Our Recent Experimental Challenges on Flibe or Flinabe ... · Our Recent Experimental Challenges on Flibe a) or Flinabe b) Coolant for Fusion Applications and Related Japanese Researches

Our Recent Experimental Challenges on Flibea) or Flinabeb) Coolant for Fusion Applications and Related

Japanese Researches

Satoshi Fukada1, Akio Sagara2, N. Yusa and H. Hashizume3

1) Advanced Energy Engineering Science, Kyushu University

2) National Institute for Fusion Science

3) Quantum Science and Energy Engineering, Tohoku University

1

IAEA WS on Challenges for coolants in fast neutron spectrum system, July 5-7, Wien

a) Flibe is 2LiF+BeF2 molten salt, and b) Flinabe is xLiF+yNaF+(1-x-y)BeF2 molten salt.

2

IAEA WS on Challenges for coolants in fast n, July 5-7, Wien 1. Advantage and disadvantages of Flibe/Flinabe for fusion reactor

blanket/coolant 1) Advantages of Flibe (2LiF+BeF2) for blanket: • Stable, no react with O2 and H2O, • Low vapor pressure (0.24Pa at 600oC), • High TBR (>1), low electric conductivity, good heat

conductivity, • High solubility for minor actinides, U and Th, • Work as coolant even under fast neutron irradiation. 2) Disadvantages of Flibe and Flinabe for blanket: • High melting point Flibe (m.p.=459oC), Flinabe

(0.31LiF+0.31NaF+0.38BeF2, m.p.=305oC), • Corrosive TF is generated in neutron irradiation. • High tritium leak through heat exchanger. • Thermal laminarization in high magnetic field.

LiF-BeF2-UF4

Coolant characteristics under irradiation Our answers to questions from the WS chair :

• (Q) Main coolants and its behavior under radiation: (A) The coolant is molten Flibe or Flinabe, which is not affected by g-ray irradiation but generates corrosive TF through 6Li(n,a)3T.

• (Q) Range of use of the coolants under irradiation (limiting constraints): (A) The range is 350oC-700oC for Flinabe (V-4Cr-4Ti) or 500oC-700oC for Flibe. The redox control to convert TF to T2 by Be is necessary. The g-ray shielding is necessary if MeV-order irradiation.

• (Q) Major issues (present state of knowledge, verification, evidence): (A) One is to reduce tritium leakage through Flibe or Flinabe. One experimental trial is to include nanoscale powder of hydrogen-absorbing metal Ti. Another one is to select primary Flinabe/secondary sc-CO2 coolant. T will be removed in a form of CT4 in CO2.

• (Q) Which coolant is adequate for each environment: (A) Flibe or Flinabe as self-cooled breeder in FFHR and for minor actinides transformer using high-energy neutron fluence in Flibe.

3

IAEA WS on Challenges for coolants in fast n, July 5-7, Wien

Contents 1) Advantages and disadvantages of Flibe/Flinabe for

tritium breeder in fusion reactors, coolant or fuel solvent in fission reactors and phase diagram

2) Neutron reaction with Flibe and tritium chemical form (T+, T0 or T-) and its desorption behavior

3) Chemical redox control of Flibe (conversion of tritium chemical form from T+ to T0)

4) Hydrogen permeation through Flibe/Flinabe and permeation control or reduction by addition of H absorbing metal

5) Prediction of molten salt properties

6) Characteristics of Flibe as a heat transfer fluid

7) FFHR design work and Flinabe/sc-CO2 proposals

4


5

• Close agreement in T desorption rate between experiment and analysis.

• Flibe desorbs tritium fast and readily exchanges with H2.

• The total T desorption amount agrees with T generation one.

2LiF+BeF2

6Li(n,a)3T

T+F-

T-Li+

T0H0

TF desorption exchange

H2+TF=HT+HF

Ar+H2 purge Ar purge

diffuse

2. Tritium release in Ar-H2(5%) after neutron irradiated Flibe, comparison between experiment and analysis

Fig. 1 Tritium desorption from neutron irradiated Flibe [14]

7Li(n,an’)3T above 2.5MeV

(thermal) neutron

6

Analysis of tritium release from neutron irradiated Flibe to Ar+H2

• Zero-A grade Ar (99.999%) <2ppm O2 <10ppm N2 <0.5ppm CO, CO2, H2O, CH4

jHTO = -DT¶qT

¶r= kexc,H2O

qTcH2O-cHTOqH

KH2O-HTO

æ

è

ç ç

ö

ø

÷ ÷

TF+H2=HF+HT

¶qT¶t

=DT

r2

¶

¶rr2 ¶qT

¶r

æ

èç

ö

ø÷+ ST

T

H2

TF

TF

TF

TF

TF+H2O=HTO+HF

H2O

TF(s)+HF(g)=HF(s)+TF(g)

TF

HF

BeF2(s)+H2O(g)=BeO(s)+2HF(g)

Neglected

jTF = -DT¶qT

¶r= kdes, TF qT -

cTF

KHenry, TF

æ

è ç ç

ö

ø ÷ ÷

jHT = -DT¶qT

¶r= kexc,H2

qTcH2-qHcHT

KH2 -HT

æ

è

ç ç

ö

ø

÷ ÷

Flibe sphere

Isotopic exchange with H2

Isotopic exchange

with H2O desorption

Neglected

Rate parameters determined are DT, kexc,H2, kdes,TF.

