Change of mechanical properties of Zircaloy-2 after long-term annealing in the presence of simulated fission products

The effect of various simulated fission products on the tensile properties of Zircaloy-2 on long-term exposure has been investigated. The fission elements and compounds, Cs, CsI, I, Br, Te, Se, Mo, Pd, Cd, and Nd2 O3, were tested for activity in the embrittlement of Zircaloy-2. Room temperature tensile tests were carried out on flat specimens annealed in argon and in the individual fission product environments to 7.2 Ms (2000 h) at 623, 773, and 973 K. Except for Nd2 O3, exposure at 623 or 773 K did not significantly affect either strength or elongation values of Zircaloy-2, though a gradual degradation of the mechanical properties was observed with annealing time. All specimens showed high reduction of area and ductile fracture morphology. The effect of Nd2 O3 is to severely embrittle the specimens on annealing at 773 K, irrespective of exposure time. At 623 K, annealing times in excess of 3.6 Ms (1000 h) were needed to cause significant embrittlement of the specimens. Exposure to these environments at 973 K, on the other hand, results in a general reduction of the tensile properties at room temperature, the exceptions being Cs and CsI environments. In fact, I, Br, Cd, Mo, and Nd2 O3 cause non-ductile fracture with little or no reduction of area. These results are discussed for their implications to fuel/cladding interactions. (orig.)