Computing neutron detector response to power reactor mechanical structure vibrations D. Dobrea*, I. Dumitrache, D. Gugiu, M. Constantin, L. Aioanei Institute for Nuclear Research, PO Box 78, 0300 Pitesti, Romania Received 9 June 2003; accepted 22 November 2003 Abstract Neutron detector response to power reactor mechanical structure vibrations is computed in order to obtain a quantitative reference for noise analysis. For a space-dependent approach in large cores, Cohn’s method of reducing time-dependent neutron balance equations to statics equations was considered. In order to produce detector response matrices, depending on many vibrating sources 1 and frequencies, a dedicated 3-D code was developed. Simulations indicated that response matrices could be used to locate vibrating sources for low local to global noise ratios and to obtain their vibration amplitudes. # 2003 Elsevier Ltd. All rights reserved. 1. Introduction The mechanical structure vibrations inside power reactor cores produce the reactor local noise through local cross-section fluctuations (Wach, 1975) and noise analysis techniques could be used to identify the vibrating structure. Usually there are several mechanical structures with near identical vibrating modes, like fuel assemblies. Moreover, spatial effects influence the detector response to local noise. Thus, characterizing the vibrating source (position, amplitude) based on detector frequency spectra is not straightforward, a quantitative reference being necessary: computed detector responses to vibrating sources. In this way long-range effects of Annals of Nuclear Energy 31 (2004) 891–909 www.elsevier.com/locate/anucene 0306-4549/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.anucene.2003.11.009 * Corresponding author. Fax: +40-248-262449. E-mail address: mdobrea@scn.ro (D. Dobrea). 1 For simplicity, instead of ‘local noise source’, the expression ‘vibrating source’ will be used.