Nuclear Structural Engineering最新文献

The construction of the vault and target rooms of the Harwell Variable Energy Cyclotron is described. The mechanical, heating, cooling, ventilation and electrical services for the building are discussed. Particular reference is made to the power operated shielding doors and to the safety circuitry associated with them.

Failures of surfacing materials on concrete floors (likewise on concrete or masonry walls) are usually due to dampness. A rapid and reliable method of determining the dryness of such structures could prevent this type of failure.

Present methods depend on conditions in the atmosphere adjacent to the floor etc. (indirect methods) or on changes in the properties of the concrete (direct methods). Indirect methods can be satisfactory if their criteria of dryness are soundly based. A well based procedure is the quasi-equilibrium method of British Standard C.P. 203, which has a long history of successful field use. Recently methods using the rate of emission of moisture have appeared. These may also be satisfactory but the bases of their criteria are not known.

Gravimetric methods are unsatisfactory because of the difficulty of obtaining a representative sample. Electrical conductivity has been used but is sensitive to factors other than moisture content. Dielectric properties vary with moisture content and have given reasonable results under laboratory conditions. Further work is needed to apply this method to field conditions. Micro-wave absorption has been used to determine moisture in walls but at present cannot be used for floor slabs on grade. The results vary with the nature of the material.

Neutron scattering has been widely used to determine moisture in soils and has been advocated for other materials including concrete. The method is direct and non-destructive and requires access to only one side of the speciment. Results have been claimed to depend solely on the water content, i.e., to be independent of the nature and density of the material. Experiments with concrete and timber have shown that this is not correct. Instrument response rises with density to such an extent that the same instrument response was obtained on a foamed concrete and a dense concrete with water contents in the ratio of 2:1. The composition of the sample also affects the response. This method therefore cannot safely be used with a common calibration curve for all substances.

The MOSEL reactor concept concerns a fluid molten-salt reactor, in which operating conditions are influenced by salt freezing and boiling temperatures. The influence of temperature limitations on heat flux and power density is shown, and the importance of the thermal conductivity of the melt illustrated. A generalized diagram is developed relating various combinations of power densities and heat fluxes as a function of unit cell dimensions and flow conditions of the fuel stream. The temperature rise of the coolant through the core is shown to be a function of core size, flow condition, and heat flux.

This paper briefly discusses some dynamic problems in structural engineering as applied to the design of nuclear power stations. The following problems are analysed: seismic design, steam generator supports, design of fluid containers, the missile problem.

High temperature thermoelectric materials show great promise for the direct conversion of nuclear energy to electricity. There are several basic reasons for this promise. An analytical technique is presented which may be used to predict and select high temperature thermoelectric materials, utilizing basic information on chemical compounds in their family groupings. This technique is demonstrated, and proposed materials are analytically evaluated for conversion efficiency and nuclear system compatibility. The predicted range of conversion efficiencies is competitive with or superior to present techniques of nuclear energy conversion. High temperature thermoelectric materials are expected to be superior to conventional thermoelectric materials because of radiation effects annealing as well as higher conversion efficiency.

Cycles of temperature up to 300°C were applied to concrete made with normal Portland cement and dolerite aggregate. Progressive loss of compressive and tensile strength was observed, combined with very large reductions of elastic modulus. Some of the effects are due to changes in the aggregate which affect aggregate stiffness and the bond with the cement paste. Conclusions are drawn in regard to suitable aggregates for operation at elevated temperature.

One of the mose important advantages of a natural salt formation as a repository for radioactive wastes is its essential impermeability due to its plastic properties. To prove the feasibility of disposal in salt mines a conceptual design has been developed and a demonstration of the storage concept is being prepared in a 1000 ft eep inactive mine in Lyons, Kansas. Economic studies show that costs for an actual disposal operation would fall well within the range allowable for competitive nuclear power. In the demonstration irradiated fuel assemblies from the Engineering Test Reactor with serve as a source of radiation in lieu of actual solidified wastes. Two radioactive arrays (one in the existing floor to check problems in the use of abandoned mines, and one in a specially excavated area) will each contain 14 assemblies in 7 cans. An electrically heated array will serve as a control. Mine renovations and additions are complete, and initiation of the two-year test is scheduled for late 1965.