24P113-P
Research on oxidation resistance of tritium barrier tubes
in a fusion reactor heat exchanger
核融合炉熱交換器におけるトリチウム回収管の耐酸化性に関する研究
Hiroe Ishihara, Mitsuo Nakai, Takayoshi Norimatsu and Hiroshi Azechi
石原宏恵, 中井光男, 乗松孝好, 疇地宏Institute of Laser Engineering, Osaka University
2-6, Yamadaoka, Suita-shi, Osaka 565-0871, Japan
大阪大学レーザーエネルギー学研究センター〒565-0871 大阪府吹田市山田丘2-6
In a fusion reactor, tritium is used as fusion fuel. Control of tritium diffusion and leakage due todiffusion is therefore necessary to prevent contamination of the coolant in the second loop and leakage toenvironment. We proposed a tritium barrier with double tubes for the heat exchanger. The double tube
has small tubes with oxidizer and carrier gas for the tritium recovery. In this experiment, we focused onoxidation of tritium barrier tubes and investigated the growth of the oxidation on the inner surfaces of thetubes.

1. Introduction
In laser fusion reactor, tritium, a radioactive
material, is used as fusion fuel. So there is a riskthat tritium melt in the thermal cycle is saturated
and passes through the furnace. To solve thisproblem,
some coating methods have been
researched. [1] We proposed a tritium barrier withdouble tubes for the heat exchanger. The double
tube has small tubes filled with oxidizer and acarrier gas for the tritium recovery. By settingthese tubes in a heat exchanger, tritium permeation
flux is supposed to reduce to 10-4-fond by ANSYS
analysis. In addition, this method can be used in
combination with other permeation methods such as
ZrO or Er2O3 coating. The concept of the double
tubes, however, has some matters such as oxidationof the inner surface of the small tube. It is
assumed that oxidation of the inner surface
somehow influences hydrogen permeation. In thisexperiment, we simulated a tritium barrier tube in aheat exchanger by using light hydrogen instead oftritium and focused on oxidation resistance of thetube. (SS 316 stainless tube)

2. Experimental apparatus
We made the experimental apparatus as shown in
Fig.2. Hydrogen is filled in the outer chamber and,an oxygen/argon mixed gas flows through the innertube.

Fig.2 Experimental apparatus
The rate of Oxygen in the mixed gas is 20%,
which is the same as that in the air. Then weobserved the inner surface of the sample with adigital microscope and SEM and measured masspercentage of oxygen by fluorescent X-ray analysis.
For comparison, the experiment without hydrogen(vacuum) was performed as well.
We experienced at various heating duration time;
1 hour, 3 hours, 5 hours and 10 hours.
The amount of hydrogen is passing throughstainless steel is given by the following equation.
(1)

Fig.1 Tritium barrier tube

J: hydrogen permeation (ml)P: hydrogen pressure of the outer chamber andthe inner tube (atm)In this experiment, the amount of hydrogen is
assumed 62 ml (standard pressure) per hour.
3. Digital microscope and SEM images
1 hour heatingvacuum

degree of oxygen or reduction by hydrogen.
But, from the amount of oxygen in Figure.5,
10-hour-heating sample of vacuum was moreoxidized. At this duration time, the inner surface
of both was similar while there was clear difference
at 5-hour-duration.

H2

Fig.3 digital microscope images
With digital microscope, we could finddifference of degree of oxidation process betweenhydrogen-filled and vacuumed at even 1 hour ofduration time. The inner surface of the tube withhydrogen atmosphere was darker and it seemed
more oxidized, both of them, however, ware enable
to measure oxygen by fluorescent X-ray analysis
because of extremely small amount.

Fig.4 SEM images at 5 hours duration
By SEM observation, clear difference of thesurface figure appeared after 5 hour-heating. This
result shows that hydrogen permeation strongly
influences oxidation of the surface. The oxidation
particles in hydrogen atmosphere looked bigger
and more coarse-grained, but they disappeared at10-hour-heating and the surface was similar tovacuumed one.
4. Rate of oxygen in hydrogen atmosphere
The amount of oxygen on the inner surface wasmeasured with fluorescent X-ray analysis, but only
long-heating-time samples were measurable;
5-hour-duration in hydrogen atmosphere and bothof 10 hours. The other unmeasurable samples, theconcentration of oxygen on them were supposed tobe less than 2 %. The longer heating time, thehigher rate of oxygen was measured. It wasassumed that the 5-hour-duration sample ofhydrogen atmosphere had more oxygen thanvacuumed one because it was measurable. It was
not clear whether it is come from the difference ofDetection Limit

Fig.5 amount of oxygen
It is also clear from Figure.5 that oxidation
was suppressed in hydrogen atmospherecompared 5 hours with 10 hours.

5. Conclusion
We experimentaly simulated a tritium barrier
tube in a heat exchanger and investigated thegrowth of the oxidation on the inner surfaces of thetube. From Fig.5, it was cleared that the innersurface of the long-time-heating sample inhydrogen atmosphere was less oxidized than thatheated in vacuum while the opposite result cameout in short-heating experiment. In long heatingtime, oxidation seemed to be suppressed because ofreduction by hydrogen. In short heating time,
however, it is not cleared why the samples inhydrogen atmosphere had more oxide than vacuum
ones.
It is necessary to measure the amount ofpermeation hydrogen at each heating time and thesurface composition change of the tube.
References[1] HATANO Yuji, TORIKAI Yuji, OYA Yasuhisa, ODA
Takuji, TANAKA Satoru et al. : Tritium Permeation,
Contamination and Decontamination J. Plasma
Fusion Research Vol.85, No.10 (2009) 726-235[2] T. Norimatsu et al., Presented at Tritium 2010,Oct.24-29, 2010, Nara, Japan