PURPOSE: To obtain a fuel assembly for a boiling water reactor wherein the cooling of a fuel rod at the central part of the fuel assembly is accelerated at the time of loss of coolant accident (LOCA), and the rise of the surface temperature of the fuel rod can be suppressed at the low state.

CONSTITUTION: A groove 19 through which coolant can be made to flow is provided in the surface of a water rod 12 or a water channel 13. The coolant is injected through a core spray system at the time of LOCA. The stagnant coolant at the upper part of a spacer caused by gas-liquid counterflow limit (CCFL) can readily flow down through the gap formed between the spacer 16 and the surface of the water rod 12 or the water channel 13 or through the guide groove 19. The cooling of the fuel rod at the central part of the fuel assembly is accelerated. The rise of the temperature of the surface of the fuel rod is suppressed at the low state.