1. Falling Liquid Film Flow along Cascade-type First Wall of Laser-Fusion Reactor
T. Kunugi, T. Nakai, Z. Kawara
Department of Nuclear Engineering
Kyoto University, Japan
Collaborated with T. Norimatsu
ILE Osaka University, Japan
Lijiang river

2. Design specification of KOYO-Fast
Net output MWe (300 MWe x 4)
Reactor module net output 300 MWe
Laser energy 1.2MJ
Target gain 167
Fusion pulse out put 200 MJ　
Reactor pulse rep-rate 4 Hz
Reactor module fusion outputr MWth
Blanket energy multiplication 1.13
Reactor thermal output 904 MWth
Total plant thermal output MWth (904 MWth x 4 )
Thermal electric efficiency %（LiPb Temperature ~500 C)
Total electric output MWe
laser efficiency 8.5% (implosion) , 5% (heating)
Laser pulse rep-rat 16 Hz
Laser recirculating power 240 MWe（1.2 MJ x 16 Hz / 0.08)
Net plant out put power 1200 MWe(1519MWe - 240MWe - 79MWe Aux.)
Total plant efficiency %( 1200 MWe/ 3616 MWth)

3. Basic design concept for PbLi chamber
No pressurized pipe or vessel in the chamber for avoiding high pressure in chamber in accidents, and for achieving simple maintenance and long life use.
Free surface fast cooling using divergent flow thorough from bulk flow (small holes or slit structure ⇒ Cascade-typed FW)
Feritic steal is used for cylindrical vessel and upper dome cover vessel
SiC/SiC is used as separate wall without pressure bulkhead
Adjusting holes or slits on the separate to control divergent flow for stabilizing and fast cooling free surface (200ms for renewal of FW)
Two layers PbLi blankets (~20 cm for free surface first wall and ~80 cm for blanket) and ~45cm graphite neutron reflector.
SiC wall
Feritic　Steal C
PbLi
PbLi
50 mm
450 mm
800 mm
200 mm

4. Cascade-typed FW Concept
LiPb Flow
Graphite 45 cm
SiC/SiC porous wall container
The coolant flows downward along FW
→ into reservoir behind FW
→ flows laterally to a slit
→ goes upward into the slit
→ past the exit of the slit
→ some of the overflowed
coolant forms a falling
liquid-film flow
Ablation control by FW inclination
Free-surface flow control by cascade passage

5. KOYO reactor cross-sectional view
LiPb flow inlet ( oC)
Laser fusion modular power plant "KOYO" design, which has four reactor chambers driven by one laser system, was proposed .
Reflector
Gas coolant outlet
Gas coolant inlet
Cascade typed Liquid wall
LiPb flow outlet( oC)
KOYO laser-fusion reactor

6. Thermal flow of KOYO-F ( One module)
300 MWe
200MJ
/shot
x 4Hz
hther-elec=30%

7. Cascade-typed Liquid Wall
Mixing is not sufficiency
Surface temperature
rises
As a result, the fluid does not mix well, and the surface temperature of the first wall is continuously rising.
Some flow resistances to maintain the surface shape.
Difficult to keep thickness of liquid film
Primary design proposal
Redesigned Cascade-typed liquid wall
The fluid covering the surface heated at the upper unit does not enter the backside of FW.
Making space between reservoir units
⇒ static pressure drop for each units could
be kept constant
30cm
The height of the first wall of each unit is set to 30cm corresponding to the surface renewal time: 4 Hz laser repetition

8. Proof-of-principle experiment
The flow visualization experiment was performed as a POP experiment.
In order to examine the performance of the new cascade-typed FW concept, numerical simulation was performed using STREAM code with k-e turbulent model.

9. Similarity Law and Flow Condition of Visualization Test
In the actual reactor, Li17Pb83 will be working fluid and SiC/SiC composite material will be used for the first wall. In this case, the wall surface might have a lower wettability. In the present experiment, we used the acrylic resin board as the FW because of its lower wettability.
　　　The major concern of this experiment is to know the stability feature of the liquid film flow, therefore, the Weber number is the key parameter ,where is based on the film thickness , velocity 　 , density 　 , and surface tension coefficient 　 .
According to the similarity law, we can estimate the flow velocity ratio.
Water： 　=7.275×10-2[N/m] 　　=9.98×102 [kg/m3]
　 Li17Pb83： 　=4.80×10-1[N/m] 　　=9.6×103 [kg/m3] 9

10. Experimental Setup Flow Condition Re:4800~9600 T=17.5[。c] Tank Pump
Drain
Valve
Flow
Meter
Electric Balance
Flow Condition
Re:4800~9600
T=17.5[。c]

11. Experimental results Overflow Liquid Film Flow
At the overflow regions, there are many small waves.
The liquid-droplet generation from the liquid surface and the large wave on the liquid-film surface were not observed.
These small waves might trigger free surface unstable motion of the falling liquid-film flow on FW.
Liquid Film Flow
The average flow velocity is 1.75 times (14 l/min) of Weber number coincident condition (8.0 l/min) with the actual reactor.

12. Break-up of FW liquid film
Film Break-up
Film Break-up
The averaged flow velocity is 0.75 times (6.0 l/min) of Weber number coincident condition (8.0 l/min) with an actual reactor condition.

13. Numerical Simulation Flow Direction Liquid Film Flow Overflow
　We performed the two-dimensional thermo-fluid simulation by using the MARS function of the STREAM (commercial 3-D thermo- fluid code, Software Cradle Co. Ltd. in Japan).
Experiment
Flow
Direction
3mm
Numerical
Simulation
Liquid Film Flow
Overflow

14. Comparison between Exp. & CFD
3mm
3mm
Computational Conditions
Mesh:782800
Fluid1:Air Fluid2:Water
Material:Acrylic resin
Re=5806, T=20.0[。c]
Experiment
Numerical Simulation

15. CFD animation

16. Comparison between Water and LiPb
Water/Acrylic plate
Li17Pb83/SiC

17. Comparison between Water and LiPb
Water/Acrylic plate
Li17Pb83/SiC

18. Conclusions
We proposed the cascade typed liquid wall concept, and conducted the POP experiments and the numerical simulation (CFD) based on the consideration of the similarity law.
The CFD result qualitatively agreed with the POP flow visualization experiment, so that the cascade-typed liquid film system will be realized.
We also confirmed that the stable liquid film with sufficient thickness (liquid wall covering the first wall) could be naturally formed.
Therefore, it seems that this liquid wall concept might be possible to apply to the real reactor.