The Belgian nuclear phase-out law imposes closing down in the 2015-2025 period seven nuclear power plants (NPPs) producing more than 50% of the domestic electricity. This creates an urgent problem in the country because of the absence of well-defined capacity-replacement plans. Though a safety-of-supply provision in the law allows for a delayed phase-out, hopes for a technically acceptable schedule have reduced after the Fukushima nuclear disaster in March 2011. In this article policy investigations are made with system dynamics. A significant finding from such modelling is that, in contrast to common expectations, a too early nuclear phase-out will not serve the deployment of renewable energy sources and rational use of energy. It is indeed found to primarily benefit to fossil fuel, creating unwanted drawbacks regarding safety of supply, dependency on foreign suppliers, price volatility, and increased use of non-renewable and CO2-emitting fossil fuels. (C) 2013 Elsevier Ltd. All rights reserved.