Spatiotemporal characteristics of runaway electrons (REs) have been investigated in the integrated commissioning of the largest superconducting tokamak, JT-60SA. Since the bulk ion species of the plasma were only H or He in the integrated commissioning, no fusion neutrons were produced. RE losses were detected with neutron flux monitors (NFMs) through measurement of photoneutrons originating from REs hitting plasma facing components (PFCs). REs are found to be generated and lost in the case when the plasma density is low, when the plasma hits the wall, or when MHD modes were present. In the latter two cases, the plasma was disruptive. In addition, poloidal locality of the RE loss on the PFCs is confirmed based on a magnitude relation of the NFM signals.