An experimental study of water penetration into a hot particle bed has been conducted. The pattern of water penetration was found to be complicated due to the formation of dry pockets and channels. Overall, the water penetrates down the bed as a single column in the central region, while the annular region near the wall remains hot and dry. After the water has reached the bottom, it starts flowing back up, filling the dry channels in the annular region. One-dimensional quench models, while reasonably successful in estimating the average quench rate, would not be adequate for describing the water penetration. These findings would be of interest in assessing the potential for concrete erosion by hot core debris in the reactor cavity.