Metallographic examination of rapsodie PNC-4(2)(3) fuel pins

Ukai, Shigeharu  ; Osato, Yukihiro*; Unno, Ichiro; not registered; not registered; Shibahara, Itaru

Rapsodie PNC-4 (2)(3) was irradiated to confirm the performance and integrity of "Monju" type fuel pin. One of test pins, K09 pin, has highest burnup and almost attained the target burnup of "Monju". Metallographic examination of K09 pin had been partially conducted at France and the integrity of this pin was confirmed. In this examination, fuel microstructure observation and elemental analyses of both K09 pin and K07 pin have been carried out in order to evaluate the irradiation behavior of high burnup fuel pin. Peak burnup and peak fluence of K09 pin and K07 pin reached 128,000 MWD/MTM, 1.2610 (E O.1 Mev) and 79,000 MWD/MTM, 7.2510 (E 0.1 Mev), respectively. Following results were obtained in this examination. (1)No fuel/cladding gap existed at the middle of fuel column of K07 pin, and it was considered that fuel cladding mechanical interaction (FCMI) occurred at entire fuel column during irradiation. On the other hand, gap width of higher burnup K09 pin reopened to 60 m due to cladding swelling. Pin diameter of this pin increased by 2.3%. (2)Maximum depth of cladding inner corrosion of K09 pin and K07 pin were 53 m and 75 m respectively. It was confirmed that cladding inner corrosion saturated at high burnup. (3)Oxygen analyses by ion microprobe analyzer made clear that Fe-Ni Phase existing on fuel side in fuel-cladding chemical interaction (FCCI) zone was identified as metallic and Cr-Mn-FP (Cs) phase on cladding side was identified as oxide. (4)At the edge of central void, plutonium concentration increased to about 27 wt% from 20 wt% of fabricated content. (5)There were gray phase and metallic inclusion as precipitation phase in the fuel. Gray phase consisted of Ba-Zr compound, Ba-Cs compound, Ba-Ce compound, and metallic inclusion consisted of Mo-Ru-Rh-Tc-Pd compound, Fe-Pd compound. (6)Clear correlation between fuel microstructure and retained xenon profile across the pellot was obtained. ...