Patent Number: 
Section: claims

1. A side-slotted nozzle type double sheet spacer grid for nuclear fuel assemblies, comprising a plurality of inner strips intersecting each other at a predetermined angle to form a plurality of four-walled cells to receive and support a plurality of fuel rods in the spacer grid, each of said inner strips comprising a plurality of unit strip parts each of which is fabricated by integrating two unit sheet parts together into a single structure, such that the two unit sheet parts face each other and a nozzle type coolant channel with an inlet and an outlet is defined between the two unit sheet parts, wherein each of said unit sheet parts is provided with a slot longitudinally formed on each side surface of a spring which is projected from the unit sheet part to support a fuel rod within a four-walled cell. 2. The side-slotted nozzle type double sheet spacer grid according to  claim 1 , wherein the slot has a width in the range from 0.35 mm to 0.8 mm, and a length in the range from 12 mm to 16 mm. claim 1 3. The side-slotted nozzle type double sheet spacer grid according to  claim 1 , wherein each of the inner strips is fabricated by integrating two thin sheets, each comprising an alternating arrangement of a plurality of first unit sheet parts not having any coolant channel outlet and a plurality of second unit sheet parts each having a coolant channel outlet, into a single structure such that one first unit sheet part and one second unit sheet part form one unit strip part. claim 1 4. The side-slotted nozzle type double sheet spacer grid according to  claim 3 , wherein the intersecting inner strips are encircled with a plurality of perimeter strips, each of said perimeter strips being fabricated by integrating an inner thin sheet comprising the second unit sheet parts each having the coolant channel outlet, and a flat outer thin sheet into a single structure. claim 3 5. The side-slotted nozzle type double sheet spacer grid according to  claim 4 , wherein each of said inner and perimeter strips has a thickness in the range from 0.25 mm to 0.40 mm, and each of the springs of said unit sheet parts has a width in the range from 7 mm to 10 mm between both side edges thereof. claim 4 6. The side-slotted nozzle type double sheet spacer grid according to  claim 4 , wherein each of the first unit sheet parts not having any coolant channel outlet comprises one or more coolant mixing blades extending from an upper end thereof. claim 4 7. The side-slotted nozzle type double sheet spacer grid according to  claim 6 , wherein the coolant mixing blades of the first unit sheet parts comprise lateral flow blades for creating a lateral flow of coolants between neighboring four-walled cells, swirl flow blades for creating a swirl flow of coolants at intersections of the strips in the spacer grid, or a combination of the swirl flow blades and the lateral flow blades. claim 6