[en] Reactor physics, fuel cycle, thermal-hydraulics and fuel cycle cost studies have been performed for this concept and are reported. The most serious drawback of previous FMSR designs, namely the level of irradiation damage to the stainless steel of the cladding and duct materials, has been greatly reduced by the new design. The peak fuel burnup level is also reduced. Work continued on earlier FMSR designs, and in particular, the centrally-moderated FMSR. Emphasis was placed on defining the first core and then the total sequence of core histories over the 30-year life of the reactor. It was found possible to define a two-year fuel cycle with limited reactivity swing over the cycle. Fuel cycle cost studies were begun. The results indicate a modest fuel cycle cost advantage for the FMSR, but the basic cost assumptions must be improved for metal fuel. Improved thermal-hydraulic analysis capabilities have greatly improved the understanding of heat transfer behavior, particularly where thter catalyst were synthesized, and seven were tested in the gas phase. In Task 3, the distributor plate foen conversion can be controlled by adjusting external variables of the coss two- fatigue stren obtained

No abstract available

[en] We model a cubic-to-tetragonal martensitic transition by a Ginzburg-Landau free energy in the symmetric strain tensor. We show in three dimensions (3D) that solving the St.Venant compatibility relations for strain, treated as independent field equations, generates three anisotropic long-range potentials between the two order parameter components. These potentials encode 3D discrete symmetries, express the energetics of lattice integrity, and determine 3D textures. Simulation predictions include twins with temperature-varying orientation, helical twins, competing metastable states, and compatibility-induced elastic frustration. Our approach also applies to improper ferroelastics

No abstract available

[en] Reactor physics and fuel cycle studies, coordinated with heat transfer and material science and structural analysis work has indicated the feasibility potential of the coupled Fast-Mixed Spectrum Reactor (FMSR) concept. This concept employs what are considered reasonable extrapolations of present fast breeder reactor technology to achieve a once-through-and-store reactor fuel cycle. Since the fuel cycle for this reactor is intended to use only natural or depleted uranium for its equilibrium feed, the resultant reactor would have excellent anti-proliferation characteristics. It would also extend utilization of natural uranium resources by a factor of about 15 relative to LWR reactors when on its equilibrium fuel cycle; startup requirements would of course reduce this factor

[en] A fast reactor concept is described which, in its antiproliferation version, can operate on a once-through-and-store fuel cycle, with natural uranium as the only feed fuel. The first core could be started on uranium enriched to less than about 11%. The resource utilization advantage over a typical LWR is about a factor of four. With reprocessing assumed, the operating strategy could be adapted towards such objectives as a considerably lengthened fuel cycle or towards sodium-void coefficient reduction. The principal features of the concept are the use of uranium metal as a high burnup fuel, as demonstrated in the EBR-II reactor, the use of advanced steel alloys now well along in the United States testing, some fuel shuffling, and sometimes zones of moderation. Reactor physics results are shown for one design for which the physics of the design was developed in co-ordination with parallel efforts in the areas of thermal-hydraulics and fuels and materials technologies. The design employs conventional technology wherever possible. The design should be competitive economically with conventional FBR design and may have some advantages in the fuels area. No new safety problems are foreseen. Some potential safety advantages are mentioned. Testing of some of the safety aspects can be performed in the near term using irradiated EBR-II metal fuel in the US TREAT transient test reactor. (author)

[en] We consider ferroelastic first-order phase transitions with N_OP order-parameter strains entering Landau free energies as invariant polynomials that have N_V structural-variant Landau minima. The total free energy includes (seemingly innocuous) harmonic terms, in the n=6-N_OP nonorder-parameter strains. Four three-dimensional (3D) transitions are considered, tetragonal/orthorhombic, cubic/tetragonal, cubic/trigonal, and cubic/orthorhombic unit-cell distortions, with, respectively, N_OP=1, 2, 3, and 2; and N_V=2, 3, 4, and 6. Five two-dimensional (2D) transitions are also considered, as simpler examples. Following Barsch and Krumhansl, we scale the free energy to absorb most material-dependent elastic coefficients into an overall prefactor, by scaling in an overall elastic energy density; a dimensionless temperature variable; and the spontaneous-strain magnitude at transition λ<<1. To leading order in λ the scaled Landau minima become material independent, in a kind of ''quasiuniversality.'' The scaled minima in N_OP-dimensional order-parameter space, fall at the center and at the N_V corners, of a transition-specific polyhedron inscribed in a sphere, whose radius is unity at transition. The ''polyhedra'' for the four 3D transitions are, respectively, a line, a triangle, a tetrahedron, and a hexagon. We minimize the n terms harmonic in the nonorder-parameter strains, by substituting solutions of the ''no dislocation'' St Venant compatibility constraints, and explicitly obtain power-law anisotropic, order-parameter interactions, for all transitions. In a reduced discrete-variable description, the competing minima of the Landau free energies induce unit-magnitude pseudospin vectors, with N_V+1 values, pointing to the polyhedra corners and the (zero-value) center. The total scaled free energies then become Z_NV+1 clocklike pseudospin Hamiltonians, with temperature-dependent local Landau terms, nearest-neighbor Ginzburg couplings, and power-law St Venant interactions that drive the elastic domain-wall texturing. The scaled free energies can be used in relaxational or underdamped dynamic simulations to study ferroelastic strain textures and their dynamical evolution pathways. The pseudospin models can similarly be studied via local meanfield treatments and Monte Carlo simulations.

