[en] For operation of a gas turbine in single-cycle arrangement with a high-temperature reactor, rupture of a main circuit pipe has to be included in the safety considerations. In the event of such an accident there may be a back flow through the turbo machines or a forward flow up to the choking limit. Tests carried out in a two-dimensional cascade wind tunnel on turbine cascades under back flow conditions are reported. By the example of three selected representative cascades, the characteristic features in turbine cascades with back flow are discussed. These cascades are a rotor blade tip section with aerofoil-like profiles and a wide pitch, a stator blade or rotor blade mean section with an usual deflection and a rotor blade root section with a narrow pitch and a large deflection. The loss coefficient with back flow is a multiple of the loss coefficient of a cascade with normal flow conditions. (U.S.)