Miniature Fission Chambers

Name: Miniature Fission Chambers
Brand: Exosens

Engineered for the world’s most demanding nuclear environments, Exosens’ Miniature Fission Chambers deliver exceptional neutron detection accuracy, rapid response, and high-temperature resilience.

Designed for performance, certified for safety, and trusted across the nuclear industry.

In-core measurements of neutron flux ranges

Watertight structure

Exceptional reliability and extended operating life

Flexible customization to meet specific user applications - Customization according to the user’s needs

Thermal and fast neutron detection capabilities

Miniature Fission Chambers

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Technical information

Product^[a]	Diameter^[b] (mm)	Sensitive Length^[b] (mm)	Thermal Neutron Sensitivity^[b][c][d]		Fast Neutron (2.5MeV) Sensitivity^[b][d][e]	Typical Material	Type^[i]
			Pulse (cps/nv)	D.C. (A/nv)	Pulse (cps/nv)
CFUZ	1.5	10	5x10^-18	-	-	Stainless Steel^[g]	Miniature
CFUR	3	oct-13	8.0x10^-6 - 1.5x10^-4	9.2x10^-19- 1.7x10^-17	-	Stainless Steel^[g]	Miniature
CFUF	4.7	27	x10^-3	^-	-	Stainless Steel^[g]	Miniature
CFUE	6	56	x10^-3	x10^-16	-	Stainless Steel^[g]	Miniature
FC4^[j]	6.3	25	0.003	^[f]	6.94x10^{-6 [e]}	Stainless Steel^[g]	Miniature
CFUE	7	56	x10^-2	x10^-15	-	Stainless Steel^[g]	Miniature
FC10^[j]	12.7	29	0.008	^[f]	1.73x10^{-5 [e]}	Stainless Steel^[g]	Miniature

[a] Significant catalogue of fission chamber designs and variants available. Table shows the most popular variants[b] Nominal values stated
[c] At 1000µg/cm2 of 235U unless otherwise stated. Alternative coating materials and densities are available which will alter performance.
[d] Standard tolerance on these devices is ±20%
[e] At 1000µg/cm2 of 238U unless otherwise stated. Alternative coating materials and densities are available which will alter performance.
[f] Estimated from mono-energetic neutron testing of PFC338/450/U238 and theoretical sensitivity factor determined from cross-section ratio (≈9x10-4)
[g] Simple reconfiguration required to optimise performance for this operational mode.
[h] May be suitable for high temperature (300°C to 600°C) or very high temperature (>600°C) operations, subject to specific configurations.
[i] Design, materials and manufacturing process are common among most of these devices. Consequently, operation capability is common and may be transferable.
[j] Available with organic cables.

Description

Exosens’ miniature fission chambers are capable of operating in pulse, fluctuation (Campbell or Mean-Squared-Voltage), or current modes to deliver accurate, reliable neutron flux measurements across startup, operational, and safety-critical conditions. Engineered for resilience in high-radiation and high-temperature applications, including custom solutions tailored to your needs.

Miniature fission chambers are critical components for reactor neutron flux monitoring and can be used to detect neutrons in high flux, to monitor the reactor fuel burn-up, and to control reactor output in the source, 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 / Mean-Squared-Voltage mode, is used to analyze the fluctuations in the signal.
Current mode is used to measure the mean of the direct current from the detector.

Miniature fission chambers offer a robust solution for a wide range of neutron flux levels and maintain performance stability, even in harsh radiation and high-temperature conditions. Their fast response time, wide dynamic range, and resilience make them critical for reactor monitoring, safety systems, and experimental applications.

Miniature fission chambers for in-core use may be designed to be movable inside the reactor core during operation. In research environments, our smaller chambers allow measurements close to the physical phenomenon.

What We Offer:

We supply a comprehensive range of fission chambers optimized for demanding applications. Our portfolio includes:

High-flux capable chambers for power reactor monitoring and control.
Customized designs tailored to specific reactor conditions or experimental needs.
Harsh environment models for extended lifetimes in high temperatures and radiation levels.

Our expertise ensures reliability, precision, and safety in all neutron detection applications, supporting the operational excellence and regulatory compliance of nuclear facilities worldwide.

Custom miniature fission chambers

With full control of the following processes, Exosens can supply custom Exosens fission chambers with the highest quality and reliability levels:

Adaptation of industrialized fission chambers to customer-specific requirements utilizing significant operational experience
Development of new fission chambers with our experienced research and development teams.
Long-term collaboration with internationally renowned organizations for modeling, qualification tests in research reactors and development.
Complete manufacturing and test process on site.
Support from all the Exosens group activities, experience, and knowledge.
Highly regulated Quality Assurance programs adapted to the customer’s environment.
Expertise in design and manufacture of nuclear instrumentation to solve customer challenges.
Export control, as an Authorized Economic Operator, Exosens acts in accordance with the EU international regulations.
Fissile material management & product storage
Calibration measurements in high radiation flux

Examples of customization of standard parts

Neutron and gamma sensitivity tailored to individual requirements.
Isotopic composition: enriched ²³⁵U, natural, ²³⁸U or ²³²Th.
Materials for high temperature (>3000°C) and very high temperature (>600°C) operation.
Adapted mechanical interface for installation (Customized external dimensions, springs, threads, hooks).
Ruggedized structure for harsh environment (radiation, temperature, humidity, mechanical stress).
Integral cables or integral connectors.
Adapted and ruggedized cable to allow propulsion in reactor core.
Customized connector type (BNC, HN, SHV and many others)

References

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

A FISSION CHAMBER FOR OPERATION AT 850 C

PWR – wide range neutron flux monitoring – ex-core fission chambers – Belgium, Switzerland, USA.
VVER – wide range neutron flux monitoring – ex-core fission chambers – Hungary, Slovakia, Ukraine.
Fuel reprocessing plant – AREVA La Hague/ORANO –fission chambers – France, Japan.
FBR – wide range neutron flux monitoring – high temperature (600 °C) fission chambers – France.
Research Reactors – internationally
Thorium High-Temperature Reactor – Germany
Boiling Water Reactor (BWR)
MAGNOX
Advanced Gas-cooled Reactor (AGR)
CANada Deuterium Uranium reactor (CANDU)
Pressurized Heavy-Water Reactor (PHWR)
Pressurized Water Reactor (PWR)
Water-Water Energetic Reactor (VVER)
Training Research Isotopes General Atomics (TRIGA)
Fast Breeder Reactor (FBR)
Research Reactors
High temperature gas-cooled reactors
Sodium cooled fast reactors
Thorium high temperature reactor
Fusion reactors