Flibe

Ar+H2 gas purge

(Diffusivity) (Rate constants)

7

3. Redox control of purified Flibe by metallic Be rod

• Tritium generated by the nuclear reaction of LiF and neutron has a chemical form of corrosive TF.

• It is experimentally tested whether TF (HF) dissolved in Flibe can be reduced by Be to H2.

• Be redox control is indispensable to avoid corrosion in a Flibe blanket of a fusion reactor.

Fig. Variations of HF concentration with time [21]

Be rod is inserted in Flibe fixed time while HF gas bubbling

2HF+Be=BeF2+H2

HF gas supply

Insert of Be rod HF HF detection

[20]

(TF)

8

Analysis of conversion of TF to T2 in self-cooled Flibe blanket system of fusion reactor

• TF material balance

• Be0 material balance

• Material balance of metallic impurity

MFlibe

dxTF

dt=QT - 2VFlibekBeF2

xBex TF-xBeF2

xT2

KBeF2xTF

æ

èçç

ö

ø÷÷

+W xTF,in - xTF,out( ) - 2VFlibekFeF2xFexTF

2 -xFeF2

xT2

KFeF2

æ

èçç

ö

ø÷÷

MFlibe

dxBe

dt= kBe -VFlibekBeF2

xBex TF-xBeF2

xT2

KBeF2xTF

æ

èçç

ö

ø÷÷

MFlibe

dxFe

dt= -VFlibekFeF2

xFexTF2 -

xFeF2xT2

KFeF2

æ

è

ç ç

ö

ø

÷ ÷

Assumptions: Complete mixing in Flibe blanket, 1st-order reaction Be + 2TF = BeF2 + T2

BeF2

LiF

TF

kBe

xTF

xTF,in xTF,out

Flibe flow in, W (mol/s)

xBeF2

Be

Flibe flow out, W

T+ generation

QT (mol/s) F-

T+

Be

T2

neutron

Li

xBe

Parameters to be determined by experiment

Related processes: Be dissolution, TF generation, T+ (TF) or T- (LiT) diffusion and reaction


ICP-mass analysis of Flibe

Fe 100ppm Cr 12 ppm

Mn 3 ppm Ni 6 ppm

MFlibe (mol)

TF generation TF→T2 conversion by Be

TF flow in/out

9

JLF-1 corrosion in purified and redox-controlled Flibe

0

100

200

300

400

500

600

-100 0 100 200 300 400 500 600

time (h)

Co

nce

ntr

ati

on

(p

pm

)

Fe content

Cr content

NaOH trend (ml)

Dissolution rate of JLF-1 to Flibe Photo of JLF-1 before and after Flibe contact

Redox control

Fe-9Cr-2W steel (JLF-1)

When Flibe is redox-controlled, corrosion rates

of Fe and Cr in RAF steel (JLF-1) are low. But

when HF concentration in Flibe increased,

their rates are enhanced.

Co

nce

ntr

ation

of F

e a

nd

Cr

in

Flib

e

Start inserting JLF-1 and Be rod into Flibe

Extraction of Be only

Continuous supply of HF

Be dissolution in Flibe for redox control

Be(dis)+2HF→BeF2+H2

10

Redox controlled Flibe: D2 or T2 diffusion in Flibe or Flinabe is similar to ion pairs diffusion in alkali halides. This is because T is converted to LiT or T2 in redox controlled Flibe. ED=30-40 kJ/mol.

Redox noncontrolled Flibe: TF diffusion in Flibe or Flinabe. The TF diffusion is related with F- ion diffusion in BeF4

2- and F--F- exchange. ED=120 kJ/mol.

10

BeF42-

Li+

Li+

BeF42- F-

Diffusion of T in Flibe/Flinabe

Chemical form of tritium in Flibe T+-F-

T--Li+

T0-H0

Fig. 4 H isotope diffusivity in Flibe and Flinabe [22]

4. Comparison of T2 pressure in equilibrium with 1ppm T among liquid blanket candidates and T permeation

11


Fig. T2 pressure in equilibrium with liquid blanket candidates

Blanket conditions • 1GWt (190g-T/day)

• TBR=1

• Self-cooled liquid breeders (Li, Li17Pb83, Flibe)

• DT=200oC (WFlibe=2.2m3/s) (self-cooled coolant temperature difference)

• Sieverts’ law is applied between Li or Li17Pb83 breeder and blanket T2 pressure.

