Fermi is a 200 MWt reactor cooled by upward flowing sodium from three loops. The vessel is enclosed in a guard tank with a bottom inlet entering from a downcomer inside the guard tank. Figure 4.35 shows a cross section of the reactor vessel.

The uranium-molybdenum fuel is clad in zirconium. The fuel and cladding are integral, being coextruded. The blanket is stainless steel clad sodium — bonded fuel. The assemblies are rigidly held together in a birdcage with grids 2 in. apart. The core is mechanically restrained and compacted toge­ther with an upper plate and spider to hold down and bring the assemblies together. This restraint was due to the uncertainty about the EBR-I stability during the Fermi design period. The addition of further grids to help with the stiffening gave an extra pressure loss and caused a derating of the plant from 300 to 200 MW.

The control rods are sodium-cooled tubes of boron carbide. They are spring assisted to 2 g and slowed after insertion by a dashpot.

The assembly was equipped with a filter inside the inlet, but there was no protection against overall blockage. Inside the vessel there is a conical flow guide which doubles as a melt-down molten fuel deflector. It sits above a melt-down delaying system composed of zirconium-plated steel plates. Outside the vessel there is a graphite-lined catch pan.

A Offset handling mechanism — <L Rotating, plug

Thermal shield-

Blsupport assembly

Subassembly transfer pot

Transfer

rotor

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