Fission chambers for ex-core use

Fission chambers for out-of-core use

Photonis manufactures a broad range of fission chambers for out-of-core use in severe environmental conditions. They are used in thermal neutron detection for up to 11 decades for wide range reactor monitoring.

Detection of thermal neutrons in wide flux ranges
Very high safety of use
Customization according to the user’s needs
Contact sales Request for a quote

Technical information

Ex-core fission chambers without integral Cable

Basic type External diameter (mm) Length (mm) Operating Range Max.
      Pulse mode Current mode  
CFUM11 25.4 227 10 - 107 107 - 1011 250
CFUL01 48 337 1 - 106 104 - 1010 250
CFUK09 60 395 0.3 - 3x105 105 - 1010 250

Ex-core fission chambers with integral Mineral Insulated Cable

Basic type External diameter (mm) Length (mm) Operating Range Max.
Basic type External diameter (mm) Length (mm) Pulse mode Current mode Max. operational temperature (°C)
CFUM18 25.4 263 10 - 107 107 - 1011 250
CFUL08 48 384.5 1 - 106 104 - 1010 250
CFUC06 48 412 1 – 105 104 - 1010 600
CFUK08 60 362 0.3 – 3x10^5 10^5 - 10^10 250
CFUP08 76.5 389 1 - 106 104 - 1010 250
CFUG08 80 419 0.2 - 2x105 105 - 7x1010 250




Their outstanding Gamma rejection capabilities allow them to be used in waste monitoring applications such as spent fuel monitoring. 

Gas filled neutron detectors are designed to operate in three modes:

  • Pulse mode analyzes and counts individual detector pulses. 
  • Fluctuation, or Campbell mode, is used to analyze the fluctuation of the direct current from the detector.
  • Current mode is used to measure the mean of the direct current from the detector.

LOCA versions of fission chamber standard models are available on demand. These fission chambers are typically designed with a maximum operating temperature of 250°C (although some versions can monitor up to 600°C) and are equipped with an integrated mineral insulated cable and a HN connector. Due to the extreme operating conditions of fission chambers, Photonis also recommends the use of a mineral insulated cable extensions designed specifically for the detector.

Custom coaxial cable extensions & connectors

By full control of the following processes, Photonis Nuclear Instrumentation can supply custom fission chambers for ex-core use with the highest quality and reliability levels:

  • Adaptation of industrialized fission chambers to customer specific requirements.
  • Development of new fission chambers with our experienced R&D team.
  • Long term collaboration with the French Alternative Energies and Atomic Energy Commission / CEA (theoretical approach, modeling, qualification tests in research reactors).
  • Complete manufacturing process on site.
  • Support from all the Photonis Group activities, experience and knowledge.
  • Certifications & Quality Assurance programs adapted to the customer environment.
  • Technical support, applying expertise.
  • Export control, as an Authorized Economic Operator, Photonis acts in accordance with the EU international regulations.
  • Fissile material management & product storage

Examples of custom versions from basic types

  • Neutron sensitivity tailored to individual requirement
  • Guard-ring (2 outputs) or coaxial (1 output) structure
  • Stainless Steel or Nickel alloy for high temperature (>250°C)
  • Adapted mechanical interface with the equipment (Customized external dimensions, springs, threads, hooks)
  • LOCA (Lose Of Coolant Accident) and post-LOCA protection
  • Ruggedized structure for harsh environment (radiation, temperature, humidity, mechanical stress)
  • Integral cable or integral connector
  • Coaxial or triaxial mineral insulated cable
  • Mineral insulated connector type (Coaxial HN, BNC, BNC HT, SMA or triaxial solutions). Reinforced types are available for high pressure, high temperature conditions
Fission chambers for ex-core use

Main features

  • Structure configuration: Coaxial or guard-ring.
  • Structure material: Aluminum for max. F32 operational temperature. 
  • Integral cable: Coaxial Mineral insulated cable for pulse and current transmission, high immunity. Integral cables are recommended for the signal and for the high voltage when operating in severe -environments.
  • Connector: HN Mineral insulated connector for pulse and current transmission. 
  • Insulators: As it is necessary to measure extremely low currents, insulators must be of very high quality and radiation resistant. Photonis only uses high-grade alumina insulators from qualified suppliers.


The French Alternative Energies and Atomic Energy Commission (CEA) selected Photonis as its technological partner for a cooperative development of neutron and gamma detectors when the French nuclear power program took shape in the sixties.

Our references

  • PWR – wide range neutron flux monitoring – ex-core fission chambers CFUG – Switzerland.
  • VVER – wide range neutron flux monitoring – ex-core fission chambers CFUL – Hungary, Slovakia, Ukraine.
  • Fuel reprocessing plant – AREVA La Hague/ORANO – numerous fission chambers – France, Japan.
  • FBR – wide range neutron flux monitoring – high temperature 600 °C fission chambers CFUC – France.





Want to know more?

Do you have a question or comment? We would like to hear from you!

Contact us today to discuss your project or request additional information. We will be in touch as soon as possible.

Contact Sales Get a quote