n the French context of increasing renewable penetration and significant nuclear power, the optimal contribution of this energy source is discussed from two viewpoints. On the one hand, from the social planner viewpoint, the nuclear optimum contribution is the one that minimizes the overall electric price, whatever the resulting load factor. The use of screening curves, often implemented to design the optimal power mix is questioned, being highly sensitive to the assumptions. On the other hand, from the plant operator viewpoint, the nuclear power plants need to amortize the capital expenses, hence achieve the longest operating time. With a view to make the two viewpoints meet, we propose to operate nuclear power plants as baseloads and consider modulation through the power use, i.e. supply electricity to the electric system when requested and use the remaining power to produce other valuable products, such as heat or hydrogen.