Filtered Containment Venting Systems at Swiss NPPs
Transcript of Filtered Containment Venting Systems at Swiss NPPs
Swiss Federal Nuclear Safety Inspectorate ENSI
Filtered Containment Venting Systems
at
Swiss NPPs and
KKL in particular January 15, 2014, Ft. Lauderdale
J. Hammer, ENSI, and A. Ritter, KKL
• Swiss Nuclear Power Plants • Filtered Containment Venting Systems (FCVS)
• Current Venting Systems in Swiss NPPs KKB, KKG and KKM
• The FCVS at Leibstadt NPP
Agenda
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The four Swiss NPPs
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Nuclear Installations in Switzerland NPPs Research Reactors Interim Storage
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Mühleberg Nuclear Power Plant (KKM)
BWR Start of commercial operations:
1972 Net electrical output:
355 MWel End of operations
scheduled for 2019 Cop
yrig
ht K
KM
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Gösgen Nuclear Power Plant (KKG)
PWR Start of commercial operations:
1979 Net electrical output:
985 MWel
Cop
yrig
ht K
KG
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Beznau Nuclear Power Plant (KKB 1 & 2)
PWR
Start of commercial operations:
KKB 1: 1969 KKB 2: 1971
Net electrical output:
380 MWel each
Cop
yrig
ht K
KB
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Leibstadt Nuclear Power Plant (KKL)
BWR Start of commercial operations:
1984 Net electrical output:
1220 MWel
Cop
yrig
ht K
KL
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KKM
KKG
KKL
KKB
EKKM
KKN
EKKB
May 2011: No nuclear new build!
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Filtered Containment Venting
i. Filtered Containment Venting (FCVS) is a measure for beyond design basis accidents.
ii. The FCVS is in general passive and does not depend on any external input such as actuation, mechanical movement or supply of power.
iii. The FCVS is important to safety; its malfunction could lead to radiation exposure of members of the public.
iv. The FCVS serves mitigate the consequences of a severe accident.
v. IAEA NS-G-1-10, 4.143 says: Where containment venting systems are installed, the discharge should be filtered to control the release of radionuclides to the environment. Typical filter systems include sand, multi-venturi scrubber systems, HEPA or charcoal filters, or a combination of these. HEPA, sand or charcoal filters may not be necessary if the air is scrubbed in a water pool.
vi. In case of a severe accident we have to deal with wet and hot gas and air mixtures. Therefore, the FCVS must resist temperatures up to 160°C and high vapor concentration.
vii. The important nuclides are 131I, 134Cs and 137Cs.
viii. The FCVS should be designed for heat removal of several MWth during 3 to 5 days
Philosophy of Filtered Containment Venting
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• The FCVS is a Safety Relevant System • In addition to the FCVS, ENSI demands a passive
ventilation system without operator action • The FCVS is always ready during power operation • Remote and Local operation, RP-conditions • Simple and passive design, no AC power need • The gas flow has to be adjustable • Exhaust via stack, two valve closing system • Exchange of water and chemicals in the filter
during operation should be possible
New Guidelines for FCVS (ENSI, preliminary)
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• Retention factor >1000 for aerosols >100 for elementary Iodine to be proven by experiments in the range of 30 to 100% of nominal flow
• Filter loading up to 150 kg aerosols • Probability for containment rupture < 0.1% • Operating time >100 hours, self-sufficient • Earthquake resistant as the containment building • Resistant to pressure peaks
as in case of hydrogen deflagration
Design Basis for FCVS (ENSI, preliminary)
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Venting Systems at Swiss NPPs
SIDRENT the FCVS of KKB 1 & 2
Technical Data max. containment pressure: 3.1 bar nominal, 6.2 bar break down Rupture Disk nominal pressure: 4.2 bar Nominal flow rate: 4.5 kg/s Filter: Air-Lift-Effect Diameter: 3.5 m Height: 7 m water capacity: 30m3
max. Filter loading: 150 kg max. Temperature: 166°C Retention factor: >1000 for aerosols >100 for Iodine (elementary) Self-sufficient operating time: 24 h
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SIDRENT the FCVS of KKB 1 & 2
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KKG Filtered Containment Venting
Technical Data max. containment pressure: 5.89 bar abs. nominal, Rupture Disk nominal pressure: 6.5 bar Nominal flow rate: ~2 m3/s Filter: Venturi Scrubber System Diameter: 3.0 m Height: 6.0 m water capacity: 15 m3
max. Filter loading: 200 kg max. Temperature: 160°C Retention factor: >1000 for aerosols >100 for Iodine (elementary) Self-sufficient operating time: 24 h
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KKG Filtered Containment Venting Scheme
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• Technical Data • max. containment pressure: 9.5 bar • Rupture Disk nominal pressure: 6.2 bar • Nominal flow rate: 25 kg/s • Filter: Multi Venturi Scrubber System • Outer torus water capacity: 1000m3
• Retention factor: >1000 for aerosols • >100 for Iodine
KKM Filtered Containment Venting CDS
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KKM - CDS
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Actual Filtered Containment Venting System • Layout • Efficiency • Radiological Impact
Planned Improvements • Hydrogen Problem • Radiation Monitor • Filter Long