Presentation on theme: "Nuclear Graphite Research Group University of Manchester, UK"— Presentation transcript:
1 Nuclear Graphite Research Group University of Manchester, UK Robert WorthNuclear Graphite Research GroupUniversity of Manchester, UKCharacterisation and Thermal Treatment of Irradiated PGA Graphite with Investigation into 3H and 14C BehaviourLorraine McDermott, Greg Black, Abbie Jones,Paul Mummery, Barry Marsden, Anthony Wickham14th International Nuclear Graphite Specialists MeetingSeattle, USA15th-18th September, 2013
2 Overview Irradiated Graphite in the UK Thermal Treatment at Manchester Future ResearchConclusions
4 UK Graphite legacyGraphite has been used in nuclear power plants worldwideHistorically, the UK has constructed many graphite-moderated reactorsThese include power production, plutonium production and research reactorsSome still operationalGraphite contributes to a significant UK waste legacyThe majority of this graphite waste is ILWConsequently, dismantling and management of radioactive graphite waste is an important issue in the UKMore than 100 NPP worldwide~96,000 te in UK, ~250,000 te worldwide44 graphite reactors in UK
5 Why treat graphite?There is no current disposal route for irradiated graphite in the UKGeological Disposal Facility (GDF)?Treatment of irradiated graphite could allow reduction in the volume of ILW (cost-saving)Utilise GDF spaceAllow disposal in current near-surface facilitiesThis could be achieved by preferential removal of radioisotopes, such as tritium and carbon-14Goal: Maximise radioisotope removal with minimal weight loss
6 Carbon-14 formationThere 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 Historically difficult to determine nitrogen content of graphite Nitrogen sensitivity~50ppm~10ppmHistorically difficult to determine nitrogen content of graphite
9 Thermal treatmentA 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 oxygenInvestigation of 14C and 3H behaviourComparison of current world data to UK-irradiated graphiteOptimisation of the processUsing pre- and post-treatment characterisation techniques
10 Isotopic inventory determination Thermal oxidation has been used as a method for 3H and 14C determinationGraphite samples are placed in a ceramic combustion boat in a Carbolite® MTT FurnaceA suitable cover gas flows past the sample and the temperature is raisedA copper oxide catalyst promotes further oxidation of any gasified 3H and 14C .Analysis done in duplicate
11 Isotopic inventory determination HTO and 14CO2 are subsequently trapped in the bubbler system for analysis using liquid scintillation counting (LSC)Bubblers have a trapping efficiency of 98%Analysis done in duplicate
12 Isotopic inventory determination Analysis done in duplicateTypical determined radioisotope content in Oldbury Magnox installed graphite:IsotopeActivity (Bq/g)3H~3740014C~63700
13 Isotopic validationHow 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 furnace3H recovery in the range of 88 – 98 %14C recovery in the range of 85 – 94 %LSC quenched standard analysis to ensure LSC efficiencyLSC 3H quenched LSC standards 99%. 14C quenched LSC standards 100%.
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 releaseThe following experimental conditions have been applied to samples machined from installed sets retrieved from the Oldbury Magnox power station:Argon1% Oxygen in ArgonTimeTemperature45678600oC--700oC800oC900oCTimeTemperature45678600oC700oC800oC900oC--Comparison of i-graphite samples pre and post treatment,A = 800°C 1% O2/Ar for 5 hours, B = 700°C 1% O2/Ar for 5 hours, C = 700°C in Argon gas for 5 hours and D = untreated sampleSample D in figure 23 is the untreated material, it can clearly been seen in the photograph that the effects of a 1% O2 environment at 800°C has had on the material structure. All samples analysed at 800°C in 1% O2 gas become heavily eroded and had a powered surface texture. This affected post thermal treatment analysis handling and unfortunately impacted on the tests that were able to carry out on these samples.
15 Thermal Treatment Experimental programme Issues with the integrity of the samples post-treatment:A B C DComparison of i-graphite samples pre and post treatment,A = 800°C 1% O2/Ar for 5 hours, B = 700°C 1% O2/Ar for 5 hours, C = 700°C in Argon gas for 5 hours and D = untreated sampleSample D in figure 23 is the untreated material, it can clearly been seen in the photograph that the effects of a 1% O2 environment at 800°C has had on the material structure. All samples analysed at 800°C in 1% O2 gas become heavily eroded and had a powered surface texture. This affected post thermal treatment analysis handling and unfortunately impacted on the tests that were able to carry out on these samples.A = 800°C in 1% O2/Ar for 5 hoursB = 700°C in 1% O2/Ar for 5 hoursC = 700°C in Argon gas for 5 hoursD = untreated sample
21 Future work - phd‘Characterisation and Thermal Treatment of Irradiated PGA Graphite with Investigation into 3H and 14C Behaviour’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 lossTemperatureoCTime3 - 9 hoursOxygen content of gas% oxygen in argon
22 Pre- & post- treatment analysis Weight Loss4 d.p. BalanceMetrologyDigital MicrometerPorosityHelium-pycnometrySurface AreaTristar BETLaser Confocal MicroscopyTo try and determine:Amount of weight loss during treatmentThe typical location of the radioisotopes before removal
23 Pre- & post- treatment analysis Radioactive ContentLiquid Scintillation CountingGamma-spectrometryAutoradiographyTo determine:Amount of radioisotope loss during treatmentIdentification of ‘hotspots’ of radioactivity, which might influence the results
27 ConclusionsIt has been demonstrated that thermal treatment in an oxidising atmosphere is a potential means of removing 3H and 14C radioisotopes from irradiated graphiteThe current data suggests that this treatment technique may be suitable for removing up to ~80% 3H and ~55% 14C from Oldbury Magnox reactor graphiteFurther work will be required to optimise this thermal treatment process and to determine the mobility and origin of these radioisotopes
28 acknowledgmentsThe authors are pleased to acknowledge EPSRC funding under agreement EP/P113315A 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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