Uncertainties of responses calculated with a "tuned" library: Geometrical and algebraic insights

R. L. Perel*

*Corresponding author for this work

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


The standard American evaluated nuclear data library ENDF/B-VII was "tuned" based on simple measured critical assemblies. This tuning was not done according to a fully defined mathematical algorithm, such as the adjustment algorithm. In this work, we investigate how tuning affects the uncertainties (covariances) of the cross-section libraries. First, we analyze what happens to cross-section uncertainties as a result of adjustment. The effect of adjustment on the uncertainties is geometrically demonstrated for simple cases. For those parts of the sensitivities of the assembly to be calculated that are parallel to the sensitivities of the assemblies on which adjustment was based, there is significant reduction in the uncertainties. For orthogonal parts, there is no change in the uncertainties. These findings are algebraically proven based on the adjustment algorithm. Then we analyze the differences between tuned libraries and adjusted libraries. We conclude that for tuned libraries, the uncertainties in the direction of sensitivities on which adjustment or tuning were based are improved, similar to the improvement for an adjusted library. However, the displacement of the nominal values of the library parameters to their tuned value, instead of their adjusted value, adds an additional uncertainty. This additional uncertainty is typically small in the direction that was improved by adjustment. The magnitude of the additional uncertainty in perpendicular directions depends on the particular details of the tuning performed.

Original languageAmerican English
Title of host publicationReactor Dosimetry
Subtitle of host publication14th International Symposium
PublisherASTM International
Number of pages18
ISBN (Print)9780803175365
StatePublished - 2012
Event14th International Symposium on Reactor Dosimetry - Bretton Woods, NH, United States
Duration: 22 May 201127 May 2011

Publication series

NameASTM Special Technical Publication
Volume1550 STP
ISSN (Print)0066-0558


Conference14th International Symposium on Reactor Dosimetry
Country/TerritoryUnited States
CityBretton Woods, NH


  • Adjustment
  • Covariance
  • Cross section library
  • Tuning


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