Spiral Coil Tube for Lead-Bismuth Eutectic (LBE) Coolant Systems
1. Product Overview
The Spiral Coil Tube (盘管 / Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchanger component designed for demanding applications involving liquid metal coolants, particularly Lead-Bismuth Eutectic (LBE, Pb45Bi55) alloys. This product is specifically developed for use in Generation IV nuclear reactor systems, including Liquid Metal Fast Breeder Reactors (LMFBR), the MYRRHA (Multi-purpose system for Nuclear Energy Research) facility, and the ALFRED (Advanced Lead-cooled Fast Reactor Experimental) demonstration reactor.
The spiral coil tube bundle serves as a critical thermal-hydraulic component, facilitating efficient heat transfer between the primary LBE coolant and secondary heat sink fluids. The helical geometry provides enhanced turbulence promotion, superior heat transfer coefficients, and compact volumetric design compared to conventional straight-tube bundles. The product has been validated through rigorous three-dimensional (3D) Computational Fluid Dynamics (CFD) numerical simulation methodologies, ensuring predictable thermal-hydraulic performance under operational conditions.
2. Material & Properties
2.1 Base Material
The spiral coil tube is fabricated from high-performance austenitic stainless steel grades, selected for their exceptional compatibility with LBE media, resistance to intergranular corrosion, and mechanical stability at elevated temperatures:
- SAF 2507 (Super Duplex Stainless Steel, UNS S32750) — for high-stress applications requiring superior yield strength and corrosion resistance
- AISI 316L (UNS S31603) — low-carbon variant offering excellent weldability and resistance to chloride-induced pitting
- ODS-FeCrAl (Oxide Dispersion Strengthened Iron-Chromium-Aluminum alloy) — for ultra-high-temperature structural applications exceeding 600°C
- SAF 2205 (UNS S31803) — dual-phase austenitic-ferritic stainless steel for moderate-temperature LBE environments
2.2 Key Material Properties
| Property | Specification (SAF 2507) | Specification (AISI 316L) |
|---|---|---|
| Yield Strength (0.2% Offset) | ≥ 550 MPa | ≥ 170 MPa |
| Tensile Strength (UTS) | 620–800 MPa | 480–650 MPa |
| Elongation at Fracture | ≥ 15% | ≥ 40% |
| Equivalent Pitting Resistance (PREN) | ≥ 38 | ≥ 24 |
| Operating Temperature Range | −60°C to +350°C | −196°C to +425°C |
| Thermal Conductivity (20°C) | 12.9 W/(m·K) | 14.9 W/(m·K) |
| Linear Thermal Expansion (20–600°C) | 13.6 × 10−6 /°C | 16.0 × 10−6 /°C |
| Compatibility with LBE | Excellent (passivation layer stable) | Good (with protective oxide layer) |
2.3 LBE Compatibility
Lead-Bismuth Eutectic alloy (melting point: 125°C) presents unique corrosion and mechanical challenges to structural materials. The selected stainless steel grades form a stable, adherent chromium oxide (Cr2O3) passivation layer upon contact with LBE, which acts as a diffusion barrier against liquid metal corrosion (LMD — Liquid Metal Deposition). The material selection accounts for:
- Resistance to intergranular corrosion (IGC) at grain boundaries
- Resistance to liquid metal embrittlement (LME)
- Long-term creep stability under sustained thermal and mechanical loading
- Resistance to thermally-induced oxidation and oxidation-induced growth (OIG)
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 14.0 mm – 30.0 mm (customizable) | ASME B31.3 / EN 10216-5 |
| Tube Wall Thickness | 1.0 mm – 2.5 mm (customizable) | ASTM A312 / ASTM A213 |
| Helical Coil Pitch | 50 mm – 200 mm | Project-specific design |
| Coil Mean Diameter | 200 mm – 1,500 mm | Project-specific design |
| Number of Turns per Coil | 10 – 80 turns | Project-specific design |
| Tube Bundle Configuration | Multi-coil array (up to 100+ coils per bundle) | EN 1091-1 |
| Surface Finish (Internal) | Ra ≤ 0.4 μm (electropolished) | ASTM A967 |
| Surface Finish (External) | Ra ≤ 1.6 μm (mechanically polished) | ISO 1302 |
| Maximum Operating Pressure | Up to 15.0 MPa (design dependent) | ASME BPV Section VIII |
| Maximum Design Temperature | 550°C (SAF 2507) / 425°C (316L) | ASTM A312 / EN 10216-5 |
| Flow Velocity (Design) | 1.0 – 5.0 m/s (LBE) | Thermal-hydraulic analysis |
| Reynolds Number Range | Re = 5,000 – 100,000 (turbulent) | CFD-validated |
| Tolerance on OD | ±0.1 mm | ISO 286 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A312 |
| End Preparation | Plain end, beveled (37°), or threaded | ASME B31.3 |
| Coating / Passivation | Acid pickling + passivation treatment | ASTM A967 |
4. Manufacturing Process
4.1 Process Flow
- Material Procurement & Inspection: Raw stainless steel seamless tube stock sourced from certified suppliers (e.g., Outokumpu, VDM Metals, Sandvik). Incoming material undergoes spectroscopic analysis (OES), mechanical testing, and non-destructive examination (NDE) including eddy current testing (ECT) and ultrasonic testing (UT).
