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The principal features of the prototype fast reactor at Dounreay which were to be proved concerned the reactor and heat exchange systems. The conventional plant was not part of the primary objective of the development programme and was therefore designed at minimal capital costs using limited standby plant. Since the reliability of this conventional system has restricted long-term power generation an improvement programme is included as part of the overall development. Tripping incidents subject the conventional steam plant and reactor to rapid transients. This paper describes plant improvements which have been instigated to reduce, and mitigate such effects. Revised protection and interlocks, controlled power setback and improved feed-water control are part of this strategy. Also the implementation of additional steam dump and condensate bypass facilities increase operating flexibility for heat removal from the reactor. Longer-term decay heat is removed from the sodium by cooling loops and guaranteed cooling fans. The paper describes the improved control for the optimisation of cooling systems to satisfy trip and incident conditions.