Methods and apparatus for supporting the lower riser assembly of a jet pump in a reactor pressure vessel (RPV) of a nuclear reactor are described. In one embodiment of the apparatus, the clamp apparatus facilitates applying compression force on the elbow. The clamp apparatus includes a lower elbow clamp, a riser clamp, and a bridge. The lower elbow clamp is positioned adjacent an interface between the elbow and the thermal sleeve of the jet pump riser pipe assembly. The riser clamp is secured to the riser pipe of the jet pump riser pipe assembly at a location adjacent an interface between the riser pipe and the elbow. The bridge rigidly couples the lower elbow clamp and the lower clamp so that as the respective clamps are secured to the lower riser assembly, a compression clamping force is placed on the piping and welds at each clamp.