Radiation Damage in Nuclear Graphite ... Graphite moderated reactors ¢â‚¬¢ > 80% current UK nuclear reactors

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  • School of something FACULTY OF OTHER

    School of Process and Chemical Engineering FACULTY OF ENGINEERING

    Radiation Damage in Nuclear Graphite

    Helen Freeman

    Institute for Materials Research

    pmhmf@leeds.ac.uk

    Sponsors:

    mailto:pmhmf@leeds.ac.uk

  • • Introducing graphite as a neutron moderator

    • What happens to graphite in a nuclear reactor?

    • Radiation damage through the length scales

    • Nanoscale – dislocations

    • Microscale – cracks and pores

    • Future of graphite moderated reactors

    • Summary

    Content

  • Graphite moderated reactors

    • > 80% current UK nuclear reactors

    • Graphite:

    • Moderates neutron energy

    • Accommodates fuel and control rods

    • Cooled by CO2 coolant

    • Low atomic weight

    • Low thermal neutron absorption cross

    section

    • High scattering cross section

    • High thermal conductivity

    • Low thermal expansion coefficient

  • Graphite moderated reactors

    • Other important properties:

    • Can be machined into intricate shapes

    • Very high melting point (4027 °C)

    • Very resistant to thermal shock

    • Provide large heat sink in case of thermal

    transients

    Theoretical carbon phase diagram

    • Challenges

    • Irradiation induced dimensional change

    (up to 8%)

    • High anisotropy

    • Radiolytic and thermal oxidation (in

    air/CO2 coolant/T>500°C

    • Longer lifetime for new reactors

  • Graphite moderated reactors

    Fuel rods Control rods

    Coolant channel

    Graphite core

    Nuclear reactor

    Electron micrograph

    Uranium

    fission

    High energy

    neutrons

    High energy

    neutrons

    released from

    fission events

    Neutrons bombard the

    graphite moderator and

    transfer energy

    Changes in strength,

    porosity, dimension etc.

    (002) planes

    (002) planes

  • Energy demand vs. reactor closure

    • EDF Energy 4 new EPRs (6.4GW) at Hinkley Point in Somerset and Sizewell in Suffolk.

    • Hitachi Ltd 2 or 3 new nuclear reactors at Wylfa on Anglesey and the same at Oldbury

    • NuGeneration up to 3.6GW of new nuclear capacity at Moorside, near Sellafield.

    https://www.gov.uk/government/policies/increasing-the-use-of-low-carbon-technologies/supporting-pages/new-nuclear-power-stations

  • • It is increasingly recognised that

    existing “mechanistic” models do not

    fully explain the observed behaviour

    of graphite in these reactors. There

    are substantial gaps in understanding,

    which have become apparent.

    • The consortium investigated

    irradiation induced dimensional

    change, creep, and other property

    changes using various

    complementary characterisation

    techniques.

    Fun.Graphite

    www.nuclear-graphite.org.uk

  • • Nanoscale (0.1 to 100 nm)

    • TEM, EELS, FIB, SEM, SPM, SANS,

    Raman, XRD

    • DFT, MD, kMC, Ab initio modelling

    • Microstructure (100nm-10micron)

    • XRD, Raman, EELS, tomography

    • Dislocation theory

    • Crystallite scale (10μm to mm)

    • XRD, EELS,

    • DFT, FE modelling

    • Macroscopic (Component) modelling:

    (mm to m)

    • FE modelling

    Fun.Graphite

    http://www.nuclear-graphite.org.uk/about/

  • Manufacture

    2.3 mm

    Removes

    volatiles

    HCs

    Extrusion:

    Alignment of

    filler particles

    Shrinkage

    Crystal

    growth,

    diffusion and

    annealing

    “Filler”

    “Binder”

  • Manufacture

    2.3 mm

    1. Filler

    2. Binder

    3. Voids

    Voids arise during

    manufacture and

    operation.

    (T / F gradients, CTE

    anisotropy, internal

    stresses)

  • Atomistic model of neutron damage NANOSCALE: BONDING AND DENSITY ANALYSIS

    The cascade model

    A 1 MeV neutron

    produces ca. 500 atomic

    displacements

    vacancy

    interstitial

    PKA = primary knock on atom

    neutron

    SDG = secondary displacement group

    PKA

    SDG

    SDG

    A= 12 (carbon)

    neutron

    energy

    transferred

    energy

  • Atomistic model of neutron damage NANOSCALE: BONDING AND DENSITY ANALYSIS

    vacancy

    interstitial

    PKA = primary knock on atom

    neutron

    SDG = secondary displacement group

    PKA

    SDG

    SDG

    Problems:

