The paper considers the issue of ensuring the reliability and nuclear safety of unique rotary equipment represented with the mobile neutron reflector of the IBR-2M research reactor. The specifics of its operation under the conditions of inaccessibility for visual control and maintenance dictates the need to use indirect methods of monitoring and diagnostics. The performed study demonstrates the efficiency of combined vibration monitoring and diagnostics for detecting operational defects of the PO-3 mobile reflector. Both conventional spectral and non-standard probabilistic methods of vibration analysis are used, including the S-discriminant analysis adapted to the reference state of equipment. The gamma-spectral analysis of radioactive impurities in the reflector lubricant oil significantly increases the reliability of recognizing the technical state of complex machinery. The example of the PO-2R mobile reflector demonstrates the applicability of the neutron activation method to identify the release of metal microparticles in the oil lubricant due to the degradation processes of exhausted equipment.