SAND (System for on-Axis Neutrino Detection) will be one of the three components of the DUNE Near Detector complex, acting as a beam monitor to control the flux and systematics uncertainties for the DUNE oscillation physics program. It consists of a solenoidal magnet, an electromagnetic calorimeter, an inner target/tracker system and a 1-ton liquid argon target named GRAIN (GRanular Argon for Interaction of Neutrinos). GRAIN will be placed in the upstream region of the inner magnetized volume. It will be instrumented with photodetectors to collect scintillation light for tagging and localizing the event in combination with the calorimeter and the tracker. GRAIN will obtain samples of ν-Ar interactions to study neutrino interactions models, provide cross-calibration for the rest of the Near Detector, and constrain nuclear effects by comparing with data from other nuclear targets (C, CH2) within SAND. This poster describes the design and role of GRAIN in SAND, including preliminary simulation results of its capabilities.