The compatibility of stainless steels with low-sulphur UCS fuels

Abstract

Sodium-bonded and vacuum-bonded compatibility tests at 600 and 700°C between stainless steels and UCS fuels of differing sulphur contents and stoichiometries revealed that, over the range of compositions studied, the amount of carburisation of the cladding is a linear function of only the total non-metal content (C + O + N + S) of the fuel, and does not depend on the actual sulphur content of the fuel. A UC and a UCS fuel with the same non-metal content therefore cause equal amounts of carburisation of the cladding. X-ray and microstructural investigations of the fuels further showed that a single-phase region does not exist at non-metal contents greater than 50 at%, and that sulphur probably behaves as a carbon equivalent in that it enters the UC lattice in solid solution, but displaces a carbon atom which is freed to form a higher carbide. The conclusion is therefore drawn that the addition of sulphur to UC fuels has no direct advantage at non-metal contents greater than 50 at% as far as the compatibility behaviour of the fuel towards the cladding is concerned.