S-P5-3
R&D of prediction system for tritium transport in pebble bed breeder blanket
微小球充填方式増殖ブランケット内のトリチウム輸送における予測システムの工学的研究
Yohji Seki, Takanori Hirose, Hisashi Tanigawa, Enoeda Mikio
関 洋治, 廣瀬 貴規, 谷川 尚, 榎枝 幹男
Japan Atomic Energy Agency
Mukoyama 801-1, Naka-shi, Ibaraki-ken 311-0193, Japan（独）日本原子力研究開発機構 〒311-0193 茨城県那珂市向山801-1
Development of test blanket module (TBM) in water cooled solid breeder is being performed as theprimary candidate of ITER-TBM of Japan. Prior to the installation of each TBM, it is necessary to develop
the capability of the prediction analyses of all essential functions of the blanket to validate the analyses
tools by the TBM. Especially the prediction tool of tritium concentration in the blanket system is one of themost important issues to control tritium recovery. From this view point, this paper discusses the flow
phenomena and the tritium transport of the helium purge gas in the pebble bed.

behavior simulation taking into account all essential
tritium transfer process contributes to anengineering design of a blanket.

Plasma side･ Beryllium neutron
multiplier ( Be )He + T2

Permeation of tritiumFirst wall

Flow of T2 + He･ Ceramic tritium
breeder ( Li2TiO3 )Tritium transfer from solid
breeder to He purge gas

HeH2O(a)Test blanket module (TBM) (b)Tritium breeder layer

Performance evaluationin real geometry

Applicability in Module Design

Fig.1. Configuration of test blanket module

Understandingof phenomena

1. Introduction
Research and development of a blanket moduleof water cooled solid breeder is being performed as
the primary candidate of ITER- test blanket module(TBM) of Japan as seen in Figure 1 (a). Prior to theinstallation of each TBM, it is necessary to develop
the capability of the analyses of all essentialfunctions of the blanket, because the validation of
the analyses tools by the TBM performance data
under the real fusion environment of ITER enables
extrapolation of the design and performance
analyses to DEMO blanket. Especially theprediction tool of tritium concentration in theblanket system is one of the most important issues
to control tritium recovery. From this view point,
this paper discusses the flow phenomena and thetritium transport of the helium purge gas in thepebble bed.
Tritium behavior in the blanket is a complex
phenomenon which consists of tritium generation,tritium diffusivity in crystal grain of Li2TiO3,tritium release from a breeder material of a pebble[1], purge gas thermo-hydraulics through the pebble
bed [2] and tritium permeation to a blanket
structural material as seen in Figure 1 (b). Objectiveof this study is shown in Figure 2, which is toconstruct an integrated simulation approach of heatand mass transfer in whole domain of the blanket
corresponding to real size. It aims to estimate agenerated tritium and its transport and to contributeto the design of blanket. Verifications andvalidations of the experimental data and empiricalequations of earlier studies are achieved by using
the prediction results of the integrated simulation.
Moreover, the prediction of the total tritium

Commercial Software(Thermo-fluid analysis)
Integration of overall model of tritium behavior tothermal hydraulic analysis code for simulation incomplex geometry
Practically available
simulation model for
overall phenomenaThis work

Investigation of microscopic
mechanism
Atom, molecule

Grain (μm）

Breeder pebble (mm)Blanket module (m)Representative Dimension of Phenomena

Fig.2. Diagram of scale of phenomena for this scope2. Computational condition
Two types for inlet and outlet

28mm

ZMembrane Panel (347℃)

First Wall (346℃)

1106mmHe＋T2

4. Conclusion
By prediction of purge gas flow using a
numerical simulation, the result indicates tritium
concentration depended on the position of thebreeder layer. Namely, the large concentration still
remains near the wall with approaching to an outlet.
(b)

(a)

2.37×10-2 mol/m3
22 cm/s･ porosity： 0.35
･ Reynolds number：Rep um D p1.28×10-2 mol/m3

 0.3

10 cm/snu : Bulk mean velocitymYX
138mm

Dp : Sphere Diameter (2mm)n : kinematic viscosity

2 cm/sHe
5.5[L/min], 50[℃], 0.1[MPa]Fig.3. Computational configuration in breeder layer
ZZ

Computational configuration in breeder layer ofTBM is shown in Figure 3. The value of porosity is0.35 on the basis of earlier experimental studies [2].
A Reynolds number is set to 0.3 so as to be 1 Pa ofpartial pressure of tritium at outlet, where theReynolds number is based on the bulk meanvelocity, sphere diameter and kinematic viscosity.
Inlet and outlet shape of pipe and porous types areapplied to observe a dependence of these shapes on
the velocity and the concentration. The thermalboundary condition and tritium source apply thevalues obtained from a neutron-thermal analysis.
Porous media model equation of fluid motion isapplied with uniform spatial porosity.
3. Results and discussion
In the case of pipe type, the contours of velocity
and tritium concentration are shown in Figure 4.
The velocity field of the Darcy flow in pebble bed
is regarded as a laminar flow. In this case, only amolecular diffusion contributes to concentration
diffusion without convection. Moreover, the profileof tritium source stays large value near the wall andexponentially decreases with increase distance fromthe first wall and membrane panel. Therefore, theconcentration of tritium near the walls still remains
near two times larger than that in the center pebble
bed without homogeneous concentration. The value
near the walls increases along streamwise inaccording with linearity principle of passive scalar.
This tendency of tritium concentration near thewalls is also similar in the case of the porous typeas shown in Figure 5. The difference near the inlet
between the pipe and the porous types has anegligible effect on the tritium concentration.

YY

Fig.4. Contours of (a) velocity and (b) tritium
concentration for outlet of pipe type
(b)

(a)

2.32×10-2 mol/m3
10 cm/s

1.23×10-2 mol/m3

2 cm/sZZYY

Fig.5. Contours of (a) velocity and (b) tritium
concentration for outlet of porous typeAcknowledgments
The parts in this study have been supported inpart by grant-in-aid for scientific research onpriority areas, 476, tritium science and technology
for fusion reactor from the ministry of education,
culture, sports, science and technology.
References[1] T. Kinjyo, M. Nishikawa, M. Enoeda and S. Fukada:Fusion Eng. Des. 83 (2008) 580-587.
[2] Y. Seki, S. Suzuki and M. Enoeda: Proc. 16th Int.
Workshop on CBBI, Portland, USA, 2011.