Improvements in or relating to nuclear reactors

Reference is made to gas cooled reactors in which the gaseous coolant is used directly as the working fluid for closed cycle gas turbines. In the system described in addition to the main circulatory system that incorporates the main gas turbines an auxiliary circulatory system is provided around which a small proportion of the coolant is arranged to flow after passage through the reactor core and in which a steam generating boiler is located, the steam being utilised to drive a steam turbine for an auxiliary electric generator. Such an arrangement enables the reactor to be started up utilising the auxiliary circulatory system independently of the main gas turbine start-up procedure. This is an advantage since the large power required to drive the compressors of gas turbine plant give rise to starting problems, and special provision has to be made to ensure that the turbine rotor attains a speed sufficient to allow the turbine drive to be self-sustaining. In addition long term heat removal, either after a reactor trip or under normal reactor shut-down conditions, can be considerably simplified by shutting down the gas turbine and removing heat by the auxiliary circulatory system. The steam turbine associated with the steam generating boiler is preferably arranged to run continuously during operation of the reactor. A number of gas turbine units can be disposed around the reactor core in chambers in the pressure vessel wall or in the space between the main pressure vessel and a secondary pressure vessel. The steam generating boilers can be similarly located around the reactor core between the gas turbine units. In the case of high temperature reactors the temperature of the gas leaving the reactor core may be too high for satisfactory operation of the steam generating boilers, in which case means may be provided for cooling the gas between the core and the boilers. For a high temperature reactor the thermal capacity of the auxiliary circulatory/steam turbine system may be 16% to 20% of the thermal capacity of the core. (U.K.)