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La Recherchev2


Low moderated 4.738-WT.%-enriched uranium dioxide fuel rod arrays reflected by water or polyethylene



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Titre du congrès :ICSBEP Technical Review Group Meeting - 2008 Ville du congrès :Prague Date du congrès :05/05/2008


A low-enriched and low-water-moderated array composed of UO2 (4.738 wt.% 235U) fuel rods at a 1.6-cm square pitch (reflected or not by water) or at a 1.075-cm, 1.1-cm-square pitch (reflected by water and by polyethylene) is considered in this experimental program. These experiments were subcritical approaches extrapolated to critical, with the multiplication factor reached being very close to 1.000 (within 0.1%). The subcritical approach parameter was the water level. These experiments were carried out in the testing equipment called "Apparatus B" in the experimental criticality facility of CEA centre at Valduc in 1998. The experimental program is described in the basic report (see Reference 1), but other reports were consulted in order to have the whole set of data (References 2 through 5). The Fuel of rods is identical to the one used in LEU-COMP-THERM-050 (Pré-FP experiments), but the AGS-clad rods are replaced by Zircaloy-4. The main concern of nuclear manufacturers is to store the highest quantity of fuel assemblies in limited areas. One solution is to decrease the pitch between fuel rods in order to decrease the reactivity of individual assemblies and then to increase the rods number. However, a strict validation of calculation methods is needed to ensure that calculations for such pitches are correct. That is the purpose of this benchmark. The total uncertainty in terms of reactivity is around 0.080% (1), which might be underestimated given the lack of knowledge of systematic uncertainties. All experiments are considered acceptable for use as benchmark.