UNCERTAINTIES OF THE NEUTRONIC CALCULATIONS AT CORE LEVEL DETERMINED BY THE KARATE CODE SYSTEM AND THE KIKO3D CODE
Nowadays, there is a tendency to use best estimate plus uncertainty methods in the field of
nuclear energy. This implies the application of best estimate code systems and the
determination of the corresponding uncertainties. For the latter one an OECD NEA
benchmark was set up. The objective of the OECD NEA Uncertainty Analysis in BestEstimate Modeling (UAM) LWR benchmark is to determine the uncertainties of the coupled
reactor physics/thermal hydraulics LWR calculations at all stages.
In this paper the uncertainties of the neutronic calculations at core level – originating from the
uncertainties of the basic nuclear data – are presented. The investigations have been made for
a VVER-1000 core (Kozloduy-6) defined in the frame of the UAM benchmark. In the first
part of the paper, the uncertainties of the effective multiplication factor, the assembly-wise
radial power distribution, the axial power distribution and the rod worth are shown. After that
the preliminary evaluation of the uncertainties of the neutron kinetic calculations are
presented for a rod movement transient at HZP state, where the uncertainties of the time
dependent core and assembly powers and the dynamic reactivity were evaluated.
In both cases, we will see that the most important quantities – at core level and at HZP state have a considerable uncertainty which is originating from the uncertainties of the basic cross
section library in these investigations.
In the frame of the OECD NEA UAM benchmark 1 there has been a large activity to
determine the uncertainties of coupled reactor physics/thermal hydraulics LWR calculations
at all stages. In order to perform this large task, 3 phases were defined in the benchmark and
these phases include the survey of the uncertainties of the stand alone neutronics (Phase I), the
time dependent neutronics, stand alone thermo-hydraulics, the fuel behavior calculations
(Phase II) and the system phase, as well.
In this paper we concentrate on the determination of uncertainties of ?core physics? (Phase I,
Exercise I-3) and partially on the determination of uncertainties of the ?Time-Dependent
Neutronics? (Phase II, Exercise II-2). It is important to note that only the uncertainties of the