The influence of parallel channel effects (PCE) on the effectiveness of the emergency core cooling systems in a boiling water nuclear reactor (BWR) was experimentally investigated. Specifically, the effectiveness of the core spray cooling system and the low-pressure coolant injection system during the emergency core cooling of a simulated 218-BWR/4 was studied. Experiments simulating conditions after a hypothetical design basis loss-of-coolant accident were performed in a special PCE test section in which Freon-114 was used as the working fluid. A detailed scaling analysis was performed to allow real-time simulation of the bypass leakage inflow, reflood rate, countercurrent flow limitation, core decay heat, and the size of postulated jet pump breaks. It was found that BWR core cooling could be adversely affected by postulated failure of the jet pump seals by observing the parallel channel effects.