Refractory Metal ZIRLO
ZIRLO is a proprietary Westinghouse Zr-Nb-Sn-Fe alloy developed for PWR fuel cladding and supplied in CWSR, PRXA, RXA and Optimized ZIRLO conditions.
Reference datasheet — ZIRLO is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the CWSR condition
ZIRLO tempers and conditions
ZIRLO is supplied in 4 conditions, soft to hard. CWSR is the default FabDigit quotes; the values on this page are for it.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Fully recrystallized annealed | Choose for spacer-grid strip and components needing maximum ductility, formability and low irradiation growth. | 320 | 470 | 28 | 152 HB | 2.6 % IACS |
Partially recrystallized annealed | Intermediate anneal used for guide tubes and some cladding designs balancing creep strength with irradiation-growth stability. | 420 | 560 | 21 | 176 HB | 2.5 % IACS |
reduced-tin variant, CWSR/PRXA tube | Lower Sn (~0.67 %) version for high-burnup cores: further reduced corrosion and hydrogen pickup at the cost of slightly lower strength. | 490 | 610 | 18 | 12 HRC | 2.5 % IACS |
CWSRDefault Cold worked and stress-relief annealed | Standard PWR fuel cladding tube condition: highest strength and creep resistance under rod internal pressure. | 530 | 650 | 16 | 14 HRC | 2.4 % IACS |
What is ZIRLO?
ZIRLO is a proprietary Westinghouse Zr-Nb-Sn-Fe alloy developed for PWR fuel cladding and supplied in CWSR, PRXA, RXA and Optimized ZIRLO conditions. Engineers specify it for improved in-reactor corrosion and creep resistance over Zircaloy-4, with 530 MPa yield, 650 MPa tensile and 16% elongation in the default condition, mainly as seamless cladding and guide tube, strip and grid stock. Limits are roughly 400 °C service temperature, low machinability (32/100), moderate formability (45/100) and licensed, restricted availability. Zircaloy-4 is the nearest alternative where the extra corrosion margin is not needed. ZIRLO has a density of 6.55 g/cm³ (0.237 lb/in³), lighter than 77% of refractory metal grades. It melts at 1,840°C (3,344 °F). ZIRLO has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 650 MPa (94.3 ksi) — stronger than 75% of refractory metal grades. Elongation at break is 16% and the elastic modulus is 99 GPa (14.4 Msi).
What is ZIRLO used for?
- PWR fuel rod cladding
- fuel assembly guide tubes
- spacer grids
- nuclear structural components
Advantages
- Lightweight — 6.55 g/cm³ (0.237 lb/in³), better than 77% of refractory metal grades
- High strength — 530 MPa (76.9 ksi), better than 75% of refractory metal grades
Limitations
- Low electrical conductivity — 2.4 % IACS, worse than 88% of refractory metal grades
- Poor heat conductor — 14.5 W/m·K (8.38 BTU/hr·ft·°F), worse than 86% of refractory metal grades
- Low stiffness — 99 GPa (14.4 Msi), worse than 79% of refractory metal grades
- High embodied carbon — 95 kg CO₂/kg, worse than 75% of refractory metal grades
ZIRLO properties
Typical room-temperature values for ZIRLO-CWSR; bars are the position among refractory metal grades.
Physical3
ZIRLO has a density of 6.55 g/cm³ (0.237 lb/in³), lighter than 77% of refractory metal grades. It melts at 1,840°C (3,344 °F).
Mechanical17
ZIRLO has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 650 MPa (94.3 ksi) — stronger than 75% of refractory metal grades. Elongation at break is 16% and the elastic modulus is 99 GPa (14.4 Msi).
Thermal6
ZIRLO is rated for continuous service to 400°C (752 °F). It conducts heat at 14.5 W/m·K (8.38 BTU/hr·ft·°F), worse than 86% of refractory metal grades. Thermal expansion is 6 µm/m·K (3.33 µin/in·°F).
Electrical3
ZIRLO conducts electricity at 2.4 % IACS, worse than 88% of refractory metal grades.
Chemical & Environmental3
Corrosion resistance is excellent (92/100), better than 86% of refractory metal grades.
Sustainability4
Producing a kilogram of ZIRLO takes about 1,500 MJ of energy and emits 95 kg of CO₂ — more than 77% of refractory metal grades. Typical recycled content is 15%.
