Detailed modeling and massive tallying of nuclear reactors lead to memory overload for a single core processor.It could not be calculated by Monte Carlo particle transport with particle parallelism only.Domain decomposition is one of solutions.Domain decomposition needs to interchange particles between processors, so that inherit technique of pseudo-random number could not make identical results between serial and parallel.Two techniques of pseudo-random number are described to obtain identical results on different numbers of domains in a Monte Carlo particle simulation code.

In order to develop large-scale transport simulation (such as simulation of whole reactor core pin-by-pin problem), we developed a neutron photon coupled transport code JMCT. In this article, developing idea of a auto modeling tool JLAMT based on field oriented development is introduced. JLAMT developed several quick and assembly modeling tools. Data structure based on hierarchical geometry tree was designed. Automatic conversion and generation of physical model input file for GDML file format are made. By using those modeling tools, complex devices (include DAYAWAN whole-core model) were created, and transformed file was delivered to JMCT for transport calculation. Results were validated for correctness of visual modeling tools.

Mesh tally function of monte Carlo method can give a detailed and intensive calculation of flux distribution in specific volumes. To realize such function in JMCT mesh tally function are designed and realized. It supports non-uniform mesh in three kinds of orthogonal geometry (xyz of rectangular coordinates, rθz of cylindrical coordinates, and rθφ of spherical coordinates). Algorithm for rectangular coordinates is discussed. Calculation on DAYAWAN reactor core pin-by-pin model, Venus benchmark model and a 1-D ITER model verifies preliminarily correctness of JMCT mesh tally. Furthermore, U-array benchmark model is used to test serial performance of JMCT mesh tally. Both JMCT and MCNP5 use same xyz mesh grids and run under same condition. It shows that JMCT takes less time consuming and has higher performance dealing with xyz geometry.

VENUS-III benchmark was simulated based on 3-D general-purpose Monte Carlo coupled neutron and photon transport code JMCT (J Monte Carlo Transport Code). It includes detailed modeling, criticality calculation and shielding calculation. Firstly, criticality calculation is done, in which k_eff eigenvalue, fluxes in importance regions and energy spectrums are calculated. Almost same results are achieved by JMCT and MCNP. Warp of k_eff is about 0.24% the flux warp is less than 1%. Then, deep penetration shielding is simulated, in which fixed source is used. Tally includes fluxes of detectors in different locations. Calculated results agree well with experimental data. The most warps of JMCT and tests are within target accuracy of ±15%. It satisfies requirement of shielding calculation. It shows that JMCT code suits well for criticality and shielding simulation.