The measurement of delayed gamma rays following neutron-induced fission is simulated with MCNP 6.1 to investigate the feasibility of fissile material detection in long-lived, medium activity radioactive waste in 870 L. The signal from homogeneously distributed fissile material in the drum is several hundred counts in the main delayed gamma peaks of interest. In a peripheral position or in the drum center, the signal is however too small to allow for a reliable measurement.