[en] The Vulpecula OB association, Vul OB1, is a region of active star formation located in the Galactic plane at 2.3 kpc from the Sun. Previous studies suggest that sequential star formation is propagating along this 100 pc long molecular complex. In this paper, we use Spitzer MIPSGAL and GLIMPSE data to reconstruct the star formation history of Vul OB1, and search for signatures of past triggering events. We make a census of young stellar objects (YSOs) in Vul OB1 based on IR color and magnitude criteria, and we rely on the properties and nature of these YSOs to trace recent episodes of massive star formation. We find 856 YSO candidates, and show that the evolutionary stage of the YSO population in Vul OB1 is rather homogeneous-ruling out the scenario of propagating star formation. We estimate the current star formation efficiency to be ∼8%. We also report the discovery of a dozen pillar-like structures, which are confirmed to be sites of small scale triggered star formation.

[en] Methanol (CH₃OH) is thought to be an important link in the chain of chemical evolution that leads from simple diatomic interstellar molecules to complex organic species in protoplanetary disks that may be delivered to the surfaces of Earthlike planets. Previous research has shown that CH₃OH forms in the interstellar medium predominantly on the surfaces of dust grains. To enhance our understanding of the conditions that lead to its efficient production, we assemble a homogenized catalog of published detections and limiting values in interstellar and preplanetary ices for both CH₃OH and the other commonly observed C- and O-bearing species, H₂O, CO, and CO₂. We use this catalog to investigate the abundance of ice-phase CH₃OH in environments ranging from dense molecular clouds to circumstellar envelopes around newly born stars of low and high mass. Results show that CH₃OH production arises during the CO freezeout phase of ice-mantle growth in the clouds, after an ice layer rich in H₂O and CO₂ is already in place on the dust, in agreement with current astrochemical models. The abundance of solid-phase CH₃OH in this environment is sufficient to account for observed gas-phase abundances when the ices are subsequently desorbed in the vicinity of embedded stars. CH₃OH concentrations in the ices toward embedded stars show order-of-magnitude object-to-object variations, even in a sample restricted to stars of low mass associated with ices lacking evidence of thermal processing. We hypothesize that the efficiency of CH₃OH production in dense cores and protostellar envelopes is mediated by the degree of prior CO depletion.

[en] Archival data from the Infrared Spectrometer of the Spitzer Space Telescope are used to study the 15 μm absorption feature of solid CO₂ toward 28 young stellar objects (YSOs) of approximately solar mass. Fits to the absorption profile using laboratory spectra enable categorization according to the degree of thermal processing of the ice matrix that contains the CO₂. The majority of YSOs in our sample (20 out of 28) are found to be consistent with a combination of polar (H₂O-rich) and nonpolar (CO-rich) ices at low temperature; the remainder exhibit profile structure consistent with partial crystallization as the result of significant heating. Ice-phase column densities of CO₂ are determined and compared with those of other species. Lines of sight with crystallization signatures in their spectra are found to be systematically deficient in solid-phase CO, as expected if CO is being sublimated in regions where the ices are heated to crystallization temperatures. Significant variation is found in the CO₂ abundance with respect to both H₂O (the dominant ice constituent) and total dust column (quantified by the extinction, A_V). YSOs in our sample display typically higher CO₂ concentrations (independent of evidence for thermal processing) in comparison to quiescent regions of the prototypical cold molecular cloud. This suggests that enhanced CO₂ production is driven by photochemical reactions in proximity to some YSOs, and that photoprocessing and thermal processing may occur independently.