Thermal Hydraulics of Accident Tolerant Fuel Concepts and a Preliminary Demonstration of CASL’s Coupled Tools for BWRs
Open Access
- Author:
- Gorton, Jacob Preston
- Graduate Program:
- Nuclear Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 06, 2018
- Committee Members:
- Nicholas Brown, Thesis Advisor/Co-Advisor
Benjamin Collins, Committee Member
Arthur Motta, Committee Member - Keywords:
- Accident Tolerant Fuel
Critical Heat Flux
Channel Box
Silicon Carbide
FeCrAl
CTF
MPACT/CTF - Abstract:
- Since the 2011 accident at the Daiichi nuclear power plant in Fukushima, Japan, there has been a worldwide effort to develop so-called accident tolerant fuel (ATF) technologies to enhance safety during design basis and beyond design basis accidents. Part of the ATF development effort involves replacing much of the zirconium-based materials in light water reactors (LWRs). This is due to the accelerated oxidation rate of zirconium at high temperatures potentially experienced during severe accidents, which led to the build-up of hydrogen gas and eventual explosions that occurred at the Daiichi nuclear power plant. To be considered as a possible alternative to zirconium, an ATF candidate material must not only have greater oxidation resistance but must also have equal or better performance than zirconium in reactor operations and safety. Two candidate materials that may meet these requirements are iron-chromium-aluminum (FeCrAl) alloys and silicon carbide fiber-reinforced, silicon carbide matrix composites (SiC/SiC). Two studies on ATF concepts are presented in this thesis, which focus on using computer simulations to evaluate the use of FeCrAl as the fuel rod cladding material in a pressurized water reactor (PWR) and the use of SiC/SiC as the fuel assembly channel box material in a boiling water reactor (BWR). Both of these studies are performed using computer modeling, which is one of the first steps for evaluating new design concepts and eventually integrating them into existing reactors. Developing tools that can accurately predict the performance of nuclear reactors with high fidelity is the goal of the Consortium for Advanced Simulation of Light Water Reactors (CASL). Also included in this thesis is a preliminary demonstration of neutronic-to-thermal-hydraulic coupled BWR simulations performed using the CASL tools MPACT and CTF. In the first study, a model of a PWR fuel assembly was created to predict the critical heat flux (CHF) of FeCrAl fuel rod cladding during an imposed 50% overpower condition, which may be representative of an accident condition. CHF is a critical parameter to evaluate for ATF candidate materials because reaching CHF in a fuel rod can cause a rapid increase in temperature in the reactor that may lead to bursting of the cladding and a loss of ability to cool the core. Current correlations used for predicting flow boiling CHF in reactors are not dependent on material or surface characteristics, but this study showed that preliminary pool boiling results could be used to modify existing CHF correlations to make them more applicable to a given material, such as FeCrAl. Preliminary transient flow boiling experiments are also analyzed in this thesis for Inconel 600 and Stainless Steel 316, which pave the way for future flow boiling experiments using FeCrAl. In the second study, BWR fuel assembly models were created with a SiC/SiC channel box to predict a spatial temperature and fast neutron flux distribution in the channel box. The temperature and fast flux distributions were then used as boundary conditions for a finite element model of the channel box created by Oak Ridge National Laboratory to determine the deflection of the channel box due to temperature and neutron flux gradients. It was found in this study that the deflection of the channel box, which was mainly a product of the nonuniform fast flux distribution causing a swelling gradient within the channel box, may lead to interference with control blades in BWR cores. The work presented in this thesis provides new information on two ATF concepts and helps lay the groundwork for future evaluations. Detailed computational evaluations are an important step in the progression and application of these concepts that have the potential to increase the safety of nuclear reactors. The development of high-fidelity computational tools like MPACT/CTF is important for providing accurate simulated results that can be used in advancing the development of ATF concepts.