Nuclear Fusion Research and Development

9-6 Confining Tritium in a Fusion Facility
ᴪ A Catalytic-Reactor Design that Ensures Tritium Oxidation under All Possible Conditions ᴪFusion facility

Detritiation system
FirePreheater

Cooler Blower Cooler

LeakingStack

FilterCatalytic oxidation
reactor system

Tritium source

Tritiated water vapor
removal system

Production rate of tritiated hydrocarbons

Fig.9-15 A schematic diagram of a detritiation system
Gaseous tritium leaked in a facility is oxidized by the catalytic-oxidation-reactor system and converted into
tritiated water vapor. After that, the tritiated water vapor is removed by an appropriate system.
0.20
Accompany gas with “Tritium”
Methane 1%
Ethylene 1%
Propylene 1%Non

0.150.10

No production of tritiated hydrocarbons
0.05

0050100150200250300350400

Fig.9-16 Production rates of tritiated hydrocarbons inthe case where tritium with hydrocarbons is introduced
into the catalytic reactor
Above the broken line in the figure, it is apparent that
tritiated ethylene (or ethane) is produced by the reaction
between tritium and ethylene only. The production rate oftritiated ethylene decreases with an increase in temperatureof the catalyst since the tritium-oxidation reaction ispromoted by temperature increase. Tritiated ethylene is notproduced at 200 °C, since it completely combusts above
this temperature.

Temperature of catalyst (℃)

A large amount of tritium is used as a fuel in nuclearfusion facilities. Since tritium is a radioactive isotope ofhydrogen, a detritiation system (DS) is installed in fusion
facilities to prevent tritium release into the environment. The
DS must ensure the detritiation efﬁciency under all possible
extraordinary events. We have investigated the effects of theevents upon the detritiation efﬁciency through experiments
and analysis to design a DS that can work efﬁciently under all
extraordinary events.
The DS comprises a catalytic-oxidation-reactor system
and a water-vapor-removal system (Fig.9-15). The catalyticoxidation-reactor system must ensure the tritium-oxidation
efﬁciency in the case where various types of gases with tritium
are fed into the system under extraordinary events. Assuming
a ﬁre event, hydrocarbons such as methane and ethylene areproduced by combustion of ﬂammable organic matter. Issues
with the catalytic-reactor system include ensuring the tritiumoxidation efﬁciency, even when tritiated hydrocarbons areproduced, and controlling excessive temperature increase
owing to hydrocarbon-combustion reactions, which inducerisks of excessive tritium permeation and explosion and so on.
We have clariﬁed that a tritiated-hydrocarbon-production
reaction only occurs to a notable extent for ethylene (Fig.9-16).
This indicates that the isotopic-exchange reaction between
tritium and hydrogen is very slow and that the hydrogenation
reaction is the dominant producer of tritiated hydrocarbon.
It is found that tritiated methane, which is combusted at a hightemperature, is produced only by isotopic-exchange reactions,and also that tritiated hydrocarbons are combusted by thecatalytic reactor, whose temperature is sufﬁcient to combust
ethylene completely. Therefore, these results suggest that acatalytic reactor at a comparative low temperature of 200 °C
ensures both the tritium-oxidation efﬁciency and the excessive
temperature rise by heat of reaction in the catalytic-reactor
system.
The Japan domestic agency is in charge of procurement ofDS for ITER construction in the south of France within theITER organization. We are conducting qualiﬁcation tests ofDS and proceeding R&D for safety of a nuclear-fusion facility.

Reference
Edao, Y. et al., Effect of Hydrocarbons on the Efﬁciency of Catalytic Reactor of Detritiation System in an Event of Fire, Journal of Nuclear Science andTechnology, vol.53, issue 11, 2016, p.1831-1838.
JAEA R&D Review 2016-17

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