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Office of Technology Assessment at the German Bundestag Office of Technology Assessment at the German Bundestag

Information on the project

Load-Following Capability of German Nuclear Power Plants

Thematic area: Energy, resources, environment
Analytical approach: Monitoring
Topic initiative: Committee on Education, Research and Technology Assessment
Status: completed
Duration: 2010 till 2014

Background and central aspects of the topic

According to the »Elftes Gesetz zur Änderung des Atomgesetzes vom 8. Dezember 2010«, the life span of German nuclear power plants has been extended by an average of 12 years beyond the average life span of 32 years that was set in the »Vereinbarung zwischen der Bundesregierung und den Energieversorgungsunternehmen vom 14. Juni 2000« and by the »Gesetz zur geordneten Beendigung der Kernenergienutzung zur gewerblichen Erzeugung von Elektrizität«.

Currently, nuclear power plants are used in Germany to cover the base load and are predominantly utilized in continuous operation at nominal load. Nuclear energy presently supplies 22% of the electricity requirement in Germany. At the same time, the Federal Government is pursuing the goal of continuously expanding the amount of renewable energy used for generating electricity. Its share of the electricity supply is supposed to account for at least 30% in 2020 and to continuously grow thereafter (§ 1 des Erneuerbare-Energien-Gesetzes, EEG). A significant share of the growth of renewable energy is based on technologies feeding the grid at fluctuating rates (wind power, photovoltaic). A consequence of this is that the residual load, i.e., the load to be covered by conventional power plants (coal, gas, nuclear power), will fluctuate strongly to an increasing degree with the growing share of electricity supplied from renewable sources. In periods of simultaneous low demand for electricity and a high wind weather situation, it has already occurred that there has been an excess supply of electricity, which has resulted in negative electricity prices on the European Energy Exchange in Leipzig. It can be anticipated that such situations could occur more frequently in the future.

Given this situation, the questions are whether German nuclear power plants exhibit sufficient operational flexibility and whether they can withstand the stress of frequently ramping power up and down (including the complete shutdown of a nuclear power plant for periods of several hours, days, or a few weeks), such that they are ready to meet the requirements resulting from renewable energy being preferentially fed into the energy grid. Further questions result with regard to the economic efficiency and the safety of nuclear power plants if they are to be run in load-following operation and if they are to be completely shut down frequently.

In the current scientific debate, there is obvious disagreement regarding the degree to which the German nuclear power fleet can be controlled and in particular the degree to which the nuclear power plants can meet the requirements of an electrical system with a large share of renewable (i.e., fluctuating) feed.

  • According to the opinion of the Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit (BMU) power control to less than 50% of the nominal power as an adjustment for load fluctuations is not possible in normal operations. Furthermore, power controls that are necessary in response to grid fluctuations would contribute to increased material fatigue in nuclear power plants. A current statement paper from the German Advisory Council on the Environment (SRU) and a study by the Fraunhofer-Institut für Windenergie und Energiesystemtechnik (IWES) both come to the conclusion that an extension of the life span of nuclear power plants is not compatible with an expansion of renewable energy and represents a de facto restriction on the preferential treatment of renewable energy.
  • In contrast, for example, the Institute of Energy Economics and Rational Energy Use (IER) argues that the load-following capability of the reactors currently in operation was a policy-determining design criterion, referring in this regard to the operators’ handbooks. According to the IER, it is clear that nuclear power plants can participate in overriding load-following operation from both a technical as well as an operational perspective.

Objectives and approach

In a progress report in the context of the monitoring »sustainable supply of energy«, the various arguments, results, and the respective assumptions used in the current discussion are to be contrasted in a transparent and comprehensible fashion. The purpose is to identify the points where scientific consensus prevails and – on the other hand – to disclose the issues for which there is no consensus and reflect on the reasons for this.

Specifically, the following research priorities are planned:

  • Present the current state of knowledge and the existing gaps in our knowledge on the basis of an evaluation of the current literature.
  • Determine the demands for flexibility on the fleet of conventional power plants, especially the nuclear power plants, that result from the further expansion of using renewable energy for generating electricity.
  • Illuminate the technical, operational, and possibly the licensing possibilities and limits of the load-following capability of German nuclear power plants.
  • Discuss the question of how far the capacity for load-following operation of nuclear power plants is compatible with the demands for flexibility on the fleet of power plants.
  • Discuss the economic factors that accompany flexible operation of nuclear power plants.
  • Take stock of foreign experience with load-following operation of nuclear power plants (e.g., France and other countries), and analyse the common features and the differences with regard to the situation in Germany.