A neutron noise-based experiment performed in the TRIGA reactor of the ENEA-Casaccia centre in Italy is presented. This experiment is part of the first phase of the international TRADE programme that seeks a global demonstration of an accelerator-driven system at power. The main objective of that first experimental phase is the measurement at zero-power of fundamental neutronic parameters. The present experiment performed in the reference critical core configuration has first of all aimed at the inference of the prompt neutron decay constant at critical, which is equal to the ratio of the delayed neutron fraction to the neutron generation time. The neutron-noise technique that has been applied is the power spectral density technique, based on the use of fission chambers operated in fluctuation mode. Two fission chambers, each with a sensitivity of 10-1 cps/nv, have been placed within the core region close to the reflector. The prompt neutron decay constant at delayed critical has been estimated at 132 ± 2 s-1 with 68% confidence level.