In a gas-cooled nuclear reactor, a tight connection having an intentionally provided leak site between a fission-gas discharge channel formed in a reactor core carrying plate as well as in a head portion of encased fuel elements that are suspended in receiving bores formed in the core carrying plate, the tight connection being formed by an annular member having a sealing surface engaging the core carrying plate at a region thereof in which an opening to the fission-gas discharge channel formed in the core carrying plate is located, a gas-tight, elastic and substantially cylindrical member, variable in length, connecting said annular member to the fission-gas discharge channel formed in the head portion of the fuel element, compression spring means biasing said annular member in a direction away from the fission gas discharge channel formed in the fuel-element head portion, and a sealing abutment plate secured to a central pin and limiting clearance for play of said annular member with respect to an annular zone thereof disposed within said sealing surface of said annular member, the leak site comprising a radial bore formed in and extending through said annular member between said annular zone and said sealing surface of said annular member.