Program - Brookhaven National Laboratory

available for ENDF/B-VII. The observed discrepancies between calculated and experimental results (see
below) were used in conjunction with the computed sensitivity coefficients and covariance matrix for nuclear
parameters in the consistent data assimilation. As for 235U and 239Pu, the GODIVA and JEZEBEL
experimental results (keff and spectral indices) were used in order to exploit information relative to the
specific isotope of interest. The results obtained by the consistent data assimilation indicate that with
reasonable modifications (mostly within the initial standard deviation) it is possible to eliminate the
original discrepancies on the Keff of the two critical configurations. However, some residual discrepancy
remains for a few fission spectral indices that are, most likely, to be attributed to the detector cross sections.
Subsequently separated isotope irradiation experiments (PROFIL and TRAPU in the PHENIX reactor)
were used for the improvement of 242Pu and 105Pd data. The results so far obtained indicate that a much
general and robust approach based on physics arguments can be envisaged to improve nuclear data for a
wider range of applications and consistently with the requirements of advanced simulation of reactors and
associated innovative fuel cycles.
OB 2 2:00 PM
Towards unified reaction cross sections through assimilation of integral and differential
experiments.
S. Hoblit, M. Herman, G. P. A. Nobre, A. Palumbo
National Nuclear Data Center, Brookhaven National Laboratory, Upton, NY 11973-5000, USA
G. Palmiotti, H. Hiruta, M. Salvatores
Idaho National Laboratory, Idaho Falls, ID, USA
M. T. Pigni
Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, USA
The classical method of adjusting multi-grouped reaction cross sections to a specific set of integral experiments
or applications often result in cross sections that are difficult to apply to other situations where the
adjustments are not applicable or the specific energy grouping or weighting is inappropriate. To address
these issues we will discuss efforts underway at the NNDC at Brookhaven National Laboratory with collaborators
at Idaho National Laboratory to assimilate integral experiments to produce adjusted differential
reaction cross sections that can be applied to a variety of applications without the need for grouping or
adjustments tailored to specific needs. This method uses the Empire code [1] to model various materials
and determine the sensitivity of the reaction cross sections to the model parameters and their covariances
as fit to differential data. Our collaborators at INL determine the sensitivity of integral experimental quantities
to the reaction cross sections. Folding these then results in sensitivities of the integral experiments
to underlying model parameters, which can then be used to fit the integral data using the covariances from
differential data. This results in a set of model parameters and reaction cross sections and uncertainties
that simultaneously account for both the differential and integral measurements which can then be applied
to a wide variety of experiments and designs without the need for further adjustment. We also will discuss
a method under development at the NNDC where the differential cross sections are used in monte-carlo
simulations of integral experiments as an alternative method for including their sensitivities to model parameters.
The results of these studies as applied to few important materials will be presented.
[1] M. Herman, R. Capote, B. V. Carlson, P. Oblozinsky, M. Sin, A. Trkov, H. Wienke, and V. Zerkin. ”Empire:
Nuclear reaction model code system for data evaluation.” Nuclear Data Sheets, 108 (12): 2655-2715,
2007.
OB 3 2:20 PM
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