Nuclear Graphite NBG-18
Grade
ASTM D7219
NBG-18 = vibration-molded medium-grain pitch-coke near-isotropic nuclear graphite
Choose for large pebble-bed reflector blocks where big billet sizes, high thermal conductivity and low irradiation-induced dimensional change dominate over fine grain size.
Values for the NBG-18 condition
Other Nuclear Graphite tempers and conditions
Nuclear Graphite is listed in 4 conditions; see the grade overview at Nuclear Graphite.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Extruded medium-grain petroleum-coke nuclear graphite | Use where large extruded sections and cost matter and mild property anisotropy (with-grain vs against-grain) is acceptable; strength is lower than isostatic grades. | — | 17 | — | — | 140 W/m·K |
NBG-18This page Vibration-molded medium-grain pitch-coke near-isotropic nuclear graphite | Choose for large pebble-bed reflector blocks where big billet sizes, high thermal conductivity and low irradiation-induced dimensional change dominate over fine grain size. | — | 22 | — | — | 150 W/m·K |
IG-110Default Isostatically molded superfine-grain isotropic nuclear graphite | Default choice for HTGR/HTR-PM fuel blocks, reflectors and molten-salt reactor components where fine grain (~20 µm), high isotropy and proven irradiation database matter. | — | 25 | — | — | 120 W/m·K |
High-density isostatic fine-grain nuclear graphite | Pick when higher strength and density than IG-110 are needed for control-rod sleeves, high-stress reflector parts or MSR components. | — | 37 | — | — | 140 W/m·K |
What is Nuclear Graphite NBG-18?
Nuclear Graphite NBG-18 is Nuclear Graphite in the NBG-18 grade — choose for large pebble-bed reflector blocks where big billet sizes, high thermal conductivity and low irradiation-induced dimensional change dominate over fine grain size. Nuclear Graphite NBG-18 has a tensile strength of 22 MPa (3.12 ksi), weaker than 87% of ceramic grades. The elastic modulus is 11.5 GPa (1.67 Msi). Nuclear Graphite NBG-18 has a density of 1.85 g/cm³ (0.0668 lb/in³), lighter than 88% of ceramic grades. It melts at 3,650°C (6,602 °F). IG-110 is the default condition FabDigit quotes; NBG-18 is available on request or by drawing note.
Advantages
- High service temperature — 2,500°C (4,532 °F), better than 98% of ceramic grades
- Easy to machine — 90/100, better than 94% of ceramic grades
- Conducts heat well — 150 W/m·K (86.7 BTU/hr·ft·°F), better than 93% of ceramic grades
- Lightweight — 1.85 g/cm³ (0.0668 lb/in³), better than 88% of ceramic grades
Limitations
- Hard to polish — 35/100, worse than 93% of ceramic grades
- Low stiffness — 11.5 GPa (1.67 Msi), worse than 90% of ceramic grades
Nuclear Graphite NBG-18 properties
Typical room-temperature values for Nuclear Graphite NBG-18; 12 are specific to this condition. Other listed values are Nuclear Graphite reference data and may not represent this condition. Bars are the position among ceramic grades.
Physical3
Nuclear Graphite NBG-18 has a density of 1.85 g/cm³ (0.0668 lb/in³), lighter than 88% of ceramic grades. It melts at 3,650°C (6,602 °F).
Mechanical10
Nuclear Graphite NBG-18 has a tensile strength of 22 MPa (3.12 ksi), weaker than 87% of ceramic grades. The elastic modulus is 11.5 GPa (1.67 Msi).
Thermal5
Nuclear Graphite NBG-18 is rated for continuous service to 2,500°C (4,532 °F). It conducts heat at 150 W/m·K (86.7 BTU/hr·ft·°F), better than 93% of ceramic grades. Thermal expansion is 4.5 µm/m·K (2.5 µin/in·°F).
Electrical2
Nuclear Graphite NBG-18 has an electrical resistivity of 9.5×10⁻⁶ Ω·m.
Chemical & Environmental2
Corrosion resistance is very good (75/100), better than 50% of ceramic grades.
Sustainability4
Producing a kilogram of Nuclear Graphite NBG-18 takes about 180 MJ of energy and emits 14 kg of CO₂ — more than 60% of ceramic grades. Typical recycled content is 0%.
