Light Water Reactor Fuel Degradation Mechanisms at High Burnup: Implications to Generation IV Materials
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Light-Water Reactor Fuel Degradation Mechanisms at High Burnup: Implications to Generation IV Materials Arthur T. Motta © 2008 Department Materials Research Society of Mechanical and Nuclear Engineering The Pennsylvania State University [email protected]
MRS Fall Meeting Symposium T November 2007
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Motivation • •
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Can we get some perspective on the development of GenIV materials if we look at LWR (light water reactor) materials? Enormous experience database, but fuel for LWR is being pushed to higher burnup and more severe duty cycles, so new degradation mechanisms can appear or existing ones change rate. Increasing mechanistic understanding of degradation processes, but still many important and fundamental phenomena not well understood. Two examples of phenomena that change with burnup:
© 2008 Materials Research Society ¾ ¾
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Dimensional Changes of Fuel Assemblies and Channel Boxes Limits of Reactivity Initiated Accidents at High Burnup
Foresight is not 20-20 – coupled degradation processes in unexplored regimes of dose, exposure and temperature are difficult to predict. We are likely to encounter some surprises also in GenIV materials.
MRS Fall Meeting Symposium T November 2007
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But.. why are we studying LWR fuel? • •
Isn’t this old technology? Don’t we have 50+ years of experience with UO2 and Zircaloy? yes
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© 2008 Materials Research Society Don’t we know everything that we need to know? not quite
Much of the knowledge is empirical and we are venturing onto new territories of operating conditions
MRS Fall Meeting Symposium T November 2007
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LWR Average Fuel Discharge Burnup is Increasing
© 2008 Materials Research Society
MRS Fall Meeting Symposium T November 2007
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Fuel Operational Challenges: Increased Fuel duty • •
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Total residence time (burnup) has increased (from 3 (30GWd/t) to ~ 5 years) => higher radiation damage and longer exposure => more corrosion The NRC Burnup limit is 62 GWd/t, some utilities have expressed interest in increasing this to 75 or 100 GWd/t => decrease waste and increase availability factor. Primary water chemistry is different (presence of Li, Zn injection, CRUD formation, hydrogen water chemistry ) Fuel is operating at higher temperatures (power uprates) Fuel cycles have been increased (18 or 24 month cycles)
© 2008 Materials Research Society
=> Utilities and fuel vendors would like to have the flexibility of increasing burnup further, while operating economically and safely
MRS Fall Meeting Symposium T November 2007
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The goal of the industry is Zero failures •
Even while the fuel duty is being made more severe, the industry has a stated goal of completely eliminating fuel failures by 2010 (cladding failures cause increased exposure to workers in outages, may force unplanned shutdowns).
© 2008 Materials Research Society •
This involves thousands of fuel assemblies and millions of fuel rods and none can fail.
MRS Fall Meeting Symposium T November 2007
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© 2008 Materials Research Society
Bold directions! Increase temperature fr
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