2.15.6.1 LWR UO2 and MOX Fuels

The LWR fuel designs are described in Section 39.3.2. There are some differences in the fuel assem­bly fabrication process between PWRs and BWRs. On the other hand, there is no major difference between UO2 and MOX with respect to the fuel assembly fabrication. As an example, the flow sheet of PWR fuel assembly fabrication is shown in Figure 26.

2.15.6.1.1 Rod fabrication

The fabrication of LWR fuel rods involves the intro­duction of fuel pellets and a spring into the cladding tube, followed by welding of the end plugs and the cladding tube. For PWRs, the rods are filled with helium at a higher pressure than for BWRs. For this purpose, the top plug has a hole through which the fuel rod is pressurized, and then the hole is arc — welded. The fuel rods are inspected for surface con­tamination, dimensions, appearance, plug welds, leak tightness, and uranium enrichment. The fabrication and inspection operations are highly automated and use advanced inspection technologies, such as an X-ray image digitizing system.