| ID | 97 |
|---|---|
| Type | H - High priority request |
| Target | 24-Cr-50 |
| Reaction | (n,g) |
| Quantity | SIG - Cross section |
| Incident energy | 1 keV - 100 keV |
| Accuracy | 8-10 % |
| Field(s) | Fission |
| Accepted date | 05-Feb-2018 |
| Status | Work in progress |
| Latest review date | 28-Apr-2022 |
Requester
Dr Roberto CAPOTE NOY at IAEA, AUT
Impact
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].
Accuracy
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.
Justification document
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)
| Reaction | ENDF/B-VII.1 | BROND-3.1 | ATLAS 2006 |
|---|---|---|---|
| Cr-50(n,g) | 7.21 | 7.21 | 11.7 +/- 0.2 |
| Cr-53(n,g) | 8.42 | 11.2 | 12.3 |
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.
References
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.
Entry status
Work in progress (as of SG-C review of May 2018)
Main recent references
Please report any missing information to hprlinfo@oecd-nea.org
Experiments
Theory/Evaluation
Validation
