The energy spectrum of prompt neutrons emitted in ssion (PFNS) plays a very important role in nuclear science and technology. A Coordinated Research Project (CRP) "Evaluation of Prompt Fission Neutron Spectra of Actinides" was established by the IAEA Nuclear Data Section in 2009, with the major goal to produce new PFNS evaluations with uncertainties for actinide nuclei. The following technical areas were addressed: (i) experiments and uncertainty quantification (UQ): New data for neutron-induced fission of 233U,235U,238U, and 239Pu have been measured, and older data have been compiled and reassessed. There is evidence from the experimental work of this CRP that a very small percentage of neutrons emitted in fission are actually scission neutrons; (ii) modeling: The Los Alamos model (LAM) continues to be the workhorse for PFNS evaluations. Monte Carlo models have been developed that describe the fission phenomena microscopically, but further development is needed to produce PFNS evaluations meeting the uncertainty targets; (iii) evaluation methodologies: PFNS evaluations rely on the use of the least-squares techniques for merging experimental and model data. Considerable insight was achieved on how to deal with the problem of too small uncertainties in PFNS evaluations. The importance of considering that all experimental PFNS data are "shape" data was stressed; (iv) PFNS evaluations: New evaluations, including covariance data, were generated for major actinides including 1) non-model GMA evaluations of the 235U(nth,f), 239Pu(nth,f), and 233U(nth,f) PFNS based exclusively on experimental data (0:02 smaller than or equal to E smaller than or equal to 10 MeV), which resulted in PFNS average energies E of 2:00 0:01, 2:073 0:010, and 2:030 0:013 MeV, respectively; 2) LAM evaluations of neutron-induced fission spectra on uranium and plutonium targets with improved UQ for incident energies from thermal up to 30 MeV; and 3) PbP calculations for 232Th, 234U and 237Np targets; and (v) data testing: Spectrum averaged cross sections (SACS) calculated for the evaluated 235U(nth,f) neutron field agree within uncertainties with evaluated SACS experimental data. Despite the observed reduction of the PFNS E by about 30 keV for neutron-induced fission of 233U,235U, and 239Pu, the criticality benchmark outcomes suggested that new evaluations can achieve the same (or better) integral performance with respect to existing evaluations, but the strong compensating effects observed need to be addressed. Summarizing, this project has signficantly improved PFNS evaluations and evaluation methodology, provided new PFNS data for applications, and also highlighted the areas for future research.
CAPOTE R.;
CHEN Y.;
HAMBSCH Franz-Josef;
KORNILOV N.;
LESTONE J.;
LITAIZE O.;
MORILLON B.;
NEUDECKER D.;
OBERSTEDT Stephan;
OHSAWA Takaaki;
OTUKA N.;
PRONYAEV V. G;
SAXENA A.;
SEROT O.;
SHCHERBAKOV O.A.;
SHU N.C.;
SMITH D. L.;
TALOU P.;
TRKOV Andrej;
TUDORA A.;
VOGT R.;
VOROBYEV A.;
2016-01-21
ACADEMIC PRESS INC ELSEVIER SCIENCE
JRC97506
0090-3752,
https://publications.jrc.ec.europa.eu/repository/handle/JRC97506,
10.1016/j.nds.2015.12.002,
