| At present,China initiative Accelerator Driven System(Ci ADS)has been supported by the “ Twelfth-Five-Year ” national major scientific and technological infrastructure,and the Ci ADS principle verification device is also under the construction.Therefore,according to the development plan of an accelerator-driven advanced nuclear energy system(ADANES)proposed by the Chinese Academy of Sciences,developing and improving a Monte Carlo particle transport software system with independent intellectual property rights suitable for the ADS system is necessary.In this paper,a new Monte Carlo photon transport code named IMPC-Photon is developed to meet the needs of software development and expansion for ADANES,which can support photon transport and shield calculations.Besides,the source code of Open MC is modified so that the neutron-initiated photon sources can be recorded and output for IMPC-Photon to perform neutron-photon external coupling transport calculations.This method allows the code to be practically applied to neutron-photon correlation calculations of reactor,and provides a reference for the merging of IMPC-Photon with the self-developed neutron transport code into a neutron-photon coupled transport code in the future.IMPC-Photon is a stand-alone photon transport code that combines a geometry building module,source particle sampling module,cross section preparing and loading module,particle transport module and a statistics module.In IMPC-Photon,XML file format is used as the standard input file,and fixed source model is adopted for photon transport.Besides,the CSG solid geometry construction technique is used to construct the 3D space geometry by surface stitching.When loading photon sources,two method including source sampling method and external source file read-in are adopted to realized pure photon transport calculation and the neutron-photon coupling transport calculation.Meanwhile,a unified energy grid acceleration algorithm is used to improve the search speed and calculation speed of the cross-section to improve the running efficiency of code.Additional,a reducing variance technique of splitting and Russian Roulette is implemented to deal with the deep penetration problem in shielding calculation.In transport module,four main photon-atomic interactions are accurately modeled,including coherent scattering,incoherent scattering,photoelectric effect and pair production.Moreover,the secondary processes which generated new photons including atomic relaxation,electron-positron annihilation and thick-target bremsstrahlung approximate are also considered.So the photon-material collisions,photon production and disappearance processes are described by the above theory.At present,the statistics of flux,surface current and surface flux are supported in the tally module.The verification work of IMPC-Photon is carried out from two aspects: unified energy grid and photon transport capability.First,the cross sections of hydrogen,oxygen,iron and uranium calculated by unified energy grid method are compared with those under the original energy grid to verify the accuracy of the unified energy grid method used in IMPC-Photon.Besides,we have selected some shielding materials such as water,graphite,boron,lead and concrete etc.that commonly used in reactor based on the benchmark of “point gamma-ray source in infinite medium” to compared the calculation time of the cross section between the unified energy grid and the original energy grid.The results show that the cross section processed by unified energy grid is same as the cross section of original energy grid.Moreover,compared with the original energy grid,the calculation time of cross section of unified energy grid of is shortened 77.5%,85.9% and 87.1% respectively when the reaction medium is water,concrete,and the mixture of above five material.It can be seen that the unified energy grid method used in processing and calculation of cross section will greatly reduce the calculation time,and computational efficiency is improved more obviously with the increase of the number of elements.Secondly,to verify the photon transport capability of IMPC-Photon,two Monte Carlo code including Open MC are used for comparison and verification.Five cases including“point gamma-ray source in infinite medium” benchmark,“gamma-ray skyshine”experimental benchmark,multi-layer nested cylindrical model,two-sphere complex material model and OECD/NEA fast reactor model are selected and the photon flux are calculated.The results show that IMPC-Photon's results are in good agreement with the results given by the reference code in general,and presents more accuracy results than Open MC under the same calculation conditions.Meanwhile,the results of IMPC-Photon are basically the same as those of reference code and experimental results given in the reference,and the computer time is close to that of reference code in the “gamma-ray skyshine” experimental benchmark.In this paper,in order to handle the neutron-photon coupling transport calculation function based on IMPC-Photon,the source code of the neutron transport generation photon module of Open MC code is modified.By tracking the source particle transport process,the neutron-induced photon sources are recorded and output in the external source file,and the neutron-photon coupling transport calculation is realized by external coupling method in combination with the function of external source file loading of IMPC-Photon.Besides,a reducing variance technique of splitting and Russian Roulette is added in Open MC to solve the deep penetration problem of the shielding calculation in coupling transport calculation.Meanwhile,the attributes of secondary particles in Open MC code are changed,and the surface information is added to make the position determination of secondary particles more accurate,and the program running time is saved.To verify the neutron-photon coupled transport function,the OECD/NEA fast reactor benchmark,the SINBAD NEA-1517/74 and NEA-1517/80 benchmark are used for the calculation.The results show that the computational results of Open MC + IMPC-Photon are close to those of Open MC and other reference code,and the calculated results are reliable.It can be concluded that the calculation results of self-developed Monte Carlo photon transport code are reliable and IMPC-Photon's results are better than Open MC's results,the only open source code that can be used for reactor problem solving.IMPC-Photon can meet the needs of photon transport and shielding calculation for accelerator-driven advanced nuclear energy system.Moreover,the implementation of the Open MC + IMPC-Photon neutron-photon coupling transport calculation function provides a reference for the merging of IMPC-Photon with the self-developed neutron transport program into a neutron-photon coupled transport program in the future. |
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