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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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Swiss AM development timeline
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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…..)
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKM: mobile flood protection walls
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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)
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
13 before installation after installation outage 2011
Protection
Poles
KKM: additional water inlet shaft for SUSAN
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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SFP SFP
KKM: 2 alternative SAM - injection feeds to the fuel storage pool (cont‘d)
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKM: new auxiliary 1000 kVA DG
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKM: tools / equipment (1): large pump
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKM: tools / equipment (2)
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKM: tools / equipment (3): 3 mobile DGs
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKM: tools / equipment (4): mobile diesel oil tanks
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKM plan: diverse water supply
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKM plan: additional coolant injection and heat removal system (2)
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
30
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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKL: Emergency SFP - measurement system for water level & temperature
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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)
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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KKL: alternate Injection with external accesses/adapters to regular systems
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IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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.
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
37
KKL: Alternate Power Supply in case of T-SBO, with SSE-safe connection plugs in both DG buildings - realized in 2011
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
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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
Willem van Doesburg / 26-29 August 2013
IAEA Technical Meeting on Evaluation of NPP
Safety Design after the Fukushima Accident
39
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