Coated structural component for a high temperature nuclear reactor

In a helium cooling circuit of a high temperature nuclear reactor, a structural component comprising

• a substratum of a nickel-base alloy containing a carbide-former, said alloy comprising in percent by weight at least
• 0.02 to 0.15% carbon
• 5.5 to 16% chromium
• 3 to 13% of the sum of molybdenum and tungsten
• 6 to 11% of the sum of aluminum and titanium
• and the remainder being nickel;
• an intermediate layer of nickel of at least 99% purity anchored on at least a portion of said substratum;
• and
• a pore-free protective layer on said intermediate layer of a metal selected from the group consisting of tungsten and molybdenum, said protective layer being sufficient to bond carbon from carbon containing impurities in said circuit into said protective layer as a carbide to form a very stable layer of protection against further carbonization;
• said intermediate layer being sufficient to inhibit a decarbonization of said substratum through a reaction of carbon therein with said protective layer.