Abstract
In the frame of the dismantling of Fukushima-Daiichi nuclear reactors, different projects were led to investigate the means to avoid radioactive aerosols dissemination during operations of fuel debris extraction. Indeed, these operations may produce a large quantity of aerosols, especially during the fuel debris cutting phase, but also during the phase of fuel debris transport in the event of a fall leading to the resuspension of radioactive matters. Furthermore, this resuspension phenomenon may also occur by the sole action of global ventilation of the PCV.
Knowing these risks, it was essential to evaluate solutions allowing to prevent the aerosols dispersion. For that, IRSN is involved in projects with ONET and CEA, and especially in the RESIN project dedicated to demonstrating the feasibility and the efficiency of fuel debris coating with different kinds of resin. These resins are of different natures and different viscosities, easing their applicability depending on the material to coat and its orientation. However, the covering of fuel debris spread on the floor may generate a potential increase of temperature under the resin which may lead to a loss of fuel debris cooling, and a potential fuel debris degradation and hydrogen production. Furthermore, the resin degradation may also occur, promoting the aerosol dispersion during cutting operations.
To answer this issue, a numerical study was conducted with the CFD code ANSYS CFX. It consists in evaluating the impact of the fuel debris coating by taking into account the residual heat of fuel debris especially just above the sumps which are full of fuel debris. A calculation was carried out to determine the temperature field at the interface between the sump and the fuel debris spread on the floor, and this temperature field was implemented as boundary condition in a calculation of heat transfer inside the pedestal by considering a layer of water and a layer of resin. Different parameters were modified to ensure the robustness of the calculation and the temperature values calculated.
The results presented in the article show that there is a strong impact of the transfer coefficient with the water just above the ground: for most cases, the temperature is low enough to avoid safety risks, but for some of them it can lead to a temperature of the water and the resin upper than 100 °C.
