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Tritium breeding blankets  


Role of blankets 

In a tokamak, the blanket is the object situated immediately behind the first wall (Cf figure opposite).



Simplified diagram of a fusion reactor.

Its main functions are as follows : 

  1. Protect the magnets and the vacuum vessel from neutron and gamma radiation.

  2. Produce the tritium necessary for continued fusion reactions.

  3. Convert neutron energy into heat and evacuate it to generate a cycle capable of supplying electricity.

These three functions may not be present at the same time (Cf chart below). In the first phase of ITER operation, only the 1st function is guaranteed (ie shield blanket). In a second phase of ITER operation, the 1st and 2nd functions are guaranteed (ie cold tritium breeding blanket). In the case of a reactor, functions 1, 2 and 3 are required (ie tritium breeding blanket).

  Current machines ITER  Reactor
1 - Protection of magnets      
2 - Production of Tritium  


3 - Converting neutron energy into heat      


function required

The "Production of Tritium" equation and notably reaching auto-sufficiency is a delicate balance. Performance in terms of auto-sufficiency is characterised by the TBR (Tritium Breeding Ratio). A TBR greater than 1 indicates that the blanket is auto-sufficiency. 

The production of tritium is achieved through the reaction n + 6Li --> T + He. The lithium–based material may be in liquid (liquid metal like LiPb) or solid form (ceramic like Li4SiO4 or Li2ZrO3 or Li2TiO3), i.e.  liquid or solid tritium breeding blanket. For solid blanket, auto-sufficiency necessitates use of a neutron multiplier like beryllium (for liquid blanket, lead in the tritium breeding material acting as multiplier).

The fusion reaction


<-- PRODUCTION of tritium

In the case of inertial fusion, the functions of Protection, Production and Conversion are also required from the blanket. The concepts developed for magnetic fusion are thus directly transferable to inertial fusion.


Activities of the EURATOM-CEA Association

Tritium breeding blankets are the subject of a specific European-level programme. Very significant results have been obtained, such as, the demonstration that auto-sufficient production of tritium was achievable in a reactor. All the concepts developed to date have a TBR greater than 1. Two concepts are being studied at the European level :

  • the WCLL concept (Water Cooled Litium Lead), developed under the coordination of the CEA, uses a liquid metal (LiPb) as the tritium breeding material and water as a coolant.

  • The HCPB concept (Helium Cooled Pebble Bed), developed under the coordination of FZK FZK website, employs a tritium breeding material in solid form (lithiated ceramic) cooled by helium. 





CEA tritium breeding blanket concept

The main subjects of study of the Association are :  

  • The design of a test module of the WCLL blanket to be set up in ITER.

  • The development of manufacturing techniques.

Model of test module manufactured
by hot isostatic pressure (HIP).


Manufacture of double tubes.

  • The development and testing of coating enables the control of aspects associated with tritium permeation (permeation barrier)


CEA loop enabling
the study of permeation barriers.

  • The physical-chemistry of LiPb (control of Li grade) and problems of steel corrosion. 

  • The development of tritium breeding ceramics (Li2TiO3). 




Semi-industrial manufacture of
tritium breeding ceramic pebble.


 For further information :

  • Fusion Technology. Annual Report of the Association EURATOM/CEA
    Blanket activitiesf

1998 issue, 75p,  3577 ko, PDF
1999 issue, 90p, 3497 ko , PDF
2000 issue: 80p,  5259 ko, PDF
2001 issue: 93p,  6969 ko, PDF
2002 issue: 78p,  5964 ko, PDF
2003 issue: 48p, 14706 ko, PDF
2004 issue (PDF)
   - pages 000-014 :
Cover, contents, introduction (518 Ko)
   - pages 113-134 : EFDA activities: breeding blanket (2 330 ko)
pages 279-282 : Underlying technologies: breeding blanket (2 663 ko)
2005 issue (PDF)
    - pages 000-004 : Cover, contents, introduction (824 Ko)
    - pages 161-220 : EFDA activities: breeding blanket 10 246 ko)
    - pages 285-296 : EFDA activities: "Reactor" studies  (720 ko)
    - pages 367-370 : Underlying technologies: breeding blanket (2 663 ko)
2006 issue (PDF)
    - pages 000-004 : Cover, contents, introduction (1.4 Mo)
    - pages 145-211 : EFDA activities: breeding blanket (12.2 Mo)
    - pages 271-280 : EFDA activities: "Reactor" studies  (1.3 Mo)
    - pages 360-361 : Underlying technologies: breeding blanket (0.5 Mo)


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