Much of the published data on steam cycles cannot be applied to modern power stations owing to the advanced steam conditions and complex cycles now used. Plant optimization therefore requires the detailed analysis of a large number of cycles over a wide range of steam conditions Modern high-speed digital computers offer the engineer relief from the tedium of lengthy calculations and the uncertainty of broad simplifying assumptions. The Ferranti ‘Mercury’ computer is used in the present work and, for economy in computing time, separate boiler and turbine programmes are written and the results combined through a short desk calculation The turbine programme, which is applicable to both conventional and nuclear stations, is sufficiently general to deal with all anticipated steam conditions and cycle arrangements and it also takes account of minor cycle corrections. Possible variations in boiler design, however, make a similarly general treatment more difficult and several separate programmes are described here, each dealing with a steam cycle and boiler design suitable for use with the low-temperature gas-cooled reactors being built in Britain at present Application of the programmes to the design optimization of a complete nuclear power station is discussed