In a recent study, researchers from the European Environmental Bureau (EEB), the Stockholm School of Economics (SSE), and the Potsdam Institute for Climate Impact Research (PIK) questioned the planned development of new nuclear capacities in the energy strategies of the United States and certain European countries.
That will not remotely cover baseline loads and is not without significant efficiency loss due to the pumping phase.
All commonly used forms of energy storage have some efficiency loss. Pumped storage is not perfect but my understanding is that it usually comes at a 10-25% loss, which isn’t all that shabby all things considered.