    • Assumes flat graphite layers

    • No quantitative fit with experiment for dimensional change

    • First principles calculations show that interstitial is much

    less mobile than thought

  • Atomistic model of neutron damage NANOSCALE: BONDING AND DENSITY ANALYSIS

    Multiple basal plane dislocations

    Single vacancies and interstitials

    Di-vacancies and interstitials

    Prismatic dislocation loops

    Basal/edge dislocation

    Stone-Wales defect

    Screw dislocation

    Stacking faults

    Ruck and tuck

    Voids

    Heggie et al. J. Nuc Mat 413(3) (2011)

    Trevethan et al. Phys. Rev. Let. 111(9) (2013)

  • Quantification of radiation damage NANOSCALE: BONDING, DENSITY AND DISLOCATION ANALYSIS

    Transmission Electron Microscopy

    Electron energy loss spectroscopy

    Selected Area Electron Diffraction

    EFTEM ratio map

    002 graphite planes

    In-situ TEM

  • High voltage

    Accelerated electrons

    High energy

    electrons

    Small wavelength

    High resolution

    Image from the Super-STEM

    facility, UK

    TEM facility at Leeds

    Transmission Electron Microscopy

    λ(light) 400 – 750 nm

    λ(e-) 1 – 4 pm

    http://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=yQhzLduqiO7oYM&tbnid=kOWSBQZpzHfJ_M:&ved=0CAUQjRw&url=http://www.phy.cuhk.edu.hk/centrallaboratory/TecnaiF20/TecnaiF20.html&ei=kFZ1UbzGIPTJ0AWu0oH4BQ&bvm=bv.45512109,d.ZWU&psig=AFQjCNF7_1Rhrn2304DV_vJL5AncOe2Pqw&ust=1366730760968899

  • Quantification of radiation damage TRANSMISSION ELECTRON MICROSCOPY

    5 nm5 nm

    5 nm

    5 nm5 nm

    5 nm

    5 nm5 nm

    5 nm

    200 kV 200 kV 200 kV

    (002) Graphite planes (002) Graphite planes (002) Graphite planes

    5 nm5 nm

    5 nm 5 nm

    5 nm5 nm

    5 nm 80 kV 80 kV 80 kV

    (002) Graphite planes (002) Graphite planes (002) Graphite planes

    1.3 x 1020 e- cm-2 5.1 x 1020 e- cm-2 3.3 x 1021 e- cm-2

  • Quantification of radiation damage

    2D image analysis and 3D image

    reconstruction and modelling of

    Pyrocarbons

  • Transmission electron microscopy NANOSCALE: 002 FRINGE ANALYSIS

    Mironov & Freeman. Carbon 83 106 – 117(2015) | Image analysis software courtesy of ‘PyroMaN’ research group – University of Bordeaux

    (002) Graphite planes

    (002) Graphite planes

  • Mironov & Freeman. Carbon 83 106 – 117 (2015) | Raynal et al. Proc. Int. Carbon conf. (2010)| Campbell et al. Carbon. 60 410-420 (2013).

    1

    1.02

    1.04

    1.06

    1.08

    1.1

    1.12

    1.14

    0 2 4 6 8 10

    T o

    rt u

    o si

    ty , τ

    Fringe length, L2 (nm)

    0.09 dpa

    0.45 dpa

    Transmission electron microscopy NANOSCALE: 002 FRINGE ANALYSIS

  • 20

    Selected area electron diffraction NANOSCALE: 002 FRINGE ANALYSIS

    Electron

    beam

    Electron diffraction  Young’s double-slit experiment

  • 21

    Selected area electron diffraction NANOSCALE: 002 FRINGE ANALYSIS

    Software courtesy of Anne Campbell, Oak Ridge National Lab, USA

  • Transmission electron microscopy NANOSCALE: 002 FRINGE ANALYSIS – INSITU HEATING

    0 min 10 mins 20 mins

    100 °C (002) Graphite planes

    0min 200C 5 n m5 n m

    200 °C (002) Graphite planes

    10min 200C 5 n m5 n m

    5 n m5 n m 20min 200C

    400 °C (002) Graphite planes

    Images courtesy

    of University of

    York in-situ TEM

    facilities

    200 kV

    electron

    beam

    exposure

    Literature* quotes the migration energy of a single vacancy

    is 1.2 eV, i.e. mobile at temperatures above 100-200 °C

    * C. Latham, et al., J. Phys. Condens. Matter 25, 135403 (2013).

    * T. Trevethan, et al., Physical Review Letters 111 (9), 095501 (2013)

  • Transmission electron microscopy NANOSCALE: 002 FRINGE ANALYSIS – INSITU HEATING

    t = 0 t = 14 min

    0.001

    dpa /s

  • Electron Ene