[en] The UK programme to study fission and corrosion product behaviour in fast reactor sodium cooled system is described. The main topics are: a) the magnitude of material and radioactivity release to the primary coolant and the respective contribution from fuel cladding and structural components. b) the pattern of corrosion product and activity deposition in various parts of the circuit. c) the accuracy of estimates of activity levels deposited on the surfaces of circuit components liable to require maintenance or repair, and associated dose rates. d) the effect of corrosion product deposition on circuit hydraulics and heat transfer

[en] 'Full text': A Molten Carbonate Fuel Cell (MCFC) is an electro-chemical energy conversion technology that runs on natural gas and employs a molten salt electrolyte. In order to keep the electrolyte in this state, the cell must be kept at a temperature above 500 C, eliminating the need for noble catalysts. There has been only a limited amount of research on modelling the transport processes inside this device, mainly due to its limited ability for mobile applications. A model for the reaction-diffusion processes within the cathode of a MCFC is developed using Fick's Law for diffusion and incorporating Darcy's Law for convection. A model for Binary Diffusion is also discussed and compared to those for Fickian diffusion. It can be shown that there exists a limiting case for diffusion across the cathode that depends on the conductivity for the liquid potential, for which there exists an analytical solution. Results are also discussed for varying diffusivities and permeabilities. Ultimately, this research focuses on the optimization of the electrode porosity to increase the power output of the fuel cell. The porosity is considered as a function of position, and is optimized using the software package MATLAB. (author)

[en] The UK position concerning the behaviour of fission and corrosion products in LMFBRs is discussed in the light of the current UK experimental programme and the future operation of PFR. The types of experiment being carried out in the UK to establish factors affecting the behaviour of these products are also identified and current views concerning the migration and possible release of fission products from failed pins and the mass-transfer behaviour of both active and non-active corrosion products in sodium systems are also briefly discussed. The role of sodium chemistry in corrosion and mass-transfer processes of the type under consideration cannot be ignored and therefore analytical methods now being used or developed in the UK are detailed in the report from this stand-point. (author)

[en] Stereo data collected by the HiRes experiment over a six-year period are examined for large-scale anisotropy related to the inhomogeneous distribution of matter in the nearby universe. We consider the generic case of small cosmic-ray deflections and a large number of sources tracing the matter distribution. In this matter tracer model the expected cosmic-ray flux depends essentially on a single free parameter, the typical deflection angle θ _s. We find that the HiRes data with threshold energies of 40 EeV and 57 EeV are incompatible with the matter tracer model at a 95% confidence level unless θ _s > 10 deg. and are compatible with an isotropic flux. The data set above 10 EeV is compatible with both the matter tracer model and an isotropic flux.

[en] Studying quasars at the highest redshifts can constrain models of galaxy and black hole formation, and it also probes the intergalactic medium in the early universe. Optical surveys have to date discovered more than 60 quasars up to z ≅ 6.4, a limit set by the use of the z-band and CCD detectors. Only one z ≳ 6.4 quasar has been discovered, namely the z = 7.08 quasar ULAS J1120+0641, using near-infrared imaging. Here we report the discovery of three new z ≳ 6.4 quasars in 332 deg² of the Visible and Infrared Survey Telescope for Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, thus extending the number from 1 to 4. The newly discovered quasars have redshifts of z = 6.60, 6.75, and 6.89. The absolute magnitudes are between –26.0 and –25.5, 0.6-1.1 mag fainter than ULAS J1120+0641. Near-infrared spectroscopy revealed the Mg II emission line in all three objects. The quasars are powered by black holes with masses of ∼(1-2) × 10⁹ M _☉. In our probed redshift range of 6.44 < z < 7.44 we can set a lower limit on the space density of supermassive black holes of ρ(M _BH > 10⁹ M _☉) > 1.1 × 10^–9 Mpc^–3. The discovery of three quasars in our survey area is consistent with the z = 6 quasar luminosity function when extrapolated to z ∼ 7. We do not find evidence for a steeper decline in the space density of quasars with increasing redshift from z = 6 to z = 7.