EFFECTIVE CROSS-SECTIONS AND NEUTRON FLUX DISTRIBUTIONS IN A NATURAL URANIUM ROD APPLICATION TO ROD 683

摘要

Effective neutron cross-sections of U-235, Pu-239, Pu-240, Pu-241 and Xe-135 and the 2200 meters per second neutron flux distribution are calculated for an NRX natural uranium metal rod assuming that the neutron flux spectrum in a rod is maintained by a purely Maxwellian incurrent or a Maxwellian incurrent to which is added a 1/E component. Results are presented for incurrent tem¬peratures of 20.44 ℃., 38℃ 227℃ and 427° C and for two rod media, the unirradiated rod and a uniformly loaded, irradiated rod. Deviations of our values of the effective cross-sections from those presented in CRRP-680 [TNCC(CAN)-7] illustrate the effects that "hardening" of the Maxwellian spectrum and self-shielding in the Pu-239 and Pu-240 resonance regions have on the cross-sections. An application of similar calculations to the analysis of rod 683 irradiation data is also discussed.