SIV-3
BAにおけるトカマク型原型炉設計の概要
Overview of Tokamak Demo Designs in Broader Approach Activity
岡野 邦彦1,2
Kunihiko Okano
1

国際核融合エネルギー研究センター、2電力中央研究所
1International Fusion Energy Research Centre, 2CRIEPI

1. Introduction
The first phase of Demo design study in theBroader Approach (BA) activity of InternationalFusion Energy Research Centre (IFERC), which
was called as Phase-1, was started in June 2007.
The study in Phase-1 was implemented by theleaderships of M. Araki (the first IFERC-ProjectLeader), D. Maisonnier of EFDA (Project managerof EU) and K. Tobita of JAEA (Project manager ofJapan). The main activity in Phase-1 was based on
workshops in order to exchange technical design
issues and to identify “common elements” for Japan– EU joint design works in the succeeding period
after Phase-1.
DEMO Design Activities (DDA) started a joint
work stage, Phase-2, after the DDA unit of theProject Team (PT) was organized in January 2011,
under the leader ship of a new IFERC ProjectLeader, N. Nakajima.
In the new framework, the activities have been
jointly conducted by the union of the DDA unit ofIFERC, EU Home Team (EU-HT) and Japan Home
team (JA-HT). The Leader of DDA unit is K.
Okano from CRIEPI, Japan. The EU-HT is
conducted by a new project manager (PM) G.
Federici, and the PM of JA-HT is K. Tobita,continuously.
In Phase-2, DEMO Design Workshops have been
replaced by Technical Coordination Meetings(TCMs), where specific technical and programmatic
issues for DEMO design are discussed by experts
from EU and Japan.
The first TCM (TCM-1) was held in
Kashiwa-Campus, near Tokyo on 19-20 January
2011, in the form of a joint DEMO Design andR&D Workshop, and included in addition of design
topics also a status report on the progress on DEMO
material R&D activities in the frame of the BA. The
second TCM (TCM-2) was held in Garching on
24-25 May and the third (TCM-3) is held in
Kashiwa on 1-3 November.
2. Joint Works in DDA

