Program - Brookhaven National Laboratory

W. Zwermann
Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) mbH, Forschungszentrum, Boltzmannstrasse 14,
85748 Garching, Germany
Due to the influence of the delayed neutrons on the reactor dynamics an accurate estimation of the effective
delayed neutron fraction (βeff ), as well as good understanding of the corresponding uncertainty,
is essential for reactor safety analysis. The interest in developing the methodology for estimating the uncertainty
in βeff was expressed in the scope of the Uncertainty Analysis in Modelling (UAM) project of
the OECD/NEA. A novel approach for the keff sensitivity and uncertainty analysis, based on the derivation
of the Bretscher’s approximate equation (prompt k-ratio method) was proposed and demonstrated
at the UAM-5 meeting in 2011 [1, 2]. This paper presents the results of the calculations of βeff and
the corresponding uncertainties obtained using both deterministic and Monte Carlo methods. A series of
critical benchmark experiments from the ICSBEP and IRPhE databases, such as GODIVA, JEZEBEL,
SNEAK-7A & -7B, LEU-SOL-THERM-02 were studied. βeff values were calculated by the exact expression
from the direct and adjoint fluxes (using SUSD3D and DANTSYS codes) and using Bretscher’s
method (MCNP, DANTSYS). The uncertainty analyses were performed using the SUSD3D deterministic
generalised perturbation code and the XSUSA random sampling code applied with multi-group neutron
transport codes (XSDRN, DANTSYS, and KENO). Using the JENDL-4 covariance matrices the typical
βeff uncertainty was found to be around 3% and is generally dominated by the uncertainty of nu-delayed;
depending on the considered assembly, nu-prompt, inelastic and fission cross-section uncertainties may also
give significant contributions. Excellent agreement between the βeff and their uncertainties, calculated
by the above methods was observed, validating in this way the mathematical methods and procedures
developed. The measurements of βeff in combination with the sensitivity profiles and the uncertainties
can be exploited for the nuclear cross-section validation, complementing thus the information obtained
from the keff measurements.
[1] I. Kodeli, “Sensitivity and Uncertainty in the Effective Delayed Neutron Fraction βeff (Method &
SNEAK-7A Example),” Proc. of the 5 th Workshop for the OECD Benchmark for Uncertainty Analysis in
Best-Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs (UAM-5), Stockholm
(April 13-15, 2011), NEA-1769/04 package, OECD-NEA Data Bank. [2] I. Kodeli, “Sensitivity And Uncertainty
in the Effective Delayed Neutron Fraction (βeff ),” Proc. PHYSOR 2012 Conference, Knoxville,
Tennessee, USA, 15-20 April 2012.
LC 3 4:20 PM
Sensitivity and Uncertainty Analysis for Minor Actinide Transmuters with JENDL-4.0
H. Iwamoto, K. Nishihara, T. Sugawara, K. Tsujimoto, T. Sasa
Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
To improve the design accuracy for the next generation of nuclear reactors, much effort has been devoted
to understanding uncertainties on the reactor physics parameters with the use of the sensitivity and uncertainty
(S/U) analysis and the corresponding covariance data. In particular, the nuclear design of the
minor actinide (MA) transmuters such as the accelerator-driven system (ADS) and fast reactor (FR) requires
reliable covariances, as well as cross-sections, for MAs. So far target nuclides and reactions used
for the S/U analysis have been limitted to major ones. However, analyses by limited data could lead to
misunderstanding about the target accuracy assessment. For example, despite the fact that fission-related
parameters such as the fission cross-section (σfis) and neutron multiplicity (ν) have considerable impacts
on the uncertainties on the reactors, contributions of the fission neutron spectrum have not yet been discussed.
To identify which parameters have an effect on the uncertainty of the design parameters on the MA
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