Conference Proceedings Paper
FUEL CHANNEL SCANNING TOOL ELONGATION MEASUREMENT “STEM”
11th International Conference on CANDU® Maintenance and Nuclear Components - 2017 Oct. 01-04
S.S. Dhaliwal (Ontario Power Generation)
A. Hong (Ontario Power Generation)
S. Mallampalli (Ontario Power Generation)
At Pickering NGS (Nuclear Generation Station), a mechanical (Linear Variable Differential Transducer LVDT/wheel) contact type STEM Tool is used to measure pressure tube axial elongation measurements at PNGS site. The raw data collected by STEM is integral for the monitoring and assessment of a pressure tube's axial elongation and for evaluating the planned service life for both PNGS 1&4 and 5-8. Axial elongation is the life-limiting mechanism at PNGS stations and confirmation of on bearing operation is required for demonstration of fitness for service. The STEM Tool is held in the Fuelling Machine (F/M) snout to scan row-by-row of reactor face to perform the linear measurement between the E-face of End-fittings and F/M reference plane. As identified, the existing mechanical contact type PNGS STEM Tool has design limitations and made unintended contact with an end fitting during PNGS unit 1 Outage in 2015. Furthermore, the existing STEM Tool has experienced many mechanical failures and does not provide enough clearance for the expected end-of-life fuel channel elongation at PNGS site. Internal/external rigorous background reviews and investigation of all available designed STEM Tools was conducted and concluded that a design change similar to DNGS STEM Tool was required to meet the PNGS site requirements. The DNGS STEM Tool non-contact type uses an ultrasonic sensor (obsolete) which gives more clearance but is less accurate than PNGS system. The “New” STEM Tool non-contact type uses laser triangulation sensor that are typically used in displacement and position monitoring applications where high accuracy, stability and low temperature drift are required. The proposed “NEW" design STEM tool will replace the old design to eliminate moving parts, contact with end fittings, swap replacement time and clearance issues. This new STEM Tool design will simplify the critical FC elongation measurement process and would be applicable to all the CANDU reactors."
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