Experiment of unique combination number due to the third-order neutron-correlation

Tomohiro Endo, Sho Imai, Kenichi Watanabe, Akio Yamamoto, Atsushi Sakon, Kengo Hashimoto, Masao Yamanaka, Cheol Ho Pyeon

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

From zero-power reactor noise measurement, the second- and third-order neutron correlation factors Y and y3 can be evaluated by analyzing mean, variance, the third-order central moment of neutron count data. Theoretically, it is expected that the neutron-correlation ratio Y3/Y2 converges to the unique combination number “3” at a near-critical state in an arbitrary system without depending on the fissile material and the neutron-energy spectrum of core, as the neutron counting gate width T increases sufficiently. Thus, the information about the difference between y3/Y2 and “3” has the potential to judge whether a target unknown system is critical or not and to roughly guess the absolute value of subcriticality. In this study, the detector dead-time effect on y3/Y2 is theoretically investigated based on the heuristic method using the single-, pair-, and trio-detection probabilities with the fundamental mode approximation. As a result, it is clarified that the saturation value of y3/Y2 converges to “3” independent of the dead time, when a target system is a critical state. For validation, actual experimental results are presented for a non-multiplication system driven by 252Cf spontaneous source, and shallow and deep subcritical systems at Japanese experimental facilities (UTR-KINKI and KUCA) under the shutdown state. Consequently, it is demonstrated that y3/Y2 shows a significant difference from “3” in the non-multiplication system. In the case of subcritical systems driven by inherent neutron sources, it is confirmed that the ratios y3/Y2 are close to the unique combination number “3,” and the slight difference from “3” is measurable by the long-time reactor noise measurement for the deep subcritical system.

Original languageEnglish
Title of host publicationInternational Conference on Physics of Reactors
Subtitle of host publicationTransition to a Scalable Nuclear Future, PHYSOR 2020
EditorsMarat Margulis, Partrick Blaise
PublisherEDP Sciences - Web of Conferences
Pages1736-1744
Number of pages9
ISBN (Electronic)9781713827245
DOIs
Publication statusPublished - 2020
Event2020 International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020 - Cambridge, United Kingdom
Duration: Mar 28 2020Apr 2 2020

Publication series

NameInternational Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020
Volume2020-March

Conference

Conference2020 International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020
Country/TerritoryUnited Kingdom
CityCambridge
Period3/28/204/2/20

All Science Journal Classification (ASJC) codes

  • Nuclear Energy and Engineering
  • Safety, Risk, Reliability and Quality
  • Nuclear and High Energy Physics
  • Radiation

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