Aircraft fuel system including a fuel vessel containing a non-mixture fuel. A protective vessel is arranged about the fuel vessel such that the fuel vessel is contained within the protective vessel and a protective space is defined between an outer surface of a vessel wall of the fuel vessel and an inner surface of a vessel wall of the protective vessel. At least one mounting structure fixedly positions the fuel vessel within the protective vessel. A fuel consumption device configured to consume the non-mixture fuel. A fuel output fluidly connects an interior of the fuel vessel to the fuel consumption device, the fuel output being fluidly isolated from the protective space. A relief output fluidly connects the protective space to a relief flow path, the relief output and relief flow path configured to vent gas from the protective space and remove any non-mixture fuel from the protective space.