A few days ago, Leibstadt Nuclear Power Plant (KKL) informed the Swiss Federal Nuclear Safety Inspectorate (ENSI) that some fuel elements do not fulfil the requirements of the applicable specifications. Accordingly, KKL decided to replace them for safety reasons. The safety of man and the environment was ensured at all times.
ENSI has issued Leibstadt NPP approval to restart subject to conditions. In an interview Ralph Schulz, Director of the Safety Analyses Division, shares some background insights.
Leibstadt NPP can restart power operation after an extended annual overhaul. The Swiss Federal Nuclear Safety Inspectorate has checked the clarification of the causes and measures derived from it for the avoidance of critical boiling conditions or dryouts. Safe operation without risk to humankind or the environment is ensured.
An inspection of fuel elements in Leibstadt NPP revealed that critical boiling states – so-called dryouts – had systematically occurred over several cycles.
The Swiss nuclear power plants use forgings for the safety-relevant main components with fully documented manufacturing and material quality certificates. This was confirmed by the operators in response to an enquiry made by the Swiss Federal Nuclear Safety Inspectorate (ENSI).
Heat is generated in the reactor as a result of nuclear fission. To guarantee optimum cooling of the fuel rods, their cladding tubes must always be covered with a film of water. If they are not completely covered with water in specific areas, this is referred to as “dryout”.