Program - Brookhaven National Laboratory

derive reliable covariances from targeted integral experiments using a re-estimation method [4][5]. Commercial
Reactors are characterized by large sizes and consequently a strong “Eigen Value Separation”
factor (EVS>20). Consequently, the radial power map calculation is very sensitive to ND perturbations.
The main uncertainty component is linked to 238 U inelastic scattering cross-section. Moreover, in GEN-4
Fast Reactors the 238 U(n,n’) contribution to Keff uncertainty (1400 pcm in 1sigma for GFR) amounts to
4 times the target-accuracy. To meet the target-accuracy required by GEN-3 and GEN-4 designs, the
238 U(n,n’) uncertainty has to be reduced from 20% (current standard deviation) to 5%. The improvement
of 238 U inelastic scattering data, and the reduction of the associated uncertainty, were obtained through
the use of targeted integral measurements. We selected experiments which show a strong sensitivity to
238 U(n,n’) : - Critical Pu spheres reflected by Unat (PMF-001, PMF-006, PMF-022 from ICSBE Handbook
[6]), compared to Pu bare spheres - Critical Uenriched sphere/cylinder/parallelepipeds reflected by Unat
(TOPSY experiments), compared to Uenriched GODIVA bare sphere - Fast Reactor lattices with Uranium
fuel at Kinf = 1 (SCHERZO experiments in MINERVE and SNEAK [7]) - 3D fission rate distribution
from start-up measurements of the French N4 PWR-1500MWe [8]. Owing to the large size of this fresh
core, the radial power map is very sensitive to 238U(n,n’) data. C/E biases were obtained from TRIPOLI4
Monte Carlo reference calculations [9] using the latest European library JEFF-3.1.1 [10]. C/E comparison
showed satisfactory results, with a small tendency to overestimate Keff when the spheres are reflected by
Unat. Sensitivity coefficients of these measured Keff (and P) to 238 U(n,n’) multigroup cross-sections were
also obtained from TRIPOLI4. The re-estimation of 238 U inelastic cross-sections, performed by our RDN
code based on a non-linear regression technique, enhanced a trend for a slight reduction of JEFF3.1.1
238 U(n,n’) above 800 keV. This method allowed the determination of the actual JEFF3 covariance matrix.
This reliable 238 U(n,n’) covariance will enable, through propagation technique, the calculation uncertainty
due to nuclear data for GEN-3 and GEN-4 neutronic parameters.
[1] M. Salvatores, R. Jacqmin, “Uncertainty and target accuracy. Assessment for innovative systems”.
Report by NEA/WPEC SG-26 (2008) [2] C. Vénard, A. Santamarina, “Calculation Error and Uncertainty
due to Nuclear Data,” Proc. NCSD2005, Knoxville, Sept 19-22, 2005. [3] T. Ivanova et al.,
“OECD/NEA Expert Group on Uncertainty Analysis for Criticality-Safety Assessment: Current Activities”,
Proc. of PHYSOR2010, Pittsburgh, USA, May 9-14, (2010). [4] A. Santamarina et al., “Reestimation
of Nuclear Data and JEFF3.1.1 Uncertainty Calculations,” Proc. Int. Conf. Advances in
Reactor Physics PHYSOR2012, Knoxville, USA, April 15-20, 2012, on CD-ROM, American Nuclear Society,
LaGrange Park, IL (2012). [5] C. De Saint Jean et al., “Estimation of multi-group cross section
covariances for 235,238U, 239Pu, 241Am, 56Fe, 23Na and 27Al,” Proc. Int. Conf. Advances in Reactor
Physics PHYSOR2012, Knoxville, USA, April 15-20, 2012. [6] B. Briggs, “International Handbook of
Evaluated Criticality-Safety Benchmark Experiments,” OCDE/Nuclear Science (2011) [7] J-P. Chaudat,
M. Darrouzet, E. Fischer, CEA Report R-4552 (1974). [8] P. Leconte, J-F. Vidal, N. Kerkar, “Validation
of the JEFF3.1.1 library for the calculation of the physical assays in the N4 Chooz-B1 PWR using
TRIPOLI4” Proc. of PHYSOR2010, Pittsburgh, USA, May 9-14, (2010). [9] J-P. Both et al., “A Survey of
TRIPOLI-4,” Proc. of 8th Conf. on Radiation Shielding, Arlington, USA, April 24-28, 1994, I, 373 (1994).
[10] A. Santamarina et al., “The JEFF-3.1.1 Nuclear Data Library,” JEFF Report 22, OECD 2009, NEA
No.6807.
HE 2 4:00 PM
Investigation of Nuclear Data Libraries with TRIPOLI-4 Monte Carlo Code for
Sodium-Cooled Fast Reactors
Yi-Kang Lee, Emeric Brun
Commissariat a l’Energie Atomique et aux Energies Alternatives, CEA-Saclay,
DEN/DANS/DM2S/SERMA, France
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