Patent Number: 
Section: claims

1. A method of installing a control rod guide assembly in a nuclear reactor fuel assembly including a top nozzle, a bottom nozzle, and a plurality of grids arranged between the top nozzle and the bottom nozzle, the method comprising:providing a guide tube and an external dashpot tube;inserting the guide tube into a skeleton of the nuclear reactor fuel assembly to a lower middle grid, the lower middle grid being a grid of the plurality of grids that is the second closest grid to the bottom nozzle;after the guide tube is inserted to the lower middle gird, installing the external dashpot tube over the guide tube;after the external dashpot tube is installed over the guide tube, inserting the guide tube into the skeleton to the bottom nozzle;attaching the guide tube to the skeleton; andbulging the guide tube onto the external dashpot tube;wherein the guide tube comprises an upper portion having a first external radius, a lower portion having a second external radius less than the first external radius, and a transition portion disposed between the upper and lower portion;wherein the guide tube linearly transitions between the first external radius and the second external radius in the transition portion;wherein the guide tube is monolithic through the first portion, the second portion, and the transition portion;wherein the plurality of grids comprise a bottom grid that is the closest grid to the bottom nozzle; andwherein, after bulging the guide tube onto the external dashpot tube, the external dashpot tube is disposed around a portion of the guide tube in an area beginning at the bottom grid and extending toward the top nozzle. 2. The method of claim 1, wherein installing the external dashpot tube over the guide tube includes installing the external dashpot tube over the lower portion of the guide tube. 3. The method of claim 1, wherein the bulging the guide tube onto the external dashpot tube includes forming a first bulge in upper halves of the guide tube and the external dashpot tube and forming a second bulge in lower halves of the guide tube and external dashpot tube. 4. The method of claim 1, wherein the external dashpot tube includes at least one weep hole formed therein. 5. The method of claim 4, wherein the at least one weep hole includes a first weep hole and a second weep hole, and wherein the first weep hole is formed in an upper half of the external dashpot tube and the second weep hole is formed in a lower half of the external dashpot tube. 6. The method of claim 3, wherein the external dashpot tube includes at least one weep hole formed therein, and wherein the at least one weep hole is formed between the first and second bulges in the external dashpot tube. 7. The method of claim 1, wherein, after bulging the guide tube onto the external dashpot tube, the external dashpot tube extending from the bottom grid towards the top nozzle and ends before reaching the lower middle grid. 8. The method of claim 2, wherein the lower portion of the guide tube is substantially cylindrical and the external dashpot tube is substantially cylindrical.