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

Technical information

Fission chamber out core
In core fission chambers optimized for pulse mode operation
Yype Ext
Operating Range


      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 - 3x106 105 - 1010 250


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In core fission chambers for current mode operation
Basic type Ext
Operating Range Max.
      Pulse mode 
Current mode 
CFUM18 25.4 263 10 - 107 107 - 1011 250
CFUL08 48 384.5 1 - 106 104 - 1010 250
CFUC06 48 372 1 – 105 104 - 1010 600
CFUK08 60 362 0.3 – 3x105 105 - 1010 250
CFUP08 76.5 428 1 - 106 104 - 1010 250
CFUG08 80 419 0.2 - 2x105 105 - 7x1010 250


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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 fission chambers for out-of-core use

By full control of the following processes, Photonis Nuclear Instrumentation can supply custom fission chambers for out-of-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 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

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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, BNCHT or triaxial solutions). Reinforced types are available for high pressure, high temperature conditions

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Main features
  • Structure configuration: Coaxial or guard-ring.
  • Structure material: Aluminum for max. 250°C 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.

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The French Atomic Energy Commission (CEA) selected Photonis as its technological partner for a co-operative 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 counters – France, Japan.
  • FBR – wide range neutron flux monitoring – high temperature 600 °C fission chambers CFUC – France.

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Fission Chambers for out-of-core use



CFUG08 Specifications(PDF file, 249.36 KB)
CFUK08 Specifications(PDF file, 252.94 KB)
CFUL01 Specifications(PDF file, 207.71 KB)
CFUL08 Specifications(PDF file, 235.6 KB)
CFUM11 Specifications(PDF file, 239.96 KB)


Resource center

Are you looking for a specification sheet or paper? Documents like these and more are available in the Photonis Resource Center. 

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