Hafnium Grade R1 mainly consists of Hafnium and contains no deliberate main alloy additions. In this nuclear quality, relevant impurities are strictly controlled so that the chemical composition is suitable for applications requiring predictable neutron absorption.
Hafnium and Zirconium naturally occur together but have very different neutron properties. For nuclear Hafnium applications, the high neutron absorption of Hafnium is functional.
Hafnium Grade R1 is specified in various ASTM standards, depending on the product form. For strip, sheet, and plate, Grade R1 is described in ASTM B776. For bar and wire, Grade R1 is described in ASTM B737. The applicable standard depends on the requested product form and dimensions.
Hafnium has a melting point of approximately 2233 B0C, a high density, and a very high absorption of thermal neutrons. This strongly distinguishes it from Zirconium, which is known for its low neutron absorption.
For Hafnium Grade R1, depending on the product form and applicable specification, requirements apply to chemical composition and mechanical properties, among others.
Grade R1 is the nuclear Hafnium quality and is chosen when strictly controlled chemical composition and nuclear requirements explicitly apply. Grade R3 is the commercial variant. Which specification applies also depends on the requested product form and dimensions.
The best-known application is in neutron-absorbing components, including control and regulating rods in nuclear reactor systems.
The suitability for a nuclear application must always be assessed against the project specification and required certification.