  Neutrino elastic scattering observation with NaI (NEON) is an experiment
designed to detect neutrino-nucleus coherent scattering using reactor electron
antineutrinos. NEON is based on an array of six NaI(Tl) crystals with a total
mass of 13.3 kg, located at the tendon gallery that is 23.7 m away from a
reactor core with a thermal power of 2.8 GW in the Hanbit nuclear power
complex. The installation of the NEON detector was completed in December 2020,
and since May 2021, the detector has acquired data at full reactor power. Based
on the observed light yields of the NaI crystals of approximately 22, number of
photoelectrons per unit keV electron-equivalent energy (keVee), and 6
counts/kg/keV/day background level at 2-6 keVee energy, coherent elastic
neutrino-nucleus scattering observation sensitivity is evaluated as more than
3$\sigma$ assuming one-year reactor-on and 100 days reactor-off data, 0.2 keVee
energy threshold, and 7 counts/keV/kg/day background in the signal region of
0.2-0.5 keVee. This paper describes the design of the NEON detector, including
the shielding arrangement, configuration of NaI(Tl) crystals, and associated
operating systems. The initial performance and associated sensitivity of the
experiment are also presented.
