The choice of Pu242 fission chambers to monitor the fast neutrons in a high flux

Philippe Filliatre, Ludovic Oriol, Christian Jammes, Ludo Vermeeren, Marcel Wéber

    Research outputpeer-review

    Abstract

    Fission chambers are widely used for on-line measurements of neutron fluxes in irradiation reactors. When the flux is high with a significant thermal component, the measurement of the fast component is a concern and implies a careful choice of the deposit material. Indeed, most fissile materials have a cross section much higher with thermal neutrons than with fast ones. Moreover, a deposit chosen to favour fissions by fast neutrons will make radiative captures in the thermal domain, leading to a gradual modification of the isotopic compositions of the deposit that may dramatically increase the fissions with thermal neutrons. Within the framework ot the FNDS (Fast neutron Detector System) project, we performed simulations of the evolution of the isotopic composition and fission rate for several deposits under high fluxes. We show that Pu242 is the best choice to extract the fast component from a flux with a significant thermal component, provided that the impurities in Pu241 and Pu239 are small enough. However, an independent measurement of the thermal component appears to be necessary to compensate for the evolution of the Pu242 deposit.
    Original languageEnglish
    Title of host publicationProc. NPIC&HMIT 2009
    Place of PublicationLa Grange Park, Illinois, United States
    StatePublished - Apr 2009
    EventSixth American Nuclear Society International Topical Meeting on Nuclear Plant Instrumentation, Control and Human-Machine Interface Technologies (NPIC&HMIT2009) - ANS, Knoxville, Tennessee
    Duration: 5 Apr 20099 Apr 2009

    Conference

    ConferenceSixth American Nuclear Society International Topical Meeting on Nuclear Plant Instrumentation, Control and Human-Machine Interface Technologies (NPIC&HMIT2009)
    Country/TerritoryUnited States
    CityKnoxville, Tennessee
    Period2009-04-052009-04-09

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