Gap estimation method between calandria tube and liquid injection nozzle in CANDU reactor

As the calandria tube (made of zirconium alloy) is sagging due to its thermal and irradiation creep during the plant operation, it possibly contacts with liquid injection nozzle crossing beneath the calandria tube, which subsequently results in difficulties on the safe operation. It is therefore necessary to check the gap for the confirmation of no contacts between the two tubes, calandria tube and liquid injection tube, with a proper measure during the life of plant. In this study, a methodology to estimate the gap between the two tubes utilizing the classical beam theory is proposed. The saggings of the calandria tube and liquid injection tube are modelled as mathematical deflection curves, the coefficient of which is determined by sagging data measured at viewing port by an ultrasonic measurement device. The proposed method was found to be well fitted to some measured data, which means that the method can be applied to Wolsung-1 for the measurement of the gap between calandria tube and liquid injection tube