Graphite Research

•  Why? –  Core of AGRs; irradiation damage during operation leads to weight

loss, change in dimensions & properties, stress and cracking –  Life-limiting component of reactors

•  See recent (BBC, Times) and upcoming news items

•  Current research activity –  Funded by industry (EDF), regulator (ONR), EPSRC, TSB, EU –  Plant life extension (PLEX) and future systems

•  Fundamentals of irradiation damage •  Irradiation creep (mitigating stress development) •  Strength and fracture •  Waste treatment

Irradiation damage •  FunGraph (EPSRC)

–  Fundamentals of Current and Future Uses of Nuclear Graphite –  Consortium of Huddersfield, Leeds, Manchester, Nottingham,

Salford, Surrey universities

•  Mechanistic understanding of irradiation effects –  Ab initio; kinetic Monte Carlo; dislocation models of defects –  Electron microscopy

•  Model (thick graphene) and irradiated material •  Evolution of damage in situ

–  Neutron and synchrotron x-ray studies •  Structural changes; crack and void closure; effects of loading

Range of model and irradiated materials

FunGraph  mee,ng  29th  –  31st  October  2012  Huddersfield  

Neutron  irradiated    samples  •  Manchester’s  samples  

•  Oldbury  (PGA  5dpa)  •  BEPO  channel  16  (PGA)  

•  80  kV  

5 nm5 nm5 nm5 nm

5 nm

5 nm5 nm

5 nm

FFT  filtered  

Oldbury  

Oldbury  

Oldbury  

Microstructure:  Irradiated  graphite  Irradiated  AGR  Near  surface    

120E20  EDND  Irradiated  AGR  Near  surface    

120E20  EDND  

Imaged  at  Central  Labs,  NNL  

Irradiation Creep

•  TSB-funded, EDF-lead –  Influence of Irradiation Creep on Plant Life Optimisation –  Manchester and Surrey universities –  NRG, Fraser-Nash, AMEC

•  Mechanistic understanding of irradiation creep –  Defect structures and mobility under load

•  Configuration; energies of formation –  Microstructural changes

•  Role of interfaces/boundaries –  Stress relaxation

Unbound and bound configurations of the V2,2bb interlayer di-vacancy.

Microstructure-based FE models for irradiation creep

Strength and Fracture

•  QUBE (EPSRC) –  Oxford, Bristol and Manchester universities

Microstructure-Sensitive Component-Scale Fracture Modelling

Department of Materials University of Oxford Parks Road Oxford OX1 3PH UK tel +44 1865 273700 fax +44 1865 273789 enquiries@materials.ox.ac.uk www.materials.ox.ac.uk

21 February 2013 Prof. Chris R. M. Grovenor Head of Department chris.grovenor@materials.ox.ac.uk +44 1865 273737

Re: Dr Saucedo-Mora; Applicant for a Junior Research Fellowship

To whom it may concern

Dr Saucedo-Mora joined the department in November 2012, as a postdoctoral researcher on a 3-year EPSRC funded research project "QUasi-Brittle fracture: a 3D Experimentally-validated approach". He is a self-motiviated scientist, who has fitted well into the Oxford research group, and is clearly on the track to a long-term academic career. His supervisor, Prof. James Marrow, fully supports his application for a Junior Research Fellowship. As head of department, I am happy to confirm that Materials will continue to provide Dr Saucedo-Mora with necessary laboratory infrastructure to support his work if is awarded a Junior Research Fellowship. Yours sincerely,

Prof. Chris Grovenor

6 Author name / Procedia Materials Science 00 (2014) 000–000

Fig. 5. From top to bottom the fracture pattern of the different models in the non linearity initiation, the peak load and the collapse. From left to right the FEM with 145 elements, FEM with 27950 elements and CAFE model with 5 elements, 4702 IPD and 212992 cells.

Acknowledgements

This work was carried out with the support of the UK EPSRC project “QUBE: Quasi-Brittle fracture: a 3D Experimentally-validated approach” (EP/J019992/1).

