Leibstadt Nuclear Power Plant: ENSI calls for improvements for long-term operation

From design and operating experience, accident analyses, organisation and personnel, through to ageing monitoring of the technology as a whole, and emergency preparedness: by means of a comprehensive safety review, operators demonstrate that their nuclear power plants (NPPs) meet the legal requirements for nuclear safety and radiation protection. Every ten years, operators submit a comprehensive safety review to ENSI - the periodic safety review (PSR). At the end of 2022, Leibstadt NPP submitted its PSR documents for the review period from 1 January 2016 to 31 December 2021. For the first time, Leibstadt NPP has, because of its age, also included a safety case for long-term operation (i.e. operation beyond 40 years) with the PSR documents. After a detailed review, ENSI is now publishing its safety statement.

• What the periodic safety review is all about

  Every ten years, an NPP licence holder must carry out a comprehensive periodic safety review (PSR). In doing so, the NPP operator performs a safety analysis of the NPP. The Nuclear Energy Act (Art. 22 para, 2 lit. e) and the Nuclear Energy Ordinance (Art. 34 and 34a) require this.

  The PSR covers the following topics:

  • Overview of the plant
  • Operation and operating behaviour
  • Safety-related plant parts
  • Maintenance and ageing monitoring
  • Deterministic safety analyses (including accident analyses)
  • Probabilistic safety analyses (including risk assessments of severe accidents)
  • Organisation and personnel
  • Emergency preparedness
  • Safety case for long-term operation (an additional analysis is required for operation beyond 40 years to demonstrate that safety limits will be complied with by a sufficient margin over the following decade of operation)

  ENSI compiles a detailed statement for each PSR. The basis for the analysis is the currently valid set of rules such as the ENSI guidelines, regulations and laws.

In its statement, ENSI concludes that Leibstadt NPP was operated prudently during the analysis period and was at a good safety level. Thus, the basic nuclear protection objectives of 'control of reactivity', 'cooling of fuel elements', 'containment of radioactive materials' and 'limitation of radiation exposure' were consistently met. The barrier concept is effective and the physical barriers are in a good condition. The defence-in-depth concept is fully implemented at all safety levels.

To further increase the plant's safety level, ENSI has set out a number of requirements. These are aimed, for example, at conducting a systematic review of the design of components important for safety, improving deterministic and probabilistic accident safety cases, and optimising fire safety and emergency preparedness. In sections 1 to 9 of the safety statement, ENSI covers these and other topics in detail.

A high safety level is the basis for long-term operation

At the end of 2024, Leibstadt NPP transitioned to long-term operation after four decades of service. To ensure a high level of safety in the future and with the increasing age of the plant, Leibstadt NPP has developed a comprehensive backfit concept in addition to its ageing monitoring programme and service life management and has already begun to implement it during the ongoing regulatory process. For large components (reactor pressure vessels with internals, coolant circulation loops, nuclear steam generation system, steel containment and concrete containment), which are difficult or impossible to replace, the operator prepares the necessary safety cases.

ENSI assesses the condition of the large components as good (see section 10 of the safety statement). Consequently, ENSI considers that the requirements for safe long-term operation are fulfilled.

• Backfit concept for long-term operation

  The backfit concept for long-term operation is based, on the one hand, on comparing the plant's design with the latest developments in science and technology. On the other hand, the backfits should fulfil the requirements of national and international regulations.

  Where the backfit concept for long-term operation is concerned, special attention must be paid to the following topics in accordance with Guideline ENSI-A03 (in German):

  • The degree of redundancy and diversity of safety functions
  • The functional independence and spatial separation of safety systems
  • The degree of automation of the safety systems
  • Protection against external influences
  • Provisions for the prevention of severe accidents

  In addition, the safety gain of the backfit concept must be demonstrated by deterministic and probabilistic safety analyses.

The backfits already carried out and planned for long-term operation, in particular within the framework of the projects YUMOD (upgrading of the reactor circulation system), ERKO (replacement of the condenser), NEX (replacement of radiation protection instrumentation) and SILT (replacement of the instrumentation and control), are considered by ENSI to be appropriate and reasonable overall.

As a result of the backfits carried out by Leibstadt NPP and the introduction of further accident management measures, ENSI considers the defence-in-depth system as further improved. ENSI welcomes the operator's proactive attitude to investment in the safety of the Leibstadt NPP for operation beyond 40 years.

All findings from the review and the ENSI requirements are summarised in section 11 'Overall evaluation' of the statement.

The PSR as part of ENSI's comprehensive oversight programme

ENSI's experts continuously maintain an overview of the safety of nuclear installations and check whether their operation complies with the legal guidelines, and also whether the latest developments in science and technology are taken into account. The PSR is part of the comprehensive ENSI regulatory programme.

Further Information

• Safety Statement on the Periodic Safety Review 2022 of Leibstadt Nuclear Power Plant (document available in German)