The core configuration of the Training Research Isotopes General Atomics (TRIGA) MARK I IPR-R1 nuclear research reactor at Nuclear Technology Development Centre (CDTN), Belo Horizonte, Brazil, has been modified six times since the first criticality and the neutron fluxes have been determined using experimental and semitheoretical methodologies determining the neutron fluxes in different irradiation channels and devices, applying different procedures and materials. This reactor operates at 100 kW; however, after new configuration for 250 kW in 2001, the carousel no longer rotates during irradiations aiming at preserving the rotation mechanism. In 2003, the spectral parameters were determined experimentally by the “Cd-ratio for multimonitor” in five specific channels aiming at the application of neutron activation analysis (NAA) k0-standardized method. The determinations were repeated applying the same procedure in 2016, 2018, and 2019. Values for thermal and epithermal neutron fluxes as well as f and α spectral parameters were determined. The experimental results for certified reference material BCR-320R were calculated by the k0-method of NAA, using the spectral parameters for irradiation channel IC-7 obtained in 2003, 2016, 2018, and 2019 and evaluated by En-score. The values showed that the differences in the results compared to those in 2003 were lower than 2.5%, inside the uncertainty of the method. It shows that the k0-method installed in CDTN is reliable and useful for various purposes. The results of the spectral parameter f presented small differences, in a period of 16 years, pointing out the stability of operation of the reactor TRIGA MARK I IPR-R1.