Terrence B. Lindemer

Thermodynamic review and calculations—alkali-metal oxide systems with nuclear fuels, fission products, and structural materials☆

Abstract This paper considers the phase equilibria of alkali metal oxides and their combinations with other oxides relevant to nuclear fuels, fission products, and structural materials. The other oxides include those of the lanthanides, the actinides, iron, nickel, aluminum, silicon, as well as those of periodic table groups IIA, IVB, VB, VIB, and VIA. The alkali metal halides, chalcogenides, and hydroxides are also included. Techniques are developed to permit calculation of phase equilibria and Ellingham diagrams in ternary and higher-order systems. These techniques include estimation of previously unknown 298.15 K values of the enthalpies of formation and the entropies of many compounds.

Chemical thermodynamic representation of

Abstract The entire 〈UO 2 ± x 〉 ★★ data base for the dependence of the nonstoichiometry, x , on temperature and chemical potential of oxygen (oxygen potential) was retrieved from the literature and represented. This data base was interpreted by least-squares analysis using equations derived from the classical thermodynamic theory for the solid solution of a solute in a solvent. For hyperstoichiometric oxide at oxygen potentials more positive than −266700 + 16.5T J/mol , the data were best represented by a [UO 2 ]-[U 3 O 7 ] solution. For O/U ratios above 2 and oxygen potentials below this boundary, a [UO 2 ]-[U 2 O 4.5 ] solution represented the data. The 〈UO 2−x 〉 data were represented by a [UO 2 ]-[U 1 3 ] solution. The resulting equations represent the experimental ln(P ★ O 2 )−ln(x) behavior and can be used in thermodynamic calculations to predict phase boundary compositions consistent with the literature. Collectively, the present analysis permits, for the first time, a mathematical representation of the behavior of the total data base.

Decomposition of YBa2Cu3O7-x and YBa2Cu4O8 for pO2≤0.1 MPa

Abstract The temperature and oxygen pressure conditions were determined by thermogravimetry for decomposition of phase-pure YBa 2 Cu 3 O 7− x and YBa 2 Cu 4 O 8 from 3 Pa to 0.1 MPA O 2 . All extant data were reviewed to determine the conditions for thermodynamic dynamic stability of phase-pure YBa 2 Cu 3 O 7− x and for compositions lying between YBa 2 Cu 3 O 7− x and CuO . Thermodynamic values for YBa 2 Cu 4 O 8 were derived, as was the 123-CuO section of the Y 2 O 3 -BaO-CuO phase diagram.

Chemical thermodynamic representations of 〈PuO2−x〉 and 〈U1−zPuzOw〉☆

All available oxygen potential-temperature-composition data for the calcium fluorite-structure 〈PuO2−x〉★★ phase were retrieved from the literature and utilized in the development of a binary solid solution representation of the phase. The data and phase relations are found to be best described by a solution of [Pu43O2] and [PuO2] with a temperature dependent interaction energy. The fluorite-structure 〈U1−zPuzOw〉 is assumed to be represented by a combination of the binaries 〈PuO2−x〉 and 〈UO2 ± x〉, and thus treated as a solution of [Pu43O2], [PuO2], [UO2], and either [U2O4.5] or [U3O7]. The resulting equations well reproduce the large amount of oxygen potential-temperature-composition data for the mixed oxide system, all of which were also retrieved from the literature. These models are the first that appear to display the appropriate oxygen potential-temperature-composition and phase relation behavior over the entire range of existence for the phases.

Chemical thermodynamics of Cs and Te fission product interactions in irradiated LMFBR mixed-oxide fuel pins

Abstract A combination of fuel chemistry modelling and equilibrium thermodynamic calculations has been used to predict the atom ratios of Cs and Te fission products (Cs:Te) that find their way into the fuel-cladding interface region of irradiated stainless steel-clad mixed-oxide fast breeder reactor fuel pins. It has been concluded that the ratio of condensed, chemically-associated Cs and Te in the interface region,Cs:Te, which in turn determines the Te activity, is controlled by an equilibrium reaction between Cs 2 Te and the oxide fuel, and that the value of Cs:Te is, depending on fuel 0:M, either equal to or slightly less than 2:1. Since Cs and Te fission products are both implicated as causative agents in FCCI (fission product-assisted inner surface attack of stainless steel cladding) and in FPLME (fission product-assisted liquid metal embrittlement of AISI-Type 316), the observed out-of-pile Cs:Te thresholds for FCCI (4:1) and FPLME (2:1) have been rationalized in terms of Cs:Te thermochemistry and phase equilibria. Also described in the paper is an updated chemical evolution model for reactive/volatile fission product behavior in irradiated oxide pins.

