What is Nuclear Safety ?

The Nuclear Safety in a nuclear installation is the whole set of measures taken at all the stages of the design, construction, operation and dismantling to provide protection to the workers, the public and the environment against the effects of the ionising radiations. Also to be mentioned are the technical measures to optimise waste and radioactive effluents management. An appropriate level of safety is achieved through a set of measures of different natures, covering technical aspects as well as organisational and cultural ones.

How to reach an adequate nuclear safety level ?

Nuclear Safety is based on the defence in depth.

The defence in depth concept is a general framework enabling to take systematically into consideration technical, human and organisational deficiencies. To alleviate these deficiencies, successive and independent levels of defence are implemented along 3 main directions:

PREVENTION : avoid the failure
SURVEILLANCE : anticipate the failure or detect it immediately
MEANS OF ACTION : mitigate the consequences of the failure

Specific design features (technical and organisational) are associated to each level of defence as for example:

• barriers between the nuclear fuel and the environment,

• safeguard systems to prevent or manage the accidents,

• support systems allowing the safeguard systems to work properly,

• analyses of accidents from either internal or external origins to check the plant design,

• hazard analyses (e.g. fire, flood, aircraft crash,…),

• severe accident analysis allowing to cope with situations not foreseen at the design phase,

• probabilistic safety assessments to track possible weak points in the design,

• …

Testing and maintenance programmes allow checking the absence of any degradation of the design features.

Specific measures are also introduced to cope with situations that were not considered in the original design: they concern the internal and external emergency and intervention plans.

The defence in depth concept must be applied during the whole lifetime of the facility through a rigorous Quality Management and a permanent Safety Culture. Safety culture is defined by that assembly of characteristics and attitudes in the organisations and with the individuals which establishes that, as an overriding priority, nuclear plant safety issues receive the priority attention warranted by their significance. The following conditions should be met by any organisation willing to establish and maintain a safety culture:

• continuous learning and improvement, particularly through experience feedback

• questioning attitude, modesty

• rigour and professionalism

• open management at all levels

• work environment where safety problems may be brought up without fear for sanction

Who is responsible for Safety ?

In Belgium, as in most countries, the licensee is the prime responsible for the safety of his nuclear facility. The Belgian Authorities and Bel V monitor the implementation of nuclear safety by the licensee.

For the Belgian Nuclear Power Plants (NPP), the design rules are derived from the ones in force in the USA. These rules, explicitly mentioned in the licence decree of each NPP, apply systematically the defence in depth concept.

In recent years, these are being complemented by Belgian legislation, such as the Royal Decree of 30 November 2011 (Belgian official journal of 21 December 2011) titled Royal Decree concerning the safety requirements for nuclear installations.

To cope with emergency cases, the licensee is bound to implement an emergency plan approved by the competent Authority. This plan is integrated in the Nuclear and Radiological Emergency Plan for the Belgian Territory, as defined by the Royal Decree of 17 October 2003.

Nuclear Safety : the overall Philosophy

To be achieved and maintained, Nuclear Safety requires a robust design with adequate margins, but also a rigorous operation.

On the basis of experience feedback, a continuous questioning attitude is necessary to identify any discrepancy against the design before it might adversely affect the environment.

This is clearly a technical approach developed in a cultural framework where competent and reliable professional people evolve with a permanent concern of self-checking without any complacency.

The role of Bel V is to ensure that the licensees for nuclear installations continuously maintain a safety level as high as practically achievable.