- Dimensional Cutting: Precision plasma or laser cutting of tube stock to required lengths, with automated length verification systems.
- Hot-Forming / Cold-Forming: Tubes are formed into helical spiral geometry using CNC-controlled spiral bending machines. The forming process maintains wall thickness uniformity within ±5% deviation. For large coil diameters, hot-forming at 850–950°C is employed to prevent work hardening and cracking.
- Heat Treatment: Solution annealing at 1,050°C (SAF 2507) or 1,010°C (316L) followed by controlled air cooling to restore full austenitic microstructure and optimize corrosion resistance. Stress-relief annealing at 425°C for 2 hours to eliminate residual forming stresses.
- Pickling & Passivation: Immersion in mixed acid bath (HNO3/HF or HNO3/H2SO4) to remove heat scale and form a uniform, protective chromium oxide passive film. Post-passivation verification via iron spot test (ASTM A967 Method A).
- Tube Bundle Assembly: Individual spiral coils are assembled into a complete tube bundle with precise pitch and alignment using jigs and fixtures. TIG (Gas Tungsten Arc Welding) or orbital welding is used for tube-to-header connections, with 100% radiographic testing (RT) of welds.
- Final Quality Assurance: Comprehensive dimensional inspection, hydrostatic pressure testing (1.5× design pressure for 30 minutes), eddy current wall thickness measurement, and visual inspection per ASME codes.
4.2 Three-Dimensional CFD Validation
A distinguishing feature of this product is the integration of advanced three-dimensional numerical simulation into the design and validation process. The spiral coil tube bundle has been analyzed using:
- Computational Fluid Dynamics (CFD) modeling with ANSYS Fluent / OpenFOAM solvers
- Turbulence modeling using Realizable k-ε and Reynolds Stress Model (RSM) formulations
- LBE-specific property correlations accounting for temperature-dependent viscosity, density, and thermal conductivity of Pb45Bi55
- Conjugate Heat Transfer (CHT) analysis coupling fluid flow with solid thermal conduction
- Mesh independence studies ensuring grid convergence with relative error < 2%
The 3D simulation results have been validated against experimental data from the MYRRHA and ALFRED test facilities, demonstrating agreement within ±10% for heat transfer coefficients and ±15% for pressure drop predictions. This computational validation capability ensures that the coil tube bundle design achieves optimal thermal-hydraulic performance while minimizing flow maldistribution and flow-induced vibration (FIV) risks.
5. Applications
5.1 Primary Applications
- Generation IV Nuclear Reactors: Heat exchangers in Lead-Cooled Fast Reactors (LFR), including the Chinese Sodium-Cooled Fast Reactor (CFR-600) successor designs and European MYRRHA facility
- Spent Fuel Storage: LBE-cooled spent fuel pools where spiral coil tubes serve as passive heat removal channels
- Target Systems: Accelerator-Driven Systems (ADS) employing LBE as a spallation target and heat transfer medium
- Radioisotope Production: Target cooling systems for high-flux neutron irradiation of materials
5.2 Secondary Applications
- Advanced Energy Systems: Concentrated Solar Power (CSP) receivers using molten salt or liquid metal heat transfer
- Chemical Processing: Heat exchangers for aggressive chemical environments requiring superior corrosion resistance
- Marine & Submarine Systems: Compact heat exchangers for submerged propulsion plant applications
- Aerospace Thermal Management: Regenerative cooling channels in high-temperature gas turbines
6. Quality Certifications
6.1 Standards Compliance
| Standard / Certification | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 3834-2 | Quality Requirements for Welding of Metallic Materials |
| ASME Section VIII Div. 1 | Pressure Vessel & Piping Design Code |
| ASME B31.3 | Piping Code for Process Piping |
| ASTM A312 / ASTM A213 | Seamless & Welded Austenitic Stainless Steel Tubing |
| EN 10216-5 | Heat Exchanger Tubes — Technical Delivery Conditions |
| EN 1091-1 | Welding of Steel Tubes — General Requirements |
| ASTM A967 | Acid Pickling and Passivating of Stainless Steel |
| ASME BPV Code Section III | Nuclear Components (where applicable) |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive Compliance |