Nonstoichiometry, decomposition and Tc of Nd1+zBa2−zCu3Oy

Abstract The temperature ( T ) and O 2 partial pressure ( p [O 2 ]) dependence of oxygen content ( y ) in Nd 1+ z Ba 2− z Cu 3 O y were determined over the entire range of z . These data were represented by chemical thermodynamic models. The T - z - p [O 2 ] dependence of high-temperature decomposition was also determined, as were the effects of various T - t - p [O 2 ] treatments on the superconducting transition temperature ( T c ). These results were compared with those from the Y and La homologs.

Study of phase behavior in the YBa2Cu3O7−x−BaCuO2+y−CuO−Ag system

Abstract The temperature ( T ) and oxygen pressure ( p O 2 ) conditions were determined from 6 Pa to 0.1 MPa O 2 for several equilibria in the YBa 2 Cu 3 O 7− x −BaCuO 2+ y −CuO−Ag system. These included the y − T − p O 2 interrelationships, the T - p O 2 conditions for decomposition of BaCuO 2+ y , and the effects of Ag on several eutectic and peritectic temperatures.

Magnetic dynamics in underdoped YBa2Cu3O7-x: Direct observation of a superconducting gap

Polarized and unpolarized triple-axis neutron measurements were performed on an underdoped crystal of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} ({ital x}=0.4{plus_minus}0.02, {ital T}{sub {ital c}}=62.7 K). Our results indicate, contrary to earlier evidence, that the spin excitations in the superconducting state are essentially the same as those in the fully doped material except that the unusual 41meV resonance is observed at 34.8meV. The normal state spin excitations are characterized by a weakly energy-dependent continuum whose temperature dependence shows the clear signature of a superconducting gap at {ital T}{sub {ital c}}. The enhancement at the resonance is accompanied by a suppression of magnetic fluctuations at both higher and lower energies. {copyright} {ital 1996 The American Physical Society.}

Chemical thermodynamics of the system Cs--U--Zr--H--I--O in the light water reactor fuel-cladding gap

Equilibrium thermodynamic calculations were performed on the Cs-U-Zr-H-I-O system that is assumed to exist in the fuel-cladding gap of light water reactor fuel under in-reactor, steam, and 50% steam--50% air conditions. The in-reactor oxygen potential is assumed to be controlled by either UO/sub 2+x/ + Cs/sub 2/UO/sub 4/ or Zr + ZrO/sub 2/. The important condensed phases in-reactor are UO/sub 2+x/, Cs/sub 2/UO/sub 4/, and CsI, and the major gaseous species are Cs, Cs/sub 2/, CsI, and Cs/sub 2/I/sub 2/. The presence of steam does not alter these species, although CsOH also becomes a major gaseous species. In a 50% steam--50% air mixture, the equilibrium condensed phases are U/sub 3/O/sub 8/ or UO/sub 3/ and Cs/sub 2/U/sub 15/O/sub 46/. Under a nonequilibrium situation where zirconium metal can react with iodine, ZrO/sub 3/ or liquid ZrI/sub 2/ is present, and the gaseous species ZrI/sub 3/ and ZrI/sub 4/ have large partial pressures.

Effects of composition and processing on the superconductivity of La1+zBa2-zCu3Oy

Abstract The effects of composition, processing time ( t ), temperature ( T ) and O 2 partial pressure ( p O 2 ) on the superconducting transition temperature, T c , were investigated for La 1+ z Ba 2- z Cu 3 O y . Tallon and Flowers prediction of T c ≈ 100 K [Physica C 204 (1993) 237] at z = 0 could not be attained. Instead, the T c maximum of 93–94K is similar to that of the yttria analog. As z was increased, the T c values increased gradually by a few kelvin until z = 0.2, which is at the orthorhombic to tetragonal transition, and then decreased more abruptly, with no superconductivity for z ≥0.5. Crucial steps in the process at all z values include the highest temperature anneal (1065°C) in 0.1 MPa O 2 , reduction of the oxygen content at 950°C and cooling to 300–400°C, both at 100–1000 Pa O 2 , and reoxygenation at 0.1 MPa O 2 during slow cooling (5–20°C/min) to T c decreased fairly monotonically with decreasing y at z = 0.08, and a La excess of 0.2 and Cu nonstoichiometry on both sides of Cu/(La+Ba) = 1 generally depressed T c .