Design and Testing of Large Gas Ducts

The paper outlines some of the problems encountered in the design and testing of the large ducts associated with present-day gas-cooled nuclear reactors. Various ways of providing ductwork with flexibility are analysed and it is shown that a design involving the use of a combination of tied expansion bellows and cascaded corners is the most economic way of meeting the need for high flexibility and low flow pressure loss. The design of large tied expansion bellows is discussed and an account is given of the tests carried out on a prototype of the bellows now being installed in the gas circuits of the Bradwell nuclear power station in Essex. A brief reference is made to the difficulties encountered in the development of large butterfly valves for reactor ductwork and performance figures are quoted for one of the valve designs which eventually proved successful under test.