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Request ID9 Type of the request General request
TargetReaction and processIncident EnergySecondary energy or angleTarget uncertaintyCovariance
 92-U-233 (n,g) nubar,SIG  Thermal-10 keV  .5 Y
FieldSubfieldCreated dateAccepted dateOngoing actionArchived Date
 Fission Molten Salt Reactors 19-APR-07 19-APR-07 Y

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Requester: Dr Adrien BIDAUD at LPSC, FR

Project (context): JEFF

U-233 is the main isotope of relevance to the Th/U fuel cycle. The present request concerns the viability of Th/U fueled molten salt reactors which requires that the amount of U-233 generated equals that which is destroyed.

0.5% in nubar, 5% for the (n,g) cross section

Justification document:
Uncertainties on the predicted regeneration gain inferred from the uncertainties of the nuclear data have been estimated showing a 4200 pcm uncertainty for a regeneration gain designed to be 200 pcm, i.e. very close to a complete balancing of production and destruction of U-233. The main culprits are nubar contributing 2200 pcm and the capture cross section contributing 3260 pcm. A target accuracy of 2000 pcm is required to facilitate defining the reprocessing scheme for a molten salt reactor.
A. Bidaud, Impact of Nuclear Data Uncertainties on a GEN IV Thorium Reactor at Equilibrium (attached document).
CEA Technical Note NT-SPRC/LEPH-05/204, G. Noguere et al (attachment 2).

Comment from requester:
Owing to the difficulty in measuring the U-233(n,g) cross section, a new evaluation could be done on the basis of the Profil results (see CEA Technical Note NT-SPRC/LEPH-05/204).

Additional file attached: U233_MSR_Impact.pdf
Additional file attached: NT-Profil.pdf

Review comment:

Any effort done to reduce the uncertainties on neutron yields and capture cross section down to less than 1% and about 5% respectively or at least to confirm their uncertainty would be very much appreciated. If the uncertainty on RG could be reduced down to 2000pcm, the needed reprocessing scheme could be designed with more confidence, and then the research on specific goals such as minor actinide and protactinium extraction could be prioritized.

Nubar is currently known to 1%, the capture cross section to 10%. The above mentioned target uncertainties implies that the desired accuracies for improved data are approximately half these numbers.

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

Main recent references:
Please report any missing information to


  • J.E. Escher and F.S. Dietrich, Cross sections for neutron capture from surrogate measurements: An examination of Weisskopf-Ewing and ratio approximations, PRC 81 (2010) 024612
  • C. Carrapico, E. Berthoumieux, et al., NIM A 704 (2013) 60-67, EXFOR 23071
  • M. Bacak, et al., A compact multi-plate fission chamber for the simultaneous measurement of 233U capture and fission cross-sections, ND2016, EPJ Conferences 146 (2017) 03027