The rupture of cooling pipes within the Water Coolant Breeding Blanket (WCLL) breeding zone, called in-box Loss Of Coolant Accident (LOCA), is one of the most critical accidental scenarios that need to be studied to ensure the safety of a fusion power plant. Contact between the high-pressure water coolant and the low-pressure liquid metal breeder is expected to generate, among other effects, intense compression waves in the latter. The characterization of the pressure transient during the WCLL in-box LOCA is actively researched at several institutions, and this proposal aims to address this problem from a hitherto neglected angle, that is to say, the effect of the magnetic field on the propagation mechanism of the shock waves. Joule dissipation is expected to contribute to the wave dissipation by decreasing the shock speed compared with ordinary hydrodynamic conditions but, however, a systematic investigation has yet to be carried out for fusion relevant conditions. Direct numerical simulations with the OpenFOAM code will be realized in a prototypical configuration, a square shock tube filled with liquid metal, by considering initial pressure conditions representative of postulated accidental transients. Our study aims to investigate and characterize the effect of the magnetic field intensity and wall conductivity on the wave propagation through extensive parametric analyses. Insights gathered on such a fundamental phenomenon for the reactor safety will be immediately beneficial for the advancement of the blanket development cycle and, moreover, will expand the relatively scarce body of knowledge on the topic.
A good characterization of the phenomena associated to the in-box LOCA in a water-cooled blanket is essential to ensure the safety of a fusion power plant (FPP) based on this architecture. Currently, a significant effort is made toward the development and validation of predictive models for the PbLi/water chemical reaction and its integration in commonly used systems and numerical safety frameworks, such as the one created around RELAP5 [1] and MELCOR [2]. At the same time, the accidental transient (and its consequences) is going to be greatly influenced by the propagation of the pressure wave generated in the breeder by the water/PbLi interaction. Even if this phenomenon is acknowledged as fundamental for blanket safety, there is still an incomplete understanding of the pressure wave propagation in the component. Experimental campaigns, like the one in progress at the LIFUS/Mod3 facility, have been planned to address this point and accrue a body of data to improve the reliability of the design strategies [3]. Unfortunately, these efforts have the shortcoming to do not consider the effect that the reactor magnetic field will have on the liquid metal movement.
This choice is understandable at the current juncture since MHD experiments are notoriously hard to conduct and even more so in a campaign which will involve high pressures, chemical interaction, multiphase flows, etc. In this framework, this research proposal aims to break the ground on the characterization of MHD shock wave propagation in a fusion reactor environment by means of numerical simulations performed in a prototypical configuration. Even if only some basic insights will be obtained in this phase, these will constitute the foundation for more complex analyses in the future and, possibly, the design of a dedicated test section to complement the hydrodynamic data that will be gathered in LIFUS/Mod3.
The knowledge gained in this activity has the potential to be valuable also in a more general context since, as demonstrated by the literature survey that we performed, the case of a shock wave propagating under a magnetic field in an incompressible fluid has not been hitherto systematically investigated. From a theoretical point of view, the numerical campaign proposed aims to quantitatively characterize the effect of the magnetic field intensity and wall conductivity on the shock wave dissipation. Currently, the effect of these parameters can only be inferred by tangentially related studies but, so far, a dedicated and detailed analysis is lacking in the literature. Our proposal aims to contribute to filling this gap and has the potential to drive this research line in the future.
References:
[1] Galleni, F., et al. "RELAP5/SIMMER-III code coupling development for PbLi-water interaction." Fusion Engineering and Design 153 (2020): 111504.
[2] D¿Onorio, M., et al. "In-box LOCA accident analysis for the European DEMO water-cooled reactor. "Fusion Engineering and Design¿ 146 (2019): 732-735.
[3] Eboli, M., et al. "Experimental activities for in-box LOCA of WCLL BB in LIFUS5/Mod3 facility." Fusion Engineering and Design 146 (2019): 914-919.