Two-component representation of the neutron spectrum of fast research reactors

Abstract

An important element of the state system for guaranteeing the unity of neutron measurements performed on nuclearphysics setups is the reference neutron field. By definition [1, 2] this field consists of a region of the neutron field of the nuclear-physics setup that is fixed in space and is certified with respect to its constant spectral characteristics.The basic principle of supporting neutron measurements on nuclear-physics setups, based on the requirements of economy and taking into account the complexity and labor intensiveness of metrological work, is decentralized by unified (regulated) reproduction of the units of quantities under conditions which approach as close as possible the working measurements with one-step transfer of the dimensions of the units directly to the means of measurement [2].It is obvious that the requirement of guaranteeing unity with the decentralized approach to the creation of the reference fields is directly associated with unification of both the means of measurements and the methods for determining the spectral characteristics from the experimental data. The latter procedure is especially important for reference fields of neutrons from pulsed reference nuclear reactors, for which the method of integral detectors (a general name for methods employing the integral form of the response of the detectors: neutron-activational, different methods with fission detectors, and others) is, with respect to all nuclear-physical factors, almost the only method of investigation and reproduction of spectral characteristics. The problem of determining the neutron spectrum from data obtained from integral detectors is an improperly posed problem, and the stability of the results of solving the problem depends, to a large degree, on the choice of the a priori (initial) approximation.Using the approach, proposed in [3], for forming an a priori spectrum and the results of the successful application of this approach for the description of the neutron spectrum for the standard field at the center of the BIR-2 core [4], we attempted to work out a unified representation of the neutron spectrum in the intracore regions of reactors with a predominately metal core. Pulsed research reactors with a metal core are employed by many scientific laboratories (SPR II, III at the Sandia National Laboratory in the USA, BIR-2 and BR-1 at the All-Union Scientific-Research Institute of Electrophysical Apparatus (VNIIt~F), BARS-2 and -5 at All-Union Scientific-Research Institute of Technophysical Apparatus (VNIITF), Russia; Caliban in France; YAYOI in Japan; CFBR II in China; etc. [5]). Because of the good screening by the fissioning materials, the neutron spectrum in the intracore cavities of such reactors is, as a rule, not influenced by the scattered neutrons of the reactor enclosure (scattering by objects and equipment surrounding the core, in the walls of the containment shell, and so on) and when a unified representation of the spectrum is possible, the spectrum can be used as a specialized standard for fast neutr...

Activation Measurement of the Neutron Spectra of the BARS-5, IGRIK, and YAGUAR Reactors

“…To this end, it is suggested in [4][5][6] on the basis of a priori considerations concerning a typical reactor spectrum that a prescribed set of model functions be used.…”

N-spline reconstruction of neutron spectra on the basis of activation measurements

“…Moreover, it is proposed in [7] that a two-component representation of the neutron spectrum as a combination of a Maxwell spectrum (for the fission neutrons) and the spectrum for inelastically scattered neutrons with a small (only four) number of unknown parameters α 1 , α 2 , a 1 , and a 2 be used in the in-core regions of reactors with a metal core. For completeness, we also note that the function [8] is a good fit to the neutron spectrum of a californium source, used as a standard in many countries.…”