Which boilers were closest to operating a nuclear reactor?

Which steam boilers came closest to operating a nuclear reactor?

German destroyer boilers, because each plant had its own operating characteristics and needed an individual balance, like the reactors in the analogy.

Alex Clarke recalls choosing German destroyer boilers when someone asked which steam plant came closest to operating a nuclear reactor. The analogy rests on individual operating characteristics within a common design. Nominally identical reactors can require slightly different balances, and the same principle is applied to destroyer boilers producing great power in a confined space. A shared scientific basis still leaves the operator needing to understand the particular plant.