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, JapanLijiang river10.24.2007

Design specification of KOYO-Fast

– Net output 1200 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 800 MWth

– Blanket energy multiplication 1.13

– Reactor thermal output 904 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 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 33.2 %( 1200 MWe/ 3616 MWth)

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.

PbLiC PbLi

SiC wall

Feritic　 Steal

50 mm 450 mm 800 mm 200 mm

F3 F2 F1Graphite 45 cm

SiC/SiC porous wall container

LiPb Flow

Ablation control by FW inclinationFree-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

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 viewLiPb flow inlet (280-300oC)

LiPb flow outlet(480-500oC)

Reflector

Gas coolant outlet

Gas coolant inlet

Thermal flow of KOYO-F( One module)

SGTurbin

500℃

300℃300℃

50MW

210MW

70MW

70MW

240MW

80MW

80MW

500℃

F2+F3 (80cm)12.84 ton/s

Average flow 7.8 cm/s

F１ (20cm)8.56 ton/s

Average flow 24.3 cm/s

Flow rate 21.4 ton /s

904MW

Watercycle

Chamber

LiPb cycle

200MJ/shot x 4Hz

300 MWe

ther-elec=30%

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 temperaturerises

Making space between reservoir units ⇒ static pressure drop for each units could be kept constant

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.

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.

　

2We u

2

1water LiPb Water Water

LiPb Water LiPb LiPb

We u

We u

1.21Water

LiPb

u

u

Water ： 　 =7.275×10-2[N/m] 　　 =9.98×102 [kg/m3]

　 Li17Pb83 ： 　 =4.80×10-1[N/m] 　　 =9.6×103 [kg/m3]

u

Experimental Setup

PumpTank

Drain

Tank

Drain

Valve

Valve FlowMeter

FlowMeter

Valve

Valve

Pump

Electric Balance

Flow Condition

Re:4800~9600

T=17.5[ 。 c]

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

OverflowAt 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.

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

Film Break-up

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

NumericalSimulation

Comparison between Exp. & CFD

Computational Conditions

Mesh:782800

Fluid1:Air Fluid2:Water

Material:Acrylic resin

Re=5806, T=20.0[ 。 c]

Experiment

3mm3mm

Numerical Simulation

CFD　animation

Comparison between Water and LiPb

Water/Acrylic plate Li17Pb83/SiC

Water/Acrylic plate Li17Pb83/SiC

Comparison between Water and LiPb

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.