Recent Graphite Research at the Nuclear Science and Engineering Institute –

University of Missouri

Sudarshan K. Loyalka

Nuclear Science and Engineering InstituteParticulate Systems Research CenterUniversity of Missouri, Columbia, USA

September 16, 2014

H d We G

OR Consolidated

Codes

Tier 1: MELC

Timeline of Nuclear

Safety Technology Evolution

Integrated Code

Tier 2: Mechanistic CodesSCDAP, CONTAIN, VICTORIA

Phenomenological Experiments(PBF, ACRR, FLHT, HI/VI, HEVA)

Phebus FP, VERCORSEuropean Codes

Deterministic Bounding Analysis

Chicago Critical Pile

Probabilistic Risk Informed Analysis

Risk Informed Regulation Atomic Energy Act of 1946

(AEC) Atomic Energy Act of 1954

USS NautilusShippingport

9-11-2001 TMI-2

Chernobyl

AEC

NUREG-1150

MOX LTA

revised 1465

1940 1980

Windscale

NRC

NPP Siting Study

NUREG 1465

alternate source term

TID 14844

source term NUREG 0772

Nuclear Technology Outlook

Optimistic

Guarded

Pessimistic

NP-2010 and Gen-IV WASH

1400 Emerging Issues

MOX, High Burnup, Life Exension Environmental ConcernsGlobal Warming and

Where are we going ?

Vulnerability to Terrorism

1950 1960 1970 1990 2000 2010

The First “Source Term”

1/2( )

( ) , 17

thus for, =3000

13.2 miles

P MWthR miles

P

R

HTGRs: Source Term

Need to understand and predict: FP diffusion through the particles and graphite FP release into and plateout from the coolant Moisture and dust interactions

Introduction

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 Particle Generation

Graphite dust is produced during PBR operation

Sources of generationFuel handling systemPebble on pebble abrasion Pebble on reactor components

Graphite Dust Particle Generation

Experimental setup

Graphite Dust Particle Generation

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.

Pore Size distribution in abrated graphite powder

Publications

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.

Oxidation of nuclear graphite

To predict the oxidation rate of nuclear-grade and matrix-grade 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

Objectives

Arrhenius equation and Ea

In the chemically-controlled Regime I of graphite oxidation,

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.

reaction velocity constant

apparent activation energy

pre-exponential factor

reaction order

reaction rate

Oxidation rate of IG-110 and NBG-18 from TGA data (600 to 1600°C)

Distribution of Oxidized Layer

There is a strong correlation between density of nuclear graphite and its physical and mechanical properties.

rod orientation

Surface of rod

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.000.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

NBG-18 IG-110

Distance from surface (mm)

Den

sity

(g/

cm3)

1.85 g/cm3 NBG-18 bulk

density

1.77 g/cm3

IG-110 bulk density

IG-110 and NBG-18, pure and oxidized in 100% air at 1023

K

PureNBG-18

PureIG-110

OxidizedNBG-18

Oxidized IG-110

Conclusions on IG-110 and NBG-18

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

Matrix-grade graphite oxidation

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).

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

“A3 recipe”

64 wt% natural graphite

20 wt% resin binder

16 wt% petroleum coke graphite

Nuclear- vs matrix-grade graphite oxidation studies

800 1000 1200 1400 1600 1800 20000

0.1

0.2

0.3

0.4

0.5

0.6

IG-110 NBG-18 GKrS

Temperature (K)

Oxi

dati

on r

ate

(g/h

r/g)

Publications

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.

Particle Deposition Experiments

TEM Images of Carbon, Silver, Palladium and Gold Nanoparticles

Carbon

Silver

Gold

Palladium

J Nanopart Res (2011) 13:6591–6601 6599

1 3

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

Thermophoretic Nanoparticle Deposition Cell

Outlet

Aluminum rod in ice cold water

Small notch to position TEM copper grid

Inlet: Argon gas with particles at higher temperature

CFD computations for thermophoretic deposition

Simulated experiment of Romay et. al. – NaCl particles in dry air Case 1: 100 nm particles Case 2: 482 nm particles

Cross-sections of two different meshes used in this computation

96.5 cm

0.4

9

cm

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.

mesh with 2,066,400 volume cells

mesh with 7,029,360 volume cells

Boundary conditions

Adsorption of fission products on graphite

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,

…

Adsorption of fission products on graphite

Review of iodine literature published in Progress of Nuclear Energy (Volume 73, May 2013, Pages 21-50)

Summary of the graphites reviewed in the paper:

Adsorption of fission products on graphite

Some data for high temperature adsorption on graphite from the review.

1073 K Isotherm 1273 K Isotherm

Iodine Adsorption

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)

Develop models from newly acquired data: Isotherm Models Polanyi Potential Adsorption Kinetics (if

possible)

Electrodynamic balance (EDB) for single particle adsorption experiments.

Packed bed-tube furnace experiment for bulk adsorption measurements.

Diffusion of Fission Products in Graphite

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.

Experimental Setup

Results

Q (kJ/mol) D0 (m2/s) D (800oC) D (1150oC) D (1600oC)

Russia 193 5.3x10-4 2.14x10-13 4.37x10-11 2.20x10-9

USA/FRG 154 5.3x10-9 1.69x10-16 9.57x10-15 2.69x10-13

Offermann 164 1.0x10-8 1.04x10-16 1.18x10-14 2.67x10-13

Present Work 1 1.03x10-15 Present Work 2 1.67x10-15

Samples were annealed for 4 days at 1150o C.

6.8171 erfc 11781.0C x x

35.8023 erfc 17415.6C x x

Publications

Thomas R. Boyle, et al., "Measurement of Silver Diffusion in VHTR Graphitic Materials." Nuc .Tech. 183(2) (2013) 149-159.

Fission Product Condensation on Graphite

VHTR aerosols are not nicely shaped for computations

Jagged shapes

Agglomerations

Porous MaterialsR. 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..

Problem:

Problem—Approximations

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 removalPlays important role on sustainability of structural integrity of materials over long period.

▪ Adhesionroughness may affect adhesion of particles to surfaces due to reduced contact areaAdhesion force is critical in understanding re-suspension of particles under LOCA

Adhesion Force- AFM

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;

Experimental Matrix

Surface Characterization

Figure 1.: AFM images, (a)Mica as benchmark, (b) Hastelloy X polished, (c) Hstelloy X 5 min oxidation, (d) 10 min oxidation, (e) 15 min oxidation.

Adhesion Force Measurements

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 XSurfaces of Different Conditions. Approach-Retract Rate is 1.7848 μms−1.Substrate Location 1 Location 2 Location 3

Fadhesion

(nN)

W

(mJ/m2)

Fadhesion

(nN)

W

(mJ/m2)

Fadhesion

(nN)

W

(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 1.30Adhesion 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

(nN)

W

(mJ/m2)

Fadhesion

(nN)

W

(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

Adhesion Force Measurements Conclusion 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.

Publications

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.

Dust Transport: Role of Charge 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.

Effects of Charge on Kernel

1,

,,

qpeqp

qp

qpe

qp

qp,1

,

,

qpqp ddkT

pqe

0

2

, 2

.

Attraction

Repulsion

qpjiji

qp ,,,

, Kernel

Test Problem 2 Size and Charge

Measurements

Unknown distribution

Transfer function

Spark generator

Sampling probe

2

1~

2

1~

2

1~

2

1~

12,,,

~

,,,

1

10

*11

max

ppp

pp

n

naeppepsp

ZZZ

ZZ

QndnZndQdne

e

Emissivity (role of graphite dust)

Hastelloy X and N and Nickel

Acknowledgements

Grad Students/Post Docs

F. De-La-Torre Aguillar

Sunita BodduMatthew A. BoraasTom Boyle Sean BranneyShawn CampbellSergio CorreraAndrew GordonRajesh GuttiPaul HardenJo Jo LeeLeroy LeeRay Maynard

Ryan MeyerNaphtali MokgalapaShawn NelsonGiang Nam NguyenJohn PalsmeierMichael ReinigMatthew SimonesJohn-David SeeligZeb SmithLynn TiptonRaymond TroyKyle WaltonNathan WhiteJason Wilson

Faculty

Tushar Ghosh – Professor & Director of Graduate Studies

Sudarshan Loyalka - Curators’ ProfessorFellow: ANS, APS; PE

Mark Prelas - Professor & Director of ResearchFellow: ANS; PE

Robert Tompson - Professor Dabir Viswanath - Emeritus Professor & Chair

of ChEFellow: AIChE; PE

Funding by U.S. Department of Energy U. S. Nuclear Regulatory Commission andU.S. Department of Education

NERI-C , VHTR Consortium, NSEI lead (with NCSU and MST) , 2007-2013, NERIC-08-043

Infrastructure for FP/Aerosol Transport, 2010-

Computations for Aerosol and FP transport, 2011-2014, NEUP -964

Adsorption/Diffusion of FP in Graphite, 2011-2015, NEUP-2982

Measurements and Modeling of Emissivity (2014-2017), NEUP-6282

Graduate Fellowships (NRC), GAANN (DOEd)