Estudo neutrônico do uso de veneno queimável em reatores Candu avançados

Abstract

The ACR (Advanced CANDU Reactor) is a reactor concept developed by AECL (Atomic Energy of Canada Limited) that is derived from the already well-established CANDU (Canadian Deuterium Uranium) line of reactors. The main difference of this advanced system is the use of light water (H2O) as coolant and slightly enriched fuel. The ACR-1000 is currently one of the new designs and uses the CANFLEX-ACR (CANDU FLEXible) advanced fuel design as its fuel element. To help control reactivity, this element uses absorbent material or burnable poison on its central rod. Still on this point, there are currently two proposals in the literature for the material to be used, the first an alloy composed of zirconium, dysprosium and gadolinium (Zr-Dy-Gd) and the second a zirconium rod coated with hafnium. In this context, the present work uses the SCALE 6.0 (Standardized Computer Analyzes for Licensing Evaluation) code to configure a fuel element. The objective is to evaluate the neutronic behavior of the fuel element for the two central rod proposals. The analyzes were divided into two stages, in the first the criticality and the CVR (Vacuity Coefficient of Reactivity) were evaluated in the steady state, varying the proportions of dysprosium and gadolinium from 1% to 5% for the Zr-Dy-Gd alloy and the thicknesses from 0.5 mm to 4.0 mm of the hafnium coating in different cases. Those that showed the best response were selected for the second stage, in which criticality and CVR during burning were analyzed. When evaluating the behavior of the CVR during burning, the 0.5 mm hafnium case is the most advantageous, however, the Dy4%-Gd3% presents lower CVR values ​​at the beginning of the burning and higher kinf at the end of the cycle. Considering that the study was developed for a fuel element, further analyzes simulating the active ACR core are necessary to determine which of the two cases would be the most appropriate.