• Henry’s Law is applied to Flibe.

12

H2 permeation through molten salts and Monel tubes

1st

2nd

3rd

Flibe or Flinabe

H2

Ar

Ar+H2

H2

Flibe or Flinabe

thickness：3.76mm

Ar in

Steady-state H2 permeation rate, J

materials composition (%) diameter (mm)

thickness (mm)

length (mm)

1st Monel400 Ni:65 Cu:33 Fe:2 3.18 0.7 720

2nd Monel400 Ni:65 Cu:33 Fe:2 12.7 1.0 530

3rd SS316 Cr:18 Ni:12 Mo:2.5 25.4 1.65 300


Atomic diffusion in inner Monel Atomic diffusion in outer Monel Molecular diffusion in Flinabe

(0.67LiF+0.33BeF2) (0.31LiF+0.32NaF+0.37BeF2)

Ar+H2 out

2a 2b

H permeability of Flinabe (LiF-NaF-BeF)

Monel-Flinabe-Monel permeation

H2 permeability through Flinabe vs. 1000/T H2 permeation rate through Flinabe vs. H2 pressure [22]

13

jT∝pH20.5

jT∝pH2

molecular diffusion in Flinabe atomic diffusion through Monel molecular diffusion in Ar

5. H permeation control when 0.5wt%Ti particles are mixed in Flibe

14

• Ti particles (325mesh) opening 44mm

1st

2nd

3rd

Flibe +Ti H2

Ar

Ar+H2

Permeated gas side

Flibe/Flinabe

Ti particles (hydrogen-absorbing metal)

High-pressure side

Fig. Overall hydrogen permeation rate for Flibe/Ti system

H2 permeation

Monel400 tube

Monel400

H2 flow

Ar purge

No permeation is observed because of diffusion time lag ℓ2/DH2

Diffusivity becomes 1/200

ℓ :Diffusion path

H2 permeation barrier by Ti particles

15

High pressure side

Fig. Hydrogen pressure distribution inside Flibe Fig. H2 pressure-composition-temperature curve for the Ti-H system

Low pressure side

(Upstream side) (Downstream side)

Plateau pressure

6) Flibe phase diagram and molecular structure

• Similar to the 2MgO+SiO2 system K.A. Romberger, J. Chem. Phys. (1972)

16

Li2BeF4

LiBeF3

BeF42-

Li+

Li+

Li2BeF4

(Be-F)/(F-F)~√3/8

tetrahedra complex


Fig. Phase diagram of LiF-BeF2 system

Flinabe phase diagram

17

BeF42-

Na+

Li+

LiNaBeF4

Similar to the MgO-CaO-SiO2

1. LiNaBeF4

0.31-0.31-0.38 2. LiNa2Be2F7

3. LiNaBe2F6

4. LiNa5Be3F12

5. LiNa3BeF6

2

3

1 4

5


BeF42-

Na+

Li+

Fig. LiF-NaF-BeF2 tertiary phase diagram

Eutectic points

Predictions of physical or chemical properties of Flinabe by molecular dynamics simulation

18

charge-charge repulsive dipole-dipole or dipole-quadrupole polarization among ions

400 500 600 7000

20

40

60

80

100

120

140

Temperature [C]

Pr

(a)

(e)

Evaluation of Pr for LiF-NaF-BeF2 and LiF-BeF2

0.31LiF-0.31NaF-0.38BeF2

0.67LiF-0.33BeF2

Polarizable ion

(Polarizable ion model)

19

7. FFHR design work in NIFS

(Flinabe/V-4Cr-4Ti)

divertor region

inner port

Plasma volume : 2000m3

Toroidal field : 4.7T Major radius : 15.6m TBR : 1.18, Fusion power : 3GWt Fast neutron flux : 2x1010n/cm2s

Superconductor YBa2Cu3O7

Allowable temp. 350oC-600oC

20

New design of Flinabe(1st)/sc CO2(2nd) coolants

FFHR

T recovery by the Sabatier reaction 4T2(Flinabe)+CO2 → CT4 + 2T2O CT4 recovery from CO2 loop, T is decomposed from CT4 on Ni. T permeation can be suppressed in the secondary CO2 loop.

• Sc-CO2 cycle can achieve 42% thermal efficiency at 480oC.

• Flinak/LiPb loop is set up in NIFS.

