Our Recent Experimental Challenges on Flibe Or Flinabe Coolant For

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

a) Flibe is 2LiF+BeF2 molten salt, and b) Flinabe is xLiF+yNaF+(1-x-y)BeF2 molten salt. 1 1. Advantage andIAEA WS disadvantages on Challenges for coolants of in fast n, July 5-7, Wien 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 o (0.31LiF+0.31NaF+0.38BeF2, m.p.=305 C), • Corrosive TF is generated in neutron irradiation. • High tritium leak through heat exchanger. • Thermal laminarization in high magnetic field. 2 LiF-BeF2-UF4 IAEA WS on Challenges for coolants in fast n, July 5-7, Wien 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 o o 500 C-700 C 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 3 transformer using high-energy neutron fluence in Flibe. 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

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

2. Tritium release in Ar-H2(5%) after neutron irradiated Flibe, comparison between experiment and analysis 7Li(n,an’)3T above 2.5MeV (thermal) neutron

2LiF+BeF2 6Li(n,a)3T T+F- diffuse T-Li+ T0H0

exchange TF desorption

H2+TF=HT+HF

Ar+HAr purge2 purge

Fig. 1 Tritium desorption from neutron irradiated Flibe [14] • 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. 5 Analysis of tritium release from neutron irradiated Flibe to Ar+H2

BeF (s)+H O(g)=BeO(s)+2HF(g) 2 2 TF+H =HF+HT TF(s)+HF(g)=HF(s)+TF(g) 2 ¶q æ q c ö H2 j = -D T = k ç q c - H HT ÷ Flibe HT T exc, H2 ç T H2 ÷ HF ¶r è K H -HT ø TF 2 T Isotopic exchange with H Neglected TF 2 ¶qT DT ¶ æ 2 ¶qT ö = çr ÷ + ST ¶t r2 ¶r è ¶r ø Ar+H2 gas purge Flibe sphere TF æ ö TF ¶qT cTF Isotopic exchange jTF = -DT = kdes, TFç qT - ÷ ¶r è K Henry, TF ø with H2O H2O TF desorption

TF+H2O=HTO+HF Neglected • Zero-A grade Ar (99.999%) ¶q æ c q ö j = -D T = k ç q c - HTO H ÷ <2ppm O2 HTO T ¶r exc, H2Oç T H2O K ÷ è H2O-HTO ø <10ppm N2 <0.5ppm CO, CO2, H2O, CH4

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

(Diffusivity) (Rate constants) 6 3. Redox control of purified Flibe by metallic Be rod Be rod is inserted in Flibe fixed time while HF gas bubbling HF HF detection Insert of Be rod

(TF)

2HF+Be=BeF2+H2

HF gas supply [20] Fig. Variations of HF concentration with time [21] • 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. 7 IAEA WS on Challenges for coolants in fast n, July 5-7, Wien

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

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

• TF material balance Flibe flow in, W (mol/s) Flibe flow out, W dx æ x x ö M TF = Q - 2V k çx x - BeF2 T2 ÷ x x Flibe T Flibe BeF2 ç Be TF ÷ TF,in TF,out dt è KBeF xTF ø TF generation 2 TF→T2 conversion by Be æ ö BeF2 xFeF xT kBe +W x - x - 2V k çx x2 - 2 2 ÷ ( TF,in TF,out ) Flibe FeF2 ç Fe TF ÷ LiF TF flow in/out è KFeF ø 2 Be • Be0 material balance neutron TF æ x x ö dxBe BeF2 T2 M = k -V k çx x - ÷ x T2 Flibe Be Flibe BeF2 ç Be TF ÷ Be dt è KBeF xTF ø 2 Be xTF • Material balance of metallic impurity T+ generation T+ dx æ x x ö M - M Fe = -V k ç x x 2 - FeF2 T2 ÷ Flibe F Flibe dt Flibe FeF2 ç Fe TF K ÷ QT (mol/s) (mol) è FeF2 ø xBeF2 Li Parameters to be determined by experiment

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

Fe 100ppm Cr 12 ppm 8 Mn 3 ppm Ni 6 ppm JLF-1 corrosion in purified and redox-controlled Flibe

Be(dis)+2HF→BeF2+H2 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.

