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Express diagnostics of WWER fuel rods at nuclear power plants

This paper discusses the use of ultrasonic and eddy current testing methods for the inspection of WWER-1000 fuel rods. It also presents a method for determining the fuel-cladding gap and measuring the oxide film thickness on the fuel rod's outer surface.

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Express diagnostics of WWER fuel rods at nuclear power plants

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  1. JSC “State Scientific Center-Research Institute of Atomic Reactors” Express diagnostics of WWER fuel rods at nuclear power plants S.V.Pavlov, S.V.Amosov, S.S.Sagalov, A.N.Kostyuchenko 8th International Conference on WWER Fuel Performance, Modelling and Experimental Support26 September – 04 October 2009, Helena Resort near Burgas, Bulgaria

  2. CONTENTS INTRODUCTION • Ultrasonic testing of failed fuel rods(FR) in WWER fuel assemblies (FA) • Eddy current testingof FR claddings • Method of determination of the diametrical fuel-cladding gap • Method of oxide film thickness measurement on the FR cladding outer surface CONCLUSION

  3. INTRODUCTION • The efficiency of technological support forstandard fuel operationand new fuel introduction depends on the completeness of irradiated fuel data in many respects as well as on the rapidity and cost of such data obtaining. • In order to increase the comprehensiveness of primary data on fuel assemblies and fuel rods immediately after their removal from the reactor, inspection test facilities are widely used for these purposes.The inspection test facilities make it possible to perform non-destructive inspection of fuel in the NPP cooling pools . • Specifically, non-destructive inspection of fuel rods at the inspection stands is conducted by different optical, ultrasonic and other methods.

  4. INTRODUCTION • For inspection of the WWER-1000 fuel rods, methods of ultrasonic testing of failed fuel rods and eddy current testing of FR claddings have been developed and proved. These methods are used at the stands for inspection and repair of TVSA at the Kalinin and Temelin NPP. • Method of determination of a diametrical fuel-cladding gap and an electromagnetic method of the oxide film thickness measurement on the FR claddingouter surface have been successfully used at RIAR for examination of irradiated WWER fuel for many years. These methods could be easily accommodated for underwater operation of the inspection stands.

  5. Ultrasonic testing of failed fuel rods Probe а b Fuel rod Water Principle of method operation Oscillogram of tight (а) and failed (b) fuel rod

  6. Ultrasonic testing of failed fuel rods [ ] А А = exp - 17 , 5 V F T Method sensitivity and results of its validation • Method validation • 8 leaking WWER-440 and WWER-1000 FAs with a burnup of 13.8 to 37.5 MW ·day/kgU were examined. • 2. All failed fuel rods were correctly identified.

  7. Ultrasonic testing of failed fuel rods Special manipulator 1-rod; 2-frame; 3-spring; 4-ultrasonic probes; 5-guiding pins

  8. Ultrasonic testing of failed fuel rods Main window of computer program

  9. Eddy current testing Position of the eddy current probe and fuel rod Signal of artificially applied defects Characterization of the artificially applied defects 1-eddy current probe body; 2-measuring coil; 3-container for fuel rod; 4-fuel rod

  10. Eddy current testing Examples of method application а b c Results of the eddy-current defectoscopy of the FR cladding (а), outer appearance (b) and cross-section of the cladding with part-through debris-defect: 1-signal of thedebris-defect

  11. Eddy current testing Examples of method application а b c Results of eddy-current defectoscopy of the defect fuel rod: а-eddy-current diagram; b – appearance of thedebris-defect; c-cladding microstructure in the region of the secondary defects; 1-signal of thedebris-defect; 2-signals of the secondary internal defects

  12. Eddy current testing Registration of local changes of FR cladding diameter Formation of goffers Results of the FR cladding testing 1-cladding; 2-fuel pellet; 3-goffers Magnitude of the eddy-current signal against fuel burnup -

  13. Method of determination of the cladding - fuel gap Method principle Typical diagram“force-deformation” Scheme of the facility 1-fuel rod; 2-loading pin;3-load sensor; 4-displacement transducer; 5-bellows; 6-charge amplifier; 7-amplifier; 8-analog-to-digital converter

  14. Method of the cladding - fuel gapdetermination Non-destructive measurement results compared to the optical metallographic examination results

  15. Method of the cladding - fuel gap determination 240 Initial gap 200 160 120 Diametrical gap, µm 80 40 0 0 5 10 15 20 25 30 35 40 45 50 55 60 Burnup, MW·day/kgU Method testing - results of non-destructive measurement - results of optical metallographic measurement

  16. Method of oxide film thickness measurement on the FR cladding surface Scheme of the facility 1-fuel rod; 2-eddy-current probe; 3-signal amplifier; 4-signal processing unit; 5, 6, 7-stepper motors; 8, 9-stepper motorcontroller; 10-computer.

  17. Method of oxide film thickness measurement on the FR cladding surface 12 10 40 8 Oxide film thickness, µm 30 6 4 20 Measured data, µm 2 10 0 0 0 20 40 60 0 10 20 30 40 Burnup, МWday/kgU Optical metallography data, µm Results of method testing with the use of WWER fuel rods Comparison between the measurement results and the results of FR cross-sections metallography Oxide film thickness versus burnup Alloy E110 - alloy E110 - alloy E635

  18. CONCLUSION • The ultrasonic testing of failed fuel rods inside the fuel assembly was developed for stands of inspection and repair of TVSA WWER-1000 for the Kalinin NPP and Temelin NPP. • This method was tested for eight leaking fuel assemblies WWER-440 and WWER-1000 with a burnup of ~14 up to 38 MWday/kgU. The ultrasonic testing proved its high degree of reliability and efficiency.

  19. CONCLUSION • The defectoscopy by means of the pulsed eddy-current method was adapted for the stand of inspection and repair of TVSA WWER-1000 for the Kalinin NPP. This method has been used at RIAR as an express testing method of FR claddings during the post-irradiation examinations of fuel assemblies WWER-440 and WWER-1000. This testing method was used for examination of 47 spent WWER fuel assemblies in total. But there were 16 failed spent fuel assemblies among them. • Methods of oxide film thickness measurement and fuel-cladding gap measurement in the WWER fuel rods have been successfully used for examination of the WWER fuel in hot cells. They can be easily adapted for use under water and can be recommended for adoption at stands of inspection and repair of TVSA WWER-1000

  20. THANK YOU FOR ATTENTION!

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