Repères - N°48 / March 2021 - The IRSN magazine - 10

SAFETY
Station blackout diesel generator
Emergency diesel generators
(EDG) constitute one of the
pillars of the " hardened safety
core " . They supply power
to the vital components of
the facility in the event that
all other sources of electricity
are lost. IRSN has evaluated
the design of this additional
equipment, designed to
withstand extreme hazards.
EDF1 has announced that
the system will be fully
operational for all its reactors
by late February 2021.

At 24 meters long, 12 meters wide
and 25 meters high, the EDG building has
an unmistakable silhouette.

Page 10 - Repères No. 48 - March 2021

ith a relatively small footprint
of 288 m2, the buildings known
as the EDG house the emergency
diesel generators and are erected in close
proximity to the nuclear island. And with
good reason, because in extreme situations,
these diesel engines have to take over to
power the hardened safety core systems
and components to prevent core melt. If
this fails, they are needed to mitigate the
consequences by preventing large-scale
releases to the environment (see p. 8). How
were safety experts involved in overseeing
the design process?
These bunkered buildings must withstand
extreme situations. " Made of reinforced
concrete, with 50 centimeter-thick walls,

Assessments made during design

Safety experts carry out inspections at the Cruas nuclear power plant (Ardèche department) as part
of the Complementary Safety Assessments (CSAs) held in the wake of the Fukushima Daiichi accident.

they built to withstand extreme natural
phenomena and the resulting effects, for
example lightning, hail, tornados and
earthquakes, " explained Marie-Hélène
Bonhomme, a civil engineering expert.
Beginning in 2016, IRSN examined the
reliability of the station blackout emergency
diesel generator (SBO-EDG), designed to
operate for 72 hours, checking its output
capacity to supply the electric power
required (3 050 kW). It subsequently published an initial technical report 2. " IRSN
found the initial design-basis scenarios
satisfactory, " Patrick Lejuste, post-Fukushima Project Manager shared.
The electrical power distribution system
for the hardened safety core supplied by
the SBO-EDG and the measures implemented to protect it were also assessed 3.
More recently 2, they assessed whether the
power provided by the diesel generator is
adequate to meet the requirements of the
equipment it is intended to supply.

Recommendations on
earthquake-resistant design

In addition to the generator, the EDG
buildings also house lubrication pumps,
fuel oil tanks, a ventilation system, batteries,
a circuit breaker panel and a fire detection
system. No human intervention is required.

In the event of a power outage, the generator starts up automatically. " The anchoring
systems on each part of the equipment
are designed to withstand the effects of a
hardened safety core-level earthquake, "
explained Lejuste.
In 2016 2, IRSN made a recommendation
regarding the seismic resistance, assumptions and methods for the design basis of
structures housing the EDGs. Operators
are required to ensure adequate safety
margins.
In 2012, ASN, the French Nuclear Safety
Authority set a delivery deadline for the
56 station blackout EDGs for 2018. By the
end of 2018, two were operational, both at
the Saint-Laurent-des-Eaux site in the Loiret-Cher department. Since then, the other
reactors in the French fleet have been
equipped gradually. According to EDF, all
were scheduled to be operational by
February 2021. n
1. Électricité de France/French national power
company.
2. IRSN notice 2016-00187, plus five additional
reports on commissioning the EDGs: 2017-00042
(P4 subseries, 1300 MWe plant series),
2017-00131 (CPY plant series), 2017-00318
(P4 subseries, 1300 MWe plant series),
2017-00344 (N4 plant series) and 2018-00109
(Bugey CP0 plant series).
3. IRSN notice 2017-00058.

Repères - N°48 / March 2021 - The IRSN magazine

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