[en] The successful UK operating experience with gas-cooled reactors is summarized. They are shown to be reliable and efficient. The safety characteristics are also shown to be favourable which makes them more acceptable to public opinion. Reasons why the gas-cooled system has not been more widely adopted are suggested. They are considered to be suitable for certain unit sizes and to be a real option for the future nuclear energy programme. (U.K.)

[en] The basic design and planned construction features of this helium cooled HTGR reactor, designed for electricity generation and high heat production for industry are given. The main parameters are tabulated and the reactor layout, including the components in the multicavity prestressed concrete pressure vessel, is given. The necessity of fuel element unloading through three tubes to ensure their uniform movement along the core cross section is shown. The desired helium temperature at core outlet is obtained without exceeding the permissable fuel temperature and with the use of one fuel element type. (U.K.)

[en] An essential component of the design of Commercial Advanced Gas Cooled Reactor fuel necessary to achieve higher discharge irradiations is the incorporation of burnable poisons. The poisons enable the more highly enriched fuel required to reach higher irradiation to be loaded without increasing the peak channel power. The optimum choice of fuel enrichment and poison loading will be made using reactor physics predictive methods developed by Berkeley Nuclear Laboratories. The paper describes these methods and the evidence available to support them from theoretical comparisons, zero energy experiments, WAGR irradiations, and measurements on operating CAGR's. (author)

[en] Thermal insulation is an important problem in the design, construction and operation of high temperature gas-cooled reactors. The level of the coolant temperature in HTGR can be up to 1000⁰C and higher. Such high temperatures approach, and occasionally exceed, the boundary of normal operation of various materials. Therefore, thermal stressed surfaces of reinforced concrete vessels, steel pipelines and reactor accessory equipment need to be insulated. With a reliable thermal insulation the decrease in thermal losses increases the whole installation efficiency. This report deals with questions related to the helium (gas permeability, thermoconductivity, working capacity) and reactor irradiation. Several types of thermal insulation have been studied; foam ceramics, fibrous and screen insulation. (U.K.)

[en] Initial materials selection for the AGR once-through boilers was uniquely influenced by corrosion considerations of both primary and secondary coolants. Prior to boiler start-up and as additional longer terms corrosion data became available, a number of detailed optimisations of local environmental conditions were necessary to meet the 250 x 10³ hr design life requirement. This paper presents an overview of factors influencing initial materials selection and the more significant of the subsequent optimisations in the several zones of the boiler. (author)

[en] The status of ongoing structural materials programs being conducted in the U.S. to support development and deployment of the high-temperature gas-cooled reactor (HTGR) is described. While the total U.S. program includes work in support of all variants of this reactor system, the emphasis of this paper is on the work aimed at support of the steam cycle/cogeneration (SC/C) version of the HTGR. Work described includes activities to develop design and performance prediction data on metals, ceramics, and graphite. (author)

[en] The heat transfer and fluid flow aspects of the development of AGR fuel from the original fuel element clusters of smooth pins proposed for but never used in the Windscale Advanced Gas-cooled Reactor to the current designs employing roughened pins is treated in detail. Topics covered include the concurrent acquisition of experimental data and the development of theoretical methods on the effects of roughness, numbers, dimensions and spacing of pins, of various design features such as support grids and braces and anti-stacking grooves, and of departures from ideal dimensions caused by pin bowing, deposits and manufacturing tolerances. Conduction in fuel and can across the intervening gap, radiation between cans and graphite, turbulent diffusion of heat, effects of varying heat flux boundary conditions and coolant physical properties are all taken into account. The philosophy behind the design of laboratory cluster experiments to check and correct the theoretical methods for predicting thermal hydraulic performance from the basic components is discussed and validation of the methods by reactor measurements is considered with due regard to the definition of nominal, peak systematic and peak random temperatures and to the difficulty of measuring temperatures in-pile. (author)

[en] The finned cladding on Central Electricity Generating Board (CEGB) Magnox fuel elements gives a large area of heat transfer surface with good cladding gas mixing. Its performance is, however, susceptible to impairment due to flow obstruction or surface deposits. Experimental determination of this impairment may not always be appropriate. Although the complexity of the heat transfer regime precludes accurate theoretical determination of the absolute performance, the change in performance can be predicted by a theoretical route incorporating limited experimental data. The approach is illustrated by its application to the case of corroded fuel elements, agreement with reactor temperature measurements being shown to be acceptable. (author)

[en] The mechanical design of the Heysham II and Torness A.G.R. boilers is described indicating areas where and why changes have been made from the parent Hinkley and Hunterston designs. Reasons for changes include operational experience, increased safety requirements, advancing design and manufacturing technology. Affected components described include platens, support structures and penetrations. Mechanical testing in support of the design is also described. (author)

[en] Significant changes were implemented between 1960 and 1970 in the fuel elements used in the French natural uranium-graphite-gas reactors. These changes and the resulting improved performance ratings are tabulated. The safety tests conducted on heavily irradiated fuel rods in the PEGASE facility, and the evolution of a number of manufacturing or controlling processes are examined. The validity of the options selected has been confirmed by the results. More than 300,000 fuel rods have been discharged (245,000 graphite-core rods and 55,000 annular rods) with a very low clad failure rate and limited consequences due to operating incidents such as channel obstructions. (U.K.)