Measurement And Simulation Of Leakage Neutron Spectra And Gamma Pulse Height Spectra From ²³⁸U Slab By Time-of-Flight Method

The evaluated nuclear database is a crucial data which is widely used in the nuclear technology.Benchmark experiments is an effective means of verifying the quality of the nuclear data.Besides,it is an important part of establishment of nuclear database.A mass of benchmark experiments based on the D-T neutron source have been carried out in the past few years.238U is not only an important component in the nuclear fuel cycle,but also a crucial material in the fusion technology.The evaluated nuclear database of 238U is regarded as one of the most important nuclides by the OECD Nuclear Energy Agency.In this work,benchmark experiments on 238U slab samples were carried out using the neutronics integral experimental facility at China Institute of Atomic Energy,the D-D neutron source?the BC501-A detector and the CLYC detector were innovative used to evaluate the leakage neutron spectra and gamma pulse height spectra in a wide energy range.Combined with the calculated results of MCNP program,the macroscopic examination study of the evaluated nuclear data of 238U was carried out.The main research progress and results are introduced as follows:1?The experimental study was completed,such as the threshold and the width of the time of flight spectrometer,? calibration,n-? screening.The key issues about data processing were discussed,such as the normalization of experimental spectra,the background rejection,the uncertainties analysis.The NEFF code was used to calculate the detection efficiency of the BC501-A detector and the CLYC detector.The leakage neutron spectra and leakage gamma pulse height spectra from 238U slab at 61°and 119°were measured on the neutronics integral experimental facility using time of flight method.2?The geometric model and material model were established as same as the experimental setup.The MCNP-4C program was used to calculate the leakage neutron spectra and the leakage ? pulse height spectra at 61° and 119° in which the evaluated nuclear data of 238U were taken from ENDF/B-?.0?CENDL-3.2 and JEFF-3.3 library.3?The calculated results of ENDF/B-?.0?CENDL-3.2 and JEFF-3.3 and the experimental results were compared.As for the leakage neutron spectra,the leakage neutron were divided into six energy ranges,the tally of the neutrons in each energy range were calculated.The NDplot program was used to figure out the spectra of the secondary neutrons which were produced by the 2.8MeV neutron interact with 238U.It is easy to draw the following conclusions by analysis the C/E and the evaluated nuclear data of 238U:1)In the energy rang of 3.2MeV-8.5MeV,the calculated results of ENDF/B-?.0 library and JEFF-3.3 library is about 10%lower than the experimental results.2)In the energy range of 2.5MeV-3.2MeV which is also the elastic scattering energy region,the elastic scatter cross section of CENDL-3.2 library is much higher,the calculated results is 10%higher than the experimental results.In addition,the elastic cross section of JEFF-3.3 library at 119° is small,the calculated results is about 10%lower than the experimental results.3)In the energy range of 1.5MeV-1.9MeV energy range,the neutron spectra of 238U(n,n')discrete reaction at the incident neutron energy of 2.8MeV of CENDL-3.2 library is obviously lower which is the reason why the calculated results is 20%lower than the experimental results.4)In the 0.8MeV-1.5MeV energy range,the calculated results by CENDL-3.2 and JEFF-3.3 libraries are about 10%lower than the experimental results.5)In the energy range of 0.2MeV-1.0MeV energy range,the calculated results of JEFF-3.3 library were in good agreement with the experimental results.However,the calculated results of ENDF/B-?.0 library are about 10%lower than the experimental results.As for the leakage ? pulse height spectra,by comparing the experimental results and the calculated results from three libraries,it was found that in the 0.15MeV-1.0MeV energy range,the calculated results of ENDF/B-?.0 and JEFF-3.3 libraries were underestimated,while the calculated results of all the three libraries were higher in the 1.0 MeV to 2.5 MeV energy range.