The United Kingdom Atomic Energy Authority has three main groups: Weapons, Industrial and Research. The Research Group carries out research and development directly relating to civilian application of atomic energy. The Industrial Group designs and operates factories for the production of uranium metal and the fissile materials uranium 235 and plutonium. It has also a design office for the design of pioneering type of nuclear power stations. The Industrial Group has also Research and Development Branch which carries out experimental research into the operational problems of the factories and into specific development problems of new plant and nuclear power stations. The nuclear power programme of the future requires the development of new types of power stations as successors to the gas-cooled graphite-moderated power stations which are now to be constructed by industry in successively improved marks. The Research and Industrial Groups together explore the different possible types of future power stations and are carrying out design studies on the most promising types. During the last year, for example, a design study on the pressurised-water reactor has been carried out in collaboration with industry and the Central Electricity Authority (CEA). The comparative merits of this and other possible Stage-2 reactors are now being assessed. At the same time, longer-range work is carried out on still more advanced reactors such as the homogeneous reactor and the fast reactor. This work combines with zero-energy reactor physics studies and is followed by construction of an experimental reactor. Each new reactor requires the development of specific technologies, particularly in the development of appropriate fuel elements and associated chemical-processing facilities for spent fuel elements. This development requires an intensive testing programme of reactor components, particularly fuel elements, and the Authority is now building three heavy-water research and fuel-element-testing reactors to speed up such testing. These reactors require associated heavily shielded and remote-handling facilities for examining the highly radioactive components. These expensive central facilities are likely to continue to be provided by the Authority. It seems also likely that fuel-element fabrication and chemical-processing facilities will be held by the Authority. Industry will take an increasing share of the research and development work and construction work, for reactors and nuclear power stations, and the pattern of co-operation is being worked out by experience. The Research Group is responsible for the production and application of radioactive isotopes and radiation. These applications are growing rapidly, at a rate of about 25% a year, and it is expected soon to have very powerful sources of radiation available for industrial processes. The Research Group also looks to the future and carries out research and long-term projects of importance to future developments.

The first part of the lecture reviews the future requirements for electricity and indicates the minimum nuclear power requirements if the importing of fossil fuels is to be avoided. The factors justifying the decision to commence a nuclear power programme with graphite-moderated gas-cooled reactors are referred to and a comparison is made between the probable costs of generation of electricity at the early nuclear power stations and costs typical of coal-fired base-load stations planned for commissioning by 1962. Some of the possible future developments in the field of power reactors and their fuel supplies are referred to. The second part of the lecture deals with the impact of base-load nuclear plant upon the design and operation of coal-fired plant, and upon schemes for pumped storage and the improvement of the night electricity load. It also discusses the question of the siting of nuclear power stations and the radical alteration brought about in the picture of future economic system development by the prospect of meeting a large part of the future electrical energy requirements by nuclear generation.

A short review of the general effects of radioactivity and ionizing radiation on human beings is given, and the basic problems of radiation protection are stated. The various features of nuclear power development, such as the nuclear reactors, chemical separation plants and waste-disposal facilities, are examined in relation to their potential occupational and public health hazards and these are compared with the health and safety problems arising elsewhere in industry. The extensive experience of the Atomic Energy Authority in this field is reviewed and used to indicate the type of protective measures and procedures which are likely to be effective in ensuring continued safe development in the new industry.

The rapid development of reactor technology is of vital importance for the achievement of economic nuclear power; the nuclear engineer has no broad background of past experience to guide him in the design and specification of nuclear power reactors but has to rely very largely on the results of theoretical calculations and laboratory experiments. The purpose of research reactors is to provide both the radiation-field and test-bed facilities to enable the behaviour of reactor materials and components to be studied and tested under simulated operating conditions and to obtain fundamental information in the field of reactor physics, chemistry and metallurgy. Not all these research and development activities can be performed in a single reactor; the present tendency is to design research reactors for fairly specific duties and the United Kingdom Atomic Energy Authority (UKAEA) have in operation or under construction reactors for the study of shielding, core geometry, materials testing and fundamental measurement. The capital and running costs of research reactors, particularly those designed for very high neutron fluxes are apt to be high and it is important to appreciate that the expense of using a single experimental facility in a high-flux reactor might easily be �100 a day.

