Effects of neutron irradiation on the microstructure of alpha-annealed Zircaloy-4

Analytical electron microscopy (AEM) was used to study the separate effects of the irradiation parameters on the evolution of the microstructure in recrystallized alpha-annealed Zircatoy-4 under controlled irradiation conditions. The effects of fast neutron flux from similar to4 X 10(13) n/cm(2)-s to similar to1.5 X 10(14) n/cm(2)-s (E > 1 MeV)(3) neutron fluence in the range of similar to15 X 10(20) n/cm(2) to similar to50 X 10(20) n/cm(2) and temperature from similar to270 to similar to330degreesC were studied. The completeness of the test matrix and the exposure in the controlled environment of the advanced test reactor permitted the separate effects of fast neutron flux, fluence, and irradiation temperature to be delineated for the first time. It was found that an increase in the neutron flux increases the degree of amorphization of the second-phase precipitates but retards the redistribution of iron out of the amorphous region (neutron fluence and irradiation temperature remaining the same), whereas increasing temperature (neutron flux and neutron fluence remaining the same) has a reverse effect. Overall, the rate of amorphization of the second-phase precipitates observed in this work was larger than that predicted by many existing literature models. Finally, neither segregation of alloying elements to grain boundaries nor precipitation of any new phases,\ were encountered.