J. Plasma Fusion Res. SERIES, Vol. 9 (2010)

Prototype Manufacturing of Small Tritium Target inside JAEA
Shigeru TANAKA, Yuichi ABE, Masaru KAWABE, Chuzo KUTSUKAKE, Yoshikazu OGINUMA,Masayuki YAMADA, Takumi SUZUKI, Toshihiko YAMANISHI and Chikara KONNO
Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan(Received: 19 November 2009 / Accepted: 12 April 2010)

Since 2006 we have conducted R&D for manufacturing a tritium target for the Fusion Neutronics Source (FNS)facility inside JAEA for ourselves. The small tritium target is produced by adsorbing tritium in a thin titanium layer
deposited on a cup-shaped copper-alloy substrate. The titanium layer of 24 mm in diameter and ~ 5 Pm in thickness
is deposited on the bottom of the substrate. We carried out many tests of adsorbing deuterium to the titanium layer
instead of tritium. As a result, we found out that the control of humidity is one of critical issues to keep high tritium
concentration in the target. We succeeded in producing small tritium targets at the Tritium Processing Laboratory(TPL) in JAEA. The small tritium target manufacturing procedure was established.
Keywords: tritium target, titanium, humidity, outgassing, FNS, TPL

diameter and ~ 5 Pm in thickness is deposited on thebottom of the substrate. The thickness of the titanium
was decided as double range of a 350-keV deuteronbeam in titanium. Figure 2 shows the picture of thesmall target for FNS.

1. Introduction

The Fusion Neutronics Source (FNS) facility inJapan Atomic Energy Agency (JAEA) is anaccelerator-based DT neutron source for fusion
neutronics research. FNS has two beam lines and uses
two types of tritiated titanium targets. One is a small
target of 30 mm in diameter with about 370 GBq tritium
at the 1st target room and the other is a large one of 310
mm in diameter with about 30 TBq tritium at the 2ndtarget room. We have imported the tritium targets so far,but the target purchase cost increased, while our budget
decreased gradually. In 2006 we started R&D for
manufacturing a tritium target for stable supply for FNS
inside JAEA for ourselves. The progress of the small
tritium target manufacture R&D is described in thispaper.

Copper alloy
target substrate

Titanium(About 5Pm Thickness)

20mm

30mm indiameter

Fig. 1 Vertical cross sectionof small target.

2. Target manufacture flow

The small tritium target is produced by adsorbing
tritium in a thin titanium layer evaporated on a
cup-shaped copper-alloy substrate. The manufacture
flow is as following;
1) Fabrication of a target substrate,2) Titanium vapor deposition,3) Activation of titanium layer if necessary,4) Tritium adsorption.

Fig. 2 Picture ofsmall target.

The tritium adsorption is influenced by titanium
grain size, which changes depending on a titanium
vapor deposition condition. In low temperature, a lot ofsmall grains form the microstructure porosity. On theother hand, in high temperature, the grain grows and themicrostructure vacancies decrease [1,2]. The suitable
substrate temperature and deposition speed in vapor
deposition are essential to adsorb a lot of tritium [3].
The preprocessing of the target substrate before thetitanium vapor deposition and the titanium vapor
deposition condition are as follows,

3. Target substrate and titanium vapor
deposition condition

The small target substrate of a cup-shaped
copper-alloy is 30 mm in diameter and 20 mm in heightas shown in Fig. 1. The titanium layer of ~ 24 mm in

Substrate cleaning : supersonic wave cleaning withmethylene-chloride

author’s e-mail: tanaka.shigeru63@jaea.go.jp

338©2010 by The Japan Society of Plasma
Science and Nuclear Fusion Research

S. Tanaka et al., Prototype Manufacturing of Small Tritium Target inside JAEA

was fully implanted. Finally it was concluded that
humidity disturbed tritium adsorption much more than theoxidation film.
The tritium gas (T2) is adsorbed to the titanium
surface and is dissociated. Dissociated tritium atoms (T)diffuse from the grain boundary to inside of titanium. It isconsidered that water molecule blocks up the adsorptionof the tritium gas to the titanium surface.
DD neutron generation ratio to that ofmaximum deuteron implanted target (%)

Outgassing of substrate :500 degrees C, 60 minutes
Vapor deposition temperature of substrate :350 degrees C
Argon sputters cleaning : -2 kV, 10 minutes
Titanium thickness : 2.3 mg/cm2
Vapor deposition area : 4.5 cm2
Vapor deposition speed : 7.8 nm/s

