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Request ID15 Type of the request High Priority request
TargetReaction and processIncident EnergySecondary energy or angleTarget uncertaintyCovariance
 95-AM-241 (n,g),(n,tot) SIG  Thermal-Fast  See details 
FieldSubfieldCreated dateAccepted dateOngoing actionArchived Date
 Fission LWR, Thermal 08-NOV-07 10-SEP-08 Y

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Requester: Dr Osamu IWAMOTO at JAEA, JPN

Project (context): JENDL and WPEC subgroup 26

The thermal value for the total cross section is inconsistent with the best value for the capture cross section. This inconsistency should be removed (JENDL). Current inconsistencies in the measured total cross section for the main low energy resonances should be removed and a capture measurement should be made to demonstrate consistency.

Design phases of selected reactor and fuel cycle concepts require improved data and methods in order to reduce margins for both economical and safety reasons. A first indicative nuclear data target accuracy assessment was made within WPEC Subgroup 26 (SG-26). The assessment indicated a list of nuclear data priorities for each of the systems considered (ABTR, SFR, EPR, GFR, LFR, ADMAB, VHTR, EPR). These nuclear data priorities should all be addressed to meet target accuracy requirements for the integral parameters characterizing those systems (see the accompanying requests originating from SG-26).

For JENDL: A new measurement with a total uncertainty of 5% for the thermal total cross section would be required to resolve the issue.
For SG-26: Target accuracies are specified per system and per energy group when they are not met by the BOLNA estimate of the current (initial) uncertainties.

Energy RangeUncertainty (%)
  InitialGFR ADMAB
67.4 -183 keV 7 4 2
24.8 -67.4 keV 8 3 2
9.12 -24.8 keV 7 3 2
2.03 -9.12 keV 7 3 2
0.454-2.03 keV 7 3 3

Justification document:
[1] Toru YAMAMOTO, "Analysis of Core Physics Experiments of High Moderation Full MOX LWR", Proc. of the 2005 Symposium on Nuclear Data, February 2-3, 2006, JAEA, Tokai, Japan, pp.7-13, JAEA-Conf 2006-009 (2006). (See attached document)
OECD/NEA WPEC Subgroup 26 Final Report: "Uncertainty and Target Accuracy Assessment for Innovative Systems Using Recent Covariance Data Evaluations" (Link to WPEC Subgroup 26 Report in PDF format, 6 Mb).

Comment from requester:
Given the present state of knowledge the above target accuracies are very tight. However, any attempt that significantly contributes to reducing the present accuracy for this quantity is strongly encouraged. Any such attempt will significantly enhance the accuracy with which reactor integral parameters may be estimated and will therefore impact economic and safety margins.

Additional file attached: Yamamoto_T(MOX-LWR)2006.pdf

Review comment:
New experimental work is ongoing at IRMM in collaboration with CEA. Recent capture measurements have taken place at Los Alamos. There appear to be no large discrepancies in thermal capture measurements dating from 2000 as long as it is clearly distinguished whether the isomer contribution is included or not. Sample material available at IRMM is not compatible with an accurate measurement of the total cross section at thermal energy.

Entry Status:
Work in progress (as of SG-C review of May 2018)
Completed at thermal energies (as of SG-C review of May 2022) - SG41 has reviewed all available data, addressed discrepancies and produced recommendations for Am-241 nuclear data. These data have been incorporated into new evaluations.
Work in progress at fast energies (as of SG-C review of May 2022)

Main recent references:
Please report any missing information to



  • G. Noguere et al., Partial-wave analysis of n+Am-241 reaction cross sections in the resonance region, PRC 92 (2015) 014607
  • K. Mizuyama et al., Correction of the thermal neutron capture cross section of 241Am obtained by the Westcott convention, JNST 54 (2017) 74
  • G. Zerovnik et al., Improving nuclear data accuracy of 241Am and 237Np capture cross sections, EPJ Conferences 146 (2017) 11035
  • H. Harada et al., Improving nuclear data accuracy of the Am-241 capture cross-section, International Evaluation Cooperation, Volume 41, NEA/WPEC-41, report NEA/NSC/R(2020)2, 2020