Redox Characterization of Simulated Nuclear Waste Glass

Abstract

Ferroudferric equilibria were determined in an alkali-iron borosilicate glass of the type that is presently being considered for nuclear waste disposal. Theoretical redox behavior is found at conditions more reducing than 1 Wa. Deviation from this behavior at more oxidizing conditions results from mutual interactions between the iron redox couple and other multivalent ions in the glass. The results suggest that the ferrous/ferric ratio can be used as a quantitative indicator of the glass oxidation state in these complex glasses. Implications regarding redox control of the vitrification process are discussed.

Role of Manganese Reduction/Oxidation (Redox) on Foaming and Melt Rate in High Level Waste (Hlw) Melters (U)

“…In the melt pool, transition metal species such as Fe +3 and Mn +4 release O 2 gas at the elevated melter temperatures [22,23,24] in the absence of any oxidizing or reducing agents in the melt. This is because Mn +3 or Mn +2 is normally the stable species in a melt at elevated temperature and even higher temperatures stabilize Fe +2 .…”

“…Jantzen and Plodinec [37] compared the recommendations of Schreiber [22], Goldman [23], Hrma [4], and others [39] and recommended that the DWPF REDOX ratio based on Fe +2 /ΣFe be controlled between 0.09 and 0.33 (i.e., the corresponding oxygen fugacity range of 10 -4 to 10 -7 atm at 10 wt% Fe).…”

Electron Equivalents Redox Model for High Level Waste Vitrification

“…The data included crucible melts [22] and data from the operation of a 1/10 th scale test melter [10]. This melter was a 1/10th scale prototype of the joule-heated, ceramic-lined melter used to vitrify wastes stored at the West Valley Demonstration Project (WVDP).…”

Chemical Oxygen Demand (COD) For Monitoring Reduction-Oxidation (Redox) Equilibrium During High Level Waste (HLW) Vitrification

“…>>0.33 Fe +2 /ΣFe. Any carbon containing species in melter feeds (coal, oxalate, formic acid, sugar) cause reduction of transition metal species such as Fe +3 and Mn +4 at the elevated melter temperatures [2,3,4]. The interaction of the carbon with the transition metal species in the waste feed occurs primarily in the melter cold cap [5,6].…”

“…Based on the work of Schreiber [2] and Goldman [3], Jantzen and Plodinec [8] originally defined acceptable REDOX ratios (based on the measured Fe 2+ /ΣFe ratio) for any DWPF-type melt to be greater than or equal to 0.09 (to prevent foaming via the deoxygenation of MnO 2 , Mn 2 O 3 , and Mn 3 O 4 to MnO) and less than or equal to 0.33 (to prevent metallic nickel and nickel sulfide formation). Formate and nitrate concentrations in the melter feed appear to be the * seven analyses if total oxalate (soluble and insoluble) and total manganese (soluble and insoluble) can be measured together major parameters influencing melt REDOX during vitrification.…”