4. Target substrate handling

Since titanium metal is very active to oxygen,oxidation film of a few nm in thickness is formed on atitanium-deposited surface in the atmosphere. At first it
was thought that this oxidation film gradually thickened
by contact with atmospheric oxygen and this oxidation
film disturbed tritium adsorption. Therefore glow
discharge cleaning of -2 kV with argon gas was carriedout for one hour to remove the oxidation film on thetitanium surface.
The adsorption chamber described in Sec. 5 heats
the target substrate with a heater during tritium
adsorption. The main gas released from the target
substrate, heater and inside of an adsorption chamber
during the heating was water vapor. Thus we consideredthat it was also important to handle thetitanium-deposited substrate and adsorption chamber in
low humidity environment. We performed deuterium
adsorption test in environment humidity of under 3%,
which was the lowest humidity level easily realized atFNS. The titanium-deposited substrate was stored in astorage vacuum chamber to avoid atmospheric humidity.
In order to examine the glow discharge cleaning
effect, we manufactured two small deuterium targets inthe same method as shown in Sec. 5. One had the glow
discharge cleaning of the titanium surface with argon gas
to remove an oxidation film of the titanium surface, while
the other did not. The titanium-deposited target substratesof the deuterium targets were kept in a storage vacuum
chamber during one month in FNS before adsorbing
deuterium gas. We measured DD neutron generation ratesof the manufactured deuterium targets by bombarding
deuteron beam at FNS in order to estimate how muchdeuterium was adsorbed. Figure 3 shows DD neutron
generation rates to that of a deuterium target in which
deuterons was fully implanted. The DD neutron
generation rates of the manufactured deuterium targets
with and without the glow discharge cleaning are around
80 % of that of a deuterium target in which deuterons wasfully implanted, which is probably due to the oxidation
film, and the difference between them is small. It was
found out that the glow discharge cleaning was notnecessary. We also examined the humidity effect. The
DD neutron generation rate of a deuterium target
manufactured in normal atmospheric humidity was lessthan 1 % of that of a deuterium target in which deuterons

10080604020with discharge cleaning
whitout discharge cleaning

0020406080100120

Incident deuteron (millicoulomb)

Fig. 3 DD neutron generation rates of manufactured
deuterium targets normalized to that of a
deuterium target in which deuterons was fully
implanted.

5. Tritium adsorption procedure

It is essential keep the target substrate in tritium gas
around 400 degrees C for a while in order to adsorb
tritium to the titanium layer deposited on the target
substrate. We developed a tritium adsorption chamber,which can keep a vacuum and have a heater for
temperature control of the target substrate.

TPTritium
storagesystem

Tritium
Absorption
ChamberPT

TMP

Vacuum Header

TMP
Grobe Box

Tritium safety system

Temperature

TMP: Turbo molecular pump

Fig. 4Tritium adsorption system.

Figure 4 shows the outline of the tritium adsorption
system. The tritium adsorption system consists of atritium adsorption chamber, tritium storage line,
circulation line, vacuum line and pressure, temperaturemonitors. The target adsorption chamber volume is 2.7339

S. Tanaka et al., Prototype Manufacturing of Small Tritium Target inside JAEA

After heating power off, the remaining tritium gas
was recovered to the storage tank by circulating to thestorage tank line. The amount of tritium adsorbed totitanium was estimated from pressure and temperature in
the adsorption chamber and Tritium Storage System(TSS).㻌Figure 5 shows the data for the amount estimationof the tritium adsorption. We calculated quantity oftritium adsorption with the formula (1) from subtracting
B and C from A shown in Fig. 5.㻌 The amounts of theadsorbed tritium in the two targets were deduced to beboth about 320 GBq, which were comparable with thoseof previously imported small targets.

liter and the heating power is 450 watts. It can handle
three small targets at a time. The metal gasket is used in
all connection flanges to keep good seal performance.
The tritium adsorption system is installed in the glove
box of the Tritium Processing Laboratory (TPL), which
can handle a large amount of tritium in Japan.
We manufactured two small tritium targets at thesame time. For one of the two target substrates the glowdischarge cleaning of the titanium surface with argon gas
was performed to remove an oxidation film on thetitanium surface. The titanium target substrates kept in
the argon gas to avoid humidity were set to theadsorption chamber in the glove box of the TPL. The
humidity in the glove box of TPL was kept to 1 ppm bycirculating through nitrogen. The tritium leak test of theaccess flange was done to verify seal performance after
the target substrate set up. The target substrate washeated up to the 430 degrees C in a vacuum, and thentritium gas of 6.5 kPa was infused to the adsorption
chamber and was kept for one hour [4].

6. DT neutron production characteristics

We measured DT neutron production performanceof the manufactured targets with FNS. The initial DT
neutron generation rate with the discharge cleaning wasabout 1.7x1011 n/s per 1 mA deuteron beam of FNS,
while that without the discharge cleaning was 1.8x1011
n/s per 1 mA deuteron beam of FNS. The initial DT
neutron generation rates of the target with and without
the discharge cleaning were almost the same. Figure 6
shows the change of the DT neutron generation rates ofthese targets and previously imported targets withbombarding deuteron beam quantity. The reason of thisattenuation is tritium release from the target due to heatof bombarding deuteron beam, not consumption due toDT reaction. The attenuation rates of the neutron
generation rate of the manufactured targets are small,while those of the most imported targets are large. It isconcluded that the neutron generation performance ofthe manufactured targets is quite good.

