GB1105477A - Nuclear reactors - Google Patents

Abstract

1,105,477. Reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. 26 Oct., 1965 [6 Nov., 1964], No. 45394/64 Heading G6C. In a nuclear reactor of the kind having fuel elements stacked within vertical channels in a solid moderator and cooled by heat exchange with gas flowing through the channels, at least some of the channels contain fuel elements stacked upon a support strut and surmounted by a non-fissile member, the support strut and non-fissile member having chambers which communicate with ambient pressure at the lower and upper ends respectively of the channels and which communicate with means for sensing pressure differential between the chambers, the means being located remotely from the channels. Where a stack of fuel elements is supported by the strut, the upper non-fissile member may be a holding-down weight for preventing levitation of the fuel elements by the coolant. Alternatively, the upper non-fissile member may be a telescopic stem supported from the upper extremities of the channel and may include thermocouple means for measuring the coolant outlet temperature of the channel. Knowledge of the pressure drop occurring over the fuel channels or a representative number of these enables accurate heat transfer calculation and adjustment of coolant mass flow through the channels to be made so that each channel can be operated at optimum coolant temperature. The coolant mass flow can be controlled by a suitable gag valve at the foot of each channel. Struts and telescopic stems may be used in one or more fuel channels which are devoid of fuel elements, to determine the pressure drop in such empty channels and hence calculate the coolant flow rate through leakage paths within the reactor core, e.g. between blocks of moderating material from which the reactor core is fabricated. Preferably, the chambers communicate with the differential pressure measuring means by means of pipes, these having portions of reduced tensile strength adjacent the strut and the upper non-fissile member so that the pipes can be readily severed and withdrawn from the channel prior to the discharge of the upper non-fissile member, fuel elements and strut from the channel.