Nuclear Fusion Research and Development

9-8 Management Scenario for Radioactive Wastes with Consideration of Public Acceptance of a Fusion Reactor
ᴪ Study on Volume Reduction of Radioactive Wastes for a Fusion Reactor ᴪSuperconducting coil Maintenance port
for blanket segment

Back plate

Blanket Segment (BS)ReactorShutdown
Detritiation (Baking)30 days
Cool down by water
7 days
1 day
Prepare for maintenance
3 daysClean up W dust
Replac. of in-vessel
components

2–4 months

Breeding blanket
modules

2 days Detritiation

Hot cell /DisassemblyDivertor plate

2 months

Cassette body

Total amount of radioactive wastes
for regular maintenance basedon fusion powers

Fig.9-21 Configuration of the DEMO reactor
Superconducting coil, Vacuum vessel with maintenanceport, Blanket segment, and Divertor cassette.

Divertor Cassette (DC)
Cassette body
Divertor plate

Disposal with recycle

140120Blanket Segment (BS)100Modules casing
T breeder& n multiplier
Back plate

80
60
40
200Base case

1.3 times

1.7 times

Fusion power, Pf

Packing /Interim storage

DisposalOnce-through disposal☆Pf=1.35 GW

4 years

2 months

Disassembly in hot cell (BS)
10 years

Temporary storage (BS)2 months

Divertor Cassette (DC)160

Storage (DC)Disassembly (DC)Temporary storage (DC)

Maintenance port
for divertor cassette
Vacuum vessel

Storage in hot cell (BS)

6 years
1 yearClassification of radioactive waste (for recycle or disposal)
3 months Prepare for packing of radioactive waste (Cut and compression)
3 months Packing of radioactive waste
20–50 years
Interim storage
Disposal: shallow land burial

Fig.9-22 Radioactive waste-management scenarios for regular
maintenance of a fusion DEMO reactor
We developed a waste management scenario for the DEMO basedon the residual heat and dose rate of the used in-vessel components,including the blanket segment and the divertor cassette.

Fig.9-23 The amount of the radioactive wastes generated by replacementof in-vessel components in the normal-operation cycle has been evaluatedwith a volume-reduction method
The replacement periods of in-vessel components such as blankets and divertors
are decided based on neutron damage.

There is a concern regarding fusion reactors that thereplacements of in-vessel components such as blanket segments(BS) and divertor cassettes (DC), as shown in Fig.9-21, may
generate a considerable amount of radioactive waste andrepresent a serious environmental burden. In this study, wehave considered a strategy for reducing the waste generated
by replacement of the components. Thus far, studies on therecycling of fusion-activated materials have focused on
reducing the amount of waste that requires ﬁnal disposal. Due tothe necessity of replacing the components, waste management
is required during the operation of a fusion reactor. Therefore,
an appropriate waste-management scenario should be developed
from the conceptual-design stage.
We have developed a waste-management scenario for a fusion
DEMO reactor based on the residual heat and dose rate of theused the components, as shown in Fig.9-22. The management
scenario for the replacement of radioactive components has an
impact upon the cooling time for residual heat reduction before
the removal of components from the reactor, the design of the
hot cell, and waste storage. The components are moved to a
hot cell through a maintenance corridor after a cooling timein the vacuum vessel of approximately one month. In order tomaintain the health of the removal components, the residual heatmust be removed using active cooling to keep the temperature
below 550 °C for a structural strength of F82H. In the hot cell,
the used components are handled as follows: blanket modules
are removed from a back plate by remote-handling equipment

after cooling for 6 years. The radiation environment in the hotcell is estimated to be 100 Gy/hr. Next, the neutron multiplierand tritium breeder are recovered from each blanket module
for recycling at a disassembling facility. After that, the empty
blanket modules and divertor plates are cut into small pieces andstored in a container. The radiation environment in the facility is
estimated to be 10 Gy/hr and storage will last for 10 years. After
waste classiﬁcation in accordance with radioactivity, the waste
is packed and stored in interim storage for disposal.
We considered a strategy for reducing the radioactive wastegenerated when the components are replaced in the DEMO.
We evaluated the amount of waste generated by replacing thecomponents during the normal operation cycle. In Fig.9-23,
we suggest that the amount of waste can be reduced to 20% byreusing the back plate and cassette body and by recycling thebreeding and multiplying materials. This result suggests thenecessity of implementing waste-reduction programs. However,reusing the back-plate and cassette body in the assembly
operation may be difﬁcult with the existing RAMI program. The
volume reduction of waste is very important for commercial
fusion plants. Therefore, R&D efforts toward the developmentof an assembly operation for the BS and the DC should beinitiated in the DEMO. The study of waste management should
continue to reduce the amount of radioactive waste produced
and to generate greater public acceptance of the construction
and operation of future fusion reactors.

Reference
Someya, Y. et al., Management Strategy for Radioactive Waste in the Fusion DEMO Reactor, Fusion Science and Technology, vol.68, no.2, 2015, p.423-427.

JAEA R&D Review 2016-17

113