1. Before infuse tritium to tritium adsorption chamber of FNS.
Tritium is infused to TSS of TPL.
Tritium adsorption
chamber of FNS
3TSS

V : 2737cm (the net volume)
T : 460 degrees C
P :0 kPaA3

V :1189.4 cm
T : 19.3 degrees C
P :23171.36 Pa
V : volume T : temperature P : pressure: Valve close: Valve open
TSS : Tritium storage system of TPL

2. Tritium is infused from TSS o f TPL to tritium adsorption
chamber of FNS. (The valve is opened till about 6.5 kPa
with pressure of the chamber slowly.)
Tritium adsorption
chamber of FNSTSS㻞㻚㻡 㽢㻝㻜

V :2737 cm3
T : 460 degrees C
P :0 kPa

Tritium adsorption
chamber of FNS

TSS

V :2737 cm3
T : 457 degrees C
P :6786.09 Pa

V : 1189.4 cm3
T : 19.6 degrees C
P :12078.97 Pa

Neutron generation rate [n/s/mA]

V :1189.4 cm3
T : 19.3 degrees C
P :23171.36 Pa
3. The target substrate of FNS is adsorbing tritium (one hour keep)

4. The target substrate completed the tritium adsorption and it iscooled till room temperature
Tritium adsorption
chamber of FNS C(after cooling)
V :2737 cm3
T : 16 degrees C
P :4519.61 PaTSSB
3

V : 1189.4 cm
T : 16.4 degrees C
P :11852.33 Pa

㻝㻝FNS#2 with discharge cleaning
FNS#3 without discharge cleaning
Previously imported targets㻞㻚㻜
㻝㻚㻡
㻝㻚㻜
㻜㻚㻡
㻜㻚㻜

A, B and C show the amount of the tritium.
The amount of the tritium adsorption is A minus B minus C.

㻜㻡㻜 㻝㻜㻜 㻝㻡㻜 㻞㻜㻜 㻞㻡㻜 㻟㻜㻜 㻟㻡㻜Incident deuteron [coulomb]

P ( Pa )273
V u P( Pa ) u 273 u 95.756 u 0.9
The amount of the tritium = V u1055( Pa ) u 273  T u 95.756 u 0.9 , (1)
10 ( Pa ) 273  TFig. 6

where 1 atm is 105 Pa, tritium activity in pure tritium gas is95.756 GBq㺃/acc and tritium purity is 90 %.

Change of the DT neutron generation rates.

We replace the target when the neutron generation
rate is less than 0.5 x 1011 n/s/mA. The neutrongeneration rate is determined by the tritium quantity inthe target, which is released due to heat by bombarding

Fig. 5 Data for the amount estimationof the tritium adsorption.

340

S. Tanaka et al., Prototype Manufacturing of Small Tritium Target inside JAEA

deuteron beam, depending on titanium deposit
temperature and a storage period of the targets. The
previously imported small targets were used from about
4 days to 12 days (7 hours/day) with an average DC
beam current of about 1mA, but the manufactured
targets were used for more than 12 days.
7. Summary
Since 2006 we have conducted R&D for
manufacturing a tritium target for FNS inside JAEA. It
was found out that it was humidity to avoid tritium
adsorption on the target. We succeeded in the tritium
adsorption of two target substrates at the same time atTPL. The initial DT neutron generation rates of the targetwith and without the discharge cleaning were almost thesame. The DT neutron generation performance of themanufactured targets was quite good. The manufacture
condition and procedure of the small target wasestablished. Now we are developing a tritium adsorption
chamber by using which eight small targets and one large
target can adsorb tritium at the same time.
[1] C. Monnin, A. Ballanger,E.Sciora,A Steinbrunn,
P.Alexandre, G.Pelcot, Characterization of deuteridetitanium targets used in neutron generators, Nucl. Instr.
Meth. A 453, 493 (2000).
[2] A. Kinbara, Hakumaku no kihon gijyutu in Japanese,
ISBN4-13-063041-5 C3350 P2266E, (1995).
[3] C. Monnin, P. Bach, P.A. Tulle, M. Rompay, A. Ballanger,
Optimisation of the manufacturing process of tritide anddeuteride used for neutron production, Nucl. Instr. Meth. A
480, 214 (2002).
[4] G. Huang, X. H.Cao, X.G. Long, B.F. Yang, W.K. Liu,
Studies on the characteristic of Titanium Tritium Reaction,
J. Fusion Energy 26, 307 (2007).

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