Plant-level licensing culminates in demonstrating the safety of a nuclear facility. As the project progresses, the accuracy of demonstrating safety deepens as the maturity of the plant’s design strengthens. In conjunction with the safety assessment, it shall be demonstrated that the nuclear facility has been designed and implemented in such a way that the safety requirements are met.

The licensing of a new nuclear facility takes place in three stages: decision-in-principle, construction licence and operating licence. The licenses are granted by the Government, with the Ministry of Economic Affairs and Employment acting as the contact authority. The content requirements for the licences are presented in the Nuclear Energy Decree (161/1988) and Guide YVL A.1.

Decision-in-principle

In practice, in the decision-in-principle phase the licensee applies for permission to start the design phase of a nuclear facility project, which in turn aims toward a construction licence application.

In the decision-in-principle stage, the licence applicant shall, in accordance with Section 24(2) of the Nuclear Energy Decree (161/1988), submit to the Radiation and Nuclear Safety Authority (STUK) a description of the technical operating principles of the planned nuclear facility and a description of the safety principles to be followed. The information appended to the application shall provide STUK with sufficient grounds for preparing the preliminary safety assessment concerning the nuclear facility project. During the decision-in-principle stage, it is assessed, in particular, whether the new nuclear facility project is in line with the overall good of society.

Construction license

The most important documentation in the construction licence phase is the Preliminary Safety Analysis Report (PSAR). Other documents to be submitted to STUK in the construction licence stage include reports on the operation and behaviour of the nuclear facility during accidents, probabilistic risk assessment (PRA) of the design phase, licensing plan, description of quality management during construction and quality manuals. In addition, a report on the fulfilment of safety requirements and a proposal for a safety classification document presenting the safety classification of structures, systems and components important to safety based on their safety significance is required. The content requirements are presented in more detail in the Nuclear Energy Decree and Guide YVL A.1.

The plant’s data shall be provided with sufficient accuracy to enable the creation of a calculation model for the plant, which in turn can be used to analyse the plant’s behaviour during operational occurrences and potential accidents in all operating conditions. The necessary information may be presented either in the safety analysis report or in supplementary topical reports. Because a nuclear facility consists of numerous systems and many times as many devices, the amount of documentation is ultimately at least tens of thousands of pages.

STUK issues a statement on the construction licence application for a nuclear facility to the Ministry of Economic Affairs and Employment and appends to it its safety assessment, an assessment of the documents referred to in the Nuclear Energy Decree and the statement of the Advisory Board on Nuclear Safety.

According to preliminary information, the ongoing reform of nuclear energy legislation in Finland may change the construction licence phase so that a so-called technology licence would enable the licensing of nuclear facilities of the same type at several plant sites, provided that the units to be built would be sufficiently similar. In particular, the new permit could facilitate the construction of smaller modular reactors.

Operating licence

As the name implies, the operating licence phase involves applying for a permit to commission the plant, i.e. for electricity production. The authorisation is applied for with the Final Safety Analysis Report (FSAR). The final safety analysis report presents the nuclear facility as it has been completed and how its design has been specified during the construction phase. In addition to the final safety analysis report, the operating licence requires, among other things, a probabilistic risk analysis, a safety classification document, an operational quality management programme, the Operational Limits and Conditions, a description of the fulfilment of safety requirements, an ageing management programme and a description of the fulfilment of safety requirements. The content requirements are presented in more detail in the Nuclear Energy Decree and Guide YVL A.1.

STUK issues a statement on the operating licence application for a nuclear facility to the Ministry of Economic Affairs and Employment and appends to it its safety assessment, an assessment of the documents referred to in the Nuclear Energy Decree and the statement of the Advisory Board on Nuclear Safety.

Demonstration of safety

The ultimate purpose of demonstrating safety is that there is no danger to people and the environment as a result of the release of too large amounts of radioactive substances. The Nuclear Safety Directive 2014/87/EURATOM sets the ultimate safety objective in Article 8a. The Member States of the European Union must ensure that nuclear facilities are designed, located, constructed, commissioned, operated and decommissioned with the aim of preventing accidents. However, if accidents do occur, efforts should be made to mitigate their consequences. In particular, planning shall aim to prevent, in practice eliminate, early radioactive releases that would require protective measures outside the nuclear facility site but for which there would not be enough time to implement. In addition, large radioactive releases that require protective measures but whose spatial or temporal consequences cannot be limited must be practically eliminated by means of planning.

However, the design takes into account and, on the other hand, “accepts” the occurrence of milder (accidental) disturbances. These transients and accidents are classified as operational occurrences, class 1 and class 2 accidents, design basis extension accidents and severe accidents. The allowable initiation event frequency for these initiation event classes decreases in the above order. The more likely the initiating event category, the lower the released amount of radioactive substances is permitted.

The main safety functions are the control of the reactivity of nuclear fuel, the management of heat removal and the prevention of the spread of radioactive substances. For each category of initiation events, so-called design-based initiation events are defined. Safety functions are designed to manage and mitigate the consequences of initiating events so that the acceptance criteria defined for the initiating event category are met and the main safety functions are mastered.

Deterministic safety analyses demonstrate the management of the initiating events of each initiating event category so that system failure assumptions are made in the analyses in accordance with the rules laid down in Guide YVL B.3. Each analysis must meet predefined acceptance criteria.

Probabilistic Risk Assessment (PRA) assesses plant safety using quantitative methods throughout the plant’s service life, from the preparation of the construction licence to final disposal. The PRA analysis is divided into three levels, the first of which assesses the core damage frequency of the facility, the second the frequency of a large radioactive release, and the third the risk to humans and the environment caused by the release. In particular, PRA has the advantage of identifying complex equipment failure combinations, which can otherwise be difficult. The PRA is maintained continuously and the so-called living PRA can be used to assess the risk impact of plant modifications.

Plant modifications

A conceptual plan shall always be drawn up for modifications made to operating nuclear facilities that particularly affect the operation of systems important to safety, change the operating principles, objectives, dependencies of the systems, or affect the functional architecture of the facility, and submit it to STUK for approval. A conceptual plan is also drawn up for other new systems important to safety (EYT/STUK) and submitted to STUK for information.

The conceptual plan shall present a general description of the modification and the systems to be modified, the initial requirements for the planning of system-level changes, a description of the effects of the modification on the plant’s operating principles and accident conditions, a description of the analyses to be prepared, and a description of the schedule of the modification. The more detailed content requirements of the conceptual design plan are described in Guide YVL B.1.

The safety of plant modifications shall be demonstrated according to the same principles as for new nuclear facility projects. The requirement of the Nuclear Safety Directive to prevent early and large radioactive releases applies only to nuclear facility projects for which a construction licence has been granted for the first time after August 14, 2014. This requirement shall also be applied in plant modification projects at operating plants so that potential improvement measures are carried out in these projects in order to reduce the possibility of early or large radioactive releases.

System-level documentation for plant modifications and their content requirements will be discussed in the next blog post. Stay tuned.

How can Platom help?

Platom has several experts with experience in the preparation and development of the above-mentioned documentation. Platom also has a strong modelling and analysis team with experience in both coordinating and conducting plant analyses and implementing complete plant models. Platom also has experience in writing preliminary and final safety analysis reports and conceptual plans and updating them.