Temperature transients in gas-cooled thermal nuclear reactors

The paper examines the transient behaviour of the Calder Hall type of reactor in terms of the design and operating parameters, the main transients examined being those arising from (a) Step changes in reactivity. (b) Steady changes in reactivity including the start-up condition. (c) Step changes in cooling. (d) Steady and other changes in cooling due to both circulator-speed and gas-pressure changes. The examination has been carried out by means of an analogue computer and by a graphical method which employs an approximate solution of the neutron-kinetic equations. The results obtained by the two methods are compared and agreement is shown to be good. The graphical method has been extended to take account of temperature gradients within the fuel elements and fission-product heating. Account is also taken in the computations of the heat generated in the graphite. The effects of non-uniformity in the axial and radial temperature distribution on the temperature transient throughout the reactor are examined and assessed. It is concluded that the graphical method is useful for studying the transient characteristics of a reactor, but, owing to the importance and complexity of the subject, experimental confirmation of the predicted results is desirable.