Construction of the Sodium Reactor Experiment

The Sodium Reactor Experiment (SRE) was a prototype reactor 27 miles NW of LA that served as a technology demonstration of sodium-cooled, graphite-moderated reactors (aka SGRs). In the 1950s, it was thought that the combination of high-temperature, low-pressure liquid metal sodium coolant with highly fuel-conservative neutron moderation would form a likely candidate for low-cost commercial nuclear power plants.

Then, as today, the best way to verify that your economic suppositions are anywhere near correct was to build and operate a prototype. Originally the SRE was going to dump all its heat to air, but they ended up hooking it up to generator and putting electricity on the local grid.

Here's the reactor building being erected using the tilt-up concrete slab method.

The Santa Susana Field Laboratory was Atomics International's nuclear reactor skunk works. They developed and tested all kinds of reactor components and reactors there.

The liquid metal sodium is pumped into the lower plenum and enters the core through the grid plate. It moves up through fuel element channels in each moderator. Helium gas at 3 psig is maintained above the upper sodium.

To keep the surrounding concrete cool during operation, this cavity liner was included, which has coolant lines filled with an organic fluid called tetralin all around it...

This is the bottom grid plate. The moderator can pedestals sit upon each hole for positioning. Coolant from the lower plenum flows through the holes and into the fuel bundles.

To slow down the neutrons, moderators of graphite were used. They were surrounded by dimpled hexagonal zirconium cans to prevent the sodium from interacting with the graphite. Some of the moderator corners were scalloped to allow room for experimental channels and control rods. With moderated neutrons, SGRs can run on low-enriched or possibly even natural uranium, whereas fast-neutron reactors require higher enrichments (e.g. HALEU/MEU) or plutonium.