ReCore-Power

ReCore-Power is the energy-conversion part of the ReCore engineering concept: a closed Brayton cycle with pure nitrogen (N₂) as the working fluid, coupled to the 720 MWth reactor class with an electrical class of about 300 MWe at a ~45% net efficiency target.

The main motivation is architectural: explore a power island without a water Rankine steam generator and the Na–H₂O reaction risk that has driven many intermediate-loop SFR layouts. Dry or low-water heat rejection is also of interest. That choice is part of the same first-principles Why? — simpler secondary chemistry where possible, industrial hardware classes, and constructability — while accepting that integrated nuclear Na–N₂ plant maturity is still low (see TRL table). Cycle efficiency is prioritised over minimising primary sodium inventory when the two conflict.

Technology readiness

TRL figures are estimates for power-conversion building blocks.

Cycle concept

At concept level the cycle is:

• closed (working fluid recirculated);
• recuperated (turbine exhaust heat returned to the compressor discharge);
• intercooled between compression stages to reduce compressor work (design intent for high net η).

Target net efficiency is on the order of 45% (docs plant class → ~300 MWe on 720 MWth). First-principles screening currently shows about 43.9% / ~316 MWe. That sits under the 45% target. It is not a guaranteed FOAK rating. Real net η depends on turbine inlet temperature, recuperator effectiveness, pressure ratio, gas-side ΔP, and turbomachinery maps. Hitting the target is preferred over cutting primary sodium inventory with unproven Na-side HX concepts.

Heat-exchanger split. The recuperator is gas-to-gas. In the screening cycle it carries slightly more heat than the reactor adds: turbine exit sits only a little above the heater inlet, while the compressor discharge is much colder. A small relative pressure drop on that duty costs net efficiency. The hardware class for that duty is a diffusion-bonded printed-circuit block: chemically etched channels, smooth enough that friction stays low, in a 316L-class plate that already has a pressure-vessel code path. A powder-bed lattice (gyroid or other TPMS) fights that job. As-built roughness and trapped powder raise ΔP, and one recuperator is far larger than today’s build volumes. Intercoolers and the precooler are gas-to-water, near compressor temperature, below the creep range. There the straightforward path is a catalog plate-and-shell or a TEMA shell-and-tube. A printed asymmetric lattice is a candidate for those coolers only, and only after powder removal and channel finish are shown not to send metal into the turbine. Detail: Advanced Engineering.

The sodium window is already tight. Hot sodium is ~600 °C because that is the structural band. Turbine inlet is ~550 °C. The recuperator returns gas at ~328 °C into a cold leg of ~400 °C. Widening the 200 K sodium rise by dropping the cold leg fights that gas inlet. Raising the hot leg fights creep in the tube. The 200 K span is a compromise among pipe flow, sodium inventory, and the cycle. It is not an unused efficiency knob.

The primary Na→N₂ heater is a vertical shrouded bayonet-tube module with a removable swirl cartridge: one 120 MWth module on each loop. The screening pressure boundary is a smooth Alloy 709 tube (~19.05 mm OD, ~1.5 mm wall, ~4.2 m active) hung from a single top tubesheet in the dry argon plenum. Alloy 800H is the commercial alternative; the choice is open (materials. Swirl ribs sit on the stainless insert, in an annulus of ~2.5 mm, at a friction drop under ~0.5 bar. The screening U is inside the ~1,200–1,600 W/(m²·K) band (white-paper result about 1,450 W/(m²·K)). Net cycle η stays the docs pin (~45% target; screening ~43.9%, which is under that target). This heater is not a reason to raise it. An ~80 bar tube shear is intended to vent upward into the argon rupture-disk path. A circulating secondary-Na loop is a fallback, not the baseline.

Load following

Closed gas cycles can vary electrical output by changing the inventory (mass) of gas in the loop while holding temperatures relatively steady. That is a known control approach for closed Brayton plants and is potentially well suited to supporting variable renewables — if control, economics, and nuclear coupling are demonstrated.

Cogeneration

Rejected heat from precoolers / intercoolers can feed district heating or low-to-medium temperature industrial uses where siting allows. Combined heat-and-power figures sometimes quoted above electrical-only efficiency are site- and demand-dependent, not universal plant ratings.

Historical precedent

Closed-cycle gas turbines are not speculative. European industrial examples include closed-cycle plants such as the Ravensburg air plant (1950s) and the Oberhausen-Sterkrade helium cogeneration plant (1970s). ReCore-Power borrows that closed-loop philosophy while selecting nitrogen for sodium compatibility and resource availability.

Comparison (qualitative)