22A02
Current and Future States of the Key Technologies to Realize Fusion Reactor –aView of Technology Maturity Assessment by Young Researchers
核融合炉実用化のためのキーテクノロジーの現在と将来―若手による技術成熟度評価活動から見えてきたもの―
Ryuta Kasada, Takuya Goto, Shinsuke Fujioka, Ryoji Hiwatari,
Naoyuki Oyama, Hiroyasu Tanigawa and Junichi Miyazawa
笠田竜太1，後藤拓也，藤岡慎介，日渡良爾，大山直幸，谷川博康，宮澤順一
Young Scientists Special Interest Group on Fusion Reactor Realization
c/o Institute of Advanced Energy, Kyoto University
Gokasho, Uji, Kyoto 611-0011, Japan

核融合炉若手実用化検討会 幹事団
京都大学エネルギー理工学研究所気付The Young Scientists Special Interest Group on Fusion Reactor Realization is an active volunteer groupwhich consists of the spirited young researchers beyond the frame of organizations or specialties who has aburning ambition to realize fusion reactors in their lifetime. To accelerate the R&D of fusion reactors, thepossible bottle-neck technology should be clearly stated and recognized by the research specialists. Also anappropriate technological communication tool is necessary to highlight the key technologies and to obtainthe supports from societies. In this study we adopted and tested a technology readiness level (TRL)
methodology to evaluate the current status of key technologies for fusion reactor. The obtained results
should be further discussed but clearly show that the bottle-neck technologies exist in the boundary area
between specialists.

1. Introduction“It takes 30 years before the fusion reactor canbe commercialized”. This is a famous phrase that
was also described in the everlasting excellent
book "Challenge to Fusion Energy" [1], which
has been giving a grand dream and hope to young
people as well as to the society suffering energy
problems. Though budget constraints may havebeen significantly severer than initially expectedby scientists, it is also inferred from the book thattechnical issues lurking in the great success ofscientific researches of nuclear fusion has
prevented the commercialization of the fusion
reactor.
Off course, our privilege as “young”
researchers living in their future as 30 years later
is not to condemn the past but is to utilize the pastexperience with a sincere effort. Now we shouldemphasize that it is important to clarify thestrategy of technological development that can betolerated by the society (or government) as aninvestor. However this is a tough work for theresearchers who always write academic papers,
reports and proposals with various professionalterminologies and parameters. Even for the fusion
research specialists (probably not only young

researchers but also senior researchers), an
understanding of the whole picture of theintegrated fusion science and technology is
becoming difficult. In order to manage thevariousengineering
subjects(orrisk)
appropriately towards the commercialization offusion reactors, some useful tools for the
researchers in different fields, the government,and society to evaluate the present condition oftechnical subjects rationally and quantitatively,
and are required to carry out theirdecision-making and consensus building.
Recently, the Young Scientists Special Interest
Group on Fusion Reactor Realization has beenassessed the technical maturity of fusion reactors
based on the evaluation of technology readinesslevels (TRLs). This is a systematic evaluation
method which has been used to support theevaluation and comparison of maturity for new
technology developments in various projects ofNASA [2] can provide a common understandingof the degree of progress of technology and its
risk management. Until now, our group is
successfully analyzing the present view of TRLof various fusion reactor technologies. Throughthis work, it is succeeding to reveal the criticalcommon subjects and to share the obtainedknowledge. In this paper, the TRLs for fusion
reactor evaluated by the newest knowledge of thespirited young researchers beyond the frame oforganizations or specialties are shown. Based on theTRL evaluation, the prospects towards the fusion
reactor commercialization are also introduced.
2. Technology Readiness Level (TRL)
A summary of the TRLs in NASA is shown inTable 1 [2]. The 9 set of specific “exit criteria”
shown is applied in conducting the technology
readiness assessment. The NASA’s TRL and its
similar concepts are widely used for measuring
technology readiness of various technologies andcomparing maturity between different types oftechnology. However, they sometimes fail to givenegative aspects when the TRL is used for therisk management of two or more projects
advanced simultaneously. Note that the TRL
indicates NOT the potential but the status of thetechnology development. The comparison of TRL
between different technologies must be
performed carefully to avoid the misleading andmisunderstanding of the project which contains a“hidden treasure” beyond the risk to be overcame.
Table 1 NASA definitions of the TRLs [2]
TRL1
TRL2
TRL3
TRL4
TRL5
TRL6
TRL7
TRL8
TRL9

Basic principles observed and reported.
Technology concept and/or application formulated.
Analytical and experimental critical function and/or
characteristic proof-of-concept.
Component and/or breadboard validation in laboratoryenvironment.
Component and/or breadboard validation in relevant
environment.
System/subsystem model or prototype demonstration ina relevant environment (ground or space).
System prototype demonstration in a space environment.
Actual system completed and “flight qualified” throughtest and demonstration (ground or space).
Actual system “flight proven” through successful
mission operations

3. A brief example of TRL evaluation on fusion
reactor technologies
The TRL setup which we propose for fusion
reactor developments is shown in Fig. 1.
Currently, it is obvious that the items of TRL 1-3
is still left behind to the tokamak, helical, laser
system and their common technologies. In orderto put a fusion reactor in practical use in 30 years,
the achievement of TRL4 and more (i.e.,engineering design phase) supported bytarget-oriented teams is required immediately.
The TRL assessment on the Tokamak typereactor has been performed by assuming the two
scales of the net electricity output as 0.3 or 1 GW.
As a result, the TRL was in the stage of 2 to 3 forboth scales as a fusion reactor power plant. For
the large-sized (low beta) system having a highTRL for the reactor core plasma, however, it wasshown that the TRL evaluation as the wholereactor system falls down due to the technicalsubject by enlargement of TF coil and so on.
The TRL of a helical prototype nuclear reactor
development is considered to be in the stage 3.
The achievement of TRL4 is expected throughR&D in a present progressive and also TRL6 is
expected in the knowledge obtained from otherequipment, such as LHD with deuterium
experiment, a large-sized engineering test facility,and ITER.
The laser fusion is verging on their ignition andburn. However it was pointed out that a technicalgap exists between FIREX/NIF of a single shot
and a reactor. Cooperative R&D with a broadorganization is required in order to shift to reactor
engineering from plasma science.
The above-evaluations still need furtherdiscussion and re-evaluation. The detailed
evaluation of TRLs broken down into engineering
components of fusion reactor concepts will bereported in the conference. Finally, it isrecommended to examine the TRL for yourresearch and development. This is an aim of thispaper to just give an opportunity of yourargument.

Fig.1. A setup of TRL for fusion reactor development.

Acknowledgments
The authors thank many young researchers togive us their kind help to investigate the TRL ofvarious fusion technologies. They also appreciatedmany senior researchers to encourage us.
References[1] 吉川庄一：核融合への挑戦―無限のエネルギーを求めて（講談社ブルーバックス，1974)[2] J. C. Mankins: A White Paper, April 6, 1995, NASA.
[3] W. L. Nolte: Did I Ever Tell You About the Whale?:Or Measuring Technology Maturity (Information
Age Pub Inc, 2008) Illustrated ed.