Yiwei Yang

Measurement of 232Th(n,f) and 232Th(n,γ) reaction rates in thorium powder cylinder bombarded with D-T neutrons†

ABSTRACT In order to provide reference for the evaluation of thorium parameters for the conceptual design of fusion–fission hybrid energy reactor, a dedicated integral experiment was carried out in a thorium powder cylinder bombarded with D-T neutrons. Thorium capture and fission rates in the 0° direction to the incident D+ beam were obtained using the activation method followed by the off-line gamma-ray technique, experimental uncertainties were ∼3.1% for thorium capture rate, and were 5.5%, 8.1%, and 6.3% for thorium fission rates based on fission products 85mKr, 143Ce, and 87Kr, respectively. The thorium fission rate based on 85mKr agreed well with the simulation employing ENDF/B-VII.0 library data. The influence of the oxygen contained in the thorium oxide powder and the scattering neutrons from the experimental hall was also evaluated. MCNP simulations employing ENDF/B-Ⅶ.0, JENDL-4.0 library data agreed with experiment within uncertainties except that employing ENDF/B-Ⅶ.1 (6.0%) and CENDL-3.1 (7.9%) for thorium fission rate, while for thorium capture rate, simulation employing JENDL-4.0 agreed with experiment best. The influence of reaction channels of thorium transport medium employing different library data on the thorium reaction rates could be neglected according to the simulation. The thorium capture to fission ratio demonstrated that the fuel breeding efficiency is quite low and energy production plays a leading role under the neutron spectra in this experiment.

A study of 239Pu production rate in a water cooled natural uranium blanket mock-up of a fusion–fission hybrid reactor

The 239Pu production rate is important data in neutronics design for a natural uranium blanket of a fusion–fission hybrid reactor, and the accuracy and reliability should be validated by integral experiments. The distribution of 239Pu production rates in a subcritical natural uranium blanket mock-up was obtained for the first time with a D-T neutron generator by using an activation technique. Natural uranium foils were placed in different spatial locations of the mock-up, the counts of 277.6 keV γ-rays emitted from 239Np generated by 238U capture reaction were measured by an HPGe γ spectrometer, and the self-absorption of natural uranium foils was corrected. The experiment was analyzed using the Super Monte Carlo neutron transport code SuperMC2.0 with recent nuclear data of 238U from the ENDF/B-VII.0, ENDF/B-VII.1, JENDL-4.0u2, JEFF-3.2 and CENDL-3.1 libraries. Calculation results with the JEFF-3.2 library agree with the experimental ones best, and they agree within the experimental uncertainty in general with the average ratios of calculation results to experimental results (C/E) in the range of 0.93 to 1.01.

Determination of the 232 Th(n,2n) 231 Th reaction rate in thorium oxide cylinder assembly under D-T neutron source

Aiming at verifying the evaluated cross-section of 232Th(n,2n) reaction for the conceptual design of thorium based subcritical blanket in fusion–fission hybrid reactor, an integral experiment was carried out using activation technique with D-T neutrons. 232Th(n,2n) reaction rates were measured in a ThO2 cylinder assembly with relative uncertainty of 8.0%. The experiment was simulated by MCNP code combining with ENDF/B-VII.0, ENDF/B-VII.1, CENDL-3.1 and JENDL-4.0 databases. The calculated 232Th(n,2n) reaction rates employing JENDL-4.0 show low discrepancy with the measured ones. The results could provide reference to the re-evaluation of 232Th(n,2n) cross-section and the design of fusion–fission hybrid reactor.