Patent Number: 
Section: claims

1. A method of pressurizing a nuclear core component having a tubular cladding with an upper and lower end, comprising the steps of:closing off a lower end of the cladding with a lower end plug fixture configured to form a gas tight seal;loading an active element into the lower end of an interior of the cladding above the lower end plug leaving an empty plenum in the interior of the cladding above the active element;inserting a spring within the empty plenum between the upper end of the cladding and the active element, the spring being configured to bias the active element towards the lower end plug fixture when the upper end of the cladding is closed off by an upper end plug fixture;closing off the upper end of the cladding with the upper end plug fixture comprising an upper end plug external piece and an upper end plug internal piece, the upper end plug internal piece configured to slide within a through opening in the upper end plug external piece and have a lower end that biases the spring towards the active element when the upper end plug fixture forms a gas tight seal at an interface of the cladding and the upper end plug at least partially closing off the upper end of the cladding, the through opening and the upper end plug internal piece configured so an upper portion of the upper end plug internal piece fits within the through opening but cannot pass through and out of an upper portion of the through opening and the spring is configured to support the upper end plug internal piece within the through opening, the upper end plug internal piece and the through opening forming a substantially gas tight seal at an upper limit of travel of the upper end plug internal piece through the through opening and a gas communication path at a point below the upper limit of travel;placing at least the upper end of the cladding, with the upper end plug fixture and the lower end plug fixture in place, in a pressure chamber;applying a vacuum to an interior of the cladding;introducing a filler gas into the pressure chamber;raising the pressure of the filler gas within the pressure chamber to a preselected pressure for a given period of time; andsealing the upper end plug internal piece to the upper end plug external piece. 2. The method of claim 1 including the step of permanently sealing the upper end plug fixture and the lower end plug fixture to the cladding. 3. The method of claim 2 including the step of removing the cladding with the upper end plug fixture and the lower end plug fixture from the pressure chamber after the given period of time and wherein the step of permanently sealing the upper end plug fixture and the lower end plug fixture to the cladding is performed after the removing step. 4. The method of claim 3 including the step of permanently sealing the upper end plug internal piece to the upper end plug external piece after the removing step. 5. The method of claim 1 wherein the step of closing off of the lower end of the cladding and the step of closing off of the upper end of the cladding is performed with a clamp or other fixture that forces the upper end plug external piece against the cladding. 6. The method of claim 5 wherein the clamp is a mechanical or hydraulic clamp. 7. The method of claim 1 including the step of placing a binding agent at an interface of a wall of the through opening and an abutting wall of the upper end plug internal piece. 8. The method of claim 7 wherein the binding agent comprises one or more of SiC paste, graphite, silver, titanium or aluminum. 9. The method of claim 1 wherein the step of sealing the upper end plug internal piece to the upper end plug external piece is performed by reducing the pressure of the filler gas within the pressure chamber after the given period of time, or otherwise removing a force pushing against the upper end plug internal piece biasing the upper end plug internal piece into an interior of the cladding. 10. The method of claim 1, prior to the step of introducing the filler gas and subsequent to the step of placing the cladding in the pressure chamber, including the step of drawing a vacuum on the pressure chamber. 11. The method of claim 1 including the step of mechanically attaching the upper end plug external piece to the cladding.