Manufacturability3
Nuclear Graphite NBG-18's machinability is excellent (90/100, better than 94% of ceramic grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Nuclear Graphite NBG-18
Is Nuclear Graphite easy to machine?
Machines dry very easily with carbide or PCD tooling at high speed, but the dust is abrasive, electrically conductive and must be vacuum-extracted; avoid cutting fluids that contaminate the pores.
Can Nuclear Graphite be welded?
Not weldable — parts are joined mechanically (threaded keys, dowels, graphite bolts) or with carbonaceous cements that are carbonized/graphitized after assembly.
Can Nuclear Graphite be formed, bent or molded?
Formed only at the green stage by isostatic pressing, vibration molding or extrusion of coke/pitch mix, then baked, pitch-impregnated, graphitized >2800 °C and halogen-purified; finished blocks are shaped only by machining.
What surface finishes work on Nuclear Graphite?
Surfaces are typically machined and cleaned by baking/vacuum outgassing; optional SiC or pyrolytic-carbon CVD coatings or phosphate-based antioxidants improve oxidation resistance above 500 °C.
Nuclear Graphite chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| ashtotal ash, typically <20–300 ppm depending on grade | ≤ 0.03 | 0 |
| Bboron equivalent typically ≤2 ppm per ASTM D7219 | ≤ 2×10⁻⁴ | 5×10⁻⁵ |
| Vresidual from petroleum coke | ≤ 5×10⁻⁴ | 1×10⁻⁴ |
| Fe | ≤ 0 | 2×10⁻⁴ |
| S | ≤ 0.01 | 0 |
| Cafter halogen purification | ≥ 99.95 (balance) | — |
Nuclear Graphite NBG-18 — frequently asked
What is Nuclear Graphite NBG-18 used for?
Nuclear Graphite NBG-18 is typically used for reactor moderator blocks, reflector components, fuel element sleeves and HTGR structural parts. In short: nuclear-qualified isotropic graphite; low boron, high purity; brittle, low tensile strength.
What is the tensile strength of Nuclear Graphite NBG-18?
Nuclear Graphite NBG-18 has a typical tensile strength of 22 MPa (3.12 ksi) — weaker than 87% of ceramic grades. Strength varies by condition: see the 4 listed tempers.
Is Nuclear Graphite NBG-18 easy to machine?
Yes — machinability is rated excellent (90/100, better than 94% of ceramic grades). Machines dry very easily with carbide or PCD tooling at high speed, but the dust is abrasive, electrically conductive and must be vacuum-extracted; avoid cutting fluids that contaminate the pores.
Can Nuclear Graphite NBG-18 be welded?
Not weldable — parts are joined mechanically (threaded keys, dowels, graphite bolts) or with carbonaceous cements that are carbonized/graphitized after assembly.
What surface finishes work on Nuclear Graphite NBG-18?
Surfaces are typically machined and cleaned by baking/vacuum outgassing; optional SiC or pyrolytic-carbon CVD coatings or phosphate-based antioxidants improve oxidation resistance above 500 °C.
Can Nuclear Graphite NBG-18 be formed, bent or molded?
Formed only at the green stage by isostatic pressing, vibration molding or extrusion of coke/pitch mix, then baked, pitch-impregnated, graphitized >2800 °C and halogen-purified; finished blocks are shaped only by machining.
What is the maximum service temperature of Nuclear Graphite NBG-18?
Nuclear Graphite NBG-18 is rated for continuous use to about 2,500°C (4,532 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM D7219 — Standard Specification for Isotropic and Near-isotropic Nuclear Graphites — ASTM International (2019)
- ASTM D7301 — Standard Specification for Nuclear Graphite Suitable for Components Subjected to Low Neutron Irradiation Dose — ASTM International (2018)
- Isotropic Graphite IG-110 / IG-430 technical data — Toyo Tanso (2020)
- NBG-18 nuclear graphite grade data — SGL Carbon (2019)
- Graphite Design Handbook / NGNP Graphite Testing and Qualification (INL/EXT reports) — Idaho National Laboratory (2011)
- IAEA-TECDOC-1154: Irradiation Damage in Graphite due to Fast Neutrons in Fission and Fusion Systems — IAEA (2000)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.