14 Mev Neutrons And The Function Of The Spherical Shell With Depleted Uranium Polyethylene Device Response Rate Of Uranium Research

In order to check the conceptual design of the subcritical reactor and to evaluate reliability of the neutronic simulation program and nuclear data libraries,3alternate depleted uranium/polyethylene-shell simulation devices were established, to carry out integral experiments of neutronics with14MeV neutrons using activation technique, measuring238U(n,y) reaction rate,238U(n,f) reaction rate,235U(n,f) reaction rate,238U(n,2n) reaction rate and the238U capture to total fission ratio. The experiments were analyzed using MCNP5code with some widely used nuclear data libraries, and the calculations were compared with the experiments with the calculation to experiment ratios(C/Es) representing their consistencies.Referred to the conceptual design of the subcritical reactor,3alternate depleted uranium/polyethylene-shell devices were established. The1st setup consisted of3suited depleted uranium shells and2polyethylene shells which were installed alternatively. After a suited polyethylene shell was installed outside the1st setup, the2nd setup was established, and the3rd setup was established by adding a suited polyethylene shell inside the2nd setup. The experiments were driven by D-T neutrons, whose intensities were measured using the associated particle method. After the depleted uranium foils were activated at90°direction to the incident D beam in the setups, each reaction rate was obtained by measuring its unique characteristic y ray with the same HPGe detector. The HPGe detector’s detection efficiencies for the characteristic y rays were measured in conjunction with a243Am source which has the same radius as the activated foils, and the self-absorption corrections of the activated uranium foils for the emitted characteristic y rays were obtained using the least squares fitting method. The self-absorption corrections were simulated using MCNP5code, and the simulations showed that the largest discrepancy between the calculations and the experiments was within1%when the uranium foils were thinner than0.02cm.By measuring the277.6keV γ ray emitted from239Np which was generated by238U(n,γ) reactions, the radial U(n,γ) reaction rate distributions on the3alternate depleted uranium/polyethylene shell-setups were obtained with relative uncertainties between3.5%and3.7%, and total plutonium productions of2.24,2.77and2.53were obtained of the3setups. The238U(n,γ) reaction rates were calculated using MCNP5code with several ENDF libraries, and the calculations using different libraries diverged little and generally accorded with the experiments within5%, and the average C/Es were between0.98and1.00. The average C/Es on the three setups were1.00,1.05and1.08when simulated with ENDF66c library, showing a trend of accretion with thickness of polyethylene shells.Meanwhile,8U(n,f) reaction rate.235U(n,f) reaction rate,38U(n,2n) reaction rate and the238U capture to total fission ratio were measured on the2nd setup. By measuring the293.3keV y-ray emitted from143Ce which is an fission fragment of238U(n,f) and235U(n,f) reactions, the radial238U(n,f) and5U(n,f) reaction rate distributions were obtained, with relative uncertainties between5.1%and6.9%, and the average C/E of the fission reaction rate was calculated to be1.05when simulated using ENDF66c library. By measuring the208keV y-ray emitted from237U which was generated by238U(n,2n) reactions, the radial38U(n,2n) reaction rate distribution in the first uranium shell was obtained, with uncertainties between5.3%and6.0%, and the average C/E of the U(n,2n) reaction rate was calculated to be1.05when simulated using ENDF66c library. By dividing the U neutron capture reaction numbers by the total fission reaction numbers, the radial distribution of the238U capture to total fission ratio was obtained, with uncertainties between3.7%and5.7%, and the average C/E of the238U capture to total fission ratio was calculated to be1.00when simulated using ENDF66c library.