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Robert Worth

Robert Worth. Characterisation and Thermal Treatment of Irradiated PGA Graphite w ith Investigation into 3 H and 14 C Behaviour. Lorraine McDermott, Greg Black, Abbie Jones, Paul Mummery, Barry Marsden, Anthony Wickham. Nuclear Graphite Research Group University of Manchester, UK.

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Robert Worth

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  1. Robert Worth Characterisation and Thermal Treatment of Irradiated PGA Graphite with Investigation into 3H and 14C Behaviour Lorraine McDermott, Greg Black, Abbie Jones, Paul Mummery, Barry Marsden, Anthony Wickham Nuclear Graphite Research Group University of Manchester, UK 14th International Nuclear Graphite Specialists Meeting Seattle, USA 15th-18th September, 2013

  2. Overview • Irradiated Graphite in the UK • Thermal Treatment at Manchester • Future Research • Conclusions

  3. Irradiated Graphite in the UK

  4. UK Graphite legacy • Graphite has been used in nuclear power plants worldwide • Historically, the UK has constructed many graphite-moderated reactors • These include power production, plutonium production and research reactors • Some still operational • Graphite contributes to a significantUK waste legacy • The majority of this graphite waste is ILW • Consequently, dismantling and management of radioactive graphite waste is an important issue in the UK

  5. Why treat graphite? • There is no current disposal route for irradiated graphite in the UK • Geological Disposal Facility (GDF)? • Treatment of irradiated graphite could allow reduction in the volume of ILW (cost-saving) • UtiliseGDF space • Allow disposal in current near-surface facilities • This could be achieved by preferential removal of radioisotopes, such as tritium and carbon-14 • Goal: Maximise radioisotope removal with minimal weight loss

  6. Carbon-14 formation • There are two dominant mechanisms by which 14C is produced in irradiated graphite in a reactor environment: (1) 13C (n,γ) 14C (2) 14N (n,p) 14C

  7. Nitrogen sensitivity ~50ppm ~10ppm Historically difficult to determine nitrogen content of graphite

  8. Thermal treatment at manchester

  9. Thermal treatment • A program of thermal treatment work has been conducted at the University of Manchester as part of the collaborative European project ‘CARBOWASTE’ • My own research is a continuation of this thermal treatment research: • Investigation of dependent variables, including temperature, time and oxygen • Investigation of 14C and 3H behaviour • Comparison of current world data to UK-irradiated graphite • Optimisation of the process • Using pre- and post-treatment characterisation techniques

  10. Isotopic inventory determination Thermal oxidation has been used as a method for 3H and 14C determination Graphite samples are placed in a ceramic combustion boat in a Carbolite® MTT Furnace A suitable cover gas flows past the sample and the temperature is raised A copper oxide catalyst promotes further oxidation of any gasified3H and 14C.

  11. Isotopic inventory determination • HTO and 14CO2are subsequently trapped in the bubbler system for analysis using liquid scintillation counting (LSC) • Bubblers have a trapping efficiency of 98%

  12. Isotopic inventory determination Typical determined radioisotope content in OldburyMagnox installed graphite:

  13. Isotopic validation How do we know we are capturing all of the 3H and 14C? Regular recovery checks are performed – a known quantity of 3H and 14C labelled sucrose standards are put through the furnace 3H recovery in the range of 88 – 98 % 14C recovery in the range of 85 – 94 % LSC quenched standard analysis to ensure LSC efficiency

  14. Thermal Treatment Experimental programme A thermal treatment programme has been designed to determine the effects of time, temperature and oxygen on 3H and 14C release The following experimental conditions have been applied to samples machined from installed sets retrieved from the OldburyMagnox power station: Argon 1% Oxygen in Argon

  15. Thermal Treatment Experimental programme Issues with the integrity of the samples post-treatment: • A = 800°C in 1% O2/Ar for 5 hours • B = 700°C in 1% O2/Ar for 5 hours • C = 700°C in Argon gas for 5 hours • D = untreated sample A B C D

  16. AUToradiography Hotspots

  17. Time Dependence Tritium, 3H Carbon-14, 14C

  18. Weight Loss Tritium, 3H Carbon-14, 14C

  19. Gamma spectrometry Cobalt-60:

  20. Future Research

  21. Future work - phd ‘Characterisation and Thermal Treatment of Irradiated PGA Graphite with Investigation into 3H and 14C Behaviour’ • Full optimisationof thermal treatment of irradiated OldburyMagnox reactor graphitewith respect to the sensitivity of: • Goal: Maximise radioisotope removal with minimal sample weight loss

  22. Pre- & post- treatment analysis Weight Loss Metrology • 4 d.p. Balance • Digital Micrometer SurfaceArea • Tristar BET • Laser Confocal Microscopy Porosity • Helium-pycnometry • To try and determine: • Amount of weight loss during treatment • The typicallocation of the radioisotopes before removal

  23. Pre- & post- treatment analysis Radioactive Content • Liquid Scintillation Counting • Gamma-spectrometry • Autoradiography • To determine: • Amount of radioisotope loss during treatment • Identification of ‘hotspots’ of radioactivity, which might influence the results

  24. Conclusions • It has been demonstrated that thermal treatment in an oxidising atmosphere is a potential means of removing 3H and 14C radioisotopes from irradiated graphite • The current data suggests that this treatment technique may be suitable for removing up to ~80% 3H and ~55% 14C from OldburyMagnox reactor graphite • Further work will be required to optimise this thermal treatment process and to determine the mobility and originof these radioisotopes

  25. acknowledgments • The authors are pleased to acknowledge EPSRC funding under agreement EP/P113315 • A portion of this work was carried out as part of the CARBOWASTE Program: Treatment and Disposal of Irradiated Graphite and Other Carbonaceous Waste,Grant Agreement Number FP7-211333

  26. thank you for listeningAny questions?

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