Fuel assembly for BWR type reactor

Cell frames disposed to spacers for supporting fuel rods and a water rod include two kinds, i.e., a cell frame having a chamferred portion to the inner side at the end of an coolant inlet and a cell frame having a chamferred portion to the outer side thereof. The cell frame chamferred at the inner side is used for the fuel rods having small thermal margin. The extent of deviation of a stream flow relative to a liquid membrane stream flowing on the surface of the fuel rod is increased by the inclination of chamferring, to promote the re-deposition of droplets and increase the thickness of the liquid membrane. On the other hand, the cell frame chamferred at the outer side is used for fuel rods having relatively large thermal margin, a short fuel rod and a water rod. The direction of the deviated flow is separated from the surface of the fuel rod by the inclination of the chamferring, to prevent re-deposition of droplets. With such a constitution, fuel cooling performance can be improved and a fuel integrity is enhanced and, in addition, operation region for fuels can be extended. (I.N.)