Particle size analysis of tungsten metal powder.

A method of particle size analysis for sub-sieve, tungsten metal powder has been developed using the Andreason pipette. Use of 1/4 percent by volume of tungsten powder in demineralised water gives minimum agglomeration. The method is useful for comparing the distribution of different batches of tungsten powder. No correlation between results from this method and the microscopic counting method used by the suppliers of the powder was found

Suggestions for work on design of heat exchangers in liquid metal fueled reactors.

The report discusses the low heat transfer film coefficient on the secondary coolant side of tubular exchangers used in the calculations in AAEC-E-1. It suggests the types of heat exchangers which should be investigated in order to improve this coefficient and in turn to reduce the relative hold-up

Preliminary kinetic study of a sodium-beryllium-uranium circulating fuel reactor.

The initial response of a 1:100:2000 U-Na-Be Reactor, operating at a power density of 1200 cals/cc/sec, to a sudden change in the fuel concentration in the circulating carrier, has been calculated on the assumption of constant inlet temperature and no delayed neutrons. The result confirmed that the peak temperatures and power can be accurately calculated by ignoring the moderator temperature rise, and that the approach to the new steady state values is given by the solution of the linearized equations. The slow moderator heating implies that the departure from the steady state are still large when the carrier and fuel have completed one transit of the external circuit. The assumption that the mean temperature is the arithmetic peak but overestimates the maximum power and outlet temperature excursions by 15 1/2% and 7% respectively

Note on the response of a circulating fuel reactor to random fluctuation in fuel concentration.

A simplified model of a Uranium "Sodium" Beryllium circulating fuel reactor has been analysed to determine the root mean square power and temperature fluctuations due to random variations in the inlet fuel concentration. The results indicate that limits of ± 2% on the fuel concentration should reduce the mean square power excursion, due to this cause, to less than ½%. The calculations based on assumptions only, as regards the specification of the statistical nature of the fuel concentration, but the method can be used to obtain more realistic estimates when experimental evidence becomes available

Behaviour of particles of U, UO2, and UC2 in a vertical tube through which liquid sodium is flowing.

This paper sets out to calculate the relation between the particle velocity and the fluid velocity in a vertical tube without making any assumptions as to the "apparent" viscosity of the suspension of particle in liquid sodium. The theory and calculations method is developed for suspensions of U, UO2 and UC2 in liquid Na in the temperature range 200º - 800ºC. At the moment, it does not help in assessing the performance of a circulating suspension in the primary coolant stream of nuclear power reactor

Neutron diffuse scattering of (1 − x)(Na0.5Bi0.5)TiO3–xBaTiO3 relaxor ferroelectric single crystals.

Peculiar L-shaped diffuse streaks along pc were observed in (Na0.5Bi0.5)TiO3 (NBT) below the Burns temperature, revealing the existence of polar nanoregions (PNRs). The displacement of Bi3+ cations is ∼0.26 Å along pc in the PNRs, with a size of ∼13 Å in NBT. The BaTiO3 doping drives the diffuse scattering patterns to evolve from the L-shape into an ellipsoidal along pc in (Na0.5Bi0.5)TiO3–xBaTiO3. An abnormally large correlation length was observed in the morphotropic phase boundary composition with x = 0.05. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved

Separating remote fetch and local mixing influences on near-surface radon gradient mesaurements

