Reactor Physics Aspects in Management of a Channel Flow Reduction in Darlington Unit 3 Post Refurbishment

Abstract

As part of Darlington Unit 3 return to service activities after its Refurbishment outage, coolant flow blockage checks and estimates of coolant flow rate through individual fuel channels were performed at various power levels during the initial power ascension. Following the reactor power raises to 22%FP and 30%FP, these checks identified fuel channel X10 as potentially having a coolant flow rate below design. Subsequent investigation revealed that X10 was fitted with a smaller pressure breakdown orifice than intended, resulting in a coolant flow rate reduction of approximately 25%. This required corresponding reductions in the channel and bundle power limits for that channel, necessitating the addition of depleted fuel bundles to suppress power and ensure compliance with the reduced limits at higher power levels. Further intervention was required during the pre- equilibrium period of operation to keep the reactor at 100%FP.

Acknowledgement

The authors of this paper wish to express their gratitude to their former colleague, Shahab Dabiran- Zohoory, for his dedication and his excellent fuelling simulations, which greatly helped to support and manage the X10 low flow issue.