Abstract: An improved nuclear fuel assembly having elongated grid straps curved in a substantially undulating wave pattern along their axial length and interleaved together to form an egg-crate configuration having a plurality of roughly square cells that support fuel rods and guide tube thimbles. The cells that support fuel rods have their outer walls curved outward to increase the contact area around the fuel rod cladding The interior straps are on a diagonal with regard to a peripheral strap and at least one cell adjacent each fuel rod cell is left empty for the unobstructed flow of coolant. Additional coolant mixing devices can be added to the empty cells. The walls of each fuel rod cell are devoid of dimples and, in one embodiment, springs.