pool school: what we can learn about nuclear fuel using...
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Pool School: What We Can Learn About Nuclear Fuel Using Poolside Measurements Frequency-scanning eddy current technique can shave months off the time required to analyze how fuel parameters may impact operating margins or future fuel designs.
EPRI has developed and demonstrated a nondestructive evaluation (NDE) technology for poolside inspection of nuclear fuel structural materials (rods, channels, spacers, etc.) that will enable nuclear plants to more quickly measure critical parameters and address regulatory and operational considerations. The frequency-scanning eddy current technique (F-SECT) has been successfully demonstrated at nuclear plants in Spain and Switzerland, and ongoing hot cell examinations will enable EPRI to benchmark the accuracy and applicability of the technology against destructive examinations results.
Under normal reactor operations, zirconium-based alloys used in fuel assembly structural components and fuel rod cladding are susceptible to hydrogen pickup, which can result in the formation of hydrides that can render the components and rods more brittle than surrounding material. If the hydrogen pickup exceeds certain levels, regulatory margins can be at risk.
Historically, fuel assembly components and fuel rods have been inspected at hot cell facilities using destructive examinations. While this provides a proven approach for measuring hydride pickup, corrosion oxide thickness, and wall thickness, it is expensive, time-consuming, and requires considerable coordination and buy-in from the nuclear plant owner and the fuel supplier. It also requires access to one of a small number of hot cell facilities available worldwide. Over the past 10-15 years, EPRI alone has invested about $20 million in benchmarking studies at hot cell facilities.
Building on technology originally developed for testing gas turbine thermal barrier coatings, EPRI collaborated with the Italian vendor Centro Elettrotecnico Sperimentale Italiano (CESI) to adapt the F-SECT technology for nuclear plant applications, including fuel. The F-SECT technology can quickly measure a number of properties critical to fuel cladding and component structural integrity, including oxide thickness, wall thickness, and hydrogen pickup. Analyzing these measurements with respect to potential impacts on operating margins or how they could affect future fuel designs could potentially be done in a matter of days compared to months to over a year for hot cell testing.
EPRI has held discussions with all of the nuclear fuel vendors regarding future use of the F-SECT technology. Three fuel vendors participated in early laboratory evaluations in 2012-2014, and one fuel supplier collaborated with EPRI to conduct field demonstrations at two European plants in 2014 and 2015. At the Cofrentes plant in Spain, F-SECT tests were conducted to evaluate oxide thickness, remaining metal wall thickness, and hydrogen content in BWR fuel
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channels susceptible to distortion due to asymmetric corrosion and hydrogen pickup. All tests were successfully completed within the scheduled timeframe, encompassing 929 total measurements, many more than the 64 originally planned. Analysis of the F-SECT data is ongoing, and when complete, these data will be compared to the destructive evaluation data from the hot cell.
Additional field trials in 2015, coupled with hot cell comparative testing and ongoing modeling, are expected to provide the data and understanding with which to assess the commercial viability of the technology. Information from the F-SECT assessments also will guide the improvement and refinement of EPRI’s fuel reliability guidelines and help inform plant owners on operational and regulatory margins.
For more information, contact Rob Daum at 704.595.2779, [email protected] or Jeremy Renshaw at 704.595.2501, [email protected].