Method for Decision of Nuclear Reaction Model Parameters

Application to decontamination is proposed of microwave discharge plasma in carbon tetrafluoride and oxygen mixture at atmospheric pressure. Preliminary cold experiments were conducted using cobalt oxide deposited on stainless steel plate. Fluorine atoms proved to be generated in high concentration in the plasma, which fluorinated the deposited metal oxide into volatile gaseous form. Upon plasma irradiation during about 200 s, the cobalt oxide deposit was removed to 100% from plate surface. Thermodynamic equilibrium calculations on CF₄-O₂ systems containing cobalt served to elucidate the mechanism of metal oxide removal by microwave discharge plasma, and similar calculations on systems containing actinides (U, Pu etc.) and lanthanides (La, Gd etc.) indicated that the process should be applicable also to the removal of these radioactive elements. It is concluded from the experimental and calculated results that decontamination is basically feasible with the proposed method of using microwave discharge plasma in a CF₄-O₂ system at atmospheric pressure.     

Calculation of Prompt Fission Product Average Cross Sections for Neutron-Induced Fission of 235U and 239Pu

Yield-weighted average cross sections of neutron radiative capture, (n,2n), and (n,3n) reactions over prompt fission products (FPs) from ²³⁵U and ²³⁹Pu are calculated. The prompt fission production yields are taken from the ENDF/B-VII.0 library. The FPs for each fissile material exist over a range of approximately 1000 neutron-rich nuclides. Several nuclear reaction codes are utilized for calculating the cross sections on each individual fission product—EMPIRE-2.19, TALYS-1.0, GNASH, and CoH. The influence of the FP isomers on the average cross sections is examined with TALYS. We investigate the dependence of the average cross sections on the number of FPs taken for averaging. It is shown that the average capture cross section is much more sensitive to the number of FPs included, compared with the (n,2n) and (n,3n) reactions. An intercomparison of the calculated cross sections with the different reaction codes is carried out. In the capture reaction, EMPIRE predicted lower cross section than TALYS and CoH owing to different default assumptions used in the γ-ray strength function modeling. Moreover, the preequilibrium models implemented in each code give different predictions for the neutron-emission reactions, although the differences are relatively small. We also discuss a difference between the macroscopic and microscopic calculation options in TALYS for the pre-equilibrium model, optical potential model, and γ-ray strength function. The predictive capability of the reaction codes for the capture reaction is examined by comparing their calculations with the ENDF data, which are based on measurements. Compared with the historic Foster and Arthur's evaluation, our new (n,2n) predictions are similar, although our capture predictions are almost an order of magnitude higher. Recommended cross sections for use in applications have been tabulated in ENDF-formatted files.