Refractory Metal ZIRLO CWSR
Heat-treated state · default condition
CWSR = cold worked and stress-relief annealed
Standard PWR fuel cladding tube condition: highest strength and creep resistance under rod internal pressure.
Values for the CWSR 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 |
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 |
CWSRDefaultThis page 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 CWSR?
ZIRLO CWSR is ZIRLO heat treated to CWSR — standard PWR fuel cladding tube condition: highest strength and creep resistance under rod internal pressure. ZIRLO CWSR 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). ZIRLO CWSR 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).
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 CWSR properties
Typical room-temperature values for ZIRLO CWSR; 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 CWSR 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 CWSR 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 CWSR 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 CWSR 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 CWSR 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 CWSR'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. Confirm any required mill or lot documentation when quoting.
Working with ZIRLO CWSR
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 CWSR — frequently asked
What is ZIRLO CWSR used for?
ZIRLO CWSR 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 CWSR?
ZIRLO CWSR 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 CWSR 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 CWSR 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 CWSR?
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 CWSR 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 CWSR?
ZIRLO CWSR 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.