Temperature coefficient of U-235 fueled thermal reactors and nuclear data on eta at thermal neutron energies and 239-Pu fission cross sections between 1 and 100 keV. Foreign trip report, December 1, 1990-December 9, 1990.

摘要

The Evaluation Cooperation Subgroup, ''Actinide Data in the Thermal Energy Range,'' met primarily to discuss problems related to the temperature coefficient of U-235 fueled thermal reactors and nuclear data on eta at thermal neutron energies, the number of neutrons emitted per neutron absorbed. The preliminary results of the eta measurements done by M. Moxon of Harwell at Oak Ridge were presented and preliminary results by H. Weigman of Geel with a new method were presented. All three measurements from Geel show a pronounced down-slope of eta with decreasing neutron energy and both measurements by Moxon show only a very slight down slope. Acceptance of the Geel results would solve about one-third of the problem in the calculated reactor temperature coefficient. The Evaluation Cooperation Subgroup, ''239-Pu Fission Cross Sections between 1 and 100 keV,'' met to discuss the 4% lower than the previously evaluated fission cross sections between 20 eV and 100 keV as evaluated from the fission data of the Weston and Todd and transmission data of J. A. Harvey (all of ORNL). These lower fission cross sections are discrepant with integral measurements, however, it is conceivable that there could be compensating effects, perhaps in the U-238 cross sections. A general meeting and a benchmark testing session of the JEF were attended as a representative of CSEWG JEF-2.2 is scheduled for general release after about another year of testing. Cooperation in evaluation of nuclear data between Europe, Japan, and the US has increased dramatically in the last few years because of manpower limitations.