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Request ID36 Status of the request High Priority request
TargetReaction and processIncident EnergySecondary energy or angleTarget uncertaintyCovariance
 92-U-238 (n,g) SIG  20 eV-25 keV  See details Y
FieldSubfieldDate Request createdDate Request acceptedOngoing action
 Fission Fast and Thermal Reactors 15-SEP-08 15-SEP-08 

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Requester: Prof. Massimo SALVATORES at CADARACHE, FR

Project (context): CEA Cadarache

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).

Target accuracies are specified per system and per energy group when they are not met by the BOLNA estimate of the current (initial) uncertainties. The weighting factor λ is explained in detail in the accompanying document. Changes from the reference value of λ=1 show the the possible allowance for other target uncertainties. Two cases (A and B) are distinguished for λ≠1 (see Table 24 of the report).

Energy RangeInitial versus target uncertainties (%)
λ=1 λ≠1,a λ≠1,b λ=1 λ≠1,a λ≠1,b λ=1 λ≠1,a λ=1 λ≠1,a λ=1 λ≠1,a λ=1 λ≠1,a λ=1 λ≠1,a
9.12 - 24.8 keV 9 3 2 2 4 3 3 3 2 2 1 2 2 5 4
2.03 - 9.12 keV 3 1 1
22.6 - 454 eV 2 1 1 1 1

Justification document:
1. 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).
2. OECD/NEA WPEC Subgroup 7 (SG-7) Final Report: "Nuclear data standards" (link to WPEC Subgroup 7 Report in PDF format, 450kb).

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.

Comments from evaluator/experimentalist:
In this particular case high accuracy is required throughout the energy range. Only the groups shown above have initial uncertainties larger than the target uncertainties. The low initial uncertainty is a result of the standards evaluation (see SG-7 report above). Concerns have been raised that despite the excellent efforts of this subgroup an independent check is in order to verify the present view on required corrections to experimental work for the unresolved resonance range.

Comments for achieved accuracy:

Review comment:
Please report any missing information to


  • A. Wallner et al., Novel Method to Study Neutron Capture of 235U and 238U Simultaneously at keV Energies, PRL 112 (2014) 192501, EXFOR 23170
  • J.L. Ullmann, et al., Cross section and g-ray spectra for 238U(n,g) measured with the DANCE detector array at the Los Alamos Neutron Science Center, PRC 89 (2014) 034603, EXFOR 14310
  • H.I. Kim et al., Neutron capture cross section measurements for 238U in the resonance region at GELINA, EPJ A 52 (2016) 170, EXFOR 23302
  • F. Mingrone et al., Neutron capture cross section measurement of 238U at the CERN n_TOF facility in the energy region from 1 eV to 700 keV, PRC 95 (2017) 034604, EXFOR 23234
  • T. Wright et al., Measurement of the 238U(n,g) cross section up to 80 keV with the Total Absorption Calorimeter at the CERN n_TOF facility, PRC 96 (2017) 064601


  • H. Derrien et al., R-Matrix Analysis of 238U High-Resolution Neutron Transmissions and Capture Cross Sections in the Energy Range 0 to 20 keV, NSE 161 (2009) 131
  • R. Dagan et al., Impact of the Doppler Broadened Double Differential Cross Section on Observed Resonance Profiles, ND2013, NDS 118 (2014) 179
  • Kopecky et al., Status of Evaluated Data Files for 238U in the Resonance region, JRC Technical Report, EUR 27504 EN (2015)
  • R. Capote et al., IAEA CIELO Evaluation of Neutron-induced Reactions on 235U and 238U Targets, NDS 148 (2018) 254
  • A.D. Carlson et al., Evaluation of the Neutron Data Standards, NDS 148 (2018) 143


Additional file attached: SG26-report.html