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Science and Technology of Nuclear Installations
Volume 2012, Article ID 620808, 14 pages
Research Article

Two-Group Theory of the Feynman-Alpha Method for Reactivity Measurement in ADS

1Centre for Energy Research, Hungarian Academy of Sciences, P.O. Box 49, 1525 Budapest, Hungary
2Department of Nuclear Engineering, Chalmers University of Technology, SE 412 96 Göteborg, Sweden

Received 30 December 2011; Accepted 21 February 2012

Academic Editor: Alberto Talamo

Copyright © 2012 Lénárd Pál and Imre Pázsit. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The theory of the Feynman-alpha method, which is used to determine the subcritical reactivity of systems driven by an external source such as an ADS, is extended to two energy groups with the inclusion of delayed neutrons. This paper presents a full derivation of the variance to mean formula with the inclusion of two energy groups and delayed neutrons. The results are illustrated quantitatively and discussed in physical terms.