FRENCH PWR’S ULTIMATE HEAT SINKS
THREATENED BY THEIR ENVIRONMENT
“Nuclear power for the people”
Nesebar, 26-29 September, 2010
Véronique BERTRAND
IRSN, France
Système de management
de la qualité IRSN certifié
SUMMARY
Heat sink: generalities
Total loss of heat sink at Cruas unit 4 in December 2009
Total loss of heat sink management from the initial design
EPR Flamanville 3 pumping station’s design
Conclusion
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Heat sink - generalities
FRENCH NPPs IMPLANTATION
58 reactors in operation
(+1 under construction–EPR at
Flamanville)
19 sites :
 4 coastal
-Flamanville (2×1300 MWe)
-Paluel (4×1300 MWe)
-Penly (2×1300 MWe)
-Gravelines (6×900 MWe)
 1 estuarine
-Blayais (4×900 MWe)
 14 riverside
(including 11 with cooling
towers)
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Heat sink - generalities
Pre-filtration and filtration in the pumping station
2 circuits supplied ensuring the reactor’s cooling
Cooling circuit of the nuclear island including safety
systems called Essential Service Water System (ESWS)
Cooling circuit of the conventional island
Conventional island
Role of the cooling circuit
The cooling circuit of the conventional island isn’t a system
important to safety
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Heat sink - generalities
REACTORS COOLING: CASE WITH COOLING TOWER
CONVENTIONAL ISLAND
Reactor
coolant
system
MSS
TURBINE
NUCLEAR ISLAND
AFS
ALTERNATOR
HEATER
FFCS
RHRS
CONDENSER
CSS
SIS
CCWS
ESWS
COOLING TOWER
Conventional
heat sink
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Safety
heat sink
Heat sink - generalities
REACTORS COOLING: A SAFETY FUNCTION
ESWS: cooling of an intermediate cooling system, the
Component Cooling Water System (CCWS)
ESWS and CCWS are systems important to safety
ESWS: two redundant trains
CCWS responsible for cooling of safety equipment
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Heat sink - generalities
PROTECTION AGAINST EXTERNAL HAZARDS
External hazards considered from the initial design
earthquakes
external flooding
cold weather
snow
extreme wind
other phenomena
External hazards underestimated
freezing
frazil ice
high air temperatures
seaweed
vegetable matter
external flooding with or without extreme wind
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Expérience feedback in 2009
TOTAL LOSS OF
HEAT SINK AT
CRUAS 4 IN
DECEMBER 2009
CRUAS NPP (900 MWe): 4 units
Date of the incident: 1st December, 2009
Rated level 2 on the INES scale
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Total loss of heat sink at Cruas 4 in December 2009
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Total loss of heat sink at Cruas 4 in December 2009
CCWS Building
ESWS Galleries
trains A & B of unit 1
Unit 1
B1
A1
CCWS Building
Unit 2
A2
Unit 3
B2
B3
A3
Unit 4
A4
B4
Intake coarse filtration
& trash removal system
(1 grid/train) – units 1&2
Intake coarse filtration
& trash removal system
(1 grid/train)– units 3&4
B1
Discharge basin
Discharge ducts
ESWS Galleries
trains A & B of unit 4
B2
Train B
A1
A2
Train A
A3
A4
B3
Train A
B4
Train B
Discharge basin
Discharge ducts
Intake channel
Rhône river bed
River Rhône
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Floating
dyke
Total loss of heat sink at Cruas 4 in December 2009
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Total loss of heat sink at Cruas 4 in December 2009
WHAT HAPPENED ?
01/12/2009 : massive unprecedented blockage
ESWS train A unavailable
Reactor 4 shutdown
ESWS train B unavailable
Unit 4: total loss of heat sink  the first time in France
concerning a PWR
National Crisis Organization activated
French public authorities (ASN)
Technical support (IRSN)
French utility (EDF)
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Total loss of heat sink at Cruas 4 in December 2009
Application of the Emergency Operating Procedures (EOPs)
Difficulties in the procedure
Unit 4 in a safe state 3 hours later
Use of the thermal inertia of the refuelling water storage
tank (RWST) reserve
Efficient cleaning of filtration device and ESWS/CCWS
exchangers
Total loss of heat sink lasted 10 hours
Units 2&3 partially lost heat sink
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Total loss of heat sink at Cruas 4 in December 2009
Canadian pondweed plants
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Total loss of heat sink at Cruas 4 in December 2009
LESSONS LEARNT
First ever occurrence on a PWR in France
Partial loss of heat sink on units 2 and 3 together with the total
loss on unit 4
Efficient management needs quick and reliable diagnosis of the
situation and mitigation means
Need to improve the emergency procedure
Use of thermal inertia of RWST water proved to be effective
On-site trash rack pre-filtration cleaning devices proved to be
insufficient
 IRSN started an in-depth analysis of this incident
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Experience feedback in 2009
OTHER EVENTS
Frazil ice event at Chooz B NPP in January
Vegetable matter ingress in Le Blayais NPP, February and
March
Drum screens clogging at Fessenheim NPP in December
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Experience feedback in 2009
CONSEQUENCES
Action plan from the utility EDF
Heat sink operating conditions and design
Operating procedures
Criteria for emergency organization activation
IRSN analysis
Characterisation of hazards
Monitoring and protection of the pumping station
Existing means, procedures, organization
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TOTAL LOSS OF HEAT SINK MANAGEMENT
FROM THE INITIAL DESIGN
Incident procedure evolution
Probabilistic safety assessment (PSA)
contribution
Loss of heat sink on all units of a NPP
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Total loss of heat sink management from the initial design of French NPPs
INCIDENT PROCEDURE EVOLUTION
Use of the thermal inertia of the refuelling water storage
tank (RWST) reserve
Emergency heat sink for cooling temporarily the
component cooling water system (CCWS)
Throughout a containment spray system (CSS) heat
exchanger
Foreseen enhancement: operation of one reactor cooling
pump and one charging pump
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Total loss of heat sink management from the initial design of French NPPs
PROBABILISTIC SAFETY ASSESSMENT (PSA)
CONTRIBUTION
PSA for PWR 900 MWe developed at IRSN
Potential scenarios resulting from a total loss of ultimate
heat sink with a high frequency
Beyond the initial design
Implementation of modifications
Automatic disconnection of the reactor coolant letdown
line
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Total loss of heat sink management from the initial design of French NPPs
LOSS OF HEAT SINK ON ALL UNITS OF A NPP
Recently subject to particular attention in France
Wide study following the partial flooding of Le Blayais NPP
Analysis of the guaranteed available on-site resources
Modifications: sufficient required capacities of steam
generator water supply
Equivalent program for next safety reviews of other series
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EPR Flamanville 3 pumping station’s design
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EPR Flamanville 3 pumping station’s design
Improvement of the pumping station’s initial design
Four independent water trains
Two diversified types of filtration devices with screens
and chain filters
Strengthening of the cleaning means of pre-filtration and
filtration devices
Enhanced reliability of head loss measurements to prefiltration trash racks and filters
New system: the ultimate cooling water system (UCWS)
Foreseen for cooling an intermediate cooling system,
which in turn cools
The containment heat removal system (CHRS)
The fuel pool cooling system (FPCS) third train
Normal supply for ESWS and UCWS: pumping station
Diversified cooling source: connexion to the outfall
structure
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CONCLUSION
Environmental conditions can impact the safety of nuclear
reactors
 Come back to the initial design
3 lines of defence
Prevention: identification and knowledge of hazards
 Appropriate design equipment
Pumping station: monitoring, detection and protection
means
 To ensure a permanent ESWS flow rate
Management of a total loss of heat sink
 To cool the reactor until the heat sink recovery
Expectation for EPR Flamanville 3 pumping station: to cope
with external hazards
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THANK YOU
FOR YOUR ATTENTION
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