Neutronic Calculation And Design Optimization For The Granular Flow Spallation Target Of C-ADS

A new type of spallation target concept — the gravity-driven dense granular flow target(DGT)— has been proposed for the China-ADS project.The granular flow target concept adopts a gravity-driven tungsten granular flow to act as target body as well as the heat carrier.The essential idea of the granular flow target concept is to treat the power deposit offline easily,just as how liquid heavy mental(HLM)target dose,and avoid the critical problems due to the adoption of the HLM at the same time.As an initiative target concept,the granular flow target is so different with other regular targets in many ways.To perform neutronics analysis and design optimization of the granular flow target,a dedicated Monte Carlo particles transport program named GMT was developed.Base on the combination of reliable nuclear reactions models,especially the sophisticated spallation models,and the dedicated design of the neutron transport method,the GMT program can be used to perform detailed neutronic simulations of the granular flow target with satisfactory reliability and high efficiency.Based on the GMT simulations,the neutronics studies,including neutron production efficiency and neutronics performance,and the design optimization,including beam energy and target dimension,for the granular flow target of C-ADS are performed.This thesis includes six chapters,which can be summarized as follows.Chapter One introduces the development background of the granular flow target and the neutronics calculation tasks of this kind of target concept.More specifically,a brief review of the development of the high-power spallation target and a short introduction to the current states of the spallation targets of the main spallation neutron sources in the world are given;a brief introduction to the worldwide R&D of ADS,the extreme challenges posed by the spallation target and the intensive China-ADS R&D project is presented;An introduction to the special calculation demands of the granular flow target and the thoughts for the development of a dedicated particles transport program for the simulations of this kind of target are given.Chapter Two introduces the investigations into the physical processes of spallation reaction and the researches of its Monte Carlo simulation models.Firstly,the intra-nuclear cascade(INC)and the de-excitation process are investigated to analyze the physics,especially the neutron production processes and the neutronics characteristics,of the spallation reactions.After that,a brief introduction to the development of INC models,especially the INCL model,and evaporation/fission models,especially the ABLA model,is presented.Chapter Three is about the development of GMT program.This chapter includes three parts: the design of the geometry and material module,the design of the transport module and the development of the GPU-based spallation models.In the first part,the adoption of the CSG method for the geometric modeling for GMT program is introduced.For the granular flow target,the voxel algorithm for particle locating and geometry searching are introduced.In the second part,firstly,the design of the tracking method for the Monte Carlo transport of particles in the granular target,which is one of the most important highlights,is presented;after that,an introduction to the designs of the cross-section calculation,the electromagnetic processes simulation and the combination of the hadronic models are given.The hadronic models play the critical role in the neutronics calculation of a spallation target.Based the combination of the INCL,the ABLA/Fermi break-up,and the data-driven model for low energy neutrons,GMT performs the calculations with a reasonable accuracy.To validate the code,a sequence of calculations of neutronics characteristics as well as heat-deposit distributions are performed to compare with the experimental data and the predictions of the versatile program such as Geant4 and FLUKA.The accuracy of GMT program was observed to be satisfactory.In the third part,a brief introduction to the development of the GPU-based spallation models and the high speed-ups that have been obtained is given.Chapter Four presents the discussions about the neutron yields and the neutronics characteristics of a spallation target with different parameters.For the representative target materials like lead and tungsten,general analyses of the neutron production efficiencies and the neutronics performances with various beam-target parameters are performed,which can provide references for the neutronics analysis and design optimization work for granular flow target.Chapter Five is about the design optimization of the beam energy and the target parameters for the granular flow target to obtain a high neutron production efficiency,a good neutronics performance and a modest power deposit distribution.First of all,the analyses of the GPU-based DEM simulation results for the granular flow are given to form the basis of the neutronics calculations.Secondly,systematic calculations of the neutron production efficiencies and the neutronics performances for various beam energies and granular flow target diameters are performed to obtain relatively optimal beam-target parameters.Based on detailed calculations and transmutation value analyses,the influences on the neutronics of the granular flow target due to the adoption of the tungsten alloy granule material are investigated.Finally,the investigation into the heat deposit characteristics for different beam energies is performed to optimize the beam energy from the perspective of neutron economy and the homogeneity of power deposition.In addition,the discussions about the ability to sustain tens of MW beam power of the granular flow target are performed.Besides,the solutions to the overheating of the granules in the disturbance region just under the beam-target interaction surface for the release of the full potential of heat removing for the granular flow target are discussed.Chapter Six is the conclusion of this thesis and the prospects for further work.