A review of the current status of nuclear data for major and minor isotopes of thorium fuel cycle - 254

In this paper an attempt has been made to perform a critical analysis of nuclear data contained in the two basic evaluated nuclear data files JENDL-3.2 and ENDF/B-VI (Rev. 5) recently released by the IAEA/NDS as a result of truly international efforts. Careful and quality assured generation of cross section line shapes at zero Kelvin, 296 Kelvin, in 175 groups and in 69 groups have been performed by pre-processing these basic evaluated nuclear data files. A number of zoomed graphs presented in this paper illustrate the discrepancies quantitatively. One of the striking discrepancies is that the resolved and unresolved resonance regions are not the same in most of the cases. The cross section lines shapes in the epithermal and resolved resonance regions are significantly discrepant for all the isotopes covered. The nuclear data of isotopes of importance to the thorium fuel cycle did not receive sufficient attention in the past. Most of these experimental data were those generated two to three decades ago. In addition, generally, these experimental data are of poor quality and very limited in comparison to the voluminous nuclear data generated for the uranium-plutonium cycle. Some comments regarding gaps in experimental data as of 1999 have also been presented in the discussion in the text. Experimental data is absent in most of the cases, and, in such cases, evaluated cross sections in the two basic evaluated nuclear data files JENDL-3.2 and ENDF/B-VI (Rev. 5) are based upon theoretical models and nuclear systematics. To mention some samples, a discrepancy of 21.6% is present in prompt ν-bar of ²³²U. The thermal fission cross section of ²³⁴U in the JENDL-3.2 file (6.22 mb) is ∼75 times smaller than the value in the ENDF/B-VI (Rev. 5) file. Retrieval and scan of EXFOR data reveals that there is no experimental data for (n, 2n) and (n, 3n) cross-sections for all the isotopes: ²³⁰Th, ²³¹Pa, ²³³Pa, ²³²U and ²³⁴U. No experimental data exists for the inelastic cross sections except in a limited way for ²³²Th and ²³³U. No direct measurement of capture cross sections of ²³³U is available in the fast energy region. A 600% discrepancy is seen in the capture cross section of ²³³U around 3 MeV and up to six orders of magnitude in 10 to 20 MeV. In the paper, the role played by ²³¹Pa and ²³³Pa in thorium fuel cycle has been reviewed. New results calculations of criticality property of ²³¹Pa and ²³³Pa have been presented in the paper using the neutron reaction data of JENDL-2, JENDL-3.2 and ENDF/B-VI (Rev. 5). The new values of k_∞ differ significantly from the earlier published values. A study of the formation of ²³¹Pa by neutron capture in ²³⁰Th in a typical Indian PHWR spectrum has also been presented