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Request ID2 Type of the request High Priority request
TargetReaction and processIncident EnergySecondary energy or angleTarget uncertaintyCovariance
 8-O-16 (n,a),(n,abs) SIG  2 MeV-20 MeV  See details Y
FieldSubfieldCreated dateAccepted dateOngoing actionArchived Date
 Fission Material recycl, adv. reactors 21-SEP-05 12-SEP-08 Y

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Requester: Mr Arnaud COURCELLE at CEA-SACLAY, FR

Project (context): LWR, Material recycling and NEA WPEC Subgroup 26

In light water reactors oxygen is present in UOX, MOX and water. The sensitivity coefficient (dk/k)/(dσ/σ)=-3.5 pcm/%. A 30% uncertainty results in an uncertainty for keff of 100 pcm. This important effect was identified by Subgroup 22 of WPEC which investigated the underprediction of the reactivity of light water reactors with the most recent nuclear data evaluations.
A second point concerns helium production which is of importance for the performance of fuel pins and clads. The O-16(n,α) reaction accounts for 25% of the total helium production and contributes 7% to its uncertainty.
A third point concerns the calibration of neutron source strengths using the manganese-sulfate bath technique (NIST). The final requested uncertainty of 1% on neutron source calibrations is very near the 0.5% uncertainty contributed by this reaction.

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 (n,a) : 5% in the whole range.
For (n,abs): 9.9 % (2.23 - 6.07 MeV) and 12.1 % (6.07 - 19.6 MeV).

Justification document:
See reference 1 attached: Need for O16(n,alpha) Measurement and Evaluation in the range 2.5 - 10 MeV A. Courcelle et al. (August 2005) and references therein.
See also 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), and
And "Nuclear data for improved LEU-LWR reactivity predictions", WPEC Vol. 22 (link to Report).

Comment from requester:
The required accuracy concerns the normalisation of the cross section. A sensitivity analysis is also presented for keff in a fast reactor. Considerable differences exist among evaluations and measurements are discrepant. Recent C-13(α,n) and C-13(α,α) measurements are identified that provide detailed knowledge about the inverse reaction. Together with an R-matrix analysis this may be used to improve the evaluation for the O-16(n,α) reaction. Feedback has been obtained from evaluators at ORNL, LANL and KAPL.

Additional file attached: SG26-report.html
Additional file attached: Need for O16(n,alpha).pdf

Review comment:

A direct measurement is in preparation using an ionisation chamber with the time projection technique. The measurement aims at providing benchmark data for the R-matrix analysis near the main resonance (En ~ 5 MeV).
A poor resolution measurement should be sufficient to check the normalisation of the R-matrix result, since resonance self-shielding is not an issue.
The recent results for the C-13(α,n) correspond to 4.8-12 MeV neutrons. This covers a part of the region of interest, but not the important range from 2.35 to 4.8 MeV.
The status of the IRMM measurements was presented as a poster in the ND2007 conference, by V. Khriatchkov, G. Giorginis, V. Corcalciuc, M. Kievets, "The cross section of the 16O(n,a)13C reaction in the MeV energy range", contribution 481, ND2007, Nice, April 2007.

The achieved accuracy is estimated to be 30%.

The request is well motivated and the response for follow-up is very encouraging.

Entry Status:
Work in progress (as of SG-C review of May 2018)

Main recent references:
Please report any missing information to


  • G. Giorginis, et al., The cross section of the 16O(n,a)13C reaction in the MeV energy range, ND2007 proceedings, EXFOR 23040
  • V.A. Khryachkov, et al., Study of (n,a) Reaction Cross Section on a Set of Light Nuclei, ISINN-18, Sept. 2011, Dubna, Russia, EXFOR 41575
  • V.A. Khryachkov, et al., (n,a) reaction cross section research at IPPE, CNR*11, EPJ Web of Conferences 21 (2012) 03005, EXFOR 41575
  • S. Harissopulos et al., Cross section of the 13C(a,n)16O reaction: A background for the measurement of geo-neutrinos, PRC 72 (2005) 062801
  • P. Mohr, Revised cross section of the 13C(a,n)16O reaction between 5 and 8 MeV, PRC 97 (2018) 064613; W.A. Peters, Comment on "Cross section of the 13C(a,n)16O reaction: A background for the measurement of geo-neutrinos", PRC 96 (2017) 029801
  • M. Febbraro, et al., New 13C(a,n)16O Cross Section with Implications for Neutrino Mixing and Geoneutrino Measurements, PRL 125 (2020) 062501
  • Planned measurements at LANL, Demokritos...


  • G. Hale and M. Paris, Status and plans for 1H and 16O evaluations by R-matrix analyses of the N-N and 17O systems, NEMEA-7/CIELO, NEA/NSC/DOC(2014)13, page 13,
  • S. Kunieda, et al., R-matrix Analysis for n +16O Cross-sections up to En = 6.0 MeV with Covariances, NDS 118 (2014) 250-253
  • L. Leal, et al., Resonance parameter and covariance evaluation for 16O up to 6 MeV, EPJ N 2 (2016) 43
  • M.B. Chadwick et al., CIELO Collaboration Summary Results: International Evaluations of Neutron Reactions on Uranium, Plutonium, Iron, Oxygen and Hydrogen, NDS 148 (2018) 189
  • Ongoing evaluation work in the framework of INDEN (CIELO follow-up), see Summary Report of the IAEA CM, 15-17 May 2019, Vienna, Report INDC(NDS)-0788