RADIATION SHIELDING AND DOSE ASSESSMENT OF THE CYCLOTRON FACILITY AT INRNE-BAS

The Institute for Nuclear Research and Nuclear Energy at the Bulgarian Academy of Sciences is working on the construction of a cyclotron centre. The facility is on a design level. At this stage of the project, an important task is the radiation shielding assessment of the facility. Nowadays, the Monte Carlo transport codes have become the tool of choice for solving this type of problem. In the current paper, the transport code FLUKA is used for the calculations. It is widely applied for shielding design and analysis of accelerators and their components. The distributions of the radiation fields inside and outside the cyclotron bunker are presented in this paper. Both different irradiation scenarios and bunker configurations are considered in the conducted Monte Carlo simulations. These results will be used as a guidance in site planning.

Evaluation of Serpent Capabilities for Hyperfidelity Depletion of Pebble Bed Cores

Accurate burnup calculation in pebble bed reactor cores is today necessary but challenging. The continuous advancement in computing capabilities make the use of Monte Carlo transport codes possible to efficiently study individual pebbles depletion without making strong assumptions. The purpose is to eliminate unnecessary typical assumptions made in existing codes, while being flexible and suitable for commonly available computing machines. Among the available codes, Serpent 2 provides extremely useful tools to make pebble beds modeling and simulation efficient. The explicit stochastic geometry definition handles irregular pebble beds with comparable performances to regular lattices. Optimization modes controlling the use of unionized energy grids, cross-sections pre-calculation and flux calculation through spectrum collapse or direct tally lead to high flexibility and optimal memory usage while limiting calculation time. Automated burnable materials division is a useful tool to lower the memory requirements while quickly generating the geometry and materials. Finally, parallelization and domain decomposition allow for decreasing unreasonable memory constraints for large cores. This work thus explores the possibilities of Serpent 2 when applying depletion in pebble beds, compares the optimization modes and quantifies the simulation time and memory usage depending on the conditions of the calculation. Overall, the results show that Serpent 2 is well adapted to the use of small to large cores calculations with commonly available resources.

The Lunar Radiation Environment: Comparisons between PHITS, HETC-HEDS, and the CRaTER Instrument

Understanding the radiation environment near the lunar surface is a key step towards planning for future missions to the Moon. However, the complex variety of energies and particle types constituting the space radiation environment makes the process of replicating such environment very difficult in Earth-based laboratories. Radiation transport codes provide a practical alternative covering a wider range of particle energy, angle, and type than can be experimentally attainable. Comparing actual measurements with simulation results help in validating particle flux input models, and input collision models and databases involving nuclear and electromagnetic interactions. Thus, in this work, we compare the LET spectra simulated using the Monte Carlo transport code PHITS with measurements made by the CRaTER instrument that is currently orbiting the Moon studying its radiation environment. In addition, we utilize a feature in PHITS that allows the user to run the simulations without Vavilov energy straggling to test whether it is the root cause of erroneous phenomena exhibited in similar studies in literature. The results herein show good agreement between the LET spectra of PHITS and the CRaTER instrument. They also confirm that using a Vavilov distribution correction would ultimately provide a better agreement between CRaTER measurements and the previous LET spectra from the transport codes HETC-HEDS and HZETRN.