| With the sustainable development of nuclear energy,the ultimate treatment scheme of spent fuel has become the center of attention.The Accelerator driven subcritical systems(ADS)is regarded as the most effective way to dispose spent fuel in the world.The research work of ADS team of Chinese Academy of Sciences has entered the stage of system integration from key technology researches.The construction of a megawatt ADS principle verification device CiADS(China initiative Accelerator Driven System)will be carried out.In the CiADS,tungsten is the major component of the granular flow spallation target and lead is the main component in the lead-bismuth coolant.The nuclear data of tungsten and lead directly affects the neutronics simulation results.In addition,the modeling process of randomly stacked tungsten particle target is complex and the time consumed in simulation is long.Simplified model is helpful to realize neutron simulation more efficiently,but the neutron effect needs to be evaluated.Macroscopic examination of tungsten and lead nuclear data and optimization of tungsten particle target modeling method will contribute to the future engineering nuclear design of CiADS.With the support of the Pilot projects-"Future Advanced Nuclear Fission Energy-ADS transmutation system" in the Chinese Academy of Sciences(CAS),the Institute of Modern Physics of the Chinese Academy of Sciences and the Chinese Institute of Atomic Energy(CIAE)have jointly built Venus-II zero-power experimental facilities,which consist of a light water reactor and a lead metal reactor.In this paper,the light water reactor is taken as the research object,and the following three aspects are studied by means of experiment and simulation.Firstly,the reactivity worth of pure tungsten cylindrical target was measured by a period method,the macroscopic examinations of tungsten nuclear data were performed.Through MCNP6 simulations with five evaluated nuclear library,namely ENDF/B-?.0,ENDF/B-?.1,CENDL-3.1,JENDL-4.0 and JEFF-3.2,the reactivity worth values of the pure tungsten cylindrical target were simulated using two methods.1.To verify tungsten nuclear data in five cross-section libraries,the non-tungsten nuclear data were only taken from ENDF/B-?.0,and the tungsten nuclear data were selected from the five different cross-section libraries.The results show that there is a great difference between the simulation results of CENDL-3.1 library and other cross-section libraries because of the difference of radiation capture cross-sections in the epithermal region.2.In order to evaluate the overall cross-section library,the nuclear data of all materials were selected from five cross-section libraries.The results show that the reactivity value of pure tungsten cylindrical target simulated using ENDF/B-?.1 is in good agreement with the experimental results,and the relative deviation is about 1.7%.It is recommended that ENDF/B-?.1 library can be used for neutron simulations of the tungsten target.Secondly,based on the experimental result of the pure lead cylindrical target reactivity worth,lead nuclear data was examinated macroscopically.Nuclear data validations were carried out using two simulation methods:1.Non-lead element nuclear data were from ENDF/B-?.0 and lead element cross sections were separately from the five different libraries.The results indicate that the pure lead cylindrical target reactivity worth is positive and the results calculated by the five cross-section libraries are in good agreement within the Monte Carlo statistical errors.Among the related reaction channels,the elastic scattering has the greatest effects on the simulated results.2.The cross sections of all materials were respectively from the five cross-section libraries.The results indicate that the simulated cylindrical lead target reactivity values of the ENDF/B-?.0,CENDL-3.1 and JEFF-3.2 library are in better agreement with the experimental result and the maximum relative deviation is 7.3%.Thirdly,based on the experimental reactivity worth of the tungsten granular cylindrical target,the tungsten granular target models were evaluated and optimized.In simulations,cross sections of all materials came from ENDF/B-?.1.Tungsten granular target was modeled by the lattice arrangement and equivalent homogenization.The results show that the reactivity values of the two models are in good agreement with the experimental results,which means that the equivalent homogenization model can be used to simulate neutronic behaviors in the coupling device which consists of the sub-critical reactor and the tungsten granular target.Subsequently,the reactivity values of the reactor-target coupling devices corresponding to different heights tungsten particles were measured by source jerk method in the subcritical state.The results show that with the increase of tungsten particle height,the effective multiplication factor Keff,the sub-critical reactor effective neutron multiplication factor Ks with external neutron source and the external source worth ?*decrease.And the Keff and Ks curves are generally S-shaped.In summary,macroscopic examinations of the nuclear data of the tungsten and lead were performed on the VUNUS-II light water reactor.Tungsten nuclear data is firstly detailedly analysed in the thermal neutron spectrum,which fills the blank in the benchmarks on the examinations of the tungsten nuclear data in the reactor.Meanwhile,the experimental reactivity worth of the pure lead cylindrical target is also as an important supplement to existing benchmark.These work providing important supports for the subsequent improvement of the nuclear database.In addition,the neutronics behaviors of the granular target were studied by experiments and simulations in the subcritical state of the core,and the influence of the target modeling methods on the neutronics parameters was evaluated.It provides important basis for the furture engineering design and safe operation of CiADS. |
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