The authors discuss the possible application to steam power stations of nuclear reactors using either light or heavy water both as the moderator and coolant. The problem of heat transfer from the fuel elements to the coolant is analysed. Some of the special difficulties with this type of reactors are discussed, in particular the problems of the pressure vessel design and the difficulties associated with corrosive action of the water in the coolant circuit. The limitations set by heat flow and thermal stresses in the fuel elements are also examined. Some different arrangements for the external steam plant are compared. The problems of using a supply of saturated steam for the turbines are discussed. Alternative arrangements involving the use of steam separators and reheat are compared. The use of a separately fired superheater is examined both from a technical and an economic point of view. Steam conditions and cycle efficiencies are compared in the different cases. The direct boiling-water reactor is examined. Some of the problems associated with steam formation inside the reactor are mentioned and the possible range of steam pressures examined. Overall cycle efficiencies are estimated for the boiling-water reactor with and without the use of a separate superheater.

The applications of liquid metals in heat-transfer problems are discussed, and comparisons are drawn between those metals whose melting points are sufficiently low to make them of interest in this respect. A number of sodium and sodium-potassium circuits which have been built and operated over the past three years are described; some of these were built in order to gain experience in handling the liquid metals, whilst others were for heat-transfer experiments. A general discussion on the design and construction of liquid-metal circuits and the components which are commonly used in them is given. A brief discussion of forced-convection heat transfer with liquid metals follows, and the results of some work on cavitation in sodium-potassium eutectic flowing through a constriction in a pipe are summarised.

The control and instrumentation of nuclear reactors is a rapidly developing subject which is becoming of ever increasing importance to a growing body of instrument engineers. Many of the problems of instrumental design are common with other industrial plants and follow conventional lines. Some, however, are more specialised, and arise principally from the radioactive nature of the reactor and its unusual dynamic behaviour. The paper presents a survey of the overall instrumentation of a typical research reactor. Emphasis is placed on the less well-known problems of measurement and control, and to assist in their understanding a brief account is given of the mode of operation of a nuclear reactor, and a short section on reactor kinetics is also included. The types of instruments in present-day use are described, and indications are given of their shortcomings. New developments are briefly reviewed. The paper concludes with a section on reactor safety. The philosophy of safety-circuit design is outlined, and examples are given of instruments and circuits which conform to this basic code and which have been used on a number of experimental reactors at Harwell.

The physical principles of nuclear reactors which affect the design of their control and instrumentation are described. Data are presented for the kinetic behaviour of the neutron flux for reactivity changes in a variety of reactor types. The nuclear reactions inherently produce various nuclides, and the effects of these on reactor control and operation are discussed. These nuclides include the delayed-neutron emitters, which cause a slowing down of the reactor kinetic response; �- and ?-emitters, which continue to produce heat for a long time after the neutron reactions producing them have been shut down; and the fission-product poisons. Reasons are given for the system of neutron-flux instruments normally used, and details are given of the principles of design of the various types of instrument.

The paper describes the design and the electrical characteristics of a neutron-sensitive d.c. ionisation chamber suitable for a wide range of applications in nuclear-reactor-control instrumentation systems. Thermal-neutron sensitivities of 10 ^-15 - 10^-14 amp/n/cm^2/sec can be obtained using boron trifluoride filling or boron-coated electrodes with hydrogen filling. The corresponding ?-radiation sensitivities are of the order of 10^-12 - -10^-11 amp/r/h. Virtually complete collection of the ionisation current is possible, up to neutron flux levels of 10^11 n/cm^2/sec, with a polarising voltage of a few hundred volts. The residual current due to neutron-induced activities in the chamber falls to less than 10^-6 times the full-power neutron current about 20 min after shut-down. The siting of ionisation chambers has an important bearing on their range of utilisation in control-instrumentation systems, and this is discussed briefly in relation to the electrical characteristics of the chambers described.

The paper outlines some of the practical design problems associated with the engineering of control mechanisms in nuclear reactors. Safety is emphasized in all the design aims, and examples are given of some of the systems in use at Harwell. The scope of the paper is limited to control mechanisms for low and moderated-power experimental reactors, although some of the problems which will be met in future power-producing reactors are mentioned.