The joint works in Phase-2 have been defined asfollows;
Phase-2a (Jan 2011-Dec 2012):
Consolidation of knowledge, to define a soundcommon basis for DEMO design, and to provide
input to parallel and future R&D needed forDEMO,
Phase-2b (Jan 2013-Dec 2014):
Detailed studies on key design issues, options
and DEMO parameters, andPhase-2c (Jan 2015-May 2017):
Development of pre-conceptual design options
for DEMO.
The present period is the Phase-2a which will besucceeded by the Phase 2b after the next January.
3. Status of Design study
There is progress in system code benchmark
regarding pulsed operation. The benchmark on
pulsed operation was carried out. The poloidal flux
supply from the poloidal coil system or the central
solenoid given the JA and EU systems codes (TPC
code of JAEA and PROCESS code of CCFE) was
validated using a Japanese MHD equilibrium code
TOSCA, which revealed a problem of evaluating
the poloidal flux supply in each code. After themodification, complete agreement between thecodes was confirmed regarding the poloidal flux
supply [1].
Using these codes, there has been significant
progress to quantify key physics & technology
necessary for a case of somewhat conservative
design options, called DEMO-1 [2], which will
make easier to start the DEMO construction in theearly 2030s.
Two cases for steady state (SS) design options
which have been proposed by JA-HT are also
considered in the activity. The design policy forthese SS variations is slightly different from theprevious Japanese example of DEMO designs
which were designed with thermal output around
3GW. Both of the new SS variations are plannedwith 2GW thermal output with the major radiusabout 7m. These options are called DEMO-2 andDEMO-3. The change of output has been done
mainly because of a aspect for safety-design. TheDEMO-2 and DEMO-3 are also planned to install aCentral Solenoid (CS) enough to achieve V*Sec ~LpIp, which make possible to ramp-up the plasma
current up to the full specification value by the CSswing [3].
Priorities of issues in Design and R&D havebeen identified. They include a work on blanket
technology including tritium extraction and control
technology, remote maintenance, magnets designand conductor optimization. Finding a reliable
solution for the heat exhaust of DEMO is a mainpriority.
The study on conventional radiative divertors
includes some extension of the range of conditions
using the simplified integrated and specific models,
allowing a model development on a more complete
description of power exhaust to use it in the systems
code, and some improvement of the designdatabases for the extrapolation of key parameters
under suitable conditions.
The extended divertor leg concept [4], which is afully detached divertor concept based on an
extended divertor leg to reduce the divertor heatload to a tolerable level, has been numericallystudied.
Advanced divertor configurations and alternative
new concepts such as “super-X” and “snow-flake”
are also assessed in light of the feasibility of themagnetic configuration [5,6].
Novel material as a solution of Plasma Facing
Components (PFC), e.g., liquid metals, has beeninvestigated. This work includes,i) to review the rationale for liquid metals as PFCs
and to determine the implications on the plasma
operation and performance,ii) to provide knowledge needed PFC components
development with liquid metals,iii) to investigate the problem of Tritium inventory
as an important issue on liquid target,iv) to identify the candidate liquid metals andreview recent experimental results, and, in parallel,v) to investigate the design integration andengineering aspects of using liquid metals in a
DEMO divertor.
Radiation environments and decay heat ofin-vessel components are assessed to consider
remote maintenance equipment and coolingmethods during the maintenance of DEMO[7]. The
temporal evolution of the decay heat from theblanket and the divertor after stopping the operation
was evaluated to help with considering the coolingsystem during transport of the blanket sectors anddivertor sectors.
The technological target-ranges relevant to super
conductors and in-vessel components have been
compiled towards a unified list of the technologies
through the face-to-face discussion between the JA
and EU experts.
4. Status of Safety Study
The Safety Research in the DEMO DesignActivities (hereafter DDA Safety Research) has
been conducted since April 2012. The goal is toanalyze accidental sequences, to develop possible
design projections for preventing and mitigating
serious accidents, and eventually to compile thesafety design guidelines.
The DDA Safety Research will be conducted in twostages:
Stage 1 (April 2012 – March 2013);“Preparation stage”
Stage 2; (April 2013 – March 2017);“Assessment stage”
The main coverage of the present Stage-1 is:i) Definition of safety requirements,ii) Definition of source terms,iii) Identification of reference events, andiv) Preparation of computer codes.
The works are being conducted in collaboration
with an EU safety expert to preliminary investigatei), ii) and iii) and to review previous fusion safetyworks (including the ITER documents).

References[1] R. Kemp, M. Nakamura, D.J. Ward, K. Tobita, G.
Federici, “Benchmarking reactor systems studies bycomparison of EU and Japanese system code results fordifferent DEMO concepts”, 24th IAEA Fusion Energy
Conference (IAEA FEC 2012).
[2] Hartmut Zohm, “Realistic operational scenarios for aDEMO tokamak”, 1st IAEA DEMO Programmeworkshop, Oct 15-18, 2012, San-Diego.
[3] K.Tobita, Y. Someya, H. Utoh, N. Asakura, K.
Hoshino, M. Nakamura, Y. Sakamoto, R. Hiwatari, H.
Takase, K. Okano,” Reconsideration of tokamak DEMO
concept based on the latest design study”, ibid.
[4] K.Hoshino et al., “Simulation Study of an Extended
Divertor Leg for Heat Control in SlimCS DEMO
Reactor”, Contrib. Plasma Physics, 52(2012)550-554.
[5] A.W. Morris, “DEMO Power Exhaust Physics, andAdvanced Divertor Configurations”, ibid.
[6] D Frigione, G. Calabro’, F. Crisanti, G. Maddaluno,
V. Pericoli, G. Ramogida, A. Tuccillo, R. Zagórski,“Novel magnetic divertor configurations and the power
exhaust of a fusion reactor”, ibid.
[7] Y. Someya, K. Tobita, “Estimation of Decay Heat inFusion DEMO Reactor”, Plasma and Fsuion Research:Regular Articles Vol. 7, 2405066 (2012).