Effect of hydrogen distribution in UZrHx on physical parameters of JSI TRIGA reactor
Sanchez, Maria (2023)
Diplomityö
2023
School of Energy Systems, Energiatekniikka
Kaikki oikeudet pidätetään.
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe20231128149598
https://urn.fi/URN:NBN:fi-fe20231128149598
Tiivistelmä
One potential issue with uranium-zirconium hydride (U-ZrH) fuel is that the hydrogen redistributes in the hydride when thermal and concentration gradients are present. The spatial hydrogen distribution within the fuel element depends on the history of operation and temperature profile. After a long period of time there is theoretical possibility that hydrogen might diffuse out of the fuel, thus affecting neutron transport in the reactor.
This masters thesis aims to gain a better understanding of how reactor physical parameters of the TRIGA (Training, Research, Isotope Production General Atomic) Mark II research reactor at the Jožef Stefan Institute (JSI) are affected by such hydrogen redistributions and to study the physical phenomena responsible for these changes.
For this purpose two different models were created with OpenMC Monte Carlo program, one containing the whole reactor, denoted as Reactor Core model, and another containing just a fuel cell surrounded by water without leakage, denoted as Unit Cell model. Different homogeneous and heterogeneous hydrogen distributions within the fuel were applied in those models. Effective neutron multiplication factor, neutron flux spectrum, reactivity and effective delayed neutron fraction were calculated for all the cases.
Firstly, homogeneous hydrogen distributions were applied showing that an homogeneously decrease in the hydrogen content in all the fuel rods of the reactor results in a decrease in the multiplication factor, while if one considers a fuel rod surrounded by water that has no leakage, multiplication factor increases as the hydrogen content decreases. It was concluded that whereas Rector Core model system is undermoderated, Unit Cell model system is overmoderated.
Secondly, different heterogeneous hydrogen distributions, axial and radial ones, were applied in the two models created. From results obtained for both models, it is observed that axially, the most sensitive zone of the fuel to hydrogen distributions is the central part of the fuel where the flux is the largest. Its hydrogen concentration affects reactor physical parameters while the concentration at the edges of the fuel practically does not affect that much reactor physical parameters.
Regarding the effect of hydrogen content in kinetic parameters of the reactor, it is concluded that the effective delayed neutron fraction does not depend significantly on the hydrogen content within the fuel.
This masters thesis aims to gain a better understanding of how reactor physical parameters of the TRIGA (Training, Research, Isotope Production General Atomic) Mark II research reactor at the Jožef Stefan Institute (JSI) are affected by such hydrogen redistributions and to study the physical phenomena responsible for these changes.
For this purpose two different models were created with OpenMC Monte Carlo program, one containing the whole reactor, denoted as Reactor Core model, and another containing just a fuel cell surrounded by water without leakage, denoted as Unit Cell model. Different homogeneous and heterogeneous hydrogen distributions within the fuel were applied in those models. Effective neutron multiplication factor, neutron flux spectrum, reactivity and effective delayed neutron fraction were calculated for all the cases.
Firstly, homogeneous hydrogen distributions were applied showing that an homogeneously decrease in the hydrogen content in all the fuel rods of the reactor results in a decrease in the multiplication factor, while if one considers a fuel rod surrounded by water that has no leakage, multiplication factor increases as the hydrogen content decreases. It was concluded that whereas Rector Core model system is undermoderated, Unit Cell model system is overmoderated.
Secondly, different heterogeneous hydrogen distributions, axial and radial ones, were applied in the two models created. From results obtained for both models, it is observed that axially, the most sensitive zone of the fuel to hydrogen distributions is the central part of the fuel where the flux is the largest. Its hydrogen concentration affects reactor physical parameters while the concentration at the edges of the fuel practically does not affect that much reactor physical parameters.
Regarding the effect of hydrogen content in kinetic parameters of the reactor, it is concluded that the effective delayed neutron fraction does not depend significantly on the hydrogen content within the fuel.