Fuel assembly for BWR

The present invention provides a structure of a fuel assembly which effectively submerges fuel rods in water for emergency cooling upon occurrence of loss of coolant accidents (LOCA) in a BWR type reactor. That is, the fuel assembly comprises a lower tie plate having fuel rods and leak holes. The fuel assembly according to the present invention has a feature in that (1) the leak holes are disposed in communication with a portion higher than the upper surface of the fuel rod support lattice of the lower tie plate, (2) the leak holes are disposed at the opposing corners of the lower tie plate for arranging fuel rods in a square lattice, or (3) the fuel assembly defined in (1) or (2) comprises a lower tie plate in which the outer portion of the fuel rod support lattice is formed higher and the diameter of the fuel rods in adjacent with the outer side is made smaller than that of the other fuel rods. In the fuel assembly having the structural feature as described above, emergency cooling can be conducted by ECCS upon occurrence of LOCA efficiently and rapidly with neither change of the reactor structure nor deterioration of the performance during usual operation. (I.S.)