[en] An operational problem of Advanced Gas Cooled Nuclear Reactors is the formation of carbonaceous deposits on the surfaces of the corrosion resistant heat conducting containers for the nuclear fuel. The heat transfer characteristics of the containers are thereby adversely affected. In the invention the containers are fabricated from a Cr-containing steel and have a surface oxide layer which is substantially free from Fe and Ni provided by annealing in an atmosphere of low oxygen partial pressure such as an atmosphere of hydrogen saturated with water. Test experiments have shown that such containers exhibit far less tendency to be subject to carbonaceous deposition than equivalent containers whose oxidised surfaces contain Fe and/or Ni. (author)