Repères - N°48 / March 2021 - The IRSN magazine - 8

SAFETY
Extreme risks

Enhanced protection for nuclear facilities
Following the accident at Fukushima Daiichi, the decision was made to assess the robustness
of French nuclear facilities and their resistance to extreme natural events. IRSN experts
then developed the concept of the " hardened safety core " , whose aim is reinforcing control
of vital safety functions, preventing large-scale releases to the environment and improving
emergency response management.

" H

ow on earth could an accident
like this happen in Japan, a
country renowned for its reliable
technology, rigorous organization and
robust construction? " recalled Patrick
Lejuste, post-Fukushima Project Manager,
as he thought back to how stupefied the
nuclear community was in 2011.
At the time, ASN, the French Nuclear Safety
Authority, asked licensees to immediately

undertake Complementar y Safety
Assessments (CSAs). They had to assess the
robustness of the facilities in the event of a
major earthquake or extreme flooding event.
Seventy-nine CSA reports were drawn up
by the licensees. They identified a number
of deviations/cases of noncompliance, points
for improvement, and presented calculations
on the length of time before releases to the
environment were likely, etc. In the space

of just a few months, IRSN had conducted
a critical analysis of all these reports and
examined licensee proposals for making
their facilities more robust.
At the beginning of 2012, based on all these
data and assessments, ASN concluded that
there was no need to close down any of
the plants. It did, however, require the
operators to check conformity with the
safety requirements and decided to raise

FOCUS
What are the first key measures of the hardened safety core?
Preventing accidents with core melt or slowing down their progression, reducing massive releases of radioactivity and making it
possible for the operator to manage emergency response-these are the three objectives of the hardened safety core program.
It is being deployed across the French nuclear power plant fleet in the wake of Fukushima Daiichi in order to equip it to withstand
extreme hazards. Having developed the initiative, IRSN is assessing its design and implementation. After 72 hours, the Nuclear
Rapid Response Force (FARN) takes over to assist on-site. Here, we take a look at the first key measures of the concept.

1 Emergency diesel generators (EDG)
These are used to restore electric power to the hardened
safety core equipment and systems. It is designed to operate
for 72 hours without requiring human intervention.
Implementation expected to be complete in February 2021*

2
3

3 Ultimate heat sink
Sourced from deep groundwater, existing pools or new reservoirs,
the ultimate makeup water supply must ensure site autonomy
for 72 hours in the event of severe natural events leading
to conditions beyond the scope of the original design basis.
It will be used to supply the steam generators, the reactor pool
and the spent fuel pool.
Implementation expected to be complete in 2021*
* Source: EDF

Page 8 - Repères No. 48 - March 2021

Implementation expected to be complete
in 2026
Commissioned in 2020* at Flamanville
NPP (Manche department)

2 Local emergency center (CCL)
This must be designed to withstand extreme
natural hazards. It houses emergency
response equipment and can accommodate a staff of about a hundred people
deployed as part of the on-site mobilization
plan and mobile response forces. These
teams carry out diagnostics to assess
facility condition, evaluate releases and
advise public authorities.

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

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