Neutronics Analysis Of Magnet System Shielding And Experimental System Of GDT-based Fusion Neutron Source

The reliability verification of fusion materials and components under complex and extreme environments(high-energy high-flux neutron irradiation,ion irradiation,strong magnetic field and high thermal load)in fusion reactor is an urgent issue to be solved before engineering application of commercial fusion reactor.Fusion neutron source based on GDT(Gas Dynamic Trap)has many advantages,such as low plasma parameter requirement,typical fusion energy spectrum,simple and compact structure,relatively low construction and operation cost,etc.,it is very suitable for the test platform of fusion nuclear materials and components.Hefei Institute of Physical Science of Chinese Academy of Sciences,with Budker Institute of Nuclear Physics of Siberian Branch Russian Academy of Sciences and other world-known institutes,jointly initiated an International Mega-science Project proposal named ALIANCE,meaning axisymmetric linear advanced neutron source.At present,the ALIANCE device is still in the conceptual design stage,in which the design of superconducting magnet shielding and experimental system are very important.The shielding design of superconducting magnet can reduce the radiation damage of magnet system,ensure the stability of superconducting magnet system and ensure the safe and stable operation of the device.In addition,the experimental system is the core system of ALIANCE to realize fusion nuclear material/component testing.Therefore,in this paper,the shielding of magnet system and experimental system of ALIANCE are preliminarily designed,and the neutronic analysis is carried out by using SuperMC code.It mainly includes the following research work:(1)Based on the compact structure layout and the characteristics of neutron flux distribution at both ends and low in the middle of ALIANCE device,a feasible shielding design for superconducting magnet system of ALIANCE is proposed.The design consists of a traditional main shielding layer and a unique shielding layer at mirror plug.The main shielding layer is made of a mixture of 316L stainless steel and water with a thickness of 40 cm.A 5 cm funnel conical shielding layer made of tungsten carbide is used for mirror plug shielding with small space to further block neutrons and charged particles at the core.Then the neutronics model of ALIANCE device is established to calculate the nuclear heating and fast neutron fluence of superconducting magnet.The results show that the nuclear heating and fast neutron fluence at the magnetic mirror coil are the highest,which are 296 W/m3 and 9×1018 n/cm2,respectively,which meet the limit of superconducting magnet for ITER.Then the activation analysis of the structural materials of the ALIANCE is carried out.And the variation of specific activity,decay heats and the main radionuclides of the structural materials with the shutdown cooling time are calculated.Combined with the classification standard of radioactive waste in China,radioactive waste classification is carried out for the structural materials of ALIANCE device.The results show that all the structural materials are reduced to low and medium level radioactive wastes after one year.Finally,according to the international standards of fusion material recovery and treatment,the subsequent treatment scheme of structure material is proposed.After 30 years of shutdown,the material of cryostat and tungsten carbide shielding layer can be treated by simple recycling technology and the material of stainless-steel shielding layer can use complex recycling techniques after 40 years.(2)According to the international requirements for fusion materials and components testing facility,the design objective of the ALIANCE experimental system is proposed.Secondly,the experimental system design of ALIANCE device is carried out,including the design of material test cell and component test cell.The design of a detachable stepped shielding and a rotating test platform are proposed to provide the possibility for remote operation to replace the test components.Then the neutronics calculation of the experimental system was carried out.According to the neutron flux,we divide the high,medium and low flux regions,and calculate the volume and neutron flux gradient.The results show that the volume of the medium-high flux region(>6.6×1013 n/(cm2·s))is about 1.8 m3.And the maximum neutron flux gradient is less than 20%/cm,both of which meet the design objectives of the ALIANCE device experimental system.Finally,the radiation damage distribution of the experimental system has been calculated,and the distribution of the test module was preliminarily designed.In conclusion,the preliminary designs and analyses of the superconducting magnet system shielding and the experimental system are carried out in this paper and,they will provide a reference for the ALIANCE fusion neutron source as a test platform for fusion materials and components.