2O3 containing MonofraxTM K-3 is a robust refractory that is used in the fiberglass industry and used in radioactive waste glass melters worldwide
Oxidizing High Level Waste (HLW) and Low Activity Waste (LAW) wastes will be vitrified at Hanford at the Waste Treatment and Immobilization Plant (WTP).[2]
The spinel phases are mixtures of the four end member spinels (Mg,Fe)O(Al,Cr)2O3 and some SiO2.[4,8,9,10,11] Cr2O3 is poorly soluble in Defense Waste Processing Facility (DWPF) glass, other components of the MonofraxTM K-3 refractory have been found to be soluble in HLW waste glass [10,11] and reduced Fe species in the refractory can oxidize when in contact with oxidizing feeds in the melter
Summary
High Cr2O3 containing MonofraxTM K-3 is a robust refractory that is used in the fiberglass industry and used in radioactive waste glass melters worldwide. Previous scale melter testing of the MonofraxTM K-3 refractory at the Savannah River National Laboratory (SRNL) had been performed using only reducing feeds containing minimal concentration of oxidizers (nitrate and nitrite).
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