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Request ID12 Status of the request High Priority request
TargetReaction and processIncident EnergySecondary energy or angleTarget uncertaintyCovariance
 92-U-235 (n,g) SIG,RP  100 eV-1 MeV  3 Y
FieldSubfieldDate Request createdDate Request acceptedOngoing action
 Fission FBR, Thermal reactors 29-AUG-07 06-NOV-07 

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Requester: Dr Yasunobu NAGAYA at JAEA, JPN

Project (context): JENDL, NEA WPEC Subgroup 29

U-235 cross sections are very important not only for major thermal reactors but for FBRs because lots of critical experiments for FBRs have been performed at critical assemblies where UO2 fuels are used as driver fuels. Experimental data obtained at such critical assemblies have a great impact on design work for FBRs. Recent studies show that calculated sodium void reactivity worths for BFS experiments underestimate the experimental results by 30-50% [1].
The significant discrepancies not only exceed the target accuracy of 20% for a FBR design but also deteriorate the design accuracy estimated with the cross-section adjustment and bias factor techniques. Thus such experimental data cannot be employed in these techniques.
The requested accuracies (relative one standard deviation) are given for energy-averaged cross sections as follows:
Energy interval and accuracy
100eV - 500eV: 5%
500eV - 1keV: 5%
1keV -2.25keV: 5%
2.25keV- 5keV: 8%
5keV - 10keV: 8%
10keV - 20keV: 8%
20keV - 30keV: 8%
30keV - 40keV: 3%
40keV - 90keV: 3%
90keV -200keV: 3%
200keV-400keV: 3%
400keV-900keV: 3%
900keV - 1MeV: 3%
(It is assumed that the resolved resonance region is below 2.25 keV and the unresolved resonance region is between 2.25 keV and 30 keV. The boundaries for the resonance regions are the same as for JENDL-3.3.)


Justification document:
Reference 1: first attached document, O. Iwamoto, "WPEC Subgroup Proposal" JAEA, March 9 (2007).
Reference 2: second attached document, viewgraph for Dr. Iwamoto's proposal at the 19th WPEC meeting.

Comment from requester:
The re-evaluation of U-235 cross sections has been already proposed at the 19th WPEC meeting on 18 - 20 April 2007, at the NEA Headquarters, Issy-les-Moulineaux, France.

Comments from evaluator/experimentalist:

Comments for achieved accuracy:

Review comment:
The proposal seems well motivated. Concerns were expressed in view of the recent changes to the evaluation that emerged from the activities of NEA/WPEC Subgroup 22 "Nuclear Data for Improved LEU-LWR Reactivity Predictions" and ENDF/B-VII benchmarking. The wider impact that new evaluations of U-235 will have, should be considered and duly accounted for by new efforts. Although, the sensitivity of the cross section for the target application is well argued, the documentation does not reveal if the problem must be uniquely attributed to the capture cross section of U-235 in the specified energy range.

Additional file attached: U235proposal.pdf
Additional file attached: Viewgraph.U235proposal.pdf