Nuclear safety starts with intelligent planning and proper design, with conservative contingency factors and back-up systems. The onus is on the technology developer to assess the physical processes in the system under different scenarios and to meet the conditions set by the nuclear regulator for the licence to construct a nuclear installation.
However, the ultimate responsibility for safety and security rests with the operator of the nuclear installation. The use of high quality materials and components in the construction and a strong safety culture on the part of the operator in the operation of the plant are the cornerstones of nuclear safety.
Safety of nuclear installations monitored by the International Atomic Energy Agency
In addition to the national nuclear regulator, which issues construction and operating licences and regulates everything from transport to storage, the safety of nuclear installations is also controlled by the International Atomic Energy Agency (IAEA).
This 171-member organisation, which also includes Estonia, has developed a large number of standards for nuclear safety and security over the decades, and the Agency actively monitors their implementation.
Essential safety (k inherent safety) and safety by design (k safety-by-design) are important terms in the design of nuclear power plants. Intrinsic safety means that a reactor has some feature that prevents a certain type of accident, while design safety means that a reactor has some deliberately engineered solution that produces a similar effect.
The first example is the choice of a fuel composition that ensures a reduction in the chain reaction in any case as the reactor temperature rises. Another example is the elimination of accidents related to leakage of coolant pipes by placing the reactor pressure vessel in a coolant-filled pool.
What to do in an emergency?
There are two types of systems for safely shutting down a reactor and keeping it shut down in the event of an emergency. Depending on how these systems are operated, they are classified as passive and active.
Historically, active safety systems have been widely used, requiring the activation of valves or pumps using an external power source to stop a chain reaction in a reactor in an emergency or to divert heat from a stopped reactor.
However, for fully passive systems to work, only the laws of physics are needed. The new Generation III+ and Generation IV nuclear reactors generally use either fully passive or semi-passive safety systems. The latter are considered to be systems that require an active signal or an instantaneous external force to ensure a long-term passive cooling process.
Nuclear power plants have a lifespan of up to 60 years, during which time a plant may undergo several upgrades or routine repairs. Any design modifications made during the lifetime of the plant that may have an impact on safety must be subject to authorisation by the nuclear regulator.