Design Safety Improvements at Swiss BWRs after Fukushima · Safety Design after the Fukushima Accident 3 Beznau 1 (KKB1)PWR 365 MWe Dez 69 Beznau 2 (KKB2)PWR 365 MWe Mar 72 Mühleberg

Design Safety Improvements at Swiss BWRs after Fukushima

IAEA Technical Meeting on

Evaluation of NPP Safety Design

in the Aftermath of the

Fukushima - Daiichi Accident

IAEA Technical Meeting, Vienna

26 - 29 August 2013 Willem van Doesburg

BKW / Switzerland

Content

Existing plant safety features and post-Fukushima

improvement targets

Evaluation of design safety and resulting plant

improvements (carried out + planned) for the

Mühleberg NPP (KKM)

Leibstadt NPP (KKL)

Willem van Doesburg / 26-29 August 2013

IAEA Technical Meeting on Evaluation of NPP

Safety Design after the Fukushima Accident

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Plant improvements Swiss BWRs




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Beznau 1 (KKB1) PWR 365 MWe Dez 69

Beznau 2 (KKB2) PWR 365 MWe Mar 72

Mühleberg (KKM) BWR 373 MWe Nov 72

Gösgen (KKG) PWR 970 MWe Nov 79

Leibstadt (KKL) BWR 1165 MWe Dec 84

Existing Safety Features

• All Swiss NPPs have Special Emergency (SE) heat removal systems (KKL: SEHR / KKM: SUSAN) additional to the normal ECCS and heat removal systems

• These special emergency systems provide alternative cooling and decay-heat removal with autarky > 10h

• The systems are bunkered, designed to withstand APC, SSE, flooding as well as acts of sabotage

• The systems constitute an appropriate countermeasure to a severe natural event including long-term T-SBO

• All CH-NPP have Filtered Containment Depressurization (Venting) Systems with adequate retainment factors for I-131 and Cs-134/137




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Swiss AM development timeline




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Post-Fukushima Safety Targets

Assure robustness to withstand and cope with any severe Swiss natural hazard

(10’000 yearly extreme weather, flooding, earthquake events or combinations)

Assure control of T-LOOP during minimum 72 h without loosing safe shutdown

condition

Assure additional SAM-hardware and necessary auxiliary material as well as

SAM staff preparedness (availability, level of training, procedures) so that

a BDB event (with T-SBO) can be controlled during minimum 72 h without

challenging safe shutdown condition

a BDB event - if safe shutdown is not possible - will be limited to the

lowest consequential level:

avoid major core damage

avoid RPV-damage

avoid H2-explosion

avoid major radiological releases to the environment

Assure safety of long-term fuel pool cooling




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Improvements after Fukushima accident

Made on the basis of:

Original Licensing Requirements

Experiences Fukushima

Additional ENSI Requirements

European Stress Test Results

Own initiatives




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Mühleberg NPP (KKM)

GE - BWR4 design, MK1 containment

Original plant design similar to the Fukushima-

Daiichi NPPs

Various design extensions (e.g. outer torus, drywell spray

and flooding system, 2 extra PRVs, emergency control

room, alternative scram/shutdown system)

Hilltop water reservoir ( 300 m3, not classified)

Special emergency cooling/heat removal (bunkered)

systems, 2 redundant trains with one DG each, classified

Filtered containment venting system via outer torus – both

passive (rupture disc) and active




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KKM – Post-Fukushima conformity evaluations

Evaluation of coolant supply to safety and auxiliary systems

Evaluation (and implementation) of site specific and of central external storage

depot for emergency tools and equipment

Spent fuel pool cooling evaluations for possible improvement measures

Upgrade auxiliary DG for supplying power to 1 SUSAN train

Depot near site for mobile equipment (DGs, pumps, etc.)

Deterministic evaluation of response to 10’000-yearly flooding event

Deterministic evaluation of response to 10’000-yearly seismic event

Deterministic evaluation of combination of seismic and flooding event (dam

break)

Development of explicit feed&bleed procedures (multiple paths) and other AMM

Evaluation of protection against H-deflagration

Evaluation of possibility for diverse water supply

Evaluations for extreme weather conditions (wind, rain, temperature, lightning,

tornados…..)




