Improved fission product model for fast reactor analysis

A new and highly effective procedure for generating fission product cross sections for LMFBR studies has been developed. The resultant simplified cross sections agree with more detailed treatments to within a few percent, and thus, are particularly valuable for fuel cycle and other studies. The proposed model consists of a two-lump fission product set, one based on the odd-A fission products and the other based on the even-A fission products with transmutation between the odd and even-A isotopes through capture. To examine the behavior of the proposed odd-even model, a detailed burnup analysis of 181 fission product elements in 84 chains was performed using the fission product code EPRI-CINDER. A 154-group fission product cross-section library generated from the ENDFB/4 library was used as the basic cross-section library. These cross sections were collapsed to a four-group set suitable for use in CINDER using two spectra, one representative of the soft spectrum zones and the other representative of the hard spectrum zones of the FMSR. The analysis was performed for Pu-239, U-235 and U-238 fission in both spectra