Abstract: In a nuclear fuel rod a cladding tube is provided having a closed inner space and manufactured from at least one of the materials in the group zirconium and a zirconium-based alloy, and a pile of nuclear fuel pellets arranged in the inner space in the cladding tube. The nuclear fuel pellets fill part of the inner space. A fill gas is arranged in the closed inner space to fill the rest of the inner space. The internal pressure of the fill gas in the nuclear fuel rod amounts to at least 2 bar (abs) or at least 10 bar (abs). The fill gas contains a proportion of inert gas a proportion of carbon monoxide that is greater than 3 volume percent of the fill gas or greater than 2 volume percent of the fill gas.