Transient Simulations of the SLOWPOKE-2 Reactor Using the G4-STORK Code

Abstract

The goal of this thesis is to study the transient behaviour of the SLOWPOKE-2 reactor using Monte-Carlo simulations with the G4-STORK code. G4-STORK is a 3-dimensional Monte-Carlo code derived from the GEANT4 physics simulation toolkit. Methods were developed for the proper treatment of delayed neutrons and a lumped capacitance model was used to track the time-dependent fuel properties (temperature, density) based on the fission power. By validating the methods in G4-STORK with experimental measurements we hope to extend our understanding of reactor transients as well as further develop our methods to model the transients of the next generation reactor designs. A SLOWPOKE-2 reactor such as the one at RMC was chosen for simulation due to its compact size, and well-known transient response of control rod removal and measured temperature feedback. Static simulations in G4-STORK find a neutron flux of order 10^12 cm−2 s−1 which agrees with experiment and a control rod worth of (4.9 ± 2.0) mk compared to the experimentally measured worth of 5.45 mk. Transient simulations from rod pluck-out find similar trends to the experimental findings as our results suggest a negative temperature feedback due to the doppler broadening of the U-238 absorption spectrum which contributes to the overall safety mechanism seen in the SLOWPOKE reactor. It is determined that the methods in G4-STORK provide a reasonable ability to simulate reactor transients and it is recommended that a full-core thermal-hydraulics model be coupled to G4-STORK to achieve a higher level of accuracy.