Start inserting JLF-1 and Be rod into Flibe

Extraction of Be only

600 Flibe Be dissolution in Flibe for redox control Fe content 500

) Cr content m

p NaOH trend (ml)

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

( 400

o i

t 300

n e

c 200

n Redox control o C 100

0 -100 0 100 200 300 400 500 600 time (h)

Concentration of Fe and Cr in Cr and Fe of Concentration Continuous supply of HF 9 Dissolution rate of JLF-1 to Flibe Photo of JLF-1 before and after Flibe contact 2- Diffusion of T in Flibe/Flinabe BeF4

- 2- F BeF4 Li+

Li+

Chemical form of tritium in Flibe T+-F- T--Li+ T0-H0 Fig. 4 H isotope diffusivity in Flibe and Flinabe [22] Redox controlled Flibe: Redox noncontrolled Flibe:

D2 or T2 diffusion in Flibe or Flinabe is similar TF diffusion in Flibe or Flinabe. to ion pairs diffusion in alkali halides. This is The TF diffusion is related with F- ion 2- - - because T is converted to LiT or T2 in redox diffusion in BeF4 and F -F exchange. controlled Flibe. ED=30-40 kJ/mol. ED=120 kJ/mol. 10 10 IAEA WS on Challenges for coolants in fast n, July 5-7, Wien

4. Comparison of T2 pressure in equilibrium with 1ppm T among liquid blanket candidates and T permeation Blanket conditions • 1GWt (190g-T/day) • TBR=1 • Self-cooled liquid breeders (Li, Li17Pb83, Flibe) o 3 • DT=200 C (WFlibe=2.2m /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.

Fig. T2 pressure in equilibrium with liquid blanket candidates 11 IAEA WS on Challenges for coolants in fast n, July 5-7, Wien

H2 permeation through molten salts and Monel tubes

Ar+H2 out Ar in

(0.67LiF+0.33BeF2) (0.31LiF+0.32NaF+0.37BeF2) Flibe or Flinabe thickness：3.76mm

2b H2 2a Ar materials composition (%) diameter thickness length (mm) (mm) (mm) 1st Monel400 Ni:65 Cu:33 Fe:2 3.18 0.7 720 H2 nd Flibe or Ar+H 2 Monel400 Ni:65 Cu:33 Fe:2 12.7 1.0 530 st 2 1 Flinabe 3rd SS316 Cr:18 Ni:12 Mo:2.5 25.4 1.65 300 2nd 3rd Steady-state H2 permeation rate, J

12 Atomic diffusion in inner Monel Molecular diffusion in Flinabe Atomic diffusion in outer Monel H permeability of Flinabe (LiF-NaF-BeF)

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

0.5 jT∝pH2

jT∝pH2

H permeation rate through Flinabe vs. H pressure 2 2 H permeability through Flinabe vs. 100013 /T [22] 2 5. H permeation control when 0.5wt%Ti particles are mixed in Flibe

• Ti particles (325mesh) opening 44mm

Ar Diffusivity becomes 1/200 H2 Flibe +Ti Ar+H2 1st 2nd rd 3 Monel400 Flibe/Flinabe High-pressure Ar purge side 2 H flow No permeation is observed because of diffusion time lag ℓ /DH2 2 Permeated Fig. Overall hydrogen permeation rate for Flibe/Ti system gas side Ti particles (hydrogen-absorbing metal) H2 permeation 14 ℓ :Diffusion path Monel400 tube H2 permeation barrier by Ti particles (Upstream side) (Downstream side) High pressure side Low pressure side

Plateau pressure

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

15 IAEA WS on Challenges for coolants in fast n, July 5-7, Wien 6) Flibe phase diagram and molecular structure

tetrahedra complex Li2BeF4 BeF 2- Li+ 4

Li+ (Be-F)/(F-F)~√3/8

Li2BeF4

LiBeF3

Fig. Phase diagram of LiF-BeF2 system K.A. Romberger, J. Chem. Phys. (1972) • Similar to the 2MgO+SiO system 2 16 IAEA WS on Challenges for coolants in fast n, July 5-7, Wien Flinabe phase diagram

