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 10.24.2007

2. Design specification of KOYO-Fast –Net output1200 MWe (300 MWe x 4) –Reactor module net output300 MWe –Laser energy1.2MJ –Target gain167 –Fusion pulse out put200 MJ –Reactor pulse rep-rate4 Hz –Reactor module fusion outputr 800 MWth –Blanket energy multiplication1.13 –Reactor thermal output904 MWth –Total plant thermal output 3616 MWth (904 MWth x 4 ) –Thermal electric efficiency 42 % （ LiPb Temperature ~500 C) –Total electric output 1519 MWe –laser efficiency8.5% (implosion), 5% (heating) –Laser pulse rep-rat16 Hz –Laser recirculating power 240 MWe （ 1.2 MJ x 16 Hz / 0.08) –Net plant out put power1200 MWe(1519MWe - 240MWe - 79MWe Aux.) –Total plant efficiency 33.2 %( 1200 MWe/ 3616 MWth)

3. Basic design concept for PbLi chamber 1)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. 2)Free surface fast cooling using divergent flow thorough from bulk flow (small holes or slit structure ⇒ Cascade-typed FW) 3)Feritic steal is used for cylindrical vessel and upper dome cover vessel 4)SiC/SiC is used as separate wall without pressure bulkhead 5)Adjusting holes or slits on the separate to control divergent flow for stabilizing and fast cooling free surface (200ms for renewal of FW) 6)Two layers PbLi blankets (~20 cm for free surface first wall and ~80 cm for blanket) and ~45cm graphite neutron reflector. PbLi C SiC wall Feritic Steal 50 mm450 mm800 mm200 mm

4. Graphite 45 cm SiC/SiC porous wall container LiPb Flow Ablation control by FW inclination Free-surface flow control by cascade passage Cascade-typed FW Concept 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

5. Laser fusion modular power plant "KOYO" design, which has four reactor chambers driven by one laser system, was proposed. KOYO laser-fusion reactor Cascade typed Liquid wall KOYO reactor cross-sectional view LiPb flow inlet (280-300 o C) LiPb flow outlet(480-500 o C) Reflector Gas coolant outlet Gas coolant inlet

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

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

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-  turbulent model.

9. Similarity Law and Flow Condition of Visualization Test In the actual reactor, Li 17 Pb 83 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] =9.98×10 2 [kg/m 3 ] Li 17 Pb 83 ： =4.80×10 -1 [N/m] =9.6×10 3 [kg/m 3 ]

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

11. Experimental results The average flow velocity is 1.75 times (14 l/min) of Weber number coincident condition (8.0 l/min) with the actual reactor. Liquid Film Flow Overflow  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.

12. Break-up of FW liquid film 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. Film Break-up

13. 3mm Numerical Simulation 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). Liquid Film Flow Flow Direction Experiment Overflow Numerical Simulation

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

15. CFD animation

16. Comparison between Water and LiPb Water/Acrylic plate Li 17 Pb 83 /SiC

17. Water/Acrylic plate Li 17 Pb 83 /SiC Comparison between Water and LiPb

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.