21-25 June 2021
Clarion Congress Hotel Prague
Europe/Prague timezone
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Dynamic Response Analysis of Fast-Spectrum Self-Powered Neutron Detectors

Not scheduled
3rd floor (Clarion Congress Hotel Prague)

3rd floor

Clarion Congress Hotel Prague

Freyova 945/33, 190 00 Prague 9 - Vysočany
Oral presentation 05 Nuclear Power Reactors Monitoring and Control




Self-powered neutron detectors (SPNDs) are attractive online flux monitoring tools as they are compact, simple, and produce a signal proportional to local neutron flux without the need for an external source of power. They are however optimized for thermal-neutron reactions and many do not have the required sensitivity to neutrons with energies approaching 1 MeV. Because neutron-capture cross sections in the fast-energy region are often orders of magnitude lower than those at thermal energies, the device performance (i.e., electrical current output at a given neutron flux level) will inevitably deteriorate in a neutron flux peaking at 0.5 MeV as is common in fast-reactor spectra. Therefore, any improvement in reaction rates within the emitter will help increase device sensitivity and boost the signal-to-noise ratio of the instrument. To date, the published efforts surrounding the development of SPNDs for use in fast reactors—what we are terming a fast- spectrum SPND (FS-SPND)—have centered around the examination of currently developed SPND technology for sensitivity to 0.5 MeV neutrons. In this work, we have performed a survey of Evaluated Nuclear Data File (ENDF) cross section data in an effort to identify materials, known and unknown, suitable for use as an emitter in a FS-SPND. As SPNDs generate an electrical current as a result of nuclear reactions within the neutron-sensitive portion of the detector, termed the emitter, we have focused our initial efforts on the identification of fast-neutron sensitive materials. To this end, we have identified five new emitter materials: tantalum, terbium, thulium, lutetium, and iridium. We have also identified two currently used emitter materials as suitable for use in a fast-spectrum reactor: rhodium and silver. Each of these emitter materials exhibits a sensitivity on par with currently used emitters operating in a thermal-neutron field. In this paper, we first derive the radiative capture and decay-chain rate equations for each emitter material to develop their dynamic response models. We then assess their anticipated performance as neutron monitoring instruments. Finally, we discuss dynamic compensation approaches to improve the tracking performance for local neutron flux changes in the vicinity of the device.

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