Pool-type Sodium-Cooled Fast Reactor (SFR).

A fuel pin consists of metallic U-10Zr fuel in HT-9 steel cladding, with sodium filling the gap between fuel and cladding. Sodium coolant flows upward through the pins, collecting heat as it goes. The core is loaded once at commissioning and runs for twenty years without refuelling.

The heated sodium, now at 510°C, rises into the hot pool inside a single sealed 5x5m vessel installed below grade. The core, the pumps, and all six heat exchangers sit inside this one structure with no external pipe connections.

Shell-and-tube exchangers across independent loops transfer heat from radioactive primary sodium to clean secondary sodium across a tube wall. Radioactivity stays on the primary side.

Centrifugal pumps in the cold pool push cooled sodium back into the core, maintaining forced circulation during normal operation. Sodium's high thermal inertia means that even if flow is interrupted, the large pool absorbs heat gradually, buying time before temperatures approach safety limits.

The pool is the first line of defence. The sheer thermal mass of the primary sodium absorbs decay heat and rejects it passively, buying not minutes but days. Dedicated loops then carry remaining decay heat through heat exchangers outside the building, transferring it to open air. Each loop is independently sufficient, without the need for pumps, power or operator.

Secondary sodium travels to the steam generators outside the vessel, producing superheated steam at 440°C. A conventional turbine-generator delivers 150 MW of electricity. The remaining thermal output can be delivered as process heat to co-located industrial users.

Control rods with boron carbide absorber fall into the core by gravity when power is cut. Safety rods form a separate, mechanically diverse system inserted by spring and gravity under any off-normal condition. Two entirely different mechanisms ensure a single failure cannot disable both simultaneously.