Fission chamber fabrication workshop
Tiret rouge

Fission chambers​​​

A unique workshop that offers 12 different fission chamber geometries.​​​​

The CEA has been developing and manufacturing different types of fission chambers to measure neutron fluxes online in various nuclear reactor technologies, from low-flux critical mock-ups to nuclear power reactors. These fission chambers are considered to be radioactive sources that we provide for our clients once the French nuclear regulator, the ASN, has given its approval.
A fission chamber converts neutrons into charged particles after having interacted with a fissile deposit coating the chamber’s anode and/or cathode. The fission products ionise the gas filling the chamber, thereby creating electrical charges that are collected by applying a polarising voltage. Without the fissile deposit, this detector is considered to be a standard ionisation chamber that can mainly be used to monitor changes in the gamma flux during in-core irradiation.
The purpose of our fission chamber fabrication workshop is to design and manufacture miniature detectors that meet the requirements of experimental programmes, collaborations and calls for tenders in the field of neutron and gamma flux measurements. It comprises a laboratory with five gloveboxes and a room equipped with an X-ray generator for non-destructive tests. Contrary to the industry, which manufactures standard fission chambers using uranium deposits alone, the CEA workshop offers customised geometries and a broad range of isotopes, making it a one-of-a-kind laboratory in France. The X-ray generator is used for both high-definition imaging to check the assembly operations, and for conducting tests to check that detectors operate correctly under X-ray flux at the end of the fabrication process. To date, we offer 12 different fission chamber geometries. New geometries can be developed to meet specific needs once their design has been approved by the ASN. The recent development of ‘regenerative’ fission chambers can increase their service life thanks to the use of a double fissile-fertile deposit.

Approved isotopes: U233, U234, U235, U238, Pu238, Pu239, Pu240, Pu241, Pu242, Np237, Am241, Th232, Cm244, Cm245.​​​​​

​Activités. © IRESNE/CEA​​


  • Fission chamber fabrication,
  • Non-destructive tests,
  • X-ray generator,
​Equipements majeurs. © IRESNE/CEA

Major equipment

  • Gloveboxes,
  • Laser and TIG welding,
  • Helium detector,
  • X-ray examinations,
  • Leak tests,
  • Furnace.
​​Chiffres clés. © IRESNE/CEA​​

​Key figures

5 R&D projects:

  • Improving the reliability of the fission chamber fabrication process,
  • Qualification of neutron spectra of different reactors,
  • Validation of nuclear data and modelling with the ALDEN programme at the ILL,
  • Spectrum characterisation and validation of computer codes and nuclear data with the AOSTA campaign at ENEA.
​​Partenaires. © IRESNE/CEA​​


About ten clients and industry partners

  • French welding institute,
  • JSI,
  • EDF
  • INL,
  • Etc​