MITIGATING THE EFFECTS OF BAFFLE-RELATED WEAR IN BABCOCK AND WILCOX NUCLEAR POWER REACTORS

摘要

Baffle-related wear phenomena are a historicreliability concern in commercial nuclear power reactors.When Fuel Assemblies operate at the core periphery(adjacent to the core baffle or shroud), complex coreflows can cause such Fuel Assemblies to physicallycontact the baffle wall, which causes wear. This wear cannegatively affect both the Fuel Assembly structuralcomponents such as spacer grids, and the fuel rodcladding. The wear reduces performance margins and ithas led to fuel rod failures and prematurely shortenedFuel Assembly lifespan.While baffle-related wear is not a new industryphenomenon, evidence exists to suggest that as the coreinternals of commercial nuclear reactors age, theassociated risk to the reliability and performance of fuelcan also increase. To minimize this risk, fuel users haveadopted various mitigating design strategies. The mostcommon of these strategies is the pre-emptive armoring ofFuel Assemblies operating in known high wear corelocations with inert fuel rods. While effective in mitigatingthe potential for resulting fuel failures, such a strategycomes at a cost, both directly as well through a negativeimpact on fuel utilization.Framatome has been actively working with commercialnuclear customers to monitor the effects of baffle-wearand develop fuel solutions to mitigate the effects of baffleaging while minimizing the impact on fuel utilization. Incollaboration with Entergy, Framatome will be deployinglead PROtect Cr-cladding fuel rods at Arkansas NuclearOne, Unit 1 in 2019 that have been developed withincreased wear resistance. These fuel rods include a thincoating of chromium applied via physical vapordeposition to the underlying zirconium matrix of the fuelrod cladding, creating a highly adherent and wearresistantsurface that has been proven in out-of-piletesting. These wear-resistant rods are being placed instrategic locations within the reactor so as to operateadjacent to known high-wear baffle locations duringCycle 29 and 31. Poolside examinations of these rods areplanned to demonstrate their in-pile wear resistancefollowing 1 x and 3 x 18-month cycles of operation.