Advanced Engineering

Industrial materials and heat transport building blocks (see TRL tables on the technology pages) are part of the concept:

Advanced helical heat exchangers

Helical shell-and-tube exchangers use tubes wound into helices inside a cylindrical shell. That geometry is the workhorse of primary Na→N₂ heat transport and can also serve N₂ Brayton recuperation and precooling where gas-side surface and pressure drop dominate.

Why helical

• High heat-transfer rate: Long tube path and cross-flow of sodium (or gas) over the bundle raise the overall heat-transfer coefficient without needing extreme velocities.
• Very low pressure drop (especially gas side): Generous shell-side and carefully managed tube-side flow areas keep ΔP small. In a closed Brayton cycle, compressor work is highly sensitive to pressure loss — low ΔP is a first-order design target.
• Thermal expansion: Helices flex in bending and torsion under temperature change, reducing mechanical stress on tubesheets and shells.
• Compact volume: High surface density in a cylindrical envelope suits modular external loops and compact power-conversion packages.

Primary Na→N₂ duty

Gas-side enhancement (high HTC, controlled ΔP)

Nitrogen flow inside the tubes is enhanced with internals:

• Internal fins — increase surface area and promote controlled turbulence on the high-pressure gas side.
• Twisted-tape inlets (and similar swirl devices) — improve mixing at the inlet and effective heat transfer without large permanent pressure losses if sized carefully.

Design trade-off is explicit: maximise heat transfer per unit volume while keeping tube-side and shell-side ΔP very low so net cycle efficiency and pumping power stay attractive.

Brayton recuperator and precooler

In the closed nitrogen cycle, the same high-HTC / low-ΔP helical philosophy applies to:

• Recuperator — gas-to-gas recovery from turbine exhaust to compressor discharge (effectiveness and low ΔP dominate net efficiency).
• Precooler (and optional intercoolers) — gas-to-coolant heat rejection before compression stages.

These are power-conversion exchangers, not sodium boundaries, but they share the same engineering goal: compact, high-rate heat transfer at minimal gas-side pressure drop.

Material selection

• Fuel cladding (baseline): HT9 — ferritic–martensitic steel proven in SFR metallic-fuel programmes. Optional later reloads may use advanced proven 9%Cr alloys (P92 / NF616 / Grade 92) once qualified; ODS is not required for the concept.
• Vessel, piping, and heat exchangers: Stainless steel 316LN for the hot-leg band around 600 °C, sodium compatibility, and weldability. One structural family for vessel and HX boundaries keeps thermal-expansion behaviour consistent.

Stainless steel 316LN

316LN (low-carbon, nitrogen-alloyed 316) is the baseline austenitic structural steel for this concept’s vessel, primary piping, and helical HX pressure boundaries.

Usability for ReCore

316LN is a standard nuclear and process industry alloy, not a research material. Nitrogen strengthens the austenite (raising allowable stress at elevated temperature relative to plain low-carbon 316L) while the low carbon limit reduces risk of weld sensitization and intergranular corrosion compared with high-carbon grades. It is widely available as plate, forgings, and seamless tube, welds with established procedures, and has a long pedigree in liquid-sodium and high-temperature water systems. For a ~600 °C sodium outlet, 316LN remains inside the usual high-temperature stainless design envelope for industrial heat-transfer equipment — suitable for modular welded vessels and helical tube-and-shell Na–N₂ exchangers without nickel superalloys.

• Elevated-temperature strength: Nitrogen solid-solution strengthening supports structural duty in the 500–600 °C class under nuclear design codes and high-temperature design practice.
• Sodium service: Austenitic 316-family grades are established for liquid-sodium loops when chemistry (oxygen/hydrogen) is controlled.
• Fabrication: Excellent weldability for tube, shell, vessel sectors, and helical HX work; same alloy family across interfaces simplifies expansion and joining analysis.

High-integrity joining: electron beam welding

Final assembly of reactor vessel modules can use electron beam welding (EBW), including local-vacuum EBW (LVEB) for thick seams with low distortion — suited to modular cylindrical sectors, bottom plate, and top plate.

Electromagnetic pumping: ALIP

Moving liquid sodium at ~600 °C uses annular linear induction pumps (ALIP): no moving parts in the sodium, no shaft seals into the primary system. Electromagnetic coils drive the fluid via Lorentz forces. Established liquid-metal pump technology for modern SFR concepts.