Neutron spectra at two beam ports of a TRIGA Mark III reactor loaded with HEU fuel H.R. Vega-Carrillo a,n , V.M. Hernández-Dávila a , F. Aguilar b , L. Paredes b , T. Rivera c a Unidad Académica de Estudios Nucleares de la Universidad Autónoma de Zacatecas, C. Ciprés 10, Fracc. La Peñuela, 98068 Zacatecas, Zac. Mexico b Instituto Nacional de Investigaciones Nucleares, Carretera México-Toluca s/n, La Marquesa Ocoyoacac, 52750 Mexico c Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada—Unidad Legaria, Av. Legaria 694,11500 México, DF. Mexico HIGHLIGHTS  Neutron spectra of a TRIGA reactor were measured.  The reactor core is loaded with HEU.  The spectra were measured at two reactor beam ports.  Measurements were carried out at 5 and 10 W. article info Available online 22 May 2013 Keywords: Research reactor Neutron spectrum Bonner sphere spectrometer abstract The neutron spectra have been measured in two beam ports, one radial and another tangential, of the TRIGA Mark III nuclear reactor from the National Institute of Nuclear Research in Mexico. Measurements were carried out with the reactor core loaded with high enriched uranium fuel. Two reactor powers, 5 and 10 W, were used during neutron spectra measurements using a Bonner sphere spectrometer with a 6 LiI(Eu) scintillator and 2, 3, 5, 8,10 and 12 in.-diameter high-density polyethylene spheres. The neutron spectra were unfolded using the NSDUAZ unfolding code. For each spectrum total flux, mean energy and ambient dose equivalent were determined. Measured spectra show fission, epithermal and thermal neutrons, being harder in the radial beam port. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Nuclear reactors are classified in several ways; in terms of their applications reactors are classified as reactors for teaching, research, isotopes production, and for power production. TRIGA is the acronym of Training, Research, Isotopes, General Atomics; there are four different versions of these reactors: Mark I, II, III and F; the main differences are the transient or stationary power level, the location of reactor pool, the amount and type of irradiation facilities and the mobility of reactor core (IAEA, 2005). Under the leadership of F. Dyson a team did the original design of TRIGA reactor with the aim of this being installed and operated in scientific institutions and universities (GAES, 2011). In 1956 the General Atomic Division of General Dynamics did create a group of scientists, under the direction of E. Teller, with the task to design a nuclear reactor so safe that even with the sudden withdrawal of all the control rods the reactor will reach the steady state without damaging the fuel (Dyson, 1979); this goal was accomplished in the design of the reactor fuel. The fuel used in the TRIGA reactors is hydrogen-containing uranium–zirconium alloy, UZrH, where U is 8% enriched with 20% of 235 U. The H in the UZrH array makes it inherently safe (GD, 1963). The moderator, the fuel features and its geometrical array in the core characterize the neutron spectrum in the core and along the beam ports. In order to use the beam ports the neutron spectra must be characterized (Marek and Viererbi, 2011; Nakamura et al., 2011; Nascimento et al., 2007). The ININ's Nuclear Center Dr. Nabor Carrillo has a TRIGA Mark III reactor; on April 24th, 1964, it became critical. Since then the reactor has been used for research, training, teaching and for radioisotopes production. Due the 235 U enrichment, the nuclear fuel is defined as high enriched uranium, HEU. In order to fulfill the international agreement to reduce the nuclear risk worldwide it was decided to change the HEU with a core of low enriched uranium, LEU (US, 2010). This change could Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes 0969-8043/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2013.04.008 n Corresponding author. Tel./fax: +52 492 922 7043. E-mail addresses: fermineutron@yahoo.com, rvega@uaz.edu.mx (H.R. Vega-Carrillo), vic_mc68010@yahoo.com (V.M. Hernández-Dávila), fortunato.aguilar@inin.gob.mx (F. Aguilar), lydia.paredes@inin.gob.mx (L. Paredes), riveramt@hotmail.com (T. Rivera). Applied Radiation and Isotopes 83 (2014) 252–255