Evaluation of the RBMK type reactor fuel can elongation during power cycling

A calculated-statistical model of kinetics of the strained-deformed state of the RBMK fuel element cans under conditions of cyclic power variation is suggested on the basis of data on the experimental investigations into thermal mechanical interaction of UO2 fuel core and a zirconium alloy can. The experimental study of the fuel elements is carried out in loop installations provided with elongation transducers. The measurement range is 0-9 mm, accuracy - +-1.5%. Analysis of the results obtained shows that during the reactor operation with the cyclic power variations (0-100%) the fuel element can undergoes irreversible elongation. During the reactor operation in the power range and under steady-state operating conditions the can can move respecting the fuel core. The moving velocity is the higher the higher the fuel core temperature. An increment in the irreversible elongation of the can has a chance character. The irreversible can elongation increases most intensively during the initial period of the reactor operation. The can diameter doesn't change practically in the process of the reactor operation wbich is attributed to the absence of fuel structure rearrangement due to low thermal loads (qsun(lsub(max))<55O W/cm) and the chance nature of the coordinate of a contact area of the fuel and can. The material creep flow durang the constant power operation after the effective power cycle (without regard for radiation growth of the can) contributes mainly to the irreversible can elongation