References

Arroyo, M., Ortiz, M., 2006. Local maximum-entropy approximation schemes: a seamless bridge between finite elements and meshfree methods. International Journal for Numerical Methods 65, 2167-2202.

Saucedo Mora, L., 2012. Meshfree methods applied to tensile fracture and compressive damage in quasi-brittle materials. Ph. D. Thesis, University of Castilla-La Mancha, Spain.

Saucedo Mora, L., Marrow, T. J., 2013a. 3D cellular automata finite element method to model quasi-brittle fracture. Twelfth Intentional Conference on Engineering Structural Integrity Assessment Conference proceedings, (ESIA12), Manchester, UK

Saucedo Mora, L., Mostafavi, M., Khoshkhou, D., Reinhard, C., Atwood, R., Zhao, S., Connolly, B., Marrow, T.J. 2013b. 3D cellular automata finite element (CAFE) modelling and experimental observation of damage in quasi-brittle nuclear materials: Indentation of a SiC-SiCfibre

ceramic matrix composite. Third International Workshop on Structural Materials for Innovative Nuclear Systems (SMINS-3), October 2013, Idaho Falls, USA

Shterenlikht, A., Howards, I. C., 2006. The CAFE model of fracture: application to a TMCR steel. Journal of Fatigue and Fracture of Engineering Materials and Structures 29, 770-787

Example: Fracture energy

Luis Saucedo Mora

Cellular FE model: Meshfree linking of microstructure-dependent heterogeneous model and coarse FE component model

FE (145 elements)

FE (27950 elements)

Cellular FE (5 elements, 212992 cells) EQUIVALENT COMPUTATIONAL TIME Luis Saucedo Mora

CA Model

Cellular FE Model

8

The CA model may be used as microstructure dependent input, providing properties of coarser “cells” in the Cellular FE model

Q U B E

AGR BCN

•  HSE(NII)  established  the  AGR  Brick  Cracking  Network  (AGR  BCN)  in  2008  to:  –  develop  an  improved  understanding  of  cracking  observed  in  

AGR  graphite  bricks  and  develop  a  predic,ve  capability  –  secure,  maintain  and  develop  sources  of  independent  advice  –  ensure  NII  is  well  informed  on  key  technical  issues  and  

therefore  able  to  make  sound  regulatory  decisions    •  AGR  BCN  is  a  tripar,te  programme  

–  The  University  of  Birmingham,  The  University  of  Manchester,  Health  &  Safety  Laboratory  

•  Two  aspects  under  inves,ga,on  –  crack  driving  force  parameters  (HSL  &  UoM)  –  materials  resistance  parameters  (UoB  &  HSL)  

Introduction •  Emulator approach

–  applied successfully for dimensional change behaviour •  inspection data •  constitutive equations

–  calibrated dimensional changes

•  inert similar to baseline

•  reduced effect of oxidation

Modelling approach

Calibrated curves

Metric

Design matrix

Emulator Calibrated parameters

Simulator

Calibration data

Strength and Fracture

•  Two TSB projects; both EDF-lead –  Fracture of Graphite Fuel Bricks

•  University of Manchester, EDF NG, EDF R&D

•  Modelling crack propagation in fuel bricks –  XFEM, energy release rates –  Comparison with experiment

•  Statistical models of core normal and seismic behaviour •  Mimic irradiation damage by bromination

–  No external driving forces for crack growth (cf in service) –  Criteria for crack initiation as function of local microstructure

Strength and Fracture

Tomographic image of brominated grapite

Comparison of crack paths with prediction

Strength and Fracture

–  Influence of Creep and Geometry on Strength of Irradiated Graphite Components

•  University of Manchester, EDF NG

•  Valid fracture data on irradiated material –  Large trepanned specimens at reactor end–of-life

•  Ex-Oldbury –  effects of notch geometries on properties

•  Crack initiation and propagation •  Comparison with AGR installed sets •  Thermal creep as basis for irradiation creep •  Effects of creep on mechanical/fracture behaviour