The Winfrith reactor is a direct cycle pressure tube reactor of 100 MW(e) output using light water as the coolant and heavy water as the principal moderator. The plant has been in operation for 14 years and has successfully demonstrated the potential of this type of pressure tube reactor. It has also produced information and experience relevant to water reactors in general. The Paper summarieses the key operating experiences and the performance of principal components of the Winfrith plant. The Zircaloy 2 pressure tubes and associated rolled joints have not presented any problems. The diametral creep of the tubes has been towards the lower end of the original predictions and axial growth is acceptable. Semi automatic equipment capable of simultaneous eddy current and ultrasonic scanning of the tubes for defects is in use. After some early problems fuel element reliability has been very good. A batch refuelling scheme with simple off-load refuelling fits in well with the annual maintenance shutdowns and the single channel access enables refuelling to be carried out with minimum interference to the inspection and maintenance programmes. Relatively simple automatic control systems are used and the performance of these has been demonstrated to be very satisfactory during manoeuvres associated with normal operation and during a series of special tests. The key health physics aspects of the plant are described and reference is made to the regular chemical decontaminations of the reactor coolant circuits which have been carried out since 1969 as part of the programme to reduce the radiation dose to personnel. The experience with main plant, including the glandless reactor coolant pumps, the unique fast acting liquid shutdown system and the saturated steam tubine are summarized. Negus,-B. (Atomic Energy Establishment, Winfrith Dorset (UK))
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