FAQ

How is nuclear safety assured?

Answer

The overriding safety objective is to protect workers, the public and the environment from the potentially hazardous radioactive materials by ensuring the containment of radioactivity under all circumstances.

Identification of risks and preventive or design measures are taken to meet this objective from the site selection, the design rules and the operating procedures even in cases of accidents. Various techniques are used like physical barriers, defence in depth, emergency plans etc. and probabilistic safety assessment.

The safety authority has the duties of producing the rules and procedures to respect, to ensure the safety analysis at all stages of the lifetime of the installations and to inspect them.

Background

The overriding safety objective is to protect workers, the public and the environment from the potentially hazardous radioactive materials by ensuring the containment of radioactivity under all circumstances.
Like any other industrial installation, a nuclear power plant is subject to industrial risks like fire, flooding, load falls and steam leaks. The preventive measures are the same except in areas where radioactivity is also present where they are stricter. In the design external events linked to human activities such as air plane crash, off site explosions shock waves from industrial next by activities and linked to major natural catastrophic events such as earthquakes, tsunamis, floods etc. are also taken into account.
Risks specific to nuclear installations are associated with the fuel and the fission reaction: controlling the chain reaction to avoid criticality risk, continuous cooling of the core even after the reactor is stopped, waiting for fission products to decay and evacuating their produced heat and finally preventing radioactive and fission products from being released outside the installation.
Safety means prevention of accidents and involves studying all possible accident sequences even with very low probabilities of occurrence and defining protective measures. The designers are using principles such as redundancies, diversity of equipments to avoid common failures, giving time for operator’s actions to prevent human errors, to design back up systems and safeguard system. For verification of such an approach, the method used for safety analysis is defence in depth with 5 levels and with 3 barriers to protect at all times: see an example on the diagram below. In addition all accidents possible are studied via “probabilistic safety assessment”, a method that helps to determine their frequencies and their consequences should they occurs.


 
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Safety is the sole responsibility of the operating organization. But the safety authority is in charge of checking how safety is addressed and included in design, in construction, in commissioning, in operation over the lifetime of the installations and in decommissioning. For prevention and study of all possible accident, probabilistic methods are used as a complement to the deterministic ones as described above.
The duty of the regulator is also to regularly inspect at all stages of the lifetime. The regulator has the power of stopping an installation until the necessary standards are fully met. Since transparency towards the public is a must, all actors must communicate on safety achievements and also on events/incidents which have happened. The international event scale is a communication tool at the disposal of journalists, media and the public for indicating the severity of the events which took place in all activities. It concerns safety, radiation protection as well as transport and radiological emergencies.
 
As a lesson learned from the Three Mile Island accident, human factors have been taken into account in all stages of the installations’ lifetime. Training has been improved especially by intensive use of simulators reproducing not only the installation behaviour in normal conditions but also in accidental conditions. Emergency procedures have been defined and are periodically tested even in real conditions with the public. Later, the Chernobyl accident led to define safety culture, to be able to appraise it and to improve it as a major element of the safety approach. Safety culture must be part of the management system in any activity or facility handling nuclear material and sources.
 
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