Two assemblies of self-powered in-core detectors have been tested in the Oconee 2 pressurized water reactor for more than 1 yr. The assemblies contain both prompt-responding hafnium and delayed-responding rhodium detectors. Four hafnium detectors are paired with four rhodium detectors in each assembly. The purpose of the experiment is to define the characteristics of the prompt and delayed detectors operating together in pairs. Data from the experiment show that the prompt detectors need to be calibrated on-line and that the rhodium detectors paired with them can be used to make the calibrations. The response of the hafnium detector to a reactor scram is given.