Non-destructive evaluation of irradiated 240 MW PHWR fuel elements

The non-destructive evaluation (NDE) of six number of fuel bundles were carried out inside hotcell facility which had seen different burn up of around 10,000 to 22,000 MWD/T. The NDE technique includes visual examinations, leak testing, profilometry and gamma scanning. Four irradiated PHWR fuel bundles having burnup of 11272, 10109, 22263 and 10647 MWd/TeU respectively were taken for non-destructive evaluation. Two bundles had seen a power transient, 27% power increase for 13 minutes. Two MOX bundles having burnup of 20331 and 10788 MWd/TeU were also taken for the non-destructive evaluation. Each bundle were visually examined through cell windows and radiation resistant cameras having tilt, rotation and zoom facility, installed in the front wall of hotcell. After dismantling and visual examinations of all the fuel elements individually, each fuel elements were subjected to liquid nitrogen - alcohol leak testing. The fuel elements are expected to have dimensional changes after in reactor operation. Diameter profile measurement of 3 fuel elements (outer, inner and central) from selected bundles were carried out using Linear Variable Differential Transformer (LVDT) probe based profilometry system. The fuel element was placed in the fuel element holding grips and was translated from one end to another. The pin outer diameter data is recorded throughout the length of the pin. Increase in diameter at pellet interfaces due to hour glass effect of the fuel elements were clearly observed during profilometry. Gamma-scanning was carried out for measuring the relative distributions of fission products in irradiated fuel elements that helps to generate information on axial burn-up distribution and distribution of specific fission products. An attempt was made to calculate the burnup of fuel bundle using fission product ratio method. (author)