Startup reactivity accountability attributed to isotopic transmutations in the irradiated beryllium reflector of the high flux isotope reactor

David Chandler, G. Ivan Maldonado, R. T. Primm

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

1 Scopus citations

Abstract

The objective of this study is to develop a methodology to predict the reactivity impact as a function of outage time between cycles of 3He, 6Li, and other poisons in the High Flux Isotope Reactor's (HFIR) beryllium reflector. The reactivity worth at startup of the HFIR has been incorrectly predicted in the past after the reactor has been shut-down for long periods of time. The incorrect prediction was postulated to be due to the erroneous calculation of 3He buildup in the beryllium reflector. It is necessary to develop a better estimate of the start-of-cycle symmetric critical control element positions since if the estimated and actual symmetrical critical control element positions differ by more than $1.55 in reactivity (approximately one-half inch in control element startup position), HFIR is to be shutdown and a technical evaluation is performed to resolve the discrepancy prior to restart. 3He is generated and depleted during operation, but during an outage, the depletion of 3He ceases because it is a stable isotope. 3He is born from the radioactive decay of tritium, and thus the concentration of 3He increases during shutdown. The computer program SCALE, specifically the TRITON and CSAS5 control modules including the KENO V.A, COUPLE, and ORIGEN functional modules were utilized in this study. An equation relating the down time (td) to the change in symmetric control element position was generated and validated against measurements for approximately 40 HFIR operating cycles. The newly-derived correlation was shown to improve accuracy of predictions for long periods of down time.

Original languageEnglish
Title of host publicationInternational Conference on the Physics of Reactors 2010, PHYSOR 2010
PublisherAmerican Nuclear Society
Pages2856-2868
Number of pages13
ISBN (Print)9781617820014
StatePublished - 2010
Externally publishedYes
EventInternational Conference on the Physics of Reactors 2010, PHYSOR 2010 - Pittsburgh, United States
Duration: May 9 2010May 14 2010

Publication series

NameInternational Conference on the Physics of Reactors 2010, PHYSOR 2010
Volume4

Conference

ConferenceInternational Conference on the Physics of Reactors 2010, PHYSOR 2010
Country/TerritoryUnited States
CityPittsburgh
Period05/9/1005/14/10

Keywords

  • HFIR Be beryllium He-3 helium reactivity

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