PURPOSE: To supply a liquid film of cooling water to the surface of a fuel rod from a water pipe, suppress the dry-out phenomenon caused by the liquid film peeling of the fuel rod, secure the cooling capability by the liquid film of the fuel rod, and assure its healthiness by forming the water pipe of a fuel assembly for a boiling water reactor into a peculiar structure.

CONSTITUTION: A liquid film shifting groove 13 in which a coolant A flows upward is formed on the surface of a water pipe main body 11 easily holding a liquid film L1. The flow of the coolant A and the steam turbulence D generated on the lower side of a spacer 4 are utilized to discharge the liquid film L1 as waterdrops A1 from the upper end outflow groove port 13a of the liquid film shifting groove 13, the waterdrops A1 are preferably directed to the lower side of the fuel rod 2 of the spacer 4 on the high side where the dry-out phenomenon most easily occurs, and the peeling of the liquid film L2 of the fuel rod 2 is prevented.