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Product

instrumentation cable seriesConcentric Triaxial MIMSPicoamp Guard-Ring DesignInconel 600 · +600 °C

MI Triaxial Signal CableInconel 600 / AISI 304L MgO mineral-insulated triaxial in-core neutron detector cable

MI Triaxial Signal Cable (Mineral-Insulated Metal-Sheathed, MIMS) featuring three concentric metallic conductors (centre signal core, inner tubular guard/return shield, and outer seamless Inconel 600 / AISI 304L pressure boundary).

Concentric Guard Tube
ASTM E844 / IEC 60568
+600 °C Inorganic
25 MPa Reactor Coolant
Order designation
MI-TRIAX-4.76-INC (.188")
Outer Ø
4.76 mm
Weight ≈
115 kg/km
Core-Guard Cap.
125 pF/m
Core-Guard Test V
1,500 V AC
All sizes (4)
Request a quoteDatasheetWhatsApp
Engineering reply in 2 business hoursCut-to-length export drumsEN 10204 3.1 certificate per drum
Architecture
3 Concentric
Core + inner guard + outer sheath
Dielectric
Dual 99.4 % MgO
Core-to-guard & guard-to-sheath
Insul. resist.
≥ 10¹² Ω·m
≥ 10⁸ Ω·m @ +600 °C
Operating temp.
-269 to +600 °C
Up to +850 °C Inconel peak
Outer diameter
3.0 to 6.35 mm
0.118" to 0.250" triaxial ODs
Leakage cancel
Driven guard rin
Eliminates HV polarisation leakage

Typical values for this cable type, based on ASTM E844 / IEC 60702-1 / IEC 60568 — confirmed in the datasheet and quotation for your order.

Application fit

Is MI Triaxial Signal Cable right for your machine?

Essential for wide-range fission chambers, Boron-10 proportional counters, Self-Powered Neutron Detectors (SPNDs) and high-temperature piezoelectric accelerometers where nanoamp/picoamp signals travel alongside 200–1,000 V DC detector bias.

Furnace, kiln & high-temp zone

Suitable

Operates directly inside the reactor core, vessel head and primary biological shield at +350 °C to +600 °C.

Fixed installation

Suitable

Inner concentric copper/Inconel guard tube isolates the signal core from reactor vessel ground currents.

Immersion & wet locations

Suitable

Seamless cold-drawn outer Inconel 600 tube forms a primary 25 MPa reactor coolant pressure boundary.

Energy chain / drag chain

Not suitable

Rigid/formable seamless metal-sheathed nuclear cable; not for industrial drag chains.

Use PUR-HF Drag-Chain Cable
Typical machinesPWR / BWR / SMR In-Core & Ex-Core Fission ChambersSelf-Powered Neutron & Gamma Detectors (SPND)Reactor Vessel Loose-Parts & Vibration AccelerometersLiquid-Metal (LMFBR) & Molten-Salt Reactor InstrumentationHigh-Temperature Jet Engine & Turbine Charge Amplifiers

Construction

Layer by layer

MI Triaxial Signal Cable showing solid OFHC copper/nickel/Inconel centre conductor, inner compacted MgO dielectric, seamless concentric copper/Inconel inner guard tube, outer compacted MgO barrier, and seamless Inconel 600 or AISI 304L outer sheath.

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Schematic, not to scale — generated from the layer data
#LayerMaterial & reference
1Solid centre signal conductorSolid OFHC copper, Nickel 200 or Inconel 600 centre rod (0.40 to 1.0 mm diameter)Carries picoamp/nanoamp ionization current or pulse-campbell signal
2Inner high-purity compacted MgO dielectricNuclear-grade ≥ 99.4 % Magnesium Oxide (MgO, low boron/cobalt) compacted around the centre conductorMaintains ≥ 10¹² Ω·m @ 20 °C and ≥ 10⁸ Ω·m @ +600 °C
3Seamless concentric inner guard / HV return tubeSeamless drawn OFHC copper, Nickel or Inconel 600 intermediate tubular shield (100 % optical coverage)Acts as driven guard ring or isolated HV bias return independent of vessel earth
4Outer compacted MgO isolation barrierSecond concentric layer of high-density 99.4 % MgO mineral insulationIsolates the inner signal/HV tube from the outer grounded pressure sheath (≥ 1,000 V)
5Seamless Inconel 600 or AISI 304L outer pressure sheathCold-drawn, bright-annealed Alloy 600 (Inconel 600) or low-cobalt AISI 304L/316L outer tube100 % helium leak-tight (< 10⁻⁹ mbar·L/s) & 25 MPa pressure boundary

