Fission Chambers for in-core use

Photonis fission chambers for in-core use can be made to operate at temperatures up to 600°C depending on the reactor types and the detection requirements.

In-core measurements of neutron flux ranges
Tight stainless steel structure
Customization according to the user’s needs

Technical information

In core fission chambers optimized for pulse mode operation:

Basic type External diameter (mm) Length (mm) Operating Range Max. operational temperature (°C)
      Pulse mode (nv) Current mode (nv)  
CFUR44 3 46 104 - 109 - 350
CFUF34 4.7 85 103 - 108 - 300

In core fission chambers for current mode operation:

Basic type External diameter (mm) Length (mm) Operating Range Max. operational temperature (°C)
      Pulse mode (nv) Current mode (nv)  
CFUZ53 1.5 49 - 2 x 1011 - 1014 350
CFUR43 3 48.5 - 1011 – 1.5 x 1014 350
CFUF43 4.7 86 - 1010 - 1014 350

In core fission chambers for wide range operation:

Basic type External diameter (mm) Length (mm) Operating Range Max. operational temperature
      Pulse mode (nv) Current mode (nv)  
CFUR64 3 42 106 - 1011 1012 - 1015 300
CFUE24 7 150 102 - 106 108 - 1012 400
CFUE32 7 150 103 - 106 109 - 1013 600


They are critical components for reactor neutron flux monitoring, and can be used to detect thermal neutrons in high flux, to monitor the reactor fuel burn-up, to control start-up, intermediate and power ranges.

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.

Fission chambers are filled with the appropriate gas for both high-temperature or fast response and are extremely radiation resistant. Depending on the type of fission chamber required, a BNC or HN connector can be mounted on the integrated mineral insulated cable designed specifically for the detector. Fission chambers for in-core use are designed to be movable inside the reactor core during operation. In research environments, our 1.5 mm external diameter subminiature chambers allow measurements close to the physical phenomenon.

> Custom fission chambers for in-core use (read more)

By full control of the following processes, Photonis Nuclear Instrumentation can supply custom fission chambers for in-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
  • Calibration in reactor for measurements in high flux
> Examples of custom versions from basic types (read more)
  • Neutron sensitivity tailored to individual requirement
  • Isotopic composition (235U enriched, natural or impoverished Uranium)
  • Adapted mechanical interface with the equipment (Customized external dimensions)
  • Ruggedized structure for harsh environment (radiation, temperature, humidity, mechanical stress)
  • Adapted and ruggedized cable for propulsion in the core
  • Mineral insulated connector type (Coaxial HN, BNC, BNCHT). Reinforced connectors are available.

Did you know?

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 programme took shape in the sixties.


  • PWR – neutron flux mapping – in-core fission chambers CFUF – Belgium, China, France, South Africa, South Korea, Slovenia.
  • ADS – wide range neutron flux monitoring – CFUF – Ukraine.
  • BWR – start-up and intermediate range – In-core movable fission chamber CFUE – Finland, Sweden
Fission Chambers for in-core use



CFUR43 Specifications(PDF file, 249.44 KB)
CFUR64 Specifications(PDF file, 266.42 KB)
CFUZ53 Specifications(PDF file, 304.95 KB)


Resource center

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

Visit the Resource Center

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