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KKM – measures taken / planned

90cm high protection walls (protect up to level of 10’000-yearly

precipitation event)

Retrofitting three additional water intake pipes (“periscopes”) in

the SUSAN – SE water inlet structure

Provision of additional injection option (inlet shaft) in the

SUSAN – SE water inlet structure, and portable pumps for

injecting water

2 alternative SAM - injection feeds to the fuel storage pool

Diverse water supply for the SUSAN – SE system

Special emergency cooling system for spent fuel pool

Additional reactor coolant & decay heat removel system

Seismic stabilization of the embankment dam upstream of KKM




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KKM: mobile flood protection walls




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Mobile flood protection equipment of the service pump building - outside …

… and inside the building. entire mounting time approx. 3 h.

KKM: debris safe suction pipes for SUSAN




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suction pipe

(periscope)

SUSAN-intake

flow direction river

river bed

protection poles

Aare river

max. height for drift of

stones, mud and sand

2 suction pipes installed, each

with 3 protection poles

Normal Operation: outlet of hot

main cooling water

KKM: debris safe suction pipes (cont’d)




13 before installation after installation outage 2011

Protection

Poles

KKM: additional water inlet shaft for SUSAN




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Special bunkered

emergency heat removal

system (SUSAN)

building

Installed during outage 2011

Aare river water level

SUSAN water intake structure

str

ain

ers

KKM: 2 alternative SAM - injection feeds to the fuel storage pool (outage 2011)




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SFP SFP

KKM: 2 alternative SAM - injection feeds to the fuel storage pool (cont‘d)




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2 redundant injection conduits

Penetrations (2x DN80) made

in the wall of the reactor

building during outage 2011

System ready for use as of

31 March 2012

KKM: (special) emergency power equipment, firmly installed

Hydro-Electric Plant (HEP) near KKM: two 16kV

lines, continuously on stand-by

Emergency DG (1800 kVA), air cooled

Special Emergency system (SUSAN): two redundant

strains, DG (800 kVA) + battery unit for each strain

Auxiliary DG (on the roof of the SUSAN building, i.e.

seismic-proof), for recharging of SUSAN batteries

Upgraded (2012), now 1000 kVA DG installed

Diesel fuel and oil tanks




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KKM: new auxiliary 1000 kVA DG




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KKM, mobile and other equipment

3 mobile DGs (10 kVA)

Pumps (2 x 1800 l/min, 2 x 10000l /min) and various

smaller pumps

Hoses / flexible tubes (up to 5 km length), connection

materials

All-terrain vehicle with crane

Boric acid, diesel fuel + oil supplies

Mostly available at net control center - location < 1 km

from site

Further supplies available at joint central storage location

(Reitnau)




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KKM: tools / equipment (1): large pump




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KKM: tools / equipment (2)




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KKM: tools / equipment (3): 3 mobile DGs




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KKM: tools / equipment (4): mobile diesel oil tanks




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KKM: new system for level and temperature measurement in SFP

Based on regulatory (ENSI)

requirement for “accident

resistant” measurement

system

Improve existing level

measurement

New level measurement:

hydrostatic pressure

difference (air bubbles tube)

Redundant temperature

measurement: Pt-100 (Pt

resistance thermometer)

ENSI-approval for

implementation recently

obtained




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KKM plan: diverse water supply




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SSE-safe water intake

from groundwater

river Saane

Connect to the SUSAN-

SE system building

SSE-safe underground

channel

KKM plan: Seismic Stabilization of the Embankment Dam upstream of KKM




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Will provide additional margin

against 10‘000-yearly seismic event

Final plans submitted, awaiting

approval

KKM plan: additional SSE-safe Emergency Fuel Pool Cooling System




27 Aare

Reaktorgebäude

Sekundärcontainment

Primär-

containment

ÄussererTorus

SUSAN

PRV

CWS

ICWS

Dieselgeneratoren

ÄussererTorus

ALPS Niederdruckeinspeisesystem

CWS KühlwassersystemPRV Druckentlastungsventile

SRV Sicherheits- und Abblaseventile

TCS Toruskühlsystem

SUSAN Spezielles unabhängiges Systemzur Abfuhr der Nachzerfallswärme

SRVPRV SV

Aare

3x

2x

3x

2x2x

TCS

EPCS

EPCS BEB-Kühlsystem

EPCS

KKM plan: additional coolant injection and heat removal system (1)

Issue: all emergency coolant injection systems

presently located in the basement of the Reactor

Building (-11 m level)

Postulated BDB flooding of the RB basement would

incapacitate emergency coolant injection

Possible solution: installation of ALTERNATE

COOLANT INJECTION SYSTEM (ACIS)

