Consultant's Meeting on
Compensating Effects due to Nuclear Reaction and
Material Cross Correlations in Integral Benchmarks
28 September - 1 October 2015, IAEA, Vienna
Motivation
The background motivation for the CM is the CIELO project, therefore the focus is on the six CIELO evaluations, namely Pu-239, U-238, U-235, Fe-56, O-16 and H-1. Current status of the CIELO evaluations is given below. Further details are available on the CIELO web page.
Objectives
- Identify the most common compensating effects in reaction cross sections and cross-material correlations.
- Define methodology for selecting a list of benchmarks that can be used to test specific sets of correlations.
- Define input files for MCNP for the selected benchmarks.
Agenda
The Tentative Agenda is available here.
Pu-239
New starter file has been assembled at LANL considering SG 34 results.
The results of the CRP on PFNS (paper sent to press) indicate that the average energy of PFNS must be reduced for all fissiles.
U-238
The "ib44" evaluation has been assembled at the IAEA. An updated evaluation is about to be released, reflecting the preliminary "Standards" evaluations and small improvements to the resonance data from IRMM.
U-235
The results of the CRP on PFNS (paper sent to press) indicate that the average energy of PFNS must be reduced for all fissiles. Two complete evaluations for U-235 are available: one from BRC and one from the IAEA. The BRC evaluation contains PFNS with very low average energy of 1.97 MeV, which is consistent with the recommended value by Kornilov. The IAEA evaluation includes PFNS with the average energy of 2.00 MeV, which is the result of the PFNS CRP and is likely to become a new preliminary evaluation for the Standards.
Fe-56
A new resonance evaluation was produced at ORNL extending to 2 MeV. A new evaluation of the cross sections above the resonance range was produced at BNL based on EMPIRE calculations. An analysis was made, which indicated that the resonance parameters above 846 keV are inadequate. A complete trial file is available from the Gforge repository at BNL, but it is not suitable for extensive benchmarking due to a large bias it introduces into the results.
O-16
Essentially, two new evaluations are available, one by G. Hale from LANL and one by L. Leal from ORNL (now IRSN). There is big discrepancy in the (n,a) channel, which needs to be resolved.
H-1
There is a new preliminary standard fit, but changes are minimal so far. There is also new scattering law data contributed by the research group from Argentina. The new data do not show a large impact on the benchmark results.
Work to be done
New evaluations for the CIELO materials need to be validated. For example, it is well known that the tentative decrease in the PFNS average energy of Pu-239 and U-235 (and other actinides) strongly increases the reactivty of the high-leakage thermal solutions and reduces the reactivity of fast systems. Assuming this effect is real, nuclear data that compensate it must be identified and corrected in order to restore good performance of the library in integral benchmarks.
Summary Report
The summary report INDC(NDS)-0694 will be prepared.