Metallographic examination of driver fuel subassembly (Fab.No.PFD003) irradiated in "JOYO" MK-II

not registered; Ukai, Shigeharu  ; Unno, Ichiro

The driver fuel Subassembly (Fab. No. PFD003) had been irradiated at location of (1B1) up to end of first cycle from startup of 100 MW in "JOYO" MK-II, and its average total burnup reached to 13,800 MWD/MTM. In order to confirm the integrity of the fuel pin and to grasp the irradiation performance during the reactor operation up to first cycle of "JOYO" MK-II, metallographic examination of fuel and cladding was carried out by optical microscope, scanning electron microscope (SEM), electron probe microanalyser (EPMA) and ion microanalyser (IMA). The results are summarized as follows ; (1)Central void of 0.43 mm in diameter and columnar grain were observed near axial midplane of fuel column. Volatile fission product such as Cesium accumulated in the fuel-cladding gap, and mass transfer of cladding constituents was slightly detected by EPMA. However, reduction of cladding thickness cased by fuel-cladding-chemical-interaction was not observed. (2)Redistribution of uranium and Plutonium did not occur. Such actinoid element was observed to be homogeneously mixed at columnar region. However, concentration of such element varied heterogeneously in unrestructured region. (3)Radial profile of Xenon in the fuel measured by EPMA showed that unrestructured fuel retained fission gas and gas release started in the densified region. Characteristic X-ray of Xe-L was not detected in the gas bubble region. (4)Burnup measured by IMA shows good agreement with calculated value. (5)IMA measurement shows the preferential deposition of manganese and preferential leaching of manganese and nickel in the depth of 2 m of cladding outer surface at the temperature region of 380C and higher than 500C respectively. Concentration change of cladding outer surface was not detected at the temperature of 450C.