Patent Number: 
Section: claims

1. A method comprising:constructing a core former by stacking a plurality of single piece annular rings wherein each single piece annular ring comprises neutron-reflecting material; andloading a nuclear reactor core inside the core former by disposing fuel assemblies comprising fissile material inside the core former,wherein the stack of single-piece annular rings does not include welds or fasteners that axially restrain adjacent single-piece annular rings together. 2. The method of claim 1 further comprising:after the constructing and loading, operating a nuclear reactor comprising primary coolant disposed in a pressure vessel also containing the constructed core former and loaded nuclear reactor core to heat the primary coolant. 3. The method of claim 1 further comprising:forging each single piece annular ring. 4. The method of claim 1 further comprising:casting each single piece annular ring. 5. The method of claim 1 further comprising:rolling a plate and welding the edges of the plate together to form each single-piece annual ring.