Graphite Irradiated
Lifetime Failure
Analysis Framework
21/8/2017
D.N Wilke, S. Kok
University of Pretoria
M.P. Hindley
USNC africa

7/7/2017 / 2 © USNC 2017
• Introduction
• Irradiated material model models
• Fluence end Temperature requirements
• Obtaining the software
• Available data
• Quick demo
• Failure criteria
• Concluding remarks
Outline

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Fluence and temperature gradients
Criteria for selection
of blocks:
• Maximum
temperature
gradients
• Maximum fluence

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The total strain in the material is
the sum of the following:
• Elastic strain
• Linear dimensional change
strain due to irradiation
• Primary and secondary
irradiation induced creep
• Thermal strain
• This needs to be implemented
in finite element analysis code
since values are different at
each location
Constitutive equations for irradiated graphite
Stress in the material

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Material model dependant on avaiable data

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Data currently used
• Gerd Haag, “Properties of ATR-2E Graphite and Property Changes due to Fast Neutron
Irradiation”, Institut für Sicherheitsforschung and Reaktortechnik, Forschungszentrum
Jülich
• Provided as a sample in Excel spreadsheet (headings of spreadsheet are important)
• Use your own data! (contribute to open source by uploading data onto GitHub)
Temperature(C) Fluence(dpa) LinearDimensionalChangesDl/l0(%)(unstressed) LinearDimensionalChangesDl/l0(%)(stressed) CreepStrainTensile & Compressive(%) TotalCreepStrain(%)
550 0,29 -0,07 -0,18 -0,11 0,11
550 0,41 -0,1 -0,21 -0,11 0,11
550 0,54 -0,15 -0,24 -0,09 0,09
550 1,66 -0,34 -0,56 -0,22 0,22
550 2,02 -0,42 -0,65 -0,23 0,23
550 2,21 -0,38 -0,61 -0,23 0,23
550 2,34 -0,49 -0,73 -0,24 0,24
550 2,38 -0,44 -0,77 -0,33 0,33
550 2,52 -0,56 -0,82 -0,26 0,26
550 2,67 -0,55 -0,77 -0,22 0,22
550 2,76 -0,56 -0,87 -0,31 0,31
550 3,92 -0,82 -1,26 -0,44 0,44
550 4,9 -1,06 -1,49 -0,43 0,43

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Software packages
Software is GNU v3 license and can be obtained from (GitHub repository)
• https://github.com/makkemal/NGIMASEM
• http://gitextensions.github.io/ (Tool for managing changes on GitHub)
Requirements
• Python anaconda with python 2.7 environment created
(https://www.anaconda.com/download/ )
• FEM packages (Code written to be FEM solver independent, it can fit into any FEM
solver )
–ANSYS (commercial verified and validated FEM code USNC will release a regulator qualified
version )
–CalCuliX (open source http://www.dhondt.de/ for academic use )
FreeCad 0.17 (open source pre post processor for CalCulix https://freecadweb.org/)

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Demo (Jupyter Notebook)

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ASME Section III DIV 5 Section HH Graphite Simple
Failure Methodology
• Simple assessment uses standard two parameter Weibull equivalent stress
• Allowable limits
–10-2
–10-3
–10-3
1
exp( )
m
n
i
sV
i c
P dv
S


 
   
 

1 exp( )
m
f V
cV
P dV
S
 
    
 

dv, i Chain
1
1 exp
m
n
j
fV j
i c
P V
S


   
    
   

1 exp( )
m
t
f
c
P dv
S
 
    
 
dv

dv
( , , ) 1
m
t
cS
t cF S m e


 
  
 
 

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ASME Section III DIV 5 Section HH Graphite Full Failure
Methodology
Group volumes
IL
IIL
v 
Equivalent stress sorted
0
0
m
v
i
c
S
X
S S
 
  
 
part I II IIIL L L L   
1 partL
The Probability of Survival (PoS) of
the part as a whole:
The Probability of Failure (PoF) is
then calculated as:1 1
, ,
I II
I
i i
i i
I IIi i
n n
n
V V
X X
V V
I IIL Le e  
  
     
     
 
 
PoS for each subgroup:
.
The modification to the Weakest Link Model essentially prescribes a minimum link size for
each link. This is achieved by grouping volumes of material experiencing a similar stress
state to form links (link volume).

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Lifetime analysis
Initial analysis show
all components
acceptable safe in
expected operating
conditions

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Concluding remarks
• This work presents a graphite simulation and analysis framework witch is open and free
for anyone to use commercially or academically
• This is a work in progress and by no means complete (no piece of software is ever
complete)
• The software is aimed at design using the ASME codes and standards as base
requirements.
• USNC will release a regulator qualified version in ANSYS

7/7/2017 / 13 © USNC 2017
Michael P Hindley PhD PrEng
Michael.Hindley@usnc.com
Questions on this work only !