Program - Brookhaven National Laboratory

FC 4 11:40 AM
Propagation of Nuclear Data Uncertainties in PWR Burnup Pin-Cell Deterministic
Calculations using the Total Monte Carlo Approach
Francesco Ferragut, Pouya Sabouri, Adrien Bidaud
Laboratoire de Physique Subatomique et Cosmologie, CNRS/Université Joseph Fourrier, Institut
Polytechnique de Grenoble
We present here the results of the PWR Burnup Pin-Cell Benchmark UAM I-1b based on the use of the
TENDL library [1] with the deterministic transport code DRAGON [2]. The evaluation of the uncertainties
uses the Total Monte Carlo method. Hundreds of TENDL evaluated files of of the most important
nuclides for this benchmark ( 235 U, 238 U, 239 Pu, 241 Pu) were processed with NJOY and other codes to produce
hundreds of WIMS libraries that DRAGON can read. Then, hundreds of burnup calculation where
done, whose spread is an image of the uncertainties in the evaluated files that is itself an image of the
uncertainties in the model parameters of TALYS. Our methodology gives very similar results than the full
stochastic Total Monte Carlo, where a Monte Carlo code such as SERPENT [3] is used for solving the
Boltzmann equation. In our case, thanks to the deterministic approach, we do not have to subtract the
statistical noise to calculate the uncertainty in the outputs such as keff or nuclide densities. Of course,
our methodology would be limited to applications that are within the recommended domain of use of the
transport code. When compared to methods based on the sampling of the deterministic XS [4],[5] the
advantage of our method is the consistency of the handling of the nuclear data all along the process. We
do not have to generate discontinuities in the cross sections to obtained our energy integrated libraries.
Our sampled libraries are build exactly as any classical groupwise libraries. Our group constants are build
from sampled but continuous cross sections themselves evaluated from sampled pre-evaluation parameters.
Furthermore, our approach is more consistent with the evaluation as we do not sample the lumped
cross sections (scattering, absorption, fission and total), but we lump sampled - probably more physical
- reactions such as elastic, inelastic scatterings and n,xn reaction for instance. Another advantage of the
use of TENDL libraries in a deterministic code is that we can use perturbation theory at least at the
first step of burn up so as to calculate not only the uncertainties but also the sensitivities as a function
of energy of Keff or nuclide inventory changes. We can then better understand which reactions are more
contributing to the uncertainties during fuel burnup. Furthermore, we have developed tools that can build
the covariance matrices of the sampled groupwise nuclear data. The folding of the sensitivities obtained by
Perturbation Theory with these calculated, self-shielded covariance matrices gives results very comparable
to the observed uncertainties calculated with GPT. Thanks to this method, we can not only calculate the
uncertainties but also track down the error down to the actual reactions described in the evaluation (and
not on the lumped ND used in the deterministic code) and give the weight in the error of them and of the
correlations between those reactions. Given the consistency of the method, our method not only complement
the results of available other methods, but also allows for a more straightforward and more coherent
link between the evaluation of the uncertainties given by the evaluator and their impacts calculated by the
reactor physicist.
Corresponding author: Pouya Sabouri
[1] D. Rochman and A.J. Koning. TENDL-2011: TALYS-based Evaluated Nuclear Data Library, PHYSOR-
2012 conference, Knoxville, Tenessee, USA, April 15-20, 2012. [2] G. Marleau, R. Roy and A. Hebert,
DRAGON: A Collision Probability Transport Code for Cell and Supercell Calculations, Report IGE-157,
Institut de genie nucleaire, ecole Polytechnique de Montreal, Montreal, Quebec (1994) [3] D. Rochman
and A.J. Koning, Propagation of 235,236,238 U and 239 Pu nuclear data uncertainties for a typical PWR fuel
element, accepted in Nucl. Technology, October 2011 [4] Artem Yankov, Makus Kleis, Marhew A. Jesse,
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