Core Design Of Electron Accelerator Driven Subcritical System

The development of nuclear power has an obvious strategic position in ensuring China energy safety and realizing low-carbon environmental protection.However,the increasing amount of spent fuel limits the sustainable development of nuclear energy,the partitioning-transmutation technology developed under the impetus of accelerator technology has become the best nuclear waste treatment technology,and accelerator driven sub-critical system(ADS)is considered to be the most reliable tool for spent fuel reprocessing.Unfortunately,so far,there are still a lot of basic scientific problems to be solved,nuclear material issues and cost issues are particularly prominent.The technical route of using electron accelerators to drive subcritical systems is concerned due to the low cost of equipment and mature technology.In the electron accelerator driven sub-critical system(eADS),the high-energy electrons accelerated and emitted by the accelerator enter the electron target,and suddenly slow down when in contact with the target material,causing bremsstrahlung radiation to emit photons,and the photons then react with the target to produce neutrons to enter the reactor core and undergo fission reaction with nuclear fuel.Based on these two reaction mechanisms,the thesis designed an electron target model and a subcritical reactor as well as explore the possibility of burning spent fuel in a subcritical system driven by an electron accelerator.Based on the NJOYprogram,the thesis produce and verify the photonuclear reaction data of related nuclides.In MCNPX,a thin metal target was bombarded with 40 MeV high-energy electrons,calculating the photon yield of bremsstrahlung and the neutron yield of the photonuclear reaction to select the optimal target parameters.The electron target is cylindrical shape and consists of two parts:bremsstrahlung target and photonuclear.Different from the liquid lead and bismuth metal target of ADS,the material of the bremstrahlung target in the solid electronic target is natural tungsten,with a radius of 5 cm and a thickness of 0.5 cm;the photonuclear reactor target material is 238U,with a radius of 8 cm and a thickness of 2.5 cm.The energy spectrum of neutrons produced by electron-photon-neutron combined transport has a large peak in the range of 10-8～10-7MeV,and most of the neutrons are thermal neutrons.Therefore,the eADS subcritical reactor design as a thermal neutron reactor.In addition,there is a small peak in the range of 0.01～5 MeV,which can use for spent fuel research.The subcritical reactor of eADS refers to the M310 reactor,and the electronic target is set at the center of the core assembly,and designed two cycles according to the operating time.According to the design requirements of the core power peaking factor and flattened neutron flux,adjust the boron concentration to control the keff in the subcritical range and the core burnable poison distribution to achieve a power peaking factor of about 1.4 with a relatively flat neutron flux distribution,and the multi-target arrangement can effectively flatten the neutron flux.In the subsequent cycle,the spent fuel 150 days after the PWR was taken out to replace the 2.4%enrichment fuel and set the 2.4%enrichment fuel in the peripheral assemblies of the core,the keff in subcritical range,the power peaking factor is 1.359,with a relatively flat level of neutron flux,and then replace the 1.6%enrichment fuel of the core with spent fuel,which also meets the requirements of the core design,Therefore,it is feasible to burn spent fuel in eADS from the perspective of core physics.