SIV7.2
原型炉に向けた炉工学研究の進展と大学における工学基盤
SIV7．2 ブランケット研究の進め方と工学基盤
7.2 Development Strategy of DEMO Blanket and Its Engineering Basis
小西哲之1、登尾一幸2、笠田竜太1
1
Satoshi Konishi, 2Kazuyuki Noborio and 1Ryuta Kasada
1

京大エネ研、京大エネ科
IAE, Kyoto University, Graduate School of Energy Science, Kyoto University,2This symposium intends to consider thestrategy for the development of first power
generating fusion reactor and to identify the mostimportant technical issues toward it. Among them,
there is no doubt that blanket is a key element,
because of its function of tritium breeding andenergy conversion. ITER TBM is the major step
toward it, and the Broader Approach emphasizes
material development as the part of DEMO R&Dproject. However if fusion would be a potentially
viable energy source, technology development for
blanket as an integrated system is the major defectin the world fusion development path.
In
comparison with the fission power plants, blanket
itself corresponds to the fuel assembly, and thepower train, such as steam generator, CVCS,
turbine and heat rejection are the core of the energy
generation.
Not only technical difficulty,
confident safety and attractiveness to the market
also depend on the technical feature of the blanket
and its power system.
It should be noted that a well-organized
integral strategy is needed to be launched. In
parallel with ITER-TBM program, some of thefundamental issues for power reactor blanket
should be evaluated and research activity must bestarted. Engineering issues require large scale
facilities.
Basic studies such as material
developments will also be needed not only forbetter understanding of scientific feature of theblanket materials, but also to establish design database and technical standards. Universities areexpected to play major roles in both engineeringand fundamental studies, although some of the large
scale facilities need special arrangements as
nationally supported projects. They will include
blanket systems test facility for neutron irradiation,
tritium and activated material handling, and energy
transfer loop. Some may be considered to be apart or extension of the blanket programs, but mostare not covered. Integration with divertor systems
as energy conversion component is also needed.

For the electricity generation plant, targetparameters for DEMO are considered to beconsiderably higher than that of ITER energy fluxand density, that requires further improved
performance of energy conversion and transfer fromin vessel components. Heat exchanger / steam
generator and power train design together withtritium confinement under the normal andoff-normal conditions are major concerns, because
environmental impact will be emphasized in thefuture market.
For this target, we propose
development and testing of blanket systems at
lower power density, lower pressure and smallerscale nuclear testing will be an alternative option
other than DEMO after ITER.
In the technical options of the blanket,
liquid concepts are considered as attractive but
more advanced design. However in the fact,liquid breeder such as liquid metal or molten salt
provides easier and simpler blanket design as thefirst step of nuclear testing. Kyoto University
proposes high temperature liquid LiPb blanket
concept for the use of fusion-biomass hybrid that
requires Q<5 plasma with lower power density inthe blanket, while only ambient pressure is involved.
Figure 1 shows the concept of the system.

Fig.1 Energy balance of the fusion reactor
for biomass fuel production.

Liquid LiPb blanket transfers heat from the small
power fusion reactor to the chemical reactor toconvert biomass to hydrogen. With fusion output
Pf to be 760MW, the plant can provide positive net
energy production of 1560MWch (chemical) as fuel,while additional 150MW of external electricity isneeded.
Feasibility of the high temperatureblanket, that seems to be challenging, is one of thekey issue of this concept. High temperature LiPb
liquid metal blanket combined with SiC/SiC
material is designed and being tested to make thisoption possible. The conceptual design of theblanket structure was made using neutronic andthermal hydraulic analyses. Figure 2 shows thesimplified flow diagram of the LiPb-He dual heattransfer loop in Kyoto University, and its photo.

Expansiontank
TTest
section2

T

heater
SiC
tube
９ ０ T

T

０℃

coolereconomizer
７００℃
PF

IHX
moduleGas
Chromatograph

T

ＥＭＰ

T

９００℃
T
Test vessel
Testsection3

heater

７００℃

PT

Test
section1
Primary loop
Dump
tank～200℃

TFGChygro
MS meterwith tritium recovery process and estimation of theinactive inventory in blanket materials should be
estimated. Figure 3 shows the flow of tritium inthe biomass-fusion reactor system with LiPb. In
any kinds of fusion plant, its environmental releasecomes from tritium transfer and permeation innormal operation. To control the tritium in theplant, as well as the emission to the environmentand dose to the public will be one of the criticaldevelopment paths for fusion energy.
The blanket technology determines thefeature of the entire fusion plant, because both
power and tritium, that are the major concern to thepublic for the energy source, comes from blanket.
And as shown in the above case, biomass-fusion
concept provides fuels instead of electricity as thefusion energy product, with smaller plant size
compared with electricity generation, and show
some advantageous feature of low system pressure
and small tritium emission. However its key
technologies require engineering verification in theintegrated experiments.
There should be many
more potentially attractive blanket concepts, but allof them require integrated test facility to identify
Net TBR 1.05

BZr

Secondary loopGCLiPb0.724 m3/s

Pb
0.652 m3/s

biomassnPlasma
Consumption
4.5E-04

BlanketIHX
HEX

Reactor

Generation
4.7E-04

Permeation
2.3E-8Permeation
2.5E-10

T3-OS14
Yamamoto[mol/s]Tritium
Recovery
System 1

Recovery
4.7E-04

T
Recovered tritium-Tritium
Recovery
System 2
Recovery
2.3E-08

Environmental
release

Stock
Stock
2.3E-05

Fig.3 tritium flow in the biomass-fusion
hybrid plant with LiPb blanket.

Fig.2 Lead Lithium loop in Kyoto university.

Verification of Tritium Breeding Ratio not
only from neutronics aspects but realistic massbalance in the integrated fuel loop is one of themajor issues to launch DEMO project withconfidence. Recovery and economy of tritium
fuel must be evaluated with ITER under limited
condition, but other neutron sources are desired forthe development of blanket concepts. Combination

technical issues for realistic design. Basic studies
on the blanket technology will also need such kindsof facility beyond the material development phase.
Neither Broader Approach nor ITER/TBM provides
this kind of research activities. The research plan
proposed by Sagara in this symposium would be
expected to be one of the possible first steps for the
next generation reactor technology study toward
fusion energy.