Mixtures of rare earth and actinide oxalates will be vitrified into boro-aluminosilicate-based glasses for intermediate term stabilization according to current plans. The reaction chemistry involved with converting these oxalate feed stocks into glass products determines the potential for foaming, redox, and other melt and off gas related phenomena associated with this process. We've undertaken a detailed study of this conversion process using a variety of complementary techniques. A closed quartz crucible contained in a vertical furnace equipped with a quartz window and video camera was used to study volume expansion of the feed/melt during heating while monitoring the off-gas using a gas chromatograph-mass spectrometer. Simultaneous thermogravimetric and differential thermal analyses were conducted on small samples of feed and frit mixtures. Samples containing Ce were analyzed using established wet chemical techniques to determine Ce3+/Ce4+ ratio (redox) as a function of temperature. We evaluate the results and provide a description of the reaction chemistry of these oxalate feeds during vitrification.

The liquidus temperatures, TL, of rare earth-alumino-borosilicate glasses were measured as a function of glass composition. The TL values ranged from 1153°C to 1405°C. Three primary crystalline phases were identified in the study. The most frequently encountered was a rare earth silicate phase in which the TL values ranged from 1153°C to 1405°C. A12O3 was encountered in glasses with an A12O3:SiO2 mass ratio greater than 1, with TL values ranging from 1242°C to 1305°C. Alumino-silicate crystals were encountered as the primary phase in glasses with less than 43 mass% of mixed rare earth oxides (Ln2O3) with TL values between 1164°C and 1255°C. A linear relationship between total mixed rare earth oxide concentration and TL was found within all three primary phase fields. In the rare earth silicate primary phase field, normalizing the Ln2O3 concentration with its mean ionic radius enhanced this linear relationship.

A study was conducted on glasses based on a simulated transuranic waste withhigh concentrations of ZrO2and Bi2O3 todetermine the compositional dependence of primary crystalline phases andliquidus temperature (TL). Starting from a baseline composition, glasses were formulated bychanging mass fractions of Al2O3, B2O3, Bi2O3, CeO2, Li2O, Na2O, P2O5, SiO2, and ZrO2, one at a time, while keeping theremaining components in the same relative proportions as in the baselineglass. Liquidus temperature was measured by heat treating glass samples for24 h in a uniform temperature furnace. The primary crystalline phase in thebaseline glass and the majority of the glasses was zircon(ZrSiO4). A change in the concentration of certain components (Al2O3, ZrO2, Li2O, B2O3 and SiO2) changed the primary phaseto baddeleyite (ZrO2), while cerium oxide (CeO2)precipitated from glasses with more than 3 wt% CeO2. ZirconTL was strongly increased by Al2O3, Zrb2 and CeO2, and slightly by P2O5 and SiO2; decreased strongly by Li2O and Na2O and moderately by B2O3. A first-order model was constructed for T L as a function of composition for zircon primary crystalline phaseglass.

Vitrification is currently being explored as an option for plutonium (Pu)scrap and residue stabilization because of its ability to convertplutonium-bearing materials into a safe, durable, and accountable waste formwith reduced need for safeguarding. To develop this glass, the effect ofcomposition on key glass properties (viscosity and chemical durability) weremeasured. A one-component-at-a-time change test matrix with 36 glasses wasdesigned. The viscosity is reported as the temperature at 5 Pas (T5), andthe durability as the normalized release of boron and sodium (Гb and ГNa)from MCC-1 and PCT static leach tests and the negative logarithm offractional aluminum and lithium release (-ln[fA1] and -ln[fLi]) from TCLP. The effects of Al2O3, B2O3, CaO, CeO2, Gd2O3, K2O, Li2O, MgO, Na2O, PbO, SiO2, SnO, TiO2, and ZrO2 were found to be linear for T5 and non-linear for chemical durability. T5 isincreased most by the addition of SiO2 followed by Al2O3, and decreased most by Li2Ofollowed by Na2O. MCC-1 ln[rB] and ln [rNa]are increased most by the addition of Li2O followed by MgO anddecreased most by Al2O3 followed by ZrO2.PCT In[rB] and In[rNa] are increased most by theaddition of MgO followed by B2O3 and decreased most by Al2O3 followed by SiO2. The relativeeffect of components on rB and rNa are similar forboth PCT and MCC-1. TCLP -ln[fAl] and ln[fLi areincreased most by the addition of SiO2 followed by SnO anddecreased most by Li2O.

The impact of crystalline phase precipitation in glass during canistercooling on chemical durability of the waste form limits waste loading inglass, especially for vitrification of certain high-level waste (HLW)streams rich in Na2O and Al2O3. This studyinvestigates compositional effects on nepheline precipitation in simulatedHanford HLW glasses during canister centerline cooling (CCC) heat treatment.It has been demonstrated that the nepheline primary phase field defined bythe Na2O-Al2O3-SiO2 ternarysystem can be used as an indicator for screening HLW glass compositions thatare prone to nepheline formation. Based on the CCC results, the componenteffects on increasing nepheline precipitation can be approximately ranked as Al2O3 > Na2O > Li2O ≈ K2O ≈ Fe2O3 > CaO > SiC2. The presence of nepheline in glass is usuallydetrimental to chemical durability. Using x-ray diffraction data inconjunction with a mass balance and a second-order mixture model for 7-dayproduct consistency test (PCT) normalized B release, the effect of glasscrystallization on glass durability can be predicted with an uncertaintyless than 50% if the residual glass composition is within the range of thePCT model.

The solubility limit of phosphate in glass was found to decrease as fluorineincreased. Amorphous phase separation was found in the glass as a result ofinteraction between phosphate and fluorine, in which Ce and Gd stronglypartitioned. The glasses exhibiting amorphous phase separation showed highernormalized B releases according to the 31-day product consistency test (PCT)compared to glasses without phase separation. Phosphate that leached fromglass into water increased the concentrations of Ce and Gd in the 7- and31-day PCT solutions by more than an order of magnitude. The liquid state 31P-NMR results suggested that phosphate in water interactswith Ce or Gd. Therefore, the observed concentration jump for Ce and Gd inthe PCT solution may be attributed to the increases in the solubility limitsof Ce and Gd as a result of phosphate complexation with Ce and Gd.

The liquidus temperature (TL) often limits the loading ofhigh-level waste in glass through the constraint that TL must beat least 100°C below the temperature at which the glass viscosity is 5 Pa-s.In this study, values of TL for spinel primary crystalline phasewere measured as a function of glass composition. The test glasses werebased on high-iron Hanford Site tank wastes. All studied glassesprecipitated spinel (Ni,Fe,Mn)(Cr,Fe)2O4 as theprimary crystalline phase. TL was increased by additions of Cr2O3, NiO, Al2O3, Fe2O3, MgO, and MnO; while Li2O, Na2O, B2O3, and SiO2 had anegative effect. Empirical mixture models were fitted to data.

The physical properties of the ceramic YBa2Cu(3-x)CoxOy have been investigated in order to evaluate its usefulness as a substrate material for YBCO superconductors. YBa2Cu(3-x)CoxOy has been found to be thermally and chemically compatible with 123 and displays adequate electrical properties for a substrate material. A material with the nominal composition of YBa2Cu2.2CO0.8O7 was investigated, extensively. The mechanical properties of this material were found to be poor, e.g., tensile strength was only 60 MPa. A semiconductor-like behavior was observed with a room-temperature resistivity of 70 mμ.cm and a resistivity equal to 4 × 106 mn.cm at 77K. [ Key words: YBa2Cu3Oy, cobalt substitution, substrate, electrical properties, thermal properties, processing]