Implementation of dynamic nuclear fuel thermo-mechanics in transient simulation of lead-cooled reactors
The nuclear industry must address the issues faced by the current new-built plants in the west- ern world if it is to remain cost-competitive with other forms of electricity generation. Serial, factory-based production of small modular reactors may address all of these issues. In this context enters...
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| Tipo de recurso: | tesis de maestría |
| Fecha de publicación: | 2021 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/340111 |
| Acceso en línea: | https://hdl.handle.net/2117/340111 |
| Access Level: | acceso abierto |
| Palabra clave: | Nuclear reactors Cooling Reactors nuclears Refrigeració Àrees temàtiques de la UPC::Física |
| Sumario: | The nuclear industry must address the issues faced by the current new-built plants in the west- ern world if it is to remain cost-competitive with other forms of electricity generation. Serial, factory-based production of small modular reactors may address all of these issues. In this context enters SEALER, a lead-cooled fast reactor designed in the most compact configuration possible for commercial power production in off-grid areas. Lead Cold and KTH Royal Institute of Technology are developing a multi-point dynamics code (BELLA) intended for use in the safety-informed conceptual design of lead-cooled fast reactors. Its development is motivated by relatively restricted options to apply modifications to currently available system codes. This master’s thesis aims to improve the accuracy of BELLA by implementing a module for simulation of nuclear fuel thermo-mechanical performance, including the effects of thermal expansion of the fuel and cladding, fission gas release, and swelling of the fuel. Moreover, it constitutes a comprehensive review of the reference code. The thermal expansion of the fuel pellet and cladding are estimated from temperature vari- ations and their respective thermal expansion coefficients. An analytical expression for the thermal conductivity of irradiated UO2 fuel is formulated considering the effects of poros- ity, solid fission products (precipitated and dissolved), and radiation damage. Fission gas release into the fuel-cladding gap is determined by assuming a total release above a burnup- dependent temperature threshold (Vitanza threshold) and a release-to-birth ratio of 1% oth- erwise. Gaseous swelling of the fuel is calculated from the density of the oxide pellet, which is described by a linear function of burnup. Solid-to-solid heat conduction between the fuel and the cladding is implemented, thus providing the possibility to simulate gap closure. The performance of SEALER under unprotected transient overpower conditions is examined using BELLA with and without the fuel thermo-mechanics extension. The results indicate that the fuel centreline temperature is underestimated by the reference code. Nevertheless, the safety margin to fuel melting is still significant. Conversely, the fuel outer temperature is overestimated. There are two reasons for this, depending on the level of burnup. At the beginning of life, the thickness of the gap decreases due to the thermal expansion of the fuel, thereby enhancing heat transfer from the fuel to the cladding. On the other hand, as burnup increases beyond 3% gap closure occurs, and improved heat conduction results from direct solid-to-solid contact. |
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