The geometry and material content of the Yalina-Booster two-zone subcritical assembly driven by external neutron sources are described, along with the instrumentation and conditions of experimental measurements. 252Cf isotope and a neutron generator with a TiT or TiD neutron-producing target are used as external neutron sources. The results are presented from analytical and experimental estimates of the levels of subcriticality in two core configurations: (1) with a fueled core (uranium dioxide of 10% enrichment in the thermal zone and uranium dioxide of 21% enrichment in the fast zone) and (2) with uranium dioxide of 10% enrichment in the thermal zone and without fuel in the fast zone. The calculated effective fractions of delayed neutrons in the considered thermal zone are compared. It is shown that the main kinetic parameters are defined by the thermal zone. The calculated results are compared to experimental ones, and the discrepancies are analyzed.

Reaction rates were measured by the foil activation technique to obtain neutron spectrum information in a subcritical core driven by an external neutron source. The experimental results are compared with Monte Carlo calculations in order to examine the capability of the Monte Carlo code MCNP together with ENDFB-6.8. JEFF-3.1.1 and CENDL-3.1 neutron cross section libraries to predict the neutron spectrum dependent reaction rates correctly in a subcritical core. The focus lies on fast neutrons. A discrepancy is found in the calculated-to-experimental values of the reaction rates and an inaccurate cross section is identified in CENDL-3.1. (C) 2011 Elsevier Ltd. All rights reserved.

Neutron noise measurements based on the Rossi-α and Feynman-α methodologies have been performed in a heterogeneous subcritical system. It is shown that the traditional single alpha-mode formulations of the Rossi-α and Feynman-α methods are not applicable due to the presence of higher alpha-modes. Formalisms taking into account multiple alpha-modes are applied resulting in satisfactory results. Three alpha-modes could be identified using the Rossi-α method, whereas only two could be obtained using the Feynman-α method. In the Feynman-α case, the possibility to obtain the fastest decaying alpha-mode was diminished due to detector dead time effects. It was found that the slowest decaying alpha-mode does not exactly correspond to the prompt decay found in pulsed neutron source measurements, which confirms the results of previous studies. Strengths and weaknesses of the multiple alpha-mode Rossi-α and Feynman-α methods observed in this study are pointed out.

Feynman-α and Rossi-α formulas including multiple α-modes are derived for stochastic and continuous neutron sources. The presented formalism is further developed to achieve spatial correction factors for the single α-mode point kinetics representations of the Feynman-α and Rossi-α formulas. As a natural extension of the multiple α-mode formalism, delayed neutrons are included in the Feynman-α formula. The obtained formulas are validated experimentally in a strongly heterogeneous system obeying multiple α-modes, resulting in good agreement with the presented theoretical framework.

Abstract The area ratio method of Sjöstrand is generally considered one of the most reliable reactivity determination methods and thus is a major candidate for off-line calibration purposes in future accelerator-driven systems for high-level waste incineration. In this work, the Sjöstrand area ratio method has been evaluated experimentally under thorough conditions in the strongly heterogeneous subcritical facility YALINA-Booster. Both strengths and weaknesses of the method have been identified. Most surprisingly, it has been found that the area ratio reactivity estimates may differ a factor of 2 depending on detector position. It is also shown that this strong spatial dependence can be explained based on a simple two-region point-kinetics model and corrected by means of correction factors obtained through Monte Carlo simulations. A new Monte Carlo correction method is proposed that includes, at the same time, the spatial disturbance and the effective delayed neutron fraction. In that way, the value of the effective multiplication factor is obtained from the measured dollar reactivity without the need of calculating the effective delayed neutron fraction explicitly, and thereby, the delayed neutron transport is performed only once. Further, it has been found that the Sjöstrand area ratio method is not sensitive to perturbations of the source multiplication factor.

A subcritical zero-power source-driven coupled core, the YALINA-Booster, has been constructed for experimental investigations of neutron kinetics of source-driven systems. In this study, the reactivity of two subcritical configurations has been determined by the area ratio method. The prompt neutron decay constants have been evaluated through slope fitting of the prompt neutron decay as well as through the pulsed Rossi-α method. It is shown that the slope fitting method and the pulsed Rossi-α method give stable results whereas the area ratio method results show spatial dependence. The reasons for the spatial spread are addressed.

The use of low energy accelerators and neutron generators to investigate the physics of multiplying systems, driven by high energy (E-p = 0.6 - -2.0GeV) particles accelerators is discussed. The prospects of the subcritical facility "Yalina" driven by a neutron generator, to study sub-critical systems driven by an external neutron sources is investigated.

The theoretical and experimental evidence of similarity of neutron spectra formed in sub-critical systems driven by external proton and neutron beams

The investigations on accelerator-driven transmutation technologies (ADTT) focus on the reduction of the amount of long-lived wastes and the physics of a subcritical system driven with an external neutron source. This paper presents the experimental facility "Yalina" which was designed and created at the Radiation Physics and Chemistry Problems Institute of the National Academy of Sciences of Belarus in the framework of the ISTC project #B-070 to study the peculiarities of ADTT in thermal spectrum. A detailed description of the assembly, neutron generator and a preliminary analysis of some calculated and experimental data (multiplication factor, neutron flux density distribution in the assembly, transmutation rates of some long-lived fission products and minor actinides) are presented.