Lower end fitting locknut for nuclear fuel assembly

1. An apparatus comprising:

a lower end fitting having a top planar surface, a bottom planar surface, a counterbore defined therebetween, an opening extending from the counterbore to the top planar surface, and a lock recess that extends both radially outwardly from the counterbore and extends inwardly into the lower end fitting from the bottom planar surface;

a guide tube having a lower end;

an end plug configured to connect with the lower end of the guide tube, the end plug having a threaded male shaft that extends away from the lower end of the guide tube when the end plug is connected with the lower end of the guide tube, the threaded male shaft being sized to pass through the opening of the lower end fitting; and

a female lock nut configured to thread onto the threaded male shaft of the end plug, the female lock nut having a deformable side wall configured to be swaged into the recess of the lower end fitting to lock the female lock nut with the lower end fitting,

wherein the lock recess remains visible as viewed from the bottom planar surface of the lower end fitting when the female lock nut is fully disposed in the counterbore.

2. The apparatus of claim 1 , further comprising:

a tool configured to rotate the female lock nut to thread it onto the threaded male shaft of the end plug and to swage the female lock nut to form a swaged locking portion engaging the recess of the lower end fitting.

3. The apparatus of claim 2 , wherein the tool is configured to connect with a torque wrench.

4. The apparatus of claim 1 , wherein the deformable side wall of the female lock nut comprises an annular deformable sidewall that is outwardly deformable into the recess of the lower end fitting to lock the female lock nut with the lower end fitting.

5. An apparatus comprising:

a lower end fitting having a top planar surface, a bottom planar surface and a plurality of counterbores defined therebetween, and at least one lock recess that extends both radially outwardly from a corresponding counterbore and extends inwardly into the lower end fitting from the bottom planar surface,

end plugs connected with corresponding lower ends of a plurality of guide tubes and having threaded male shafts extending from the lower ends of the guide tubes and passing through openings of the lower end fitting, and

female lock nuts threaded onto the threaded male shafts of the end plugs, each female lock nut including at least one swaged locking portion that extends radially outwardly into a corresponding lock recess of the lower end fitting to secure the lower end fitting to the lower ends of the guide tubes, wherein each female lock nut is fully disposed in a corresponding counterbore between the top and bottom planar surfaces,

wherein the at least one lock recess remains visible as viewed from the bottom planar surface of the lower end fitting when each female lock nut is fully disposed in the corresponding counterbore.

6. The apparatus of claim 5 , further comprising:

a plurality of fuel rods comprising fissile material;

a plurality of guide tubes interspersed amongst the fuel rods, and

an upper end fitting connected with upper ends of guide tubes.

7. The apparatus of claim 5 , further comprising:

dashpot tubes disposed in the lower ends of the guide tubes and connected to the end plugs, the female lock nuts not engaging the dashpot tubes.

8. The apparatus of claim 5 , wherein the female lock nuts have locking portions outwardly deformed into the lock recesses of the lower end fitting.

9. The apparatus of claim 8 , wherein the locking portions comprise portions of outboard annular walls of the female lock nuts that are outwardly deformed into the lock recesses of the lower end fitting.

10. The apparatus of claim 9 , wherein the locking portions comprise two locking portions of outboard annular walls of the female lock nuts that are outwardly deformed into the lock recesses of the lower end fitting.

11. The apparatus of claim 8 , wherein the locking portions comprise N locking portions arranged with N-fold symmetry around the female lock nut that are outwardly deformed into the lock recesses of the lower end fitting.

12. The apparatus of claim 5 , wherein the end plugs are welded to the lower ends of the guide tubes.

13. The apparatus of claim 5 , further comprising:

a tool configured to rotate a female lock nut to thread it onto a threaded male shaft of an end plug connected with the lower end of a guide tube and to swage the female lock nut to form swaged locking portions of the lock nut that engage the lock recesses of the lower end fitting to lock the lock nut with the lower end fitting.