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NGRG INGSM-14 Seattle, USA Robert Worth Nuclear Graphite Research Group University of Manchester, UK Lorraine McDermott, Greg Black, Abbie Jones, Paul.

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Presentation on theme: "NGRG INGSM-14 Seattle, USA Robert Worth Nuclear Graphite Research Group University of Manchester, UK Lorraine McDermott, Greg Black, Abbie Jones, Paul."— Presentation transcript:

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

2 NGRG INGSM-14 Seattle, USA  Irradiated Graphite in the UK  Thermal Treatment at Manchester  Future Research  Conclusions

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4 NGRG INGSM-14 Seattle, USA 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 significant UK 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 NGRG INGSM-14 Seattle, USA 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) Utilise GDF 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 NGRG INGSM-14 Seattle, USA There are two dominant mechanisms by which 14 C is produced in irradiated graphite in a reactor environment: (1) 13 C (n,γ) 14 C (2) 14 N (n,p) 14 C

7 NGRG INGSM-14 Seattle, USA ~10ppm ~50ppm

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9 NGRG INGSM-14 Seattle, USA 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 14 C and 3 H behaviour Comparison of current world data to UK- irradiated graphite Optimisation of the process — Using pre- and post-treatment characterisation techniques

10 NGRG INGSM-14 Seattle, USA  Thermal oxidation has been used as a method for 3 H and 14 C 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 gasified 3 H and 14 C.

11 NGRG INGSM-14 Seattle, USA  HTO and 14 CO 2 are subsequently trapped in the bubbler system for analysis using liquid scintillation counting (LSC)  Bubblers have a trapping efficiency of 98%

12 NGRG INGSM-14 Seattle, USA Typical determined radioisotope content in Oldbury Magnox installed graphite: IsotopeActivity (Bq/g) 3H3H~ C~63700

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

14 NGRG INGSM-14 Seattle, USA  A thermal treatment programme has been designed to determine the effects of time, temperature and oxygen on 3 H and 14 C release  The following experimental conditions have been applied to samples machined from installed sets retrieved from the Oldbury Magnox power station: Time Temperature o C o C 800 o C o C-- Time Temperature o C 700 o C 800 o C 900 o C-- Argon1% Oxygen in Argon

15 NGRG INGSM-14 Seattle, USA  Issues with the integrity of the samples post-treatment: A B C D A = 800°C in 1% O 2 /Ar for 5 hours B = 700°C in 1% O 2 /Ar for 5 hours C = 700°C in Argon gas for 5 hours D = untreated sample

16 NGRG INGSM-14 Seattle, USA Hotspots

17 NGRG INGSM-14 Seattle, USA Tritium, 3 HCarbon-14, 14 C

18 NGRG INGSM-14 Seattle, USA Tritium, 3 HCarbon-14, 14 C

19 NGRG INGSM-14 Seattle, USA Sample Pre- Treatment Activity (kBq/g) Post- Treatment Activity (kBq/g) Percent Loss OM % OM % OM % OM %

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21 NGRG INGSM-14 Seattle, USA Full optimisation of thermal treatment of irradiated Oldbury Magnox reactor graphite with respect to the sensitivity of: Goal: Maximise radioisotope removal with minimal sample weight loss ‘Characterisation and Thermal Treatment of Irradiated PGA Graphite with Investigation into 3 H and 14 C Behaviour’ Temperature o C Time3 - 9 hours Oxygen content of gas % oxygen in argon

22 NGRG INGSM-14 Seattle, USA Helium-pycnometry 4 d.p. Balance Tristar BET Laser Confocal Microscopy  To try and determine:  Amount of weight loss during treatment  The typical location of the radioisotopes before removal Digital Micrometer

23 NGRG INGSM-14 Seattle, USA  To determine:  Amount of radioisotope loss during treatment  Identification of ‘hotspots’ of radioactivity, which might influence the results Liquid Scintillation Counting Gamma-spectrometry Autoradiography

24 NGRG INGSM-14 Seattle, USA Laser Confocal Microscopy (LCF)

25 NGRG INGSM-14 Seattle, USA LCF Height Mapping

26 NGRG INGSM-14 Seattle, USA LCF 3D Image

27 NGRG INGSM-14 Seattle, USA  It has been demonstrated that thermal treatment in an oxidising atmosphere is a potential means of removing 3 H and 14 C radioisotopes from irradiated graphite  The current data suggests that this treatment technique may be suitable for removing up to ~80% 3 H and ~55% 14 C from Oldbury Magnox reactor graphite  Further work will be required to optimise this thermal treatment process and to determine the mobility and origin of these radioisotopes

28 NGRG INGSM-14 Seattle, USA The authors are pleased to acknowledge EPSRC funding under agreement EP/P 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 FP

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