|Type||H - High priority request|
|Quantity||SIG - Cross section|
|Incident energy||1 keV - 100 keV|
|Status||Work in progress|
|Latest review date||28-Apr-2022|
Dr Roberto CAPOTE NOY at IAEA, AUT
Neutron absorption in the Cr isotopes of structural materials affects the criticality of fast reactor assemblies [Koscheev2017]. These cross sections are also of interest for stellar nucleosynthesis [Kadonis10].
8-10% in average cross-sections and calculated MACS at 10, 30, 100 keV.
Selected criticality benchmarks with large amounts of Cr (e.g., PU-MET-INTER-002, and HEU-COMP-INTER-005/4=KBR-15/Cr) show large criticality changes of the order of 1000 pcm due to 30% change in Cr-53 capture in the region from 1 keV up to 100 keV [Trkov2018]. On the other side different evaluations (e.g., BROND-3.1, ENDF/B-VII.1, ENDF/B-VIII.0 and JEFF-3.3) for Cr-53(n,g) are discrepant by 30% in the same energy region. For Cr-50, evaluated files show better agreement at those energies but they are lower than Mughabghab evaluation of the resonance integral by 35%. These discrepancies are not reflected in estimated uncertainty of the evaluated files (e.g., JEFF-3.3 uncertainty is around 10% which is inconsistent with the observed spread in evaluations). Due to these differences we request new capture data with 8-10% uncertainty to discriminate between different evaluations and improve the C/E for benchmarks containing Chromium and/or SS.
Criticality benchmarks can test different components of stainless steel (SS), including Cr which is a large component of some SS. Currently, a large part of the uncertainty in SS capture seems to be driven by uncertainty in Cr capture [Koscheev2017]. Indeed, some benchmarks highly sensitive to Cr (as a component of SS) indicate a need for much higher capture in Cr for both Pu and U fueled critical assemblies (e.g., HEU-COMP-INTER-005/4=KBR-15/Cr and PU-MET-INTER-002=ZPR-6/10).
Capture in natural Cr is driven by capture on Cr-50 and especially in odd Cr-53.
For Cr-53(n,g) there is a very large spread in MACS(30) values in different libraries compared to recommended KADoNiS 1.0 [Kadonis10] value of 41 +/- 10 mb (the latter is 25% larger). Existing measurements from the 70s are even larger being close to 60 mb with 30% uncertainty.
Note also discrepancies in resonance integrals (in barns) between evaluated libraries and ATLAS [Mughabghab2006] for both Cr-50(n,g) and Cr-53(n,g)
|Cr-50(n,g)||7.21||7.21||11.7 +/- 0.2|
Finally, the re-evaluation for ENDF/B-VIII.0 of the ORNL TOF measurement on enriched Cr-53 target [Guber2011] contradicts the increase suggested in Ref. [Koscheev2017] where preliminary data have been used.
Such contradictions need to be resolved thanks to new measurements and evaluation.
Comment from requester
- Cr-50(n,g) may be measured by activation or TOF. An accurate activation measurement at 5 and 25 keV may help in solving the puzzle of Cr capture.
- Cr-53(n,g) can only be measured by TOF. There is no publication of the final analysis of the ORNL TOF measurement using enriched Cr-53 sample.
- Lead Slowing Down Spectrometer (LSDS) measurements of Cr-50, Cr-53 and Cr-52 enriched samples and of Cr-nat sample could be extremely important to validate and select a proper evaluation of Cr capture cross section below 100 keV. These measurements are strongly encouraged as complementary to TOF and feasible activation measurements.
Work in progress (as of SG-C review of May 2018)
Main recent references
Please report any missing information to email@example.com