During a severe accident in a nuclear reactor, the melting of the core may lead to the formation of a multiphase liquid pool (corium) in the vessel lower head. The heat transfer at the boundary with the vessel is affected by diffusive and convective mass fluxes. In particular, the development of Rayleigh–Taylor instabilities influence the thickness of the top metallic layer and therefore the “focusing effect” of the heat flux, which is the main risk for the vessel integrity. We use a Cahn–Hilliard pseudo-binary model to describe the uranium/oxygen/zirconium/iron mixture. The diffusion and the convection are governed by the Cahn–Hilliard equation and the Navier–Stokes equations under the Boussinesq approximation. In this work, the model is isothermal and the buoyancy force is only due to the gradient of chemical composition. The model is solved in three dimensions with a pseudo-spectral code. The initial configuration consists of a light layer of iron-rich fluid above a heavy layer of uranium/oxygen/zirconium mixture. A thin layer of heavier metallic phase lays at the interface and eventually triggers a Rayleigh–Taylor instability. The metallic phase forms a plume which falls downward and then breaks up into droplets due to the Rayleigh-Plateau instability. The phenomenon is alimented by diffusion which generates the heavy metallic phase at the interface. The droplet formation observed in an experiment of corium stratification transient from the literature is qualitatively captured. The mobility, the viscosity and the surface tension are shown to have an influence on the mass transfer.

在核反应堆发生严重事故期间，堆芯的熔化可能导致在容器下盖内形成多相液池（皮质）。容器边界处的热传递受扩散和对流质量通量的影响。特别是，瑞利泰勒不稳定性的发展会影响顶部金属层的厚度，从而影响热通量的“聚焦效应”，这是血管完整性的主要风险。我们使用Cahn–Hilliard伪二元模型来描述铀/氧/锆/铁混合物。扩散和对流由Boussinesq近似下的Cahn–Hilliard方程和Navier–Stokes方程控制。在这项工作中，模型是等温的，浮力仅是由于化学成分的梯度引起的。该模型使用伪光谱代码在三个维度上求解。初始配置包括一层轻的富铁流体，上面是一层重的铀/氧/锆混合物。界面处有一薄层较重的金属相，最终触发了瑞利-泰勒不稳定性。金属相形成羽状流，由于Rayleigh-Plateau的不稳定性，其羽状流下降，然后分解为液滴。这种现象因扩散而得到缓解，扩散在界面处产生了重金属相。定性地捕获了从文献中观察到的皮质分层瞬变实验中观察到的液滴形成。显示出迁移率，粘度和表面张力对传质有影响。初始配置包括一层轻的富铁流体，上面是一层重的铀/氧/锆混合物。界面处有一薄层较重的金属相，最终触发了瑞利-泰勒不稳定性。金属相形成羽状流，由于Rayleigh-Plateau的不稳定性，其羽状流下降，然后分解为液滴。这种现象因扩散而得到缓解，扩散在界面处产生了重金属相。定性地捕获了从文献中观察到的皮质分层瞬变实验中观察到的液滴形成。显示出迁移率，粘度和表面张力对传质有影响。初始配置包括一层轻的富铁流体，上面是一层重的铀/氧/锆混合物。界面处有一薄层较重的金属相，最终触发了瑞利-泰勒不稳定性。金属相形成羽状流，由于Rayleigh-Plateau的不稳定性，其羽状流下降，然后分解为液滴。这种现象因扩散而得到缓解，扩散在界面处产生了重金属相。定性地捕获了从文献中观察到的皮质分层瞬变实验中观察到的液滴形成。显示出迁移率，粘度和表面张力对传质有影响。界面处有一薄层较重的金属相，最终触发了瑞利-泰勒不稳定性。金属相形成羽状流，由于Rayleigh-Plateau的不稳定性，其羽状流下降，然后分解为液滴。这种现象因扩散而得到缓解，扩散在界面处产生了重金属相。定性地捕获了从文献中观察到的皮质分层瞬变实验中观察到的液滴形成。显示出迁移率，粘度和表面张力对传质有影响。界面处有一薄层较重的金属相，最终触发了瑞利-泰勒不稳定性。金属相形成羽状流，由于Rayleigh-Plateau的不稳定性，其羽状流下降，然后分解为液滴。这种现象因扩散而得到缓解，扩散在界面处产生了重金属相。定性地捕获了从文献中观察到的皮质分层瞬变实验中观察到的液滴形成。显示出迁移率，粘度和表面张力对传质有影响。定性地捕获了从文献中观察到的皮质分层瞬变实验中观察到的液滴形成。显示出迁移率，粘度和表面张力对传质有影响。定性地捕获了从文献中观察到的皮质分层瞬变实验中观察到的液滴形成。显示出迁移率，粘度和表面张力对传质有影响。