99mTc is a widely used radionuclide for SPECT (Single Photon Emission Computed Tomography) diagnostics thanks to its short half-life (about 6h) and the low-energy gamma ray emission (140 keV) well suited for diagnostic devices. In medicals, 99mTc is mostly provided through its precursor 99Mo. In 2009 the Nuclear Energy Agency (NEA) formed the High-Level Group on Security of Supply of Medical Radioisotopes (HLG-MR), in order to study the supply chain of 99Mo/99mTc in the world for short, medium and long term period. The HLG-MR delivered a report highlighting how the shortage of 99mTc supply was mostly due to the well-established but aged production chain essentially based on old nuclear reactors. A review of different technologies for producing 99Mo/99mTc was also provided by the HLG-MR based respectively on: a) HEU (highly enriched Uranium) and LEU (low enriched Uranium) targets in fission reactors; b) 98Mo thermal neutron activation in nuclear reactors; c) direct cyclotron production; d) photo-fission reactions on 238U; e) 99Mo photo-production and f) fast neutron-induced reactions. In this contribution, the production of 99mTc via 100Mo(n,2n)99Mo reaction is discussed in detail as it was investigated also in ENEA. The 99Mo activity achieved by means of 14 MeV neutron irradiation on natural Molybdenum sample at the Frascati Neutron Generator (FNG) facility, at the Research Centre of ENEA-Frascati, was accurately assessed, by tracing it to the standards provided by the Italian National Institute of Ionizing Radiation Metrology (INMRI), located at the Research Centre of ENEA-Casaccia. The results of 99Mo specific activity obtained at ENEA were then compared with those documented in feasibility studies of a Japanese research group, which used the same technique, showing a good agreement within the uncertainties of measurements. The whole experiment carried out in ENEA was supported by simulations performed with the Fluka Monte Carlo code, whose predictions have been benchmarked against the experimental data collected at ENEA-FNG relying on the traceability to the activity standards developed and maintained at the ENEA-INMRI laboratories.