A new measurement technique is being developed to determine fission rates in fresh and spent power reactor fuel following irradiation in a zero-power research reactor. The technique is required for the future experimental program LIFE@PROTEUS, one goal of the program being the investigation of power profiles across fresh and burnt fuel interfaces typical of a newly reloaded power reactor. In order to discriminate against the intrinsic activity of spent fuel, the approach described here uses high-energy γ-rays (above 2200 keV) emitted by freshly produced short-lived fission products. To demonstrate the feasibility of such a technique, fresh and spent UO₂ fuel samples with nominal bum-ups of 0, 36,46 and 64 GWd/t were irradiated in the PROTEUS reactor and their γ-ray activities were recorded directly after the irradiations. For the first time, following irradiation in a zero-power research reactor, it was possible to compare the freshly induced short-lived γ-ray activity from spent fuel samples having high intrinsic γ-ray backgrounds with corresponding activities induced in fresh fuel. In this paper, first results of derived fission rate ratios between a fresh and a 36 GWd/t spent sample based on four high-energy peaks (¹⁴²La (2542 keV), ⁸⁹Rb (2570 keV), ¹³⁸Cs (2640 keV) and ⁹⁵Y (3576 keV)) are presented. The measured fission rate ratios from the various fission products agree within 1-2 standard deviations, the 1σ uncertainties being ∼2.5-4.5%. At the current state of analysis, calculated and measured fission rate ratios agree within 1-2σ, but a bias of about 4% could be observed.