ENSI’s Remit

ENSI monitors the operation of nuclear plants


ENSI reviews reporting by the operators, holds regular supervisory discussions and monitors the nuclear plants (including their organisation and operation) by means of more than 400 on-site inspections each year. ENSI only allows individuals to hold safety-related positions in nuclear plants if they have the necessary abilities and training.


Each year in summer, every nuclear power plant carries out an inspection lasting several weeks during which maintenance work and repairs are undertaken in the plant. Fuel is renewed at the same time. These inspection shutdowns for nuclear power plants are followed through and monitored by ENSI.

Radiation monitoring

In order to protect staff, the population and the environment, ENSI monitors compliance with the radiation protection regulations and dose limits. It monitors discharges of radioactivity from the nuclear plants and compliance with the discharge limits, as well as determining the radiation exposure for the population and the plant staff.

Safety assessment

ENSI collates all the data obtained during a year into one comprehensive safety assessment, from which it derives any measures that may be required as well as its future supervision plans. In its annual reports, ENSI informs the general public about the safety of nuclear plants, radiation protection and the experience accumulated from operation and from its own research.

ENSI assesses nuclear plants


The assessment and monitoring of nuclear plants are based on laws, guidelines and underlying technical and scientific documentation, which transparently set out the safety requirements and criteria that ENSI applies for its assessments. ENSI continues to develop the underlying documentation and guidelines in accordance with the latest status of science and technology. For example, the guidelines specify radiation protection targets for the operation of nuclear plants, reporting on operation, and the organisation of nuclear power plants, as well as defining the requirements for deep geological repositories.

Assessment reports

ENSI draws up safety assessments when operators of nuclear plants submit applications which go beyond the scope of their existing operating licences – for example, the Periodic Safety Reviews of all the nuclear power plants are assessed by ENSI and the results are recorded in an assessment report, together with any conditions that may be imposed. The licensing procedure for new nuclear power plants and deep geological repositories is based on ENSI’s safety assessments.


Applications for modifications to nuclear plants that are covered by existing operating licences are dealt with by ENSI, which issues a permit if the decision is positive. Examples include changes to components and systems classified as relevant to safety, and changes to technical specifications.