Simulation Study And Measurement Method Investigation On²³⁸U Fission Products Induced By D-D/D-t Fast Neutron

After more than60years’development, nuclear power technology using lower enriched235U as nuclear fuel has matured. With the new nuclear technology development of fast neutron breeder reactor and uranium-thorium cycle reactor, a new demand on the fission yield of U induced by fast neutron is put forward. At the same time,238U fission yield nuclear data is also one of the important data for thermal reactor safety control, post-processing of spent fuel and so on. In addition, the fission product data have important significance in the fission reaction mechanism basic research field.For the experiment measurement subject of fission yield induced by fast neutron using directly gamma method, Geant4code was employed to simulate the238U fission process induced by the D-T(about14MeV energy) and D-D(about2.5MeV energy) fast neutron. The changing relationship between deposit ratio of fission fragments in the238U sample with the sample thickness was given, and the optimum thickness of238U experiment samples was determined. For238U fission induced by the two energy fast neutron, the fragments distribution, fragments kinetic energy distribution, fission yield distribution, fission neutron energy spectrum distribution, and other important parameters were simulated. Above simulated data were compared with the ENDF evaluation data for checking the simulation program. In addition,the gamma energy spectrum of238U samples after D-T/D-D neutron irradiation were simulated in different cooling time. Put above gamma energy spectrum into MCNP code, the gamma response spectra in high-purity germanium detector(HPGe) were presented using MCNP code. By the analyzing of the gamma response spectra, the measurement sequence and the fission products which can be detected were determined.For the HPGe-y spectrometer system, The experimental study and Simulation of detection efficiency were carryied out. Experimental efficiency calibration data were given in59.5keV to1332keV energy region.MCNP5program is used to simulate the detection efficiency of HPGe gamma spectrometer, the simulated data were compared with the experiment data in59.5keV to1332keV area, and a good conformity was showed.According to the gamma spectrum zone (about4MeV) of the238U sample after irradiation, the detection efficiency simulation data in higher energy region (1332kev～4000kev) were investigated though simulation.