Predictions of weather and climate conditions are crucially reliant upon the fidelity of model parameterisations that represent the integrated behaviour of key physical processes responsible for transport and mixing in the atmospheric boundary layer. Distributions of trace gases and aerosols with respect to their natural or anthropogenic sources, as well as their removal through deposition, are also controlled by these processes. However, scientific understanding of many aspects of mixing and transport processes still requires substantial refinement, or even fundamental revision. In the stably stratified boundary layer vertical mixing processes remain poorly understood, particularly in very stable conditions when surface inversions can be extremely shallow and the thermodynamic structure of the lowest 50−100 m very complex. At the surface, for even simple investigations of atmospheric chemistry, there is a need to improve our understanding of the processes controlling the spatial/temporal variability in vertical exchange rates between the roughness elements (canopy/buildings) and the atmosphere above. Two-point radon gradients provide a direct, unambiguous measure of near-surface atmospheric mixing. A 31-month dataset of hourly radon measurements at 2 and 50 m is used to characterise the seasonality and diurnal variability of radon concentrations and gradients at a site near Sydney. Vertical differencing allows separation of remote (fetch-related) effects on measured radon concentrations from those due to diurnal variations in the strength and extent of vertical mixing. With the help of model-derived back trajectories and boundary layer depths, we were able to characterise the pronounced seasonal variability in afternoon surface radon concentrations in the Sydney region in terms of air mass fetch, contact time with land, ABL dilution and regional variability of the radon source function. Influences of coastal sea breeze circulations and the local topography were identified, superimposed upon the dominant seasonal variations in regional circulation patterns. Diurnal composites, grouped according to the maximum nocturnal radon gradient (ΔCmax), reveal strong connections between radon, wind, temperature and mixing depth on sub-diurnal timescales. Comparison of the bulk Richardson Number (RiB) and the turbulence kinetic energy (TKE) with the radon-derived bulk diffusivity (KB) helps to elucidate the relationship between thermal stability, turbulence intensity and the resultant mixing. On nights with large ΔCmax, KB and TKE levels are low and RiB is well above the “critical” value. Conversely, when ΔCmax is small, KB and TKE levels are high and RiB is near zero. For intermediate ΔCmax, however, RiB remains small whereas TKE and KB both indicate significantly reduced mixing. The relationship between stability and turbulence is therefore non-linear, with even mildly stable conditions being sufficient to suppress mixing

10Be in last deglacial climate simulated by ECHAM5-HAM – Part I: Climatological influences on 10Be deposition

Reconstruction of solar irradiance has only been possible for the Holocene so far. During the last deglaciation, two solar proxies (10Be and 14C) deviate strongly, both of them being influenced by climatic changes in a different way. This work addresses the climate influence on 10Be deposition by means of ECHAM5-HAM atmospheric aerosol–climate model simulations, forced by sea surface temperatures and sea ice extent created by the CSIRO Mk3L coupled climate system model. Three time slice simulations were performed during the last deglaciation: 10 000 BP ("10k"), 11 000 BP ("11k") and 12 000 BP ("12k"), each 30 yr long. The same, theoretical, 10Be production rate was used in each simulation to isolate the impact of climate on 10Be deposition. The changes are found to follow roughly the reduction in the greenhouse gas concentrations within the simulations. The 10k and 11k simulations produce a surface cooling which is symmetrically amplified in the 12k simulation. The precipitation rate is only slightly reduced at high latitudes, but there is a northward shift in the polar jet in the Northern Hemisphere, and the stratospheric westerly winds are significantly weakened. These changes occur where the sea ice change is largest in the deglaciation simulations. This leads to a longer residence time of 10Be in the stratosphere by 30 (10k and 11k) to 80 (12k) days, increasing the atmospheric concentrations (25–30% in 10k and 11k and 100% in 12k). Furthermore the shift of westerlies in the troposphere leads to an increase of tropospheric 10Be concentrations, especially at high latitudes. The contribution of dry deposition generally increases, but decreases where sea ice changes are largest. In total, the 10Be deposition rate changes by no more than 20% at mid- to high latitudes, but by up to 50% in the tropics. We conclude that on "long" time scales (a year to a few years), climatic influences on 10Be deposition remain small (less than 50%) even though atmospheric concentrations can vary significantly. Averaged over a longer period, all 10Be produced has to be deposited by mass conservation. This dominates over any climatic influences on 10Be deposition. Snow concentrations, however, do not follow mass conservation and can potentially be impacted more by climate due to precipitation changes. Quantifying the impact of deglacial climate modulation on 10Be in terms of preserving the solar signal locally is analysed in an accompanying paper (Heikkilä et al., 10Be in late deglacial climate simulated by ECHAM5-HAM – Part 2: Isolating the solar signal from 10Be deposition). © Author(s) 2013