BeF 2- Na+ 4 Eutectic points

1. LiNaBeF4 0.31-0.31-0.38 Li+ 2. LiNa2Be2F7 LiNaBeF 4 BeF 2- 3. LiNaBe2F6 Na+ 4 4. LiNa5Be3F12 5. LiNa3BeF6 Li+ 3 4 1 2

Fig. LiF-NaF-BeF2 tertiary phase diagram Similar to the MgO-CaO-SiO2 17 Predictions of physical or chemical properties of Flinabe by molecular dynamics simulation (Polarizable ion model)

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

140

120 (a) (e) 100

80 0.31LiF-0.31NaF-0.38BeF2 Pr 60

20 0.67LiF-0.33BeF2 0 Polarizable ion 400 500 600 700 Temperature [C]

18 Evaluation of Pr for LiF-NaF-BeF2 and LiF-BeF2 7. FFHR design work in NIFS

(Flinabe/V- 4Cr-4Ti) Allowable temp. Superconductor 350oC-600oC YBa2Cu3O7 inner port

divertor region

Plasma volume : 2000m3 Toroidal field : 4.7T Major radius : 15.6m TBR : 1.18, Fusion power : 3GWt Fast neutron flux : 2x1010n/cm2s 19 st nd New design of Flinabe(1 )/sc CO2(2 ) coolants 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.

FFHR 550oC

Flinabe • Sc-CO2 cycle can achieve 42% thermal efficiency at 480oC. 350oC • Flinak/LiPb loop is set up in NIFS. 20 Minor actinides transmutation in fusion Flinabe blanket MA(n,g) reaction MA(n,fission) reaction

Fig. MA cross sections of neutron capture and fission reaction [5] MeV neutron in fusion blanket is effective for MA transmutation MA Loading (ton) 80 Fusion Output (GW) 1 Fig. Poloidal cross section of MA loading position MA Loading Thickness (cm) 10 MA Volume Ratio (vol.%) 46.8 Heat Generation (MW) 590 Reflector candidates: Average Power Density (W/cm3) 56.4 Pb or C Total Reduction (kg/year) 707.5 21 IAEA WS on Challenges for coolants in fast neutron spectrum system, July 5-7, Wien 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 2- tetrahedral ion combinations of BeF4 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 n, July 5-7, Wien Diffusion of T in Flibe/Flinabe

Chemical form of tritium in Flibe T--Li+ T+-F- T0-H0

2- BeF4

- 2- F BeF4 Li+

Fig. 4 H isotope diffusivity in Flibe and Flinak [22] Li+ 23 IAEA WS on Challenges for coolants in fast n, July 5-7, Wien 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, o • Low vapor pressure (pFlibe=0.24Pa at 600 C), • 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

Gamma ray shield

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

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

26 Permeation flux through Flinabe vs. H2 pressure Permeation flux through Flinabe vs. 1000/T Material balance equations of HF and Be for Redox control experiment

For HF Mass-transfer coefficient dx æ x x ö M HF = Q - 2V k ç x x - BeF2 H2 ÷ Flibe dt HF Flibe BeF2 ç Be HF K x ÷ è BeF2 HF ø æ x x ö 2 FeF2 H 2 +W (x HF,in - x HF,out ) - 2VFlibe kFeF ç xFe x HF - ÷ 2 ç K ÷ è FeF2 ø For Be Dissolution rate dx æ x x ö M Be = r - V k ç x x - BeF2 T2 ÷ Flibe dt Be Flibe BeF2 ç Be TF K x ÷ è BeF2 TF ø For impurity (Fe) dx æ x x ö M Fe = -V k ç x x 2 - FeF2 T2 ÷ Flibe dt Flibe FeF2 ç Fe TF K ÷ è FeF2 ø

The analytical calculation (broken line) can fit to the experimental HF concentration profiles (solid lines).

Variations of HF to H2 when a Be rod is inserted in Flibe 27