4. Zr-Nb alloys

This family of Zr-Nb alloys (table ) is widely used for cladding tubes and fuel assembly structural components. It offers an extremely attractive alternative to Zircaloys, particularly for Candu reactors (Z _r N _b 2.5%), but also for VVERs, RBMKs (E110) and PWRs (M5ä).

• At the end of the 1990s, PWR operators' requirements increased, particularly in terms of discharge depletion > 65 GWj/tU and extremely demanding operating conditions for the cladding tube (high Li, Zn injection, increased power, high void ratio). To achieve this, designers and manufacturers have proposed alloys which, under the conditions described...