Spot welding gun and welding method for the nuclear fuel skeleton

A spot welding device for assembling a nuclear fuel skeleton, wherein the nuclear fuel skeleton includes

• a spacer grid having a plurality of cells,
• an instrumentation tube hole disposed at a center of the nuclear fuel skeleton, and
• four guide tube holes disposed symmetrically around the instrumentation tube hole, wherein each of the four guide tube holes has a diameter (D) and a radius (R) and is placed at an interval (M) with a neighboring guide tube hole, the spot welding device comprising:
• a body;
• a first holder including
• a horizontal extension extending from a side of the body,
• a vertical extension on which a first electrode is disposed, and
• a bent portion having a horizontal thickness (T) and connecting the horizontal extension and the vertical extension with a predetermined degree such that a vertical distance between an outer surface of the horizontal extension and a virtual center line of the first electrode is a first height (H1);
• a second holder including
• an upper extension extending from the side of the body,
• a lower extension on which a second electrode is disposed, wherein the second electrode is opposite to the first electrode at an end and a virtual center line of the second electrode is coincide with the virtual center line of the first electrode,
• a stepped portion stepwise connecting the upper extension and the lower extension such that a vertical distance between an outer surface of the upper extension and the virtual center line of the second electrode is a second height (K);
• and
• a driving unit disposed on the body and configured to adjust a distance between the electrodes;
• and
• a robot connected to the welding spot device and configured to rotate the first and second holders on an axis parallel to the virtual centerline of the first electrode,
• wherein the interval (M) between the guide tubes is larger than the horizontal thickness (T) of the bent portion, and a shortest distance (S) between the stepped portion of the second holder and the bent portion of the first holder is larger than the diameter (D) of the guide tubes, and
• the bent portion and the horizontal extension are connected such that an interior angle between a virtual central axis of the bent portion and a virtual central axis of the horizontal extension is larger than 90 degrees, and the bent portion and the vertical extension are connected such that an interior angle between the virtual central axis of the bent portion and a virtual central axis of the vertical extension is larger than 90 degrees.