Areva EPR

■ SAFETY
DEFENSE IN DEPTH
The concept of “defense in depth” involves ensuring the resistance
of the protective barriers by identifying the threats to their integrity
and by providing successive lines of defense which will guarantee
high effectiveness:
• first level: safe design, quality workmanship, diligent operation,
with incorporation of the lessons of experience feedback in order
to prevent occurrence of failures,
• second level: means of surveillance for detecting any anomaly
leading to departure from normal service conditions in order to
anticipate failures or to detect them as soon as they occur,
• third level: means of action for mitigating the consequences of
failures and prevent core melt down; this level includes use of
redundant systems to automatically bring the reactor to safe
shutdown; the most important of these systems is the automatic
shutdown by insertion of the control rods into the core, which stops
the nuclear reaction in a few seconds; in addition, a set of
safeguard systems, also redundant, are implemented to ensure the
containment of the radioactive products,
• beyond, the defense in depth approach goes further, as far as
postulating the failure of all these three levels, resulting in a “severe
accident” situation, in order to provide all the means of minimizing
the consequences of such a situation.
† By virtue of this defense in depth concept,
the functions of core power and cooling
control are protected by double or triple
systems – and even quadruple ones as in
the EPR – which are diversified to prevent
a single failure cause from concurrently
affecting several of the systems providing
the same function.
† In addition, the components and lines
of these systems are designed to
automatically go to safe position
in case of failure or loss of electrical
or fluid power supply.
The training for steam
generator inspection
illustrates:
† the first level of
defense in depth
relating to the quality
of workmanship,
† the second barrier,
as the training relates
to steam generator
tubes which form part
of the primary system.
Lynchburg technical center (Va, USA): training for steam generator inspection.
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