Masumi, Ryoji;

Fuel assembly

A fuel assembly attains high burnup and increases reactor shut-down margin when loaded into a reactor core wherein a water gap width on a control rod side and a water gap width on a side opposite to the control rod side are almost equal to each other. The fuel assembly has a plurality of fuel rods arranged in a square lattice pattern, each fuel rod being filled with nuclear fuel pellets and also has at least one neutron moderator rod shifted toward one corner where a control rod is inserted, away from a cross sectional center of the fuel assembly.

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What is claimed is:

1. A fuel assembly for being loaded into a reactor core wherein a control rod-side water gap width and an opposite-side water gap width are almost equal to each other, comprising:

a plurality of fuel rods arranged in a square lattice pattern, each fuel rod being filled with nuclear fuel pellets, distances between adjacent fuel rods in row and column directions are the same; and

at least one neutron moderator rod shifted toward one corner where a control rod is inserted, away from a cross sectional center of the fuel assembly.

2. A fuel assembly for being loaded into a reactor core wherein a control rod-side water gap width and an opposite-side water gap width are almost equal to each other, comprising:

a plurality of fuel rods arranged in a square lattice pattern, each fuel rod being filled with nuclear fuel pellets, distances between adjacent fuel rods in row and column directions are the same; and

at least one neutron moderator rod, a center of said at least one neutron moderator rod being shifted toward one corner where a control rod is inserted, away from a cross sectional center of the fuel assembly.

3. A fuel assembly for being loaded into a reactor core wherein a control rod-side water gap width and an opposite-side water gap width are almost equal to each other, comprising:

a fuel bundle having a plurality of fuel rods arranged in a square lattice pattern and at least one neutron moderator rod, each fuel rod being filled with nuclear fuel pellets, distances between adjacent fuel rods in row and column directions are the same;

an upper tie plate and a lower tie plate-holding upper end portions and lower end portions of said fuel rods respectively; and

means for fixing a channel box covering said fuel bundle to one corner of said upper tie plate by a channel fastener, a center of said at least one neutron moderator rod being shifted toward said one corner, away from a cross sectional center of the fuel assembly.

4. A fuel assembly for being loaded into a reactor core wherein a control rod-side water gap width and an opposite-side water gap width are almost equal to each other, comprising:

a plurality of fuel rods arranged in a square lattice of 10-rows by 10-columns, each fuel rod being filled with nuclear fuel pellets, distances between adjacent fuel rods in row and column directions are the same; and

one water rod disposed in an area of 3-rows by 3-columns in said square lattice, a center of said one water rod being shifted toward one corner where a control rod is inserted with respect to a cross sectional center of the fuel assembly.

5. A fuel assembly for being loaded into a reactor core wherein a control rod-side water gap width and an opposite-side water gap width are almost equal to each other, comprising:

a fuel bundle having a plurality of fuel rods arranged in a square lattice of 10-rows by 10-columns and one water rod disposed in an area of 3-rows by 3-columns in said square lattice, each fuel rod being filled with nuclear fuel pellets, distances between adjacent fuel rods in row and column directions are the same;

an upper tie plate and a lower tie plate holding upper end portions and lower end portions of said fuel rods respectively; and

means for fixing a channel box covering said fuel bundle to one corner of said upper tie plate by a channel fastener, a center of said one water rod being shifted toward said one corner with respect to a cross sectional center of the fuel assembly.

6. A fuel assembly for being loaded into a reactor core wherein a control rod-side water gap width and an opposite-side water gap width are almost equal to each other, comprising:

a plurality of fuel rods arranged in a square lattice pattern, each fuel rod being filled with nuclear fuel pellets, distances between adjacent fuel rods in row and column directions are the same; and

at least one neutron moderator rod shifted toward one corner where a control rod is inserted, away from a cross sectional center of the fuel assembly so as to cause the distribution of neutron moderators within a cross section to be shifted toward said one corner.

7. A fuel assembly for being loaded into a reactor core wherein a control rod-side water gap width and an opposite side water gap width are almost equal to each other, comprising:

a plurality of fuel rods arranged in a square lattice pattern, each fuel rod being filled with nuclear fuel pellets, distances between adjacent fuel rods in row and column directions are the same; and

at least one neutron moderator rod, a center of said at least one neutron moderator rod being shifted toward one corner where a control rod is inserted, away from a cross sectional center of the fuel assembly so as to cause the distribution of neutron moderators within a cross section to be shifted toward said one corner.