Remaining life prediction of irradiated fuel channels for Boiling Water Reactor by ultrasonic testing

The fuel channel forms an outer cover of the fuel assembly for the Boiling Water Reactor at Tarapur Atomic Power Station, (TAPS) Tarapur. Fuel channels are made of Zircaloy-4 material having square section of 113.5 × 113.5mm, wall thickness of 1.5mm and length of 4029mm. The two major factors which affect fuel channel´s performance are `Bulge´ and `Bow´, mainly attributed to the neutron flux gradient across the channel´s faces, and therefore, to some extent, they may be linked with the exposure to the neutron radiation, undergone by the fuel channel. Fuel channel bulge, if allowed to proceed unchecked could eventually create interference between the control rod and fuel channels. Under the surveillance programme, fuel channel is discharged once it reaches an optimum exposure limit, which is assumed to be attained if fuel channel does not pass through a limit gauge, designed for qualitative inspection. Considering the need for the determination of remaining life, quantitative measurement system namely `Channel Growth Measuring Device´ (CGMD) was developed by Centre for Design and Manufacture (CDM) and TAPS. CGMD is a non-contact, remotely operated underwater dimensional inspection device, based on ultrasonic immersion method. The system was successfully used for establishing a relation between the actual bulge and exposure level of the channel. This paper highlights the principle, design, calibration and operation of CGMD along with analysis of the results for predicting the remaining life of fuel channels manufactured indigenously by Nuclear Fuel Complex (NFC) Hyderabad.