MI-TRIAX-3.0-INC (3.00 mm · .118 in)

Compact 3.0 mm Inconel 600 triaxial cable for in-core fission chambers and SPND thimbles

MI-TRIAX-4.76-INC (4.76 mm · .188 in)

Standard 3/16" Inconel 600 triaxial cable with low-loss copper inner core & guard tube

MI-TRIAX-6.35-304L (6.35 mm · .250 in)

Heavy-duty 1/4" 50 Ω triaxial cable for ex-core wide-range neutron channels

Technical data

Ratings & operating limits

Typical values: Typical values for this cable type, based on ASTM E844 / IEC 60702-1 / IEC 60568. Values for your order are confirmed in the datasheet and quotation.

Electrical

Characteristic impedance
50 ± 4 Ω (core-to-inner-shield) or low-capacitance charge geometry
Insulation resistivity
≥ 10¹² Ω·m (@ 20 °C) · ≥ 10⁸ Ω·m (@ +600 °C) both layers
Core-to-guard capacitance
110 to 165 pF/m (@ 1 kHz)
Dielectric test voltage
1,000–1,500 V AC (core-guard) · 1,000 V AC (guard-sheath)

Thermal

Continuous operating temp.
-269 °C to +600 °C (up to +850 °C peak for Inconel 600)
Thermal cycling stability
Zero dielectric cracking across 100 thermal cycles (+20 ↔ +600 °C)
Fire & outgassing
100 % inorganic; zero outgassing or combustion

Mechanical

Min. cold bend radius
4 × OD (fixed forming) · 6 × OD (recommended layout)
Coolant pressure rating
25 MPa (250 bar) external hydrostatic pressure at +350 °C
Helium leak rate
< 1 × 10⁻⁹ mbar·L/s (100 % mass-spectrometer tested)

Resistance

Neutron & gamma fluence
> 10¹⁰ Gy gamma and > 10²² n/cm² neutron fluence
Transfer impedance (triax)
< 1 mΩ/m from 10 kHz to 30 MHz (solid tubular double shield)
Low cobalt purity
Co ≤ 0.05 % (500 ppm) nuclear grade alloy

Reference standards

Nuclear MIMS standard
ASTM E844, IEC 60702-1 & IEC 60568 (In-Core Instrumentation)
Quality assurance
ISO 19443 / ASME NQA-1 / 10 CFR 50 App B
RoHS & REACH
2011/65/EU & EC 1907/2006 compliant

Identification

Sheath finish
Bright annealed seamless Inconel 600 or AISI 304L/316L tube
Customs tariff (HS)
8544.2000
Traceability
Laser-etched heat lot tag with CMTR chemical & boron/cobalt assay

Sizes

4 standard MI Triaxial Signal Cable configurations

Concentric triaxial dimensions, metallurgy, capacitance and dielectric test voltages.

Dimensions & triaxial electrical data
Order designationOuter / Inner Tube / CoreOuter Ø
mm		Weight ≈
kg/km		Core-Guard C
pF/m		Core-Guard V
V AC		Enquiry
Mineral-Insulated Metal-Sheathed (MIMS) Triaxial Cables
MI-TRIAX-3.0-INCInconel 600 / Inconel 600 / Ni (MgO)3.00461551,000
MI-TRIAX-4.0-INCInconel 600 / OFHC Cu / OFHC Cu (MgO)4.00821351,200
MI-TRIAX-4.76-INC (.188")Inconel 600 / OFHC Cu / OFHC Cu (50 Ω)4.761151251,500
MI-TRIAX-6.35-304L (.250")AISI 304L / OFHC Cu / OFHC Cu (50 Ω)6.351981151,800
  • Typical values for this cable type; dimensions and weights for your order are confirmed in the quotation.
  • Both MgO insulation layers are simultaneously vacuum-baked and tested to ≥ 10¹² Ω·m before hermetic end sealing.

