SII-1
Study on Maintenance, Recycle, and Radioactive Waste Management ofFusion Reactor
Part I: Brief introduction of symposium
核融合炉の保守・リサイクル・バックエンド対策に関する検討
１．趣旨説明Arata Nishimura
西村 新
National Institute for Fusion Science322-6, Oroshi, Toki, Gifu 509-5292, Japan
核融合科学研究所 〒509-5292 土岐市下石町322-6
A fusion reactor will generate 14 MeV neutrons and the kinetic energy of these neutrons will be transferredto the thermal energy which will be taken out of the reactor to generate the electricity. In this study, acertain maintenance process was assumed and several issues were discussed which must be considered in
the design phase. In the symposium, an image of maintenance will be presented and practical works will belisted. One of the key issues is “activation.” Therefore, radioactive waste management must be considered.
The other key issue is “tritium.” All the materials used in the plasma vacuum vessel contain tritium.

1. Maintenance of Fusion Reactor
A fusion reactor will realize deuterium-tritium(D-T) reaction in high temperature and highdensity plasma which will generate 14 MeV
neutrons and 3.5 MeV alpha particles. There aretwo items which must be taken into account whenthe maintenance, recycle and radioactive waste
management of the fusion reactor are discussed.
The first one is “activation” of the material.
Most of the generated fusion neutrons will becaught by blanket modules. Since the neutron has
the energy of 14 MeV, it can pass through a thinfirst wall and a structural material and reach theblanket. In the blanket module, there is a coolant
to take out the nuclear heat to outside of thefusion reactor. Lead lithium or lithium oxide will
be adopted as the coolant which will breed thetritium by getting the neutrons. At the same time,
beryllium particles will absorb the neutron andmultiply the neutrons. These reactions will occur
in the blanket and the blanket is a shielding
component against neutrons. Unfortunately, someneutrons will penetrate the blanket and others will
stream out of the ports. These neutrons will comeout of the plasma vacuum vessel and reach thesuperconducting magnets and other components
located in the cryostat. Therefore, most of thematerials in the cryostat will be activated andemit radiation.
The second is “tritium.” The tritium and thedeuterium are fuel of the fusion reactor. These areisotopes of hydrogen and both can diffuse and betrapped in the materials. The deuterium exists innature and it is harmless, but the tritium does notexist in nature and the half decay period is 12.3
years. It is harmful for a human body. So, thetritium in the fusion reactor must be controlled
perfectly. During the maintenance, the componentof the fusion reactor will be replaced. Since allcomponents in the vacuum vessel contain thetritium, the components must be insulated withthe cold space. At the same time, the tritium
detection system must work in the cold area andthe tritium removal system must stand by for 24hours.
2. Image of Maintenance Flow
The discussion on the maintenance, the recycle
and the radioactive waste will be carried out
based on these two words, activation and tritium.
The maintenance flow image of the component in
the vacuum vessel is as follows:
2.1 Unit for MaintenanceThe blanket and diverter modules must bereplaced after the operation in a certain period. Incase of ITER, the modules are taken out one byone. However, the modules in the fusion reactor
will be activated much heavier than ITER, a large
unit such as “Sector” will be replaced at one time
and transferred to the hot cell. It is called as“Sector system.” It will be safer and save a lot oftime. The total weight which must be transferred
will become large and the special transfer line
will be prepared.
2.2 Carry to Hot cell
The maintenance of the sector will be carriedout at the hot cell. To transfer the sector, the huge
cast or the container will be connected to thefusion reactor and connections will be madeperfectly to avoid gas leakage from the plasma
vacuum vessel to the reactor hall because the gas
contains the tritium. Then the sector will beturned to the torus direction and to the proper
position to transfer to the cask. All the coolingchannels and connections will be separated andconnected again in the cask when the sector ispulled into the cask. The cask might have an
independent cooling system to cool down thecomponents continuously.
On the process, the remote handling system
will be operated. The sector must be insulatedwith the air in the cold area and tritium detection
system will be available. Since the tritium unites
with oxygen in the air resulting in forming water,
HTO, the fusion reactor hall might be filled withdried and oxygen free nitrogen gas.
2.3 Storage and Disassemble in Hot Cell
The sector will be stored in the hot cell for acertain period to wait for the reduction of theradiation emission. One sector will be settled in
an individual cell where the independent airconditioning system and cooling channels will beoperated to keep the sector temperature lower.
After the radiation emission becomes weaker, thesector will be moved to the disassemble hall andtaken apart. The disassemble hall will be filledwith dried and oxygen free nitrogen and every
task will be performed by the remote handling.
The neutron multiplier of the beryllium oxide
will be reused for the other sets of the sector. So,
the reusable materials will be separated andstored for the second use. Since the reuse material
will be set in the new sector in the hot cell, thefinal assembly of the new sets of the sector will
be performed in the hot cell.
The plasma vacuum vessel structure will berecycled and the other highly activated materials
will be treated as the underground disposal. The
waste materials will be cut into small pieces andstorage into the special cask. The cask will be
stored in the cold area until the delivery.
The recovery of the tritium is an importantwork in the hot cell. The component will bewarmed up and the tritium will be collected fromthe out gas.
3. Some Special Facilities
3.1 Tritium Facility
The tritium facility is one of the key facilities
in the fusion reactor. The facility will accept thetritium from the outside, store the tritium in thesite, recover the tritium from the fusion system,and detect the tritium in the halls and in the site.
For the maintenance of the fusion reactor and thefacility, the quantitative tritium control and thetritium detection is very important. Since theoperation will continue for long term, the work
for maintenance must be carried out without thesystem interruption. The redundant system will beinstalled.
3.2 Remote Handling System
The remote handling system will be installed ininside the reactor, the reactor hall, and the hot cell
where the tritium will be treated. The system forin-vessel maintenance will be stored in the properarea when the fusion reactor is in operation. The
each tool and system must be repairable withother remote handling system. Once the machine
touches a polluted material or a part, the special
attention must be paid when it is maintenance.
3.3 Hot Cell
Hot cell will have a role for the storage ofactivated sector for waiting for the decay, thedisassemble task of the sector, the blanket and thediverter, the recovery of the tritium, cutting andpackaging of the disposals, and the storage of thecask for the final disposal. The space for the workwith the activated components will be separated
definitely. The utilities of the air conditioning
system and the cooling water system will be also
separated and redundant. The electric power will
have own generation system for emergency.
The draft of the related regulation or rule must
be prepared and it will be helpful to discuss thesafety guard system in the hot cell and in the site.
3. Program of Symposium
The symposium program will be as follows:
1. Outline of the symposium by Arata Nishimura,
NIFS. (10 minutes)
2. Research trend of maintenance, recycle,
radioactive waste management case study byKenji Tobita, JAEA. (15 minutes)
3. Outline of the maintenance engineering of thereactor by Hiroyasu Utoh. (15 minutes)
4. Remote control system in reactor hall and hot
cell by Kenichi Fukumoto, Fukui University. (15minutes)
5. Some issues related to maintenance in hot cellby Satoshi Yanagihara, Fukui University. (15minutes)
6. Some issues on tritium treatment during
maintenance and storage of activated devices inhot cell by Takumi Hayashi, JAEA. (15 minutes)
7. General discussion by Shinzaburo Matsuda,
Tokyo Institute of Technology. (20 minutes)