ZIRCONIUM ALLOY IRRADIATION HARDENING: YIELD AND ULTIMATE STRESS COMPARISON OF OPTIMIZED ZIRLO™ CLADDING AND ZIRLO~® CLADDING

摘要

As a result of an extensive development program, Westinghouse developed in early 2000 a new alloy, Optimized ZIRLO™ cladding, that is highly resistant to corrosion. Optimized ZIRLO™ cladding has a low tin content and, unlike its predecessor ZIRLO~® cladding, is fabricated with a Partial Recrystallized Anneal (PRXA). The low tin content of the alloy and PRXA heat treatment result in a slightly reduction of the unirradiated yield and ultimate stresses relative to ZIRLO~® cladding. However, these differences are expected to be eliminated by irradiation hardening. In order to establish this Westinghouse, ENUSA and Spanish utilities developed a joint program, the Almaraz Post-Irradiation Examination Program, to determine the fast fluence level where Optimized ZIRLO™ cladding is mechanically the same as ZIRLO~® cladding. Post-Irradiation Examination ring tensile tests and fast fluence measurements were performed on an Optimized ZIRLO™ rod and a ZIRLO~® rod irradiated in the Almaraz 2 NPP for one cycle. Many of the tests on both claddings were performed in the plenum region, and a few were performed in the fuel region. The results show that difference between the Optimized ZIRLO cladding and the ZIRLO cladding yield and ultimate stresses rapidly decrease with increasing fast fluence and is eliminated at a low fast fluence level.