Manufacturability8
ZIRLO's machinability is poor (32/100, better than 67% of refractory metal grades); weldability good (68/100); formability fair (45/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the refractory metal family
Yield strength against density for every refractory metal grade FabDigit runs. ZIRLO is highlighted; hover a dot for its name, or open the interactive family chart.
Working with ZIRLO
Is ZIRLO easy to machine?
Machine slow with sharp, positive-rake carbide, heavy flood coolant and no dwelling; fine chips are pyrophoric so keep swarf wet and segregated.
Can ZIRLO be welded?
GTAW with high-purity argon/helium plus full trailing and back purge, or EB/laser in vacuum; any O/N/H pickup embrittles the joint, and post-weld stress relief ~500–550 °C is common.
Can ZIRLO be formed, bent or molded?
Tube produced by repeated cold pilgering with intermediate vacuum anneals; strip forms well in RXA condition but strong basal texture makes properties markedly anisotropic.
ZIRLO 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 |
|---|---|---|
| Nbprimary corrosion/creep alloying addition | 0.8 – 1.2 | 1 |
| Sn≈0.6–0.8 % in Optimized ZIRLO | 0.8 – 1.2 | 1 |
| Fe | 0.09 – 0.13 | 0.1 |
| Ocontrolled for strength | 0.09 – 0.16 | 0.12 |
| Hfnuclear grade, low neutron-absorption limit | ≤ 0.01 | 0.01 |
| C | ≤ 0.03 | 0.02 |
| N | ≤ 0.01 | 0 |
| Zr | balance |
What surface finishes work on ZIRLO?
Final surface is pickled and autoclaved (400 °C steam) to grow a protective black oxide; avoid iron contamination and fluoride-bearing pickling residues.
How much does ZIRLO cost?
ZIRLO is a high-cost refractory metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
ZIRLO — frequently asked
What is ZIRLO used for?
ZIRLO is typically used for PWR fuel rod cladding, fuel assembly guide tubes, spacer grids and nuclear structural components. In short: upgraded PWR cladding alloy; better creep than Zircaloy-4; low neutron absorption.
What is the yield strength of ZIRLO?
ZIRLO has a typical yield strength of 530 MPa (76.9 ksi) and a tensile strength of 650 MPa (94.3 ksi) — stronger than 75% of refractory metal grades. Strength varies by condition: see the 4 listed tempers.
Is ZIRLO easy to machine?
Not especially — machinability is rated poor (32/100, better than 67% of refractory metal grades). Machine slow with sharp, positive-rake carbide, heavy flood coolant and no dwelling; fine chips are pyrophoric so keep swarf wet and segregated.
Can ZIRLO be welded?
Yes — weldability is rated good (68/100). GTAW with high-purity argon/helium plus full trailing and back purge, or EB/laser in vacuum; any O/N/H pickup embrittles the joint, and post-weld stress relief ~500–550 °C is common.
What surface finishes work on ZIRLO?
Final surface is pickled and autoclaved (400 °C steam) to grow a protective black oxide; avoid iron contamination and fluoride-bearing pickling residues.
Can ZIRLO be formed, bent or molded?
Tube produced by repeated cold pilgering with intermediate vacuum anneals; strip forms well in RXA condition but strong basal texture makes properties markedly anisotropic.
What is the maximum service temperature of ZIRLO?
ZIRLO is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between ZIRLO CWSR and ZIRLO-RXA?
CWSR is the default condition — standard PWR fuel cladding tube condition: highest strength and creep resistance under rod internal pressure. RXA: choose for spacer-grid strip and components needing maximum ductility, formability and low irradiation growth. Yield strength is 530 MPa in CWSR versus 320 MPa in RXA.
How much does ZIRLO cost?
ZIRLO is a high-cost refractory metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM B811 — Wrought Zirconium Alloy Seamless Tubes for Nuclear Reactor Fuel Cladding — ASTM International (2021)
- ASTM B350/B350M — Zirconium and Zirconium Alloy Ingots for Nuclear Application — ASTM International (2022)
- ZIRLO / Optimized ZIRLO fuel cladding topical reports — Westinghouse Electric Company (2010)
- ASM Handbook Vol. 2 — Properties of Zirconium and Zirconium Alloys — ASM International (1990)
- MATPRO / SCDAP-RELAP5 zirconium alloy material property correlations — US NRC / INL (2003)
- IAEA TECDOC — Waterside corrosion of zirconium alloys in nuclear power plants — IAEA (1998)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.