Flinabe

350oC

550oC

Minor actinides transmutation in fusion Flinabe blanket

21

MA(n,g) reaction MA(n,fission) reaction

MeV neutron in fusion blanket is effective for MA transmutation

Fig. MA cross sections of neutron capture and fission reaction [5]

Reflector candidates: Pb or C

MA Loading (ton) 80

Fusion Output (GW) 1

MA Loading Thickness (cm) 10

MA Volume Ratio (vol.%) 46.8

Heat Generation (MW) 590

Average Power Density (W/cm3) 56.4

Total Reduction (kg/year) 707.5

Fig. Poloidal cross section of MA loading position

Conclusions (answer to the comments from WS chair) • Radiation chemistry. Radiolysis:

– (Q) Main effects for the different coolants: (A) Although Flibe or Flinabe is stable, corrosion is the main effect. The redox control can suppress the effect.

– (Q) Limits of use (temperature window, irradiation limits, susceptibilities to materials): (A) m.p. of Flibe is 459oC or that of Flinabe is 305oC.

– (Q) Examples: (A) Since less radioactive materials are generated except for tritium, limitation of Flibe or Flinabe for coolant is small.

• Activation, Species production, Computational models:

– (Q) Main effects for the different coolants: (A) Prediction of physical or chemical properties for different compositions of fluoride salts can be made based on molecular dynamics calculations.

– (Q) Limits of use: (A) There are correct MD parameters have been presented and information of tetrahedral ion combinations of BeF4

2- may not been sufficient.

– (Q) Examples (experimental experiences): (A) There are less experimental data for the tertiary component fluorides.

• Coolant processing and handling procedures:

– (Q) Kind of processes (limitations, scaling issues): (A) Although Pr of Flibe or Flinabe is around 20, the values are increased exponentially with the increase of BeF2 composition. Permeability of T in Flibe or Flinabe is large, T leakage to the secondary coolant should be suppressed.

– (Q) Major difficulties (purification, resources): (A) Impurities such as Li2O, BeO in salts can be removed by using HF and the Redox control is described as BeO+2HF→BeF2+H2O. If the salt is used for nuclear transmutation of minor actinides, further purification is necessary.

– (Q) New approaches: (A) Ti powder mixed in Flibe or Flinabe is proposed and investigated.

22

IAEA WS on Challenges for coolants in fast neutron spectrum system, July 5-7, Wien

Fig. 4 H isotope diffusivity in Flibe and Flinak [22]

Diffusion of T in Flibe/Flinabe

23

BeF42-

Li+

Li+

BeF42- F-


Chemical form of tritium in Flibe T--Li+

T+-F-

T0-H0

Advantages of Flibe/Flinabe coolant

• Moderate Prandtl (cPm/kT) number as coolant (Pr~13) leading to less thermal stress in reactors,

• Use for coolant at higher temperature (m.p.=459oC) and having no reaction with H2O or O2,

• Low vapor pressure (pFlibe=0.24Pa at 600oC),

• Low electric conductivity resulting in low MHD effect,

• Promising coolant candidate even under fast neutron irradiation conditions.

24


Molten salt fission reactor “FUJI” proposed by JAEA

25

Gamma ray shield

Permeation flux through Flinabe vs. 1000/T Permeation flux through Flinabe vs. H2 pressure

• Monel-Flinabe-Monel system • Tertiary circular tube permeation

apparatus

Steady-state permeation rate vs. pressure and vs. temperature

26

27

Material balance equations of HF and Be for Redox control experiment

Variations of HF to H2 when a Be rod is inserted in Flibe

MFlibe

dxBe

dt= rBe -VFlibekBeF2

xBexTF-xBeF2

xT2

KBeF2xTF

æ

è

ç ç

ö

ø

÷ ÷

MFlibe

dxFe

dt= -VFlibekFeF2

xFexTF2 -

xFeF2xT2

KFeF2

æ

è

ç ç

ö

ø

÷ ÷

M Flibe

dxHF

dt=QHF - 2VFlibekBeF2

xBe x HF-xBeF2

xH2

KBeF2xHF

æ

è

ç ç

ö

ø

÷ ÷

+W xHF,in - xHF,out( ) - 2VFlibekFeF2xFe xHF

2 -xFeF2

xH2

KFeF2

æ

è

ç ç

ö

ø

÷ ÷

For HF

For Be

For impurity (Fe)

Mass-transfer coefficient

Dissolution rate

The analytical calculation (broken line) can fit to the

experimental HF concentration profiles (solid lines).

Documents

Our Recent Experimental Challenges on Flibe or Flinabe ... · Our Recent Experimental Challenges on Flibe a) or Flinabe b) Coolant for Fusion Applications and Related Japanese Researches