Neutron Interrogation Of Uranium In Fuel Rods Of Pressurized Water Reactor(PWR) Using Common Neutron Sources In The GEANT4 Monte Carlo Code

Neutron interrogation technique is one of non-destructive assay(NDA)methods of analysis of nuclear materials.The NDA measurement techniques are showing an increasing importance and convenience in the application of safeguards and control of nuclear materials.As a nuclear safeguards technique,neutron interrogation using neutron as incident particles is being developed for quantitative analysis of special nuclear material.Measurements of NDA of determining the content of uranium have also been carried out in nuclear materials,such as spent nuclear fuel.To estimate,improve and develop measurement techniques,it is important to have reliable simulation tools.Simulations can help to check measurement items,setups.Besides,because of the difficult access to some specific nuclear samples due to the national and international regulation of nuclear material safety and safeguards,simulations allow for the modeling of samples,such as fuel rods of pressurized water reactor(PWR)assembly.In addition,simulations can make up for the weakness of experimental set-up.In this paper,based on the open-source Monte Carlo simulation tool GEANT4,the 9×9 and 18×18 PWR fuel rods were established and three common neutron sources(AmLi,D-D,D-T neutron sources)are simulated.Simulations of neutron interrogation for these fuel rods using polyethylene-moderated neutrons from AmLi,D-D and D-T neutron generators were performed.The average fission probabilities of 235U and 238U and the probability of fission per gram as well as the proportions of fission neutrons of 235U and were computed automatically by the coded program.By changing the thickness of the moderator and the abundance of 235U in fuel rods,the influence of the moderator and the abundance of 235U were studied.Moreover,the 235U fission neutron multiplicity was also studied.The results of the study indicate that under certain conditions,the neutron flux is the main factor affecting the fission reactions of 235U and 238U in the fuel rods with a low abundance of 235U in fuel(less than 5%on an atom basis),while the neutron energy is less important.Meanwhile,neutron production by 235U and 238U fission is relatively high so that they should not be overlooked for the neutron interrogation.