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Molecular dynamics simulation for PBR pebble tracking simulation via a random walk approach using Monte Carlo
Kyoung O Lee1, Thomas W Holmes, Adan F Calderon
1Center for Engineering Applications of Radioisotopes, Department of Nuclear Engineering, North Carolina State University, Raleigh, 27695-7909, United States.
Summary
Monte Carlo simulations tracked pebbles in a biased gravity field, incorporating viscosity damping and Gaussian fluctuations. This method correlates with Molecular Dynamics simulations for Pebble Bed Reactors, enabling transient gamma-ray spectra analysis.
Area of Science:
- Computational physics and nuclear engineering.
Background:
- Pebble Bed Reactors (PBRs) utilize randomly packed pebbles for nuclear fuel.
- Accurate modeling of pebble dynamics is crucial for PBR safety and efficiency.
- Understanding pebble movement under gravity and damping forces is essential for reactor design.
Purpose of the Study:
- To develop and validate a simulation framework for pebble tracking in PBRs.
- To investigate the influence of viscosity damping and random fluctuations on pebble motion.
- To establish a foundation for analyzing transient gamma-ray spectra from radioactive tracers within pebbles.
Main Methods:
- Utilized Monte Carlo (MC) simulations for random walk-based pebble tracking in 2D.
- Incorporated a biased gravity field and viscosity damping with Gaussian fluctuations.
- Employed Molecular Dynamics (MD) simulations based on Hertz-Mindlin theory for particle interactions.
- Established a correlation between MC and MD simulation outputs.
Main Results:
- Successfully simulated pebble random walks in a biased gravitational field.
- Quantified the effects of viscosity damping and random fluctuations on pebble trajectories.
- Demonstrated the correlation between MC pebble tracking and MD-based particle dynamics.
- The simulation framework is extendable for radioactive tracer analysis.
Conclusions:
- The combined MC and MD simulation approach provides a robust method for modeling pebble dynamics in PBRs.
- Viscosity damping and random fluctuations significantly impact pebble movement.
- This framework facilitates the analysis of transient gamma-ray spectra for pebble position determination.
- Future work can focus on inverse analysis for realistic measurement uncertainty assessment.
