MTR Project BLACKSTONE Tjark van Staveren, NRG Steven Knol, NRG Matthew Brooking, EDF Energy September 18, 2013

Contents Graphite irradiation experiments at NRG Introduction project Blackstone Irradiation results Blackstone Phase II –Temperature → sensitivity analysis –Oxidation and weight loss –Neutron dose Development of post-irradiation characterisation techniques 2

Experiment assembly Graphite irradiation projects at NRG 3 IrradiationPost-irradiation examination Pre-irradiation examination

Graphite irradiation projects at NRG Supporting EDF Energy AGR life-time extension –BLACKSTONE: irradiation of graphite samples under oxidising conditions –ACCENT: irradiation of graphite samples under stress (V)HTR development –Multiple graphite irradiation experiments at different temperatures 4

Project BLACKSTONE Aim Expanding graphite property database to neutron doses and weight loss beyond current operation of reactors Gain understanding of graphite property changes under radiolytical oxidation 5

6 Neutron dose Weight loss AGR trepanning data Project Blackstone data Future AGR operation Project BLACKSTONE

Project Blackstone Phase I –Graphite samples from Hinkley Point B / Hunterston B –One capsule irradiated under inert conditions –One capsule irradiation under oxidising conditions –PIE successfully completed in 2011 Phase II –Graphite samples from Hartlepool / Heysham 1 –Two capsules irradiated under oxidising conditions –PIE started in

Blackstone Phase II Two irradiation capsules Targets: 7.4 and 11.0 dpa Temperature target 420°C Both contain oxidising environment (CO2/CO) Two different oxidation rates Continuous online monitoring of oxidation by analysing ingoing and outgoing gas composition 8

After irradiation (1)… 9 Beam 0M22: 57.5% weight loss 5.7 mm Tomograph GE Phoenix X-Ray Nanotom S 2.5 µm resolution for Ø8 mm graphite samples Possibility of full sample high resolution imaging Usage: –To study porosity evolution –To support destructive testing –To check homogeneity of oxidation

After irradiation (2)… 10 But first… DIC system installed in hot cell and glove box in 2013 High resolution imaging of flexural, compressive and tensile tests Next step: determination static Young’s modulus Beam 3M02: 32% weight loss

Key irradiation challenges Control of temperature: stable and on target Control of oxidation and weight loss during irradiation Neutron dose on target 11

Drum based design 24 thermocouples per capsule Primary gas flow through and around drums CO2/CO mixture Secondary gas around capsule: stationary He/Ne mixture for temperature control Oxidation is measured by gas chromatography on inlet and outlet of experiment Design principles

Thermomechanical design Principles –Heating by neutrons and gamma radiation –Temperature determined by many factors –heat input (neutron and gamma fluxes) –density of parts –thermal conductivity of parts –gas composition –gas flow –gas gap sizes Two step temperature determination approach Measured Modeled T sample = T thermocouple + dT

Thermomechanical design Quattro tube Containment tube Sample holder (aluminium drum) Outer gas gap (He/Ne mixture) Inner gas gap (He or CO 2 mixture) Gas tube Specimen gas gap (He or CO 2 mixture) Specimen Thermocouple gas gap (He or CO 2 mixture) Thermocouple dT

Finite element model Quattro tube Containment tube Sample holder (aluminium drum) Outer gas gap (He/Ne mixture) Inner gas gap (He or CO/CO 2 mixture) Specimen Thermocouple Finite element model programmed in ANSYS

Aim To assess the sensitivity / dependence of the sample temperature to all relevant parameters Determine dT using parameter set of choice A large number of parameters is varied, such as: Sample properties Properties of irradiation rig 8000 runs are performed with different sets of parameters Temperature sensitivity study Parameter value dT

Sensitivity study Description ParameterUnits Heating  [W/kg] Drum radius R drum,o [mm] Conductivity Helium k He [%] Sample radius R sample [mm] Conductivity sample k sample [W/mK] Thermal expansion sample α sample [um/mK] Sample density ρ sample [kg/m 3 ] Thermocouple density Ρ TC [kg/m 3 ] Aluminium density ρ alu [kg/m 3 ] Thermal expansion aluminium α alu [um/mK] Conductivity aluminium k alu [W/mK] Eccentric samplee sample [mm] Eccentric TCe TC [mm] dT Al conductivity Sample density

Temperature Assessment Start and end of irradiation sample temperatures are assessed Sample parameters data: –Measured data from dimensional, CTE, LFA measurements –Measured conductivity data for most samples, if not, modelled data is used Heating, adjusted based on Blackstone Phase I experience Assumption that drum shrinkage occurs early in irradiation

Excellent correlation between modelled and measured thermocouple readings Temperature Assessment

Based on measured temperature and modeled temperature difference, temperatures at BOI are slightly higher and EOI slightly lower. Weight loss affects sample temperature

Gas handling system Goal Oxidise and irradiate the specimens simultaneously Control a flow of an oxidising gas mixtures around the specimens Switch to helium during reactor start up and in case of emergency Be able to measure the concentrations of the following components: –Water, ethane, methane, CO, hydrogen, neon (reference)

Gas handling system Solution A dedicated gas handling system is built. Gas chromatographs measure concentrations at inlet and outlet of experiments A measurement is made every 15 minutes every day of the irradiation The data is analysed quickly and can be used to tune the oxidation rate Oxidation rate can be adjusted by changing gas composition or gas flow

Weight loss and neutron dose Blackstone 04 weight loss: Target was g Based on online GC data: g Based on PIE data g Blackstone 04 neutron dose: Target was > 7.4 dpa Based on online calculations: dpa Based on PIE monitor sets: dpa

Summary Succesfull irradiation of first capsule Blackstone Phase II –Temperatures within specification, more accurate determination of sample temperatures after sensitivity analysis –Neutron dose within specification –Excellent weight loss control Samples recovered from capsule 04 PIE Campaign ‘capsule 04’ started Next Phase II ‘capsule 03’ expected to be dismantled in November