In accordance with the Nuclear Energy Act, the starting point for the design, construction and operation of a nuclear power plant is that the plant must be safe and it shall not cause injury to people or damage to the environment or property. This is complied with through precautionary measures in the design, construction and operation of the plant, functions protecting the plant
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in cases of disturbance and damage, and as functions mitigating the consequences of accidents.
The design, construction and operation of the nuclear power plant shall be implemented in accordance with the Government Decision on the general regulations for the safety of nuclear power plants (GD 395/91). The arrangements to prevent unlawful actions against the nuclear power plant shall be implemented in accordance with the Government Decision on the general regulations for the physical protection of nuclear power plants (GD 396/91), and the arrangements to limit nuclear damage within the nuclear power plant and its area shall be implemented in accordance with the Government Decision on the general regulations for emergency response arrangements at nuclear power plants (GD 397/91). This will be complied with by extending the emergency response arrangements of the existing plant units to cover the new plant unit. The design of the plant unit shall also observe the most recent international safety recommendations. Essential sets of requirements include the European Utility Requirements (EUR) specified by European power companies. The power plant unit’s compliance with the requirements set in the YVL guides is proven by means of safety analyses that examine the behaviour of the plant unit in disturbances and accidents.
10.2.1 Multi-layered defence in depth principle of safety
The high level of safety of the planned nuclear power plant unit is based on the defence in depth principle.
The defence in depth principle refers to ensuring the safety of a nuclear power plant by preventing the harmful effects of damage and radiation through successive and mutually redundant functions and structural levels.
All functions significant to safety shall be backed up by several redundant systems and devices, and the design of all equipment and functions shall observe a high level of quality requirements and sufficient safety margins. The starting point is that a severe accident cannot be caused solely by operating error or equipment failure even if several devices fail simultaneously.
The first level of protection constitutes the prevention of operational transients and accidents in advance. In relation to this, proven or otherwise carefully examined high-quality technology shall be employed in design, construction and operation. The safety culture for the operations is also at a high level. The second level of protection constitutes systems by means of which operational transients and accidents can be quickly and reliably detected, and the aggravation of any event can be prevented. The third level of protection mitigates the consequences of accidents through efficient technical and administrative arrangements. In preparation for accident situations, the plant has a designated emergency organisation, and its operations and the functionality of emergency preparedness plans are tested in annual emergency drills carried out together with rescue authorities.
According to the defence in depth principle, accidents are prevented through sound design, a high level of quality and diligence of operating activities. Should a
disturbance or accident take place despite this, it can be controlled by safety systems. Should this also fail, the environmental impacts of the accident shall be mitigated as efficiently as possible.
10.2.2 Multiple barriers
The starting point for nuclear power plant design is that no significant amounts of radioactive substances shall be discharged into the environment as a consequence of potential disturbances or accidents. The dispersion of consisting of several redundant subsystems. Therefore the failure of one subsystem does not prevent the appropriate safety function. Subsystems are implemented using different operating principles and structural arrangements in order to prevent the simultaneous failure of all subsystems due to a similar fault. Systems so that operating personnel will be allowed at least 30 minutes to consider their actions. The inherent properties
10.2.3 Precautions for external hazards
The design of the new plant unit allows it to endure extreme weather conditions that are estimated to be very rare or improbable at the site, including high and roads and air traffic routes. However, the plant unit design takes an aeroplane crash or other external impact into account. The plant unit shall be implemented so that an aeroplane crash or other external impact will not cause any damage that could immediately discharge a significant amount of radioactive substances into the environment. Precautions for external threats arising from terrorism or other illegal activity are taken through comprehensive security arrangements.
10.2.4 Precautions for severe accidents
The design of the new nuclear power plant shall include precautions for extensive reactor core damage, also
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Envir onmental Impact Assessment
known as a severe accident. The requirement applies primarily to the design of the containment because a severe accident means that the integrity of the inner barriers (fuel cladding, primary circuit) will be lost.
The successful control of a severe accident calls for a strategy that gives due consideration to the specific features of the plant and the phenomena threatening the containment building. Such a strategy must define sound methods for preventing or controlling the energetic phenomena related to the development of the accident (e.g. hydrogen burn, high-pressure melt eruption, energetic molten core-coolant interaction). Additionally, the strategy must ensure the cooling of the molten core and the removal of residual heat from the containment building in such a way that the containment building remains intact during the accident and for a long time thereafter.
The systems designed for controlling severe accidents must perform their functions even if any single piece of equipment in the system fails. The systems to be designed for controlling severe accidents must be independent of other safety systems. A severe accident must be controllable in all operational states of the nuclear power plant, not only during power operation but also during shutdowns.
10.2.5 Safety analyses
The safety features of a nuclear power plant shall be proven through detailed analyses. The safety analyses constitute a foundation, using which the authorities will form their opinion on the plant’s ability to recover from different situations of damage and disturbances. The safety analyses are presented to the authorities in connection with the plant’s preliminary safety analysis report when applying to the Government for a construction licence.
The final safety analysis report supplements the safety analyses with the effects of details associated with the construction of the plant. The final safety analysis report will be presented to the authorities when applying to the Government for an operating licence.
The analyses to justify the technical solutions for a nuclear power plant unit must assess the discharges of radioactive substances in anticipated operational transients and accidents in accordance with YVL Guide 2.2. Furthermore, analyses shall be made for the planning of emergency preparedness arrangements, and preparations shall be made to assess the spreading of radioactive substances in real-time during an accident situation in accordance with YVL Guide 7.4.
10.2.6 Regulatory control
In Finland, all operations associated with the production of nuclear energy are subject to permit. In addition to safety supervision, nuclear facilities and the use of nuclear materials are supervised to prevent misuse. The operation of nuclear power plants is continuously supervised in accordance with the Nuclear Energy Act and the Nuclear Energy Decree. Authorities supervise the operation of plant units in accordance with strict guidelines. According to the Nuclear Energy Act, the control and supervision of the nuclear energy sector in Finland is the ultimate responsibility of the Ministry of Trade and Industry, the tasks of which transferred to the Ministry of Employment and the Economy as of 1 January 2008.
The Radiation and Nuclear Safety Authority is responsible for supervising the operation and safety of nuclear energy. TVO provides regular reports of its operations to the Radiation and Nuclear Safety Authority.
Through the licensing process (see Section 5), the Radiation and Nuclear Safety Authority ensures that safety requirements are taken into account in the design, construction and operation of a plant. The Radiation and Nuclear Safety Authority supervises the fulfilment of safety requirements during design, construction, staff training, plant operation and decommissioning. Nuclear fuel is also controlled by the International Atomic Energy Agency (IAEA) and the European Atomic Energy Community (Euratom).
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