ACIS capability equivalent to existing ALPS (low

pressure injection)

ACIS to be located at higher elevation

Design for AMM




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KKM plan: additional coolant injection and heat removal system (2)




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Leibstadt NPP (KKL)

GE – BWR6 design, MK3 containment

Original plant design with design extensions:

Special emergency cooling/heat removal (bunkered) system

(SEHR), 2 redundant trains with water supply from deep

groundwater spring and one DG for each train

Filtered containment venting system




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Leibstadt NPP (KKL)

EU Stress Test - results: even without measures taken

after the Fukushima accident

KKL has a high degree of design provisions against

DB accidents and a remarkable high level of SAM

provisions

KKL demonstrates high safety margins against all

BDB external and internal accident initiators,

especially in a T-SBO case




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Leibstadt NPP (KKL)

Only few ENSI requirements on further SAM

modifications

Accident resistant water level and temperature measurement

system in spent fuel pools (outage 2013)

Review H2 management effectiveness and, if necessary,

backfitting (2013 - 2014)

Seismic enforcement of FCVS (2014)

Improve SAM procedures / documentation (2013)

Integration of Reitnau external SAM storage facility hardware

in KKL SAM process and logistics (2013)

KKL has proactively initiated some further

improvements




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KKL: Emergency SFP - measurement system for water level & temperature




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Regulatory (ENSI) requirement

• Redundant

• Separation

• Safety Class 3, Seismic Class I

Implementation:

• Level: air bubbling - measurement

• Temp: Pt-100 probe

• Foreseen for outage 2013

KKL: Hydrogen control




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Parameter Goal Action

Igniters & PARS:

H2- concentration

during SA

Low H2-concentration even

under SBO condition

(passive protection)

No detoriation of FCVS

during venting!

1. Improve MELSIM higher nodalisation

2. Simulate spatial H2 distribution during

core melt accident (Containment &

FCVS)

3. Evaluate need for additional PARs

4. Install

Leibstadt NPP (KKL)

Proactive current projects

2 SAM DGs to feed emergency power trains (batteries) >>5h (done)

2 additional diverse SRV for fast & stable pressure relief (2017)

Backfitting of additional alternative injection points for SAM in seismic

stable environment (2013 - 2015)

Facility for fast alternative Boron injection via CST (2015)

Seismic resistant garages for fire trucks & fire fighting device (2017)

Seismic resistant location for SAM devices ( DGs, pumps, tools etc.)

(2013)

Pressure equalization drywell – containment for harmonized SAM

flooding (2013- 2014)

Improvement RCIC logics for continuous operation (2014)




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KKL: alternate Injection with external accesses/adapters to regular systems




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1. Injection to Fuel Pools

2. Injection to

1. RCIC, CRD, HPCS suction lines

2. Re- filling CST

3. Injection to ESW B

3. Injection to RPV via Feed Water

Line

Mainly extension/adaptation of

already available nozzles / access

points for mobile or fire fighting

equipment

KKL: Alternate Supply Systems e.g. to increase reliability of pressure relief of RPV in a severe accident situation – realized

in 2011

Purchase of

Alternate Power Supply

a. Power supply for e.g. SRV with mobile SAMG Diesel Generator (150kVA)

Alternate Air supply

a. DG powered mobile air

compressor

Mobile pumps, etc.




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KKL: Alternate Power Supply in case of T-SBO, with SSE-safe connection plugs in both DG buildings - realized in 2011




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Regular Emergency Diesel Generator

Safety relevant DC-consumers: motors, solenoid valves (SRV), instrumentation, emergency lights, etc.

battery charger

«SAM DG» 150kVA

KKL: plan for further SAM optimizations after Fukushima: long-term depressurization of the RPV DC-MOV-SRV




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Most important requirements in a SA situation:

• External connection plugs for supply

with compressed air ( mobile compressor unit) to keep safety relief valves (SRV) permanent open

• External connection plugs for power supply for opening of solenoid valves with mobile SAMG Diesel generator (150kVA)

• Relevant modification: 2 additional,

diverse DC-motor operated safety relief valves (MOV-SRV) for stable «open position» to depressurize the RPV for extended time

Documents

Design Safety Improvements at Swiss BWRs after Fukushima · Safety Design after the Fukushima Accident 3 Beznau 1 (KKB1)PWR 365 MWe Dez 69 Beznau 2 (KKB2)PWR 365 MWe Mar 72 Mühleberg