Quality & approvals

Testing & inspection

Routine tests on every production length, sample and type tests per batch — documented on an EN 10204 3.1 inspection certificate.

  1. ConductorClass 5 stranding
  2. Spark test100 % in-line
  3. Lay-upCores, earth, fillers
  4. SheathingInner, braid / screen, outer
  5. Electrical testsAC voltage, resistance
  6. DimensionsOD, wall thickness
  7. Inspection documents & dispatchDrum & dispatch
Testing & inspectionTest value / referenceFrequency
Routine tests
100 % dual-layer IR (@ 500 V DC), AC hi-pot & TDR checkCore-to-guard and guard-to-sheath IR ≥ 10¹² Ω·m @ 20 °CEvery manufactured coil
100 % Helium mass-spectrometer leak & 25 MPa hydrotestLeak rate < 1 × 10⁻⁹ mbar·L/s and zero sheath deformationEvery manufactured coil
Sample tests
+600 °C guard-ring leakage current & breakdown testMaintains ≥ 10⁸ Ω·m on both concentric MgO walls at +600 °CPer production lot

Inspection certificate

Issued with every drum, listing the routine test results for that length.

Product approvals

ASTM E844 & IEC 60568IEC 60702-1 MIMS StandardISO 19443 / ASME NQA-1 QA

Company certificates

ISO 9001ISO 14001ISO 45001VDE marks approvalUL / cULCE · LVD / EMC

Marking & supply

Ordering & delivery

Sheath marking

Laser-etched tag: TEBAOFLEX MI-TRIAX INCONEL 600 / MgO ASTM E844
Delivery form
Fumigated wooden drums, steel reels or precision spools
Standard lengths
500 m · 1000 m (or custom cut/spooled lengths)
MOQ
100 m (standard) · 500 m (custom)
Lead time
2–4 weeks ex-works
Incoterms
EXW, FOB, CIF, DAP

Technical documents

Downloads

PDFMI Triaxial Signal Cable – technical datasheet4 sizes · construction, technical data, approvalsXLSXMI Triaxial Signal Cable spec data (Excel)All 4 sizes with dimensions and data, for your BOM or quotation
Revision
2026-10-20
Updated
2026-10-20

FAQ

Questions engineers ask first

Not covered here? Send your drawing — an engineer replies within 2 business hours.

Why do in-core fission chambers and wide-range neutron detectors require a Triaxial MI cable instead of a Coaxial MI cable?
Fission chambers operate with 200–800 V DC bias while measuring ionization currents down to picoamps/nanoamps at +350–600 °C. In a simple coaxial cable, the outer sheath touches the grounded reactor structure (causing ground-loop noise) and any thermal drop in MgO resistance leaks HV bias current into the signal path. In a Triaxial MI cable, the inner seamless tube is driven at the same guard potential as the centre conductor (zero voltage across the inner MgO = zero leakage current), while the outer Inconel sheath serves purely as an grounded Faraday shield and pressure boundary.
How is a solid-metal inner guard tube formed inside an MI Triaxial cable?
The cable is assembled as a large-diameter preform consisting of the centre rod, inner MgO preforms, seamless intermediate metal tube, outer MgO preforms, and outer Inconel/stainless tube, then progressively cold-drawn and bright-annealed through precision dies to final diameter.
Why does solid tubular shielding achieve < 1 mΩ/m transfer impedance?
Unlike braided wire shields which have optical weave apertures that leak RF magnetic fields above 10 MHz, a seamless drawn metal tube has zero apertures, so skin-effect attenuation actually improves as frequency increases.
Can MI Triaxial cables be supplied as integral mineral-insulated detector assemblies?
Yes. We supply both bulk hermetically sealed triaxial coils and custom-length assemblies with ceramic-to-metal triaxial connectors or transition splices to 74C068 K1 containment cables.

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