Geometrical Dependency Research Articles

Kinematics and Thermodynamics of Non-Stoichiometric Oxidation Phase Transitions in Spent Fuel

ABSTRACTAt low temperatures (<200°C), spent fuel from power reactors oxidizes from its UO2 lattice to a U4O9 lattice but with an oxygen-to-uranium (O/U) ratio of ∼2.4. Also, the weight gain time response has a plateau as the O/U approaches 2.4. Part of this response results from a geometrical dependency as a U4O9 oxidation front propagates into grain volumes of UO2. It may also be indicative of a metastable, non-stoichiometric U4O9 phase whose existence may inhibit the transition kinetics to the next expected phase of U3O8. To gain a mechanistic understanding and to plan future oxidation tests, lattice kinematic and thermodynamic models are developed for lattice deformations and energetics of lattice phase changes (UO2 → U4O9 → U3O7 → U3O8) that include zeroth order influences on oxidation kinetics due to interstitial oxygen atoms and vacancies plus interstitial and substitutional actinides and fission decay products in spent fuel.

Current Noise of Resin Type and Cermet Type Thick Film Resistors

The current noise indices (C.N.I.) depend linearly on the logarithmic values of sheet resistivity (log⁡ ρS), in both carbon black/resin and thallium oxide/glass resistors, and can be expressed as C.N.I. = A + B log⁡ ρS. The geometrical dependency on C.N.I. in both types of resistor can be expressed as C.N.I. = A′ − B′ log⁡ (L, W, T), where A, B, A′ and B′ are constants. The dependency of noise e.m.f. (νn) on the applied dc voltage (V), i.e., the values of α in , can be obtained from the slope of C.N.I. versus log⁡ (L) lines, associated with a model based on the noise generator approximation.