The full-scale scientific research complex IREN will comprise a 200-MeV linear accelerator LUE-200 with a beam power of about 10 kW, a subcritical multiplying target, and beam infrastructure with experimental pavilions, as well as technological, control, safety and service systems. The characteristics of the full-scale complex IREN (integral neutron yield of 1015 n/s and pulse width of 0.6 µs) will allow it to rank among the best neutron sources of such class as GELINA (Belgium) and ORELA (USA). The realization of the project is conducted in several stages. The first stage includes the construction of the LUE-200 linear accelerator and nonmultiplying target. This will make it possible to carry out experiments which require precision neutron spectroscopy in the energy range from fractions of eV to hundreds of eV already at the first stage of IREN. The results of the physical start-up of the first stage of the IREN facility at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research are presented. The general scheme and current status of the electron linac are described. The achieved parameters are: pulsed electron beam current – 2.0 A; electron energy – 30 MeV; pulse width – 100 ns; repetition rate – 25 Hz; integral neutron yield (3÷5)×1010 n/s.