phodgson,
The jet fuel corrosiveness is linked to the sulfur compounds and to the microbiological activity in the stagnant fuel. I don't believe that any sulfur compound can be counted corrosive at the mentioned temperature (close to 500 deg C). Without checking the fuel saturation curves, is the jet fuel still liquid at the given temperature and pressure?. Also, isn't the corrosion linked to the presence of oxygen? My understanding is that the chamber is Nitrogen pressurized, displacing the air/oxygen. I believe that you'll be fine with 316 stainless steel and even with carbon steel at the given conditions.
Cheers,
gr2vessels