Sudarshan K. Loyalka
Nuclear Science and Engineering Institute
Particulate Systems Research Center
University of Missouri, Columbia, USA
September 16, 2014
Tier 1: MELC
Integrated Code
H
d We G
ORConsolidated
Timeline of Nuclear
Tier 2: Mechanistic CodesSCDAP,
CONTAIN, VICTORIA
Codes
Safety Technology
Phenomenological Experiments(PBF,
ACRR, FLHT, HI/VI, HEVA)
Evolution
Phebus FP,
VERCORSEuropean Codes
Deterministic Bounding Analysis
Probabilistic Risk Informed Analysis
Chicago Critical Pile
Atomic Energy Act of 1946 (AEC)
Risk Informed Regulation
Atomic Energy Act of 1954
USS NautilusShippingport
TMI-2
AEC
9-11-2001
Chernobyl
NUREG-1150
MOX LTA
revised1465
1940
1950
1960
1970
Windscale
1980
NRC
1990
NPP Siting Study
2000
2010
NUREG 1465
alternatesourceterm
TID 14844
NUREG 0772
source term
Nuclear Technology Outlook
NP-2010 and Gen-IV
WASH 1400
Optimistic
Guarded
Pessimistic
Emerging Issues
MOX, High Burnup, Life Exension
Environmental ConcernsGlobal Warming and
Where are we going ?
Vulnerability to Terrorism
 P ( M W th ) 
R ( m iles )  

17


thus for, P =3000
R  13.2 m iles
1/ 2
,
Need to understand and predict:
 FP diffusion through the particles and graphite
 FP release into and plateout from the coolant
 Moisture and dust interactions

Renewed interest in graphite-fueled reactors

Need for measurement of modern nuclear graphite
properties and interactions

Research areas:
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
HTGR source term issues
Graphite dust particle generation
Graphite oxidation
Adsorption of fission products on graphite
Fission products diffusion in graphite
Fission products transport to aerosols
Dust adhesion to surfaces
Dust re-suspension
Coagulation
Emissivity
 Graphite dust is produced during
PBR operation
 Sources of generation
 Fuel handling system
 Pebble on pebble abrasion
 Pebble on reactor components
Experimental setup
Surface area and Sliding Distance
Surface properties of graphite samples
* Data from nitrogen adsorption at 77 K. The BET surface area is calculated using the
Brunauer - Emmett - Taylor equation. The total pore volume is measured at maximum
nitrogen pressure.
R. Troy, R. Tompson, T. Ghosh, and S. Loyalka,
"Generation of graphite particles by
rotational/spinning abrasion and their
characterization," Nuclear Technology, vol. 178,
(2012) 241-257 .
A Paper on sliding friction is to appear in
Nuclear Technology (2014-15). Others on
nuclear graphites in preparation.
Objectives
To predict the oxidation rate of nuclear-grade and matrixgrade graphite under various air ingress accident
conditions for VHTR
Study the oxidation attack mechanism
Characterize the surface and microstructural changes
Model the oxidation rate in air using the Arrhenius equation
In the chemically-controlled Regime I of graphite oxidation,
reaction rate
pre-exponential factor
apparent activation energy
reaction velocity
constant
reaction order
Ea , A and n are determined experimentally. The slope of
the mass loss plot = - Ea/R, where R is the ideal gas
constant.
From collision theory, before a reaction can occur the
molecules of reactants must have an energy of activation Ea
above their normal, or average energy.
There is a strong correlation between density of nuclear graphite and its
physical and mechanical properties.
2.50
Density (g/cm3)
2.00
1.77 g/cm3
IG-110 bulk
density
1.85 g/cm3
NBG-18 bulk
density
1.50
1.00
0.50
NBG-18
0.00
0.00
Surface of rod
1.00
2.00
3.00
4.00
Distance from surface (mm)
rod orientation
IG-110
5.00
6.00
7.00
Pure
NBG-18
Oxidized
NBG-18
Pure
IG-110
Oxidized
IG-110

IG-110 oxidized more rapidly and more uniformly
in the same experimental conditions as NBG-18

IG-110 is more porous and therefore experiences
larger increases in surface area in the kinetic
regime

ORNL manufactured GKrS by using the German A3 recipe but with modern
materials and hot pressing method (we thank ORNL for providing us with
this material).
“A3 recipe”
64 wt% natural graphite
20 wt% resin binder
16 wt% petroleum coke graphite

While nuclear-grade graphite is almost fully graphitized at temperatures
around 2800°C, matrix-grade graphite is only “partially graphitized”
<2000°C fuel fabrication temperature

Air ingress into matrix graphite can affect retention properties of the fuel
and we have shown the oxidation rate is high in the kinetic regime
0.6
Oxidation rate (g/hr/g)
0.5
0.4
0.3
0.2
0.1
0
800
1000
1200
IG-110
1400
Temperature (K)
NBG-18
1600
GKrS
1800
2000

Jo Jo Lee, Tushar K. Ghosh, Sudarshan K. Loyalka, “Oxidation rate
of graphitic matrix material GKrS in the kinetic regime for VHTR
air ingress accident scenarios,” Journal of Nuclear Materials, 451
(2014) 48-54.

Jo Jo Lee, Tushar K. Ghosh, Sudarshan K. Loyalka, “Oxidation rate
of nuclear-grade graphite IG-110 in the kinetic regime for VHTR air
ingress accident scenarios,” Journal of Nuclear Materials, 446
(2014) 38-48.

Jo Jo Lee, Tushar K. Ghosh, Sudarshan K. Loyalka, “Oxidation rate
of nuclear-grade graphite NBG-18 in the kinetic regime for VHTR
air ingress accident scenarios,” Journal of Nuclear Materials, 438
(2013) 77-87.
Silver
Carbon
Gold
Palladium
J
Nanopart Res (2011) 13:6591–6601 6599
Fig.
8 SEM images of some larger nanoparticles a1 gold, b1 silver, and c1 palladium. Energy dispersive X -ray spectra (EDS) of the particles a2 gold, b2 silver, and c2 palladium,
confirms the particles for gold, silver, and palladium, respectively
1
3
Inlet: Argon gas with particles at higher
temperature
Outlet
Small notch to position
TEM copper grid
Aluminum rod in
ice cold water

Simulated experiment of Romay et. al. – NaCl particles in dry air
 Case 1: 100 nm particles
 Case 2: 482 nm particles
96.5 cm
mesh with 2,066,400
volume cells
mesh with 7,029,360
volume cells
Cross-sections of two different meshes
used in this computation
Boundary conditions
Inlet flow velocity
4.42 m/s
Tube wall temperature
293 K
Totally four meshes (465,520, 899,160, 2,066,400, 7,029,360 volumes) were used in this study.
Objectives

Review pervious works on the adsorption of iodine to graphite.
 Examine experimental methods used in the past.
 Determine the usability of data with adsorption isotherm equations
and Polanyi's Potential.

Design and build experiments for iodine adsorption with more
accurate means for generating and measuring iodine vapor

Obtain adsorption isotherms of IG-110:
 For a single particle (up to 300 °C)
 For bulk powder (up to 1000 °C)
 Model data with for newly acquired data: isotherm models, kinetics, …
Review of iodine literature published in Progress of
Nuclear Energy (Volume 73, May 2013, Pages 2150)
 Summary of the graphites reviewed in the paper:


Some data for high temperature adsorption
on graphite from the review.
1073 K Isotherm
1273 K Isotherm

Obtain adsorption
isotherms of IG-110:
 Both single particle and
bulk powder forms
 Temperature range: Low
(room to 200 °C) and high
(300 to 1000 °C)

Electrodynamic balance (EDB) for single particle adsorption
experiments.
Develop models from
newly acquired data:
 Isotherm Models
 Polanyi Potential
 Adsorption Kinetics (if
possible)
Packed bed-tube furnace experiment for bulk adsorption
measurements.
Objectives

Characterize physical properties of the nuclear
grade graphite (i.e. density and porosity).

Determine the diffusion coefficient of silver
through nuclear grade graphite.

Model the diffusion of silver through nuclear
grade graphite.
Russia
USA/FRG
Offermann
Present Work 1
Present Work 2
Q (kJ/mol)
193
154
164
D0 (m2/s)
5.3x10-4
5.3x10-9
1.0x10-8
D (800oC)
2.14x10-13
1.69x10-16
1.04x10-16
D (1150oC)
4.37x10-11
9.57x10-15
1.18x10-14
1.03x10-15
1.67x10-15
C  x    35.8023  erfc  17415.6  x 
C  x    6.8171  erfc  11781.0  x 
Samples were annealed for 4 days at 1150o C.
D (1600oC)
2.20x10-9
2.69x10-13
2.67x10-13

Thomas R. Boyle, et al., "Measurement of
Silver Diffusion in VHTR Graphitic
Materials." Nuc .Tech. 183(2) (2013) 149-159.
Problem:
R. Troy, R. Tompson, T. Ghosh, and S. Loyalka, "Generation of
graphite particles by rotational/spinning abrasion and their
characterization," Nuclear Technology, vol. 178, pp. 241-257, 2012.
.

VHTR aerosols are not
nicely shaped for
computations

Jagged shapes

Agglomerations

Porous Materials
Z. Smith and S. Loyalka, "Numerical Solutions of the Poisson Equation:
Condensation/Evaporation on Arbitrarily Shaped Aerosols," NUCLEAR
SCIENCE AND ENGINEERING, vol. 176, pp. 154-166, 2014.
R. Troy, R. Tompson, T. Ghosh, and S. Loyalka, "Generation of
graphite particles by rotational/spinning abrasion and their
characterization," Nuclear Technology, vol. 178, pp. 241-257,
2012.
Objective:

To understand the adhesion of graphite particles and fission products (with and
without the influence of surface roughness) to reactor materials of interest Hastelloy X, Haynes 230, and Alloy 617
▪ Oxidation
Important for reactor design, safety and system analysis because it increases surface
roughness which affects emissivity and decay heat removal
Plays important role on sustainability of structural integrity of materials over long
period.
▪ Adhesion
roughness may affect adhesion of particles to surfaces due to reduced contact area
Adhesion force is critical in understanding re-suspension of particles under LOCA

Hastelloy X material surface conditions:
 Oxidized for 5, 10, and 15 min @ ~800 0C and 10 -6 torr
 As receive and polished surfaces

Mica as a benchmark (standard)

Particle of interaction:
 Graphite cluster as a particle (size ~ 6 µm ) produced in VHTR
among fission products aerosols

Conditions and parameters of interest:
 Environment – Air; Approach rate -1.7848 µm/s;
Measurements of Adhesion Force (nN) and work of energy (mJ/m2) obtained when a 6 μm diameter
Irregular Graphite Particle Probe (Approximated as a Sphere) Interacts with Graphite Sprinkled Hastelloy X
Surfaces of Different Conditions. Approach-Retract Rate is 1.7848 μms−1.
Substrate
Location 1
Location 2
Location 3
Fadhesion
W
Fadhesion
W
Fadhesion
W
(nN)
(mJ/m2)
(nN)
(mJ/m2)
(nN)
(mJ/m2)
HX polished
18.90
1.34
24.23
1.71
46.09
3.26
HX as received
14.64
1.04
13.57
0.96
27.97
1.98
HX 5min Ox
15.70
1.11
11.44
0.81
12.50
0.88
HX 10min Ox
10.90
0.77
11.97
0.85
10.90
0.77
HX 15min Ox
18.90
1.34
17.84
1.26
18.37
1.30
Adhesion Force (nN) and work of energy (mJ/m2) calculated using the JKR Theory and Assuming a Spherical
Graphite Particle witha 6 μm Diameter Estimated using Optical Microscope.
Substrate
Graphite (C)
Highly Ordered Pyrolytic Graphite
Fadhesion
W
Fadhesion
W
(nN)
(mJ/m2)
(nN)
(mJ/m2)
MICA
6849.30
484.49
12718.70
899.66
Hastelloy X
2637.30
186.55
4897.30
346.41
HOPG/Graphite
820.00
58.00
2827.40
199.99

The adhesion force was relatively small in all cases, especially,
when when compared to the theoretical values.
 Graphite particle was a cluster and not well characterize and surface asperities of
the particle where not included.
 Large difference between calculated values from JKR theory and measured
values may be due to assuming the particle to be spherical in shape.

The pikes seen during measurement may be caused by many
factors
 large loading force applied on sample by the probe.
 Interaction of particle with graphite first then with Hastelloy X or other nano-
graphite particles on the surface.

Mokgalapa, N. M., Ghosh, T. K., & Loyalka, S.
K, “Graphite Particle Adhesion to Hastelloy X:
Measurements of the Adhesive Force with an
Atomic Force Microscope,” Nuc.Tech., 186(1)
(2014) 45-59.

VHTRs generate charged aerosols during normal
operation.

All reactors can release charged aerosols during
severe accidents.

Charged aerosol behavior is complex.
 Charge effects on coagulation
 Electrostatic forces

Current codes and models are inadequate, relying on
numerical techniques which do not account for charge
effects.
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 p ,q
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 p ,q
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 p ,q
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Attraction
  p ,q
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n 1 d p  Q s 
max
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
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*
p
n e 1
Sampling probe
Spark
generator
Transfer function
Unknown distribution
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p

 


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2


~
~
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 Z p  1    
 Z p  1    
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

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
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

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
Grad Students/Post Docs
F. De-La-Torre Aguillar
Sunita Boddu
Matthew A. Boraas
Tom Boyle
Sean Branney
Shawn Campbell
Sergio Correra
Andrew Gordon
Rajesh Gutti
Paul Harden
Jo Jo Lee
Leroy Lee
Ray Maynard
Ryan Meyer
Naphtali Mokgalapa
Shawn Nelson
Giang Nam Nguyen
John Palsmeier
Michael Reinig
Matthew Simones
John-David Seelig
Zeb Smith
Lynn Tipton
Raymond Troy
Kyle Walton
Nathan White
Jason Wilson


Tushar Ghosh – Professor & Director of Graduate Studies
Sudarshan Loyalka - Curators’ Professor
Fellow: ANS, APS; PE
Mark Prelas - Professor & Director of Research
Fellow: ANS; PE

Robert Tompson - Professor
Dabir Viswanath - Emeritus Professor & Chair of ChE
Fellow: AIChE; PE






NERI-C , VHTR Consortium, NSEI lead (with
NCSU and MST) , 2007-2013, NERIC-08-043
Infrastructure for FP/Aerosol Transport, 2010Computations for Aerosol and FP transport,
2011-2014, NEUP -964
Adsorption/Diffusion of FP in Graphite, 20112015, NEUP-2982
Measurements and Modeling of Emissivity
(2014-2017), NEUP-6282
Graduate Fellowships (NRC), GAANN (DOEd)