Recent Progress in Helium-Cooled Ceramic Breeder (HCCB) Blanket Module R&D and Design Analysis

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Recent Progress in Helium-Cooled Ceramic Breeder (HCCB) Blanket Module

R&D and Design Analysis

Ying, Alice

With contributions fromM. Narula, H. Zhang, D. Papp

FNST Meeting August 12-14, 2008

UCLA

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HCCB Blanket Module Design

RAFS FW with He coolant channels

He purge gas pipe

Be (Be12Ti) pebbles

Ceramic breeder pebbles

Cooling plateHe coolant manifolds

for FW/Breeding zones

Helium (~8 MPa) coolant operating (350C-500C)

Low pressure (0.1-0.2 MPa) helium/%H2 purge gas to extract tritium

HCCB TBM module (710 389 510 mm)

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SummarySummary

• Efforts are being carried out in the following areas:– Utilizing the strain dependent thermo physical

characteristics of Be pebble beds for tritium performance optimization

– Investigate the creep failure of Li2TiO3 pebbles at high temperatures (as a part of thesis research for a master degree)

– Perform tritium permeation analysis for purge gas flow design (as a part of thesis research for a master degree)

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Strain dependent thermo physical property on tritium performance optimization

• The amount of the allowable beryllium in a breeding zone is limited by a maximum operating temperature of 600C

• The effective thermal conductivity of a Be pebble bed depends on:

keff = f(T, , )

Analysis method: neutronics and coupled thermo-fluid and thermo-mechanics analysis

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The trend of analysis is to incorporate a CAD model with various physics simulation codes

Be pebble bed zones

Breeder zone and associated coolant panels

FW coolant CAD model

Major parts of a 1/5th model of the HCCB module CAD model

6Fe structure HeBe Li2TiO3

This CAD model was translated to a MCNP model input using MCAM (developed at ASIPP) for Neutronics analysis

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Overall temperature distributions in a Neutronics module are in the lower end of the allowable

temperature windows A look-alike test blanket module due to a lower neutron wall load of ITER as compared to that of a typical DEMO value

ITER 0.78 MW/m2

DEMO 2- 3 MW/m2

Be pebble bed strain profiles at 1 cm away from the back of the FW. Top: first iteration; bottom: second iteration.

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Impact on Design

1st Iteration 2nd Iteration 3rd Iteration

Keff increases as temperature and strain increase Be zone temperature

The effective thermal conductivity (near the FW region) increases from 2.25 to 5.8 W/m2K during the first iteration and decreases to 5.4 W/m2k at the second iteration; while the maximum temperature decrease of 43C at the first iteration and 1C at the second iteration.

This amount of temperature difference attributes to an additional 20% of Be added into the front zone region, where neutron multiplication can be enhanced.

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High temperature creep study for Li2TiO3 pebbles

Properties Li2TiO3

Density (g/cm3) 3.189

Porosity % 16

E young (GPa) 200.6

Coeff. Poisson ν

0.27

Tensile strength (MPa)

139

Compressive Strength

(MPa)1113

Conductivity (W/mK) at 298

K3.28

Li2TiO3 = 1.8 - 2 mm

All pebbles was checked at SEM to evaluate surface irregularities, cracks and shape before the tests

linear velocity-displacement transducer (LVDT)

Error < 0.1 μm

Deadweights to provide a

compressive load

Pebble under test

The tests were performed at:Temperature: 700, 800, 950 °C ;Load: 8, 16, 24, 30 N.

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SEM Images of deformed pebbles

Pebble after 4h deformation at 800C, under 16N load (left)

Pebble, cracked after 15hrs deformation at 800C under 20N load (right)

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Creep Failure Map (JAERI LiCreep Failure Map (JAERI Li22TiOTiO33 pebbles) pebbles)

Loading pressure (MPa)Ave

rag

eco

nta

ctfo

rce

s(N

)

0 2 4 6 8 100

10

20

30

DEM results

y = 3.413 x

Force distribution at contact under an applied loading of 2.0 MPa

The forces exerted on the pebbles during the operation should be less than 15 N; or the pressure applied to the pebble bed from containing structural less than ~ 5 MPa.

Preliminary finding

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Experiments provided time dependent deformation data for pebble creep deformation rate derivation (in progress)

Deformation along the axial direction

800C, 8N load

An FEM model was developed to predict the behavior of pebbles at high temperature under compressive loads.The material behavior was assumed to follow the general power-law rule:

nTBAet

/

Creep deformation rate is needed for the pebble bed thermo-mechanics analysis

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Tritium permeation analysis for purge gas flow design

Purge gas velocity profiles

breederbreeder

structure

coolant

Purge gas in

Neutronics (nuclear heating & tritium production rate) Fluid flow (velocity profile) Heat transfer (temperature)Tritium transport (permeation)

Purge gas out

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Tritium concentration profiles in various parts

Purge gas in

in Li2TiO3 bed

in He coolant in Structure

Purge gas out

4 3 2 1x10-5

Experiments are being conducted to validate numerical calculations:- blanket relevant pressure regime - with purge gas flow

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Some experimental results concerning pressure dependence on permeation

T = 673K, P0=13Pa, 6.65Pa, 1.3Pa

0 3600 7200 10800

0

1

2

3

4

5

Pdriving

= 5Torr = 665PaTemp = 623K

Exp1 Exp2 Cal. p=0.5 Cal. p=0.5 shift

Pre

ssur

e(P

a)

Time(s)

Compare with Calculation, P0=665Pa, T=623K, it is a good match with the Experimental result

T = 723K, P0=13Pa, 6.65Pa, 1.3Pa

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22

22

2/12/12/1

0

exp)1(2

6)()(

n

nt

td

nD

nD

dPp

D

dPpt

d

PpdttJtQ

The total amount of gas which has permeated after time t is

J( t) DK sp

1/ 2

d1 2 ( 1)n exp D

n2 2

d2t

n1

D is the diffusion coefficient, Ks is its Sieverts’ constant. P = DKs is the permeability of the material

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Experimental set-up underway to study the effect of velocity profile on tritium permeation