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TRAMO is a Monte Carlo code which is specially designed for geometries of nuclear power plants. In recent years, TRAMO has undergone a number of technical developments. In addition to the conversion to modern Fortran, standardized models for VVER-440 and VVER-1000 for the evaluation of monitor experiments on the surface of the reactor pressure vessel were developed, and the corresponding pre- and post-processing was automated. The new TRAMO version is continuously validated and verified. Here we present comparisons with experimental data from unit 1 of the Greifswald nuclear power plant and with MCNP calculations. Earlier calculations with TRAMO showed good agreements in the middle region of the reactor core, but significant deviations outside. A possible explanation is the wrong documentation of the experimental data – especially the heights of the monitors. Assuming a downward shift of the monitor positions by about 24cm, experimental and calculated data show very good agreement.

MCNP code provides numerous variance reduction techniques that are mainly used to optimize the analog Monte Carlo simulations. These techniques can reduce the statistical uncertainty of the simulation results while minimizing computational costs. Weight window is one such technique that is commonly used to optimize shielding calculations. However, for complex shielding problems such as deep penetration, the existing MCNP weight window generator is not efficient enough to generate the appropriate weight parameters for the weight window in a single run. To address this issue, an automated algorithm was developed using the code TRAWEI, which is based on recursive Monte Carlo methodology. The TRAWEI code can generate suitable weight values in a single run with less calculation time. This paper focuses on the verification of TRAWEI-generated weights using a simplified cask model. Further, the results of MCNP simulation using TRAWEI-generated weights are compared with those using weights generated by an existing MCNP weight window generator.

In nuclear engineering, Monte Carlo (MC) methods are commonly used for reactor analysis and radiation shielding problems. These methods are capable of dealing with both simple and complex system models with accuracy. The application of MC methods experiences challenges when dealing with the deep penetration problems that are typically encountered in radiation shielding cases. It is difficult to produce statistically reliable results due to poor particle sampling in the region of interest. Therefore, such calculations are performed by the Monte Carlo N-Particle Transport (MCNP) code in association with the weight window (WW) variance reduction technique, which increases the particle statistics in the desired tally region. However, for large problems, MCNP's built-in weight window generator (WWG) produces zero WW parameters for tally regions located far from the source. To address this issue, the recursive Monte Carlo (RMC) method was proposed. This paper focuses on the RMC methodology and its implementation in the Helmholtz-Zentrum Dresden-Rossendorf's (HZDR's) in-house code TRAWEI, which is responsible for producing optimal zone weight parameters used for optimizing deep penetration MC calculations. In addition, this paper discusses the verification of the TRAWEI weight generator program to that of an existing MCNP WWG. The performance of TRAWEI-generated weight values is assessed using a handful of test cases involving two shield materials. Globally, the TRAWEI-generated weight values improved not only the statistical variance and computational efficiency of the MC run compared to the analog MCNP simulation but also those of the simulation with WW values generated by the standard MCNP WWG. [ABSTRACT FROM AUTHOR]