STABILIZING EFFECTS OF OXIDE ADDITIONS TO URANIUM OXIDE

An investigation of the stabilizing influence of oxide additions to uranium oxide was continued. These additions are employed to eliminate the phase transformation to U/sub 3/O?sub 8/ which occurs when UO/sub 2/ is exposed to an oxidizing environment at elevated temperatures and to reduce the volatility or transpiration losses of uranium oxide which become appreciable in air at temperatures in excess of 1200 deg C. The results show that CaO may be successfully employed in partial substitution for La/sub 2/O/sub 3/ and Y/sub 2/O/ sub 3/. The resulting solid solutions exhibited high-temperature stability comparable to that of the "binary" solid solutions of UO/sub 2/ containing La/sub 2/O/sub 3/ or Y/sub 2/O/sub 3/. On the basis of thes e and other results some alternative approaches appear possible to reduce the amount and cross section of additive required for stabilization. (auth

STABILIZING EFFECTS OF OXIDE ADDITIONS TO URANIUM OXIDE

An investigation of the stabilizing influence of oxide additions to uranium oxide was continued. These additions are employed to eliminate the phase transformation to U/sub 3/O?sub 8/ which occurs when UO/sub 2/ is exposed to an oxidizing environment at elevated temperatures and to reduce the volatility or transpiration losses of uranium oxide which become appreciable in air at temperatures in excess of 1200 deg C. The results show that CaO may be successfully employed in partial substitution for La/sub 2/O/sub 3/ and Y/sub 2/O/ sub 3/. The resulting solid solutions exhibited high-temperature stability comparable to that of the "binary" solid solutions of UO/sub 2/ containing La/sub 2/O/sub 3/ or Y/sub 2/O/sub 3/. On the basis of thes e and other results some alternative approaches appear possible to reduce the amount and cross section of additive required for stabilization. (auth

Spherically symmetric dissipative anisotropic fluids: A general study

The full set of equations governing the evolution of self--gravitating spherically symmetric dissipative fluids with anisotropic stresses is deployed and used to carry out a general study on the behaviour of such systems, in the context of general relativity. Emphasis is given to the link between the Weyl tensor, the shear tensor, the anisotropy of the pressure and the density inhomogeneity. In particular we provide the general, necessary and sufficient, condition for the vanishing of the spatial gradients of energy density, which in turn suggests a possible definition of a gravitational arrow of time. Some solutions are also exhibited to illustrate the discussion.Comment: 28 pages Latex. To appear in Phys.Rev.

Topological Orthoalgebras

We define topological orthoalgebras (TOAs) and study their properties. While every topological orthomodular lattice is a TOA, the lattice of projections of a Hilbert space is an example of a lattice-ordered TOA that is not a toplogical lattice. On the other hand, we show that every compact Boolean TOA is a topological Boolean algebra. We also show that a compact TOA in which 0 is an isolated point is atomic and of finite height. We identify and study a particularly tractable class of TOAs, which we call {\em stably ordered}: those in which the upper-set generated by an open set is open. This includes all topological OMLs, and also the projection lattices of Hilbert spaces. Finally, we obtain a topological version of the Foulis-Randall representation theory for stably ordered TOAsComment: 16 pp, LaTex. Minor changes and corrections in sections 1; more substantial corrections in section

Monte-Carlo Simulations of Radiation-Induced Activation in a Fast-Neutron and Gamma- Based Cargo Inspection System

An air cargo inspection system combining two nuclear reaction based techniques, namely Fast-Neutron Resonance Radiography and Dual-Discrete-Energy Gamma Radiography is currently being developed. This system is expected to allow detection of standard and improvised explosives as well as special nuclear materials. An important aspect for the applicability of nuclear techniques in an airport inspection facility is the inventory and lifetimes of radioactive isotopes produced by the neutron and gamma radiation inside the cargo, as well as the dose delivered by these isotopes to people in contact with the cargo during and following the interrogation procedure. Using MCNPX and CINDER90 we have calculated the activation levels for several typical inspection scenarios. One example is the activation of various metal samples embedded in a cotton-filled container. To validate the simulation results, a benchmark experiment was performed, in which metal samples were activated by fast-neutrons in a water-filled glass jar. The induced activity was determined by analyzing the gamma spectra. Based on the calculated radioactive inventory in the container, the dose levels due to the induced gamma radiation were calculated at several distances from the container and in relevant time windows after the irradiation, in order to evaluate the radiation exposure of the cargo handling staff, air crew and passengers during flight. The possibility of remanent long-lived radioactive inventory after cargo is delivered to the client is also of concern and was evaluated.Comment: Proceedings of FNDA 201

Stability measurements on cored cables in normal and superfluid helium

The relative stability of LHC type cables has been measured by the direct heating of one of the individual strands with a short duration current pulse. The minimum energy required to initiate a quench has been determined for a number of cables which have a central core to increase the effective inter-strand cross-over resistance. Experiments were performed in both normal helium at 4.4 K and superfluid at 1.9 K. Conductors in general are less stable at the lower temperature when measured at the same fraction of critical current. Results show that the cored-cables, even when partially filled with solder or with a porous-metal filler exhibit a relatively low stability at currents close to the critical current. It is speculated that the high inter-strand electrical and thermal resistance inherent in these cables may effect the stability at high currents