2 research outputs found
Spectral shift operated smAHTR to improve cycle length and discharge burnup simultaneously
No full textFluoride High Temperature Reactors (FHRs) are envisioned to be next generation reactors due to their inherent safety design characteristics and high efficiency from their use of salt-based coolants. FHRs use TRistructural-Isotropic (TRISO) fuel for its benefits of encapturing fission gases and fission products in its layers. One of the main disadvantages of using TRISO fuel is that its fabrication costs are a lot higher (in range of 30,000 per Uranium) compared to current pellet-based fuel ($300 per Uranium). In this study, we propose and develop a spectral shift method to operate this type of reactors. This spectral shift method is based on varying neutron energy spectrum. As a result, both cycle length and discharge burnup are improved simultaneously while eliminating the need of burnable poison.Ph.D.M.S
INVESTIGATING THE RESPONSE OF YTTRIUM HYDRIDE MODERATOR DUE TO CHANGES IN STOICHIOMETRY AND TEMPERATURE
No full textMicroreactors are designed to be compact, truck-transportable, and self-regulating with power levels rated anywhere between 1 kWe to 10 MWe. Microreactors are envisioned to be utilized for terrestrial as well as space power applications. Originally, microreactors were envisioned to use HEU fuel with fast spectrum core operation, however, this poses regulatory concerns. As such, recent endeavors rely on the application of Low Enriched Uranium (LEU) fuel. In order to maintain a relatively compact reactor-core with LEU fuel, effective neutron moderation is required; and hence LEU mandates the use of moderators. Solid metal hydrides are being considered due to their structural, neutronic, and containment benefits. Out of all the metal hydrides, Yttrium Hydride (YH_(2-x)) is considered as the primary candidate as it provides relatively high hydrogen density combined with high maximum operating temperature. However, hydrogen dissociation and migration at higher temperatures within the YH_(2-x) element raises concerns as it changes the reactor behavior during operation. The diffusion of hydrogen within the YH_(2-x) matrix under a temperature-gradient causes local shifts in the material properties as YH_(2-x) is altered to YH_((2-x)±Δ). As such, stoichiometric and temperature responses of the YH_(2-x) moderator properties are investigated in this dissertation. To create these properties, atomistic simulations, using Density Functional Theory (DFT), are performed. Furthermore, thermal scattering laws (TSLs) are generated using DFT phonon density of states and NJOY2016 for sub-stoichiometric YH_(2-x) to account for shifts in neutron cross sections at thermal energies. The properties generated from atomistic modeling is further validated with the neutron diffraction experiments performed by Los Alamos Neutron Science Center (LANSCE) and available literature. Finally, a coupling capability is developed and implemented using the Monte-Carlo code MCNP along with the Finite Element based code ABAQUS. The coupled framework is realized via Picard iterations, and allows the investigation of neutronics, heat transfer, and hydrogen mass diffusion. This dissertation provides a general framework to model the design space and performance of YH_(2-x) moderated reactors.Ph.D
