Refractory Metal ZIRLO OPT-ZIRLO
Grade
Lower Sn (~0.67 %) version for high-burnup cores: further reduced corrosion and hydrogen pickup at the cost of slightly lower strength.
Values for the OPT-ZIRLO condition
Other ZIRLO tempers and conditions
ZIRLO is listed in 4 conditions; see the grade overview at ZIRLO.
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 |
OPT-ZIRLOThis page 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 OPT-ZIRLO?
ZIRLO OPT-ZIRLO is ZIRLO in the OPT-ZIRLO grade — lower Sn (~0.67 %) version for high-burnup cores: further reduced corrosion and hydrogen pickup at the cost of slightly lower strength. ZIRLO OPT-ZIRLO has a yield strength of 490 MPa (71.1 ksi) and a tensile strength of 610 MPa (88.5 ksi) — stronger than 75% of refractory metal grades. Elongation at break is 18% and the elastic modulus is 99 GPa (14.4 Msi). ZIRLO OPT-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). CWSR is the default condition FabDigit quotes; OPT-ZIRLO is available on request or by drawing note.
Advantages
- Lightweight — 6.55 g/cm³ (0.237 lb/in³), better than 77% of refractory metal grades
- High strength — 490 MPa (71.1 ksi), better than 75% of refractory metal grades
Limitations
- Low electrical conductivity — 2.5 % IACS, worse than 86% of refractory metal grades
- Poor heat conductor — 14.8 W/m·K (8.55 BTU/hr·ft·°F), worse than 83% 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 OPT-ZIRLO properties
Typical room-temperature values for ZIRLO OPT-ZIRLO; 23 are specific to this condition. Other listed values are ZIRLO reference data and may not represent this condition. Bars are the position among refractory metal grades.
Physical3
ZIRLO OPT-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 OPT-ZIRLO has a yield strength of 490 MPa (71.1 ksi) and a tensile strength of 610 MPa (88.5 ksi) — stronger than 75% of refractory metal grades. Elongation at break is 18% and the elastic modulus is 99 GPa (14.4 Msi).
Thermal6
ZIRLO OPT-ZIRLO is rated for continuous service to 400°C (752 °F). It conducts heat at 14.8 W/m·K (8.55 BTU/hr·ft·°F), worse than 83% of refractory metal grades. Thermal expansion is 6 µm/m·K (3.33 µin/in·°F).
Electrical3
ZIRLO OPT-ZIRLO conducts electricity at 2.5 % IACS, worse than 86% of refractory metal grades.
Chemical & Environmental3
Corrosion resistance is excellent (94/100), better than 94% of refractory metal grades.
Sustainability4
Producing a kilogram of ZIRLO OPT-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 OPT-ZIRLO's machinability is poor (32/100, better than 67% of refractory metal grades); weldability very good (70/100); formability fair (48/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with ZIRLO OPT-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.
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.
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 | — |
ZIRLO OPT-ZIRLO — frequently asked
What is ZIRLO OPT-ZIRLO used for?
ZIRLO OPT-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 OPT-ZIRLO?
ZIRLO OPT-ZIRLO has a typical yield strength of 490 MPa (71.1 ksi) and a tensile strength of 610 MPa (88.5 ksi) — stronger than 75% of refractory metal grades. Strength varies by condition: see the 4 listed tempers.
Is ZIRLO OPT-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 OPT-ZIRLO be welded?
Yes — weldability is rated very good (70/100). 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 OPT-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 OPT-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 OPT-ZIRLO?
ZIRLO OPT-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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.