Requester: Dr Luiz Carlos LEAL at IRSN, FR
Email: luiz.leal@irsn.fr

Project (context): Thermal reactors

Impact:
Improve the estimation of k_eff as well as the moderator temperature coefficient for thermal systems. In particular, this concerns MOX cores and Pu solutions.

References:
[1] A. Santamarina, Improvement of the Pu239 Evaluation for JEFF3, JEF/DOC-1158 (attached below)
[2] Russell D. Mosteller, "ENDF/B-VII, ENDF/B-VI, and JENDL-3.3 Results for Unreflected Plutonium Solutions and MOX Lattices", Joint International Topical Meeting on Mathematics & Computation and Supercomputing in Nuclear Applications (M&C + SNA 2007) Monterey, California, April 15-19, 2007, on CD-ROM, American Nuclear Society, LaGrange Park, IL (2007), Los Alamos report: LA-UR-06-6903
[3] D. Bernard, E. Fort, A. Courcelle, A. Santamarina, G. Noguère, "²³⁹Pu nuclear data improvements in thermal and epithermal neutron ranges, International Conference on Nuclear Data for Science and Technology 2007, Contrib #708.
[4] H.Weigmann, B.Keck, J.A.Wartena,P.Geltenbort, K.Schreckenbach, Int.Conf.on the Physics of Reactors: Operation, Design and Computation, Marseille, 23-27 Apr 1990.

Accuracy:
< 1 % for fission cross section and < 2 % for capture cross section

Justification document:
Recent benchmark calculations indicate that the shape of sig(n,g), sig(n,f), eta and/or alpha at low energy need to be revised. A similar problem was seen about 10 years ago with the U-235 cross section. In that case the shape of eta at low energy was found to be slightly varying with energy. It appears that a similar problem exists for Pu-239. Existing experimental data have not helped much to solve the puzzle. Measurements of these quantities in the range from 1 meV to 1 eV, including the 0.3 eV resonance, will be of utmost importance.

Comment from requester:
Existing measurements of the Pu-239 fission and capture cross sections (alpha) do not help to resolve a longstanding problem with thermal benchmarks regarding Pu-239. The measurements of Ref. [4] helped resolve a similar problem that previously existed for U-235.

Review comment:
Since the request refers to the resonance region, measurements would be needed to address this request. Quite different measurement samples and detectors would be required for the (n,f) and (n,g) cross section measurements with individual uncertainties that would be easily in excess of 1%. Therefore, to achieve the accuracy, measurements should aim at measuring either eta or alpha in function of energy striving for minimal systematic errors. Such an eta or alpha measurement would need to be combined with a precise fission cross section from an evaluation or an independent measurement. Calibrating a fission deposit mass to 1%, is possible, but poses a challenge. Interested experimental groups should consult Ref. [4].

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

Main references:
Please report any missing information to hprlinfo@oecd-nea.org

Experiments