french pwr’s ultimate heat sinks threatened by their environment “nuclear power for the...

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 managementde la qualité IRSN certifié

Nuclear power for the people – 26-29 September, 2010 – Nesebar, Bulgaria –

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


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)

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



REACTORS COOLING: CASE WITH COOLING TOWER

CONVENTIONAL ISLAND

ALTERNATOR

TURBINE

HEATER

CONDENSER

MSS

AFS

FFCS

CSS

RHRS

Conventional heat sink

NUCLEAR ISLAND

SIS

COOLING TOWER

Reactorcoolantsystem

CCWS

Safetyheat sink

ESWS



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



PROTECTION AGAINST EXTERNAL HAZARDS

External hazards considered from the initial design

earthquakesexternal floodingcold weathersnowextreme windother phenomena

External hazards underestimatedfreezingfrazil icehigh air temperaturesseaweedvegetable matterexternal flooding with or without extreme wind



CRUAS NPP (900 MWe): 4 units

Date of the incident: 1st December, 2009

Rated level 2 on the INES scale

TOTAL LOSS OF

HEAT SINK AT

CRUAS 4 IN

DECEMBER

2009

Expérience feedback in 2009


Total loss of heat sink at Cruas 4 in December 2009



Train B

Unit 1 Unit 2

Train A Train B

Unit 4Unit 3

Train A

Navigation Channel

River Rhône

Discharge basinDischarge ducts

B1 A1 A2 B2 B3 B4A3 A4

B1 B2 A1 A2 A3 B4A4 B3

Intake channel

Rhône river bed


Floating dyke

ESWS Galleries trains A & B of unit 1 ESWS Galleries

trains A & B of unit4

Intake coarse filtration& trash removal system (1 grid/train) –units 1&2

Train B

Unit 1 Unit 2

Train A Train B

Unit 4Unit 3

Train A

Navigation Channel

River Rhône


B1 A1 A2 B2 B3 B4A3 A4

B1 B2 A1 A2 A3 B4A4 B3

Intake channel

Rhône river bed


Floating dyke

ESWS Galleries trains A & B of unit 1

CCWS Building CCWS Building

ESWS Galleries trains A & B of unit4

Intake coarse filtration& trash removal system (1 grid/train) –units 1&2

Intake coarse filtration& trash removal system (1 grid/train) –

Intake coarse filtration& trash removal system (1 grid/train) units

3&4


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)



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



Canadian pondweed plants



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



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

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

Experience feedback in 2009


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


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

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



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



Improvement of the pumping station’s initial designFour independent water trainsTwo diversified types of filtration devices with screens and chain filtersStrengthening of the cleaning means of pre-filtration and filtration devicesEnhanced reliability of head loss measurements to pre-filtration trash racks and filters

New system: the ultimate cooling water system (UCWS)

Foreseen for cooling an intermediate cooling system, which in turn coolsThe 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



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


THANK YOUFOR YOUR ATTENTION

french pwr’s ultimate heat sinks threatened by their environment “nuclear power for the...

Documents

people nesebar

summary heat sink

bulgaria page

environment nuclear

intermediate cooling

safety esws

conventional island

safety function esws