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No description available.

No description available.

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During the refill stage of a Loss of Coolant Accident (LOCA) in Pressurised Water Reactor (PWR) the effectiveness with which the emergency coolant penetrates to the lower plenum, and hence to the core, is of paramount importance. This thesis presents the results of experimental and theoretical work carried out at the University of Strathclyde on two-1/10 scale planar test sections of a PWR downcomer annulus. The experiments involved the countercurrent flows of air and water and the data were compared with existing flooding correlations for tubes. The comparison revealed the inadequacy of the existing correlations. In the Phase 1 test section arrangement, it was found experimentally that, as the inlet air flowed upwards against two opposing waterfalls, an increase in air flowrate caused the waterfalls to move closer together until a critical air flowrate was reached where the waterfalls collapsed. A theoretical model was also developed to define this collapse condition which was shown to be-analogous to the choked flow of air through a nozzle whose cross sectional area varied with pressure. Whilst this phenomenon was not directly related to the PWR refill problem, it was an interesting feature in its own right. Use was made of previous experimental results for steam-water mixtures on similar test sections, in conjunction with the present air-water data, to study condensation effects. Here the non-equilibrium effects were isolated and correlated against the dependent parameters of inlet water flowrate, inlet subcooling and downcomer wall temperature. A theoretical model for the condensation process was developed which gave good qualitative and quantitative agreement with experiment. Its superiority over a current BCL correlation is demonstrated.

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In the present work the neutron emission spectra from a graphite cube, and from natural uranium, lithium fluoride, graphite, lead and steel slabs bombarded with 14.1 MeV neutrons were measured to test nuclear data and calculational methods for D - T fusion reactor neutronics • The neutron spectra measured were performed by an organic scintillator using a pulse shape discrimination technique based on a charge comparison method to reject the gamma rays counts. A computer programme was used to analyse the experimental data by the differentiation unfolding method. The 14.1 MeV neutron source was obtained £ran T(d,n)4He reaction by the bombardment of T - Ti target with a deuteron beam of energy 130 KeV. The total neutron yield was rronitored by the associated particle method using a silicon surface barrier detector. The numerical calculations were performed using the one - dimensional discrete - ordinate neutron transport code ANISN with the ZZ - FEWG 1/ 31 - lF cross section library. A computer programme based on Gaussian smoothing function was used to srrooth the calculated data and to match the experimental data. There was general agreement between measured and calculated spectra for the range of materials studied. The ANISN calculations carried out with P3 - S8 calculations together with representation of the slab assemblies by a hollow sphere with no reflection at the internal boundary were adequate to model the experimental data and hence it appears that the cross section set is satisfactory and for the materials tested needs no modification in the range 14.1 MeV to 2 MeV. Also it would be possible to carry out a study on fusion reactor blankets, using cylindrical geometry and including a series of concentric cylindrical shells to represent the torus wall, possible neutron converter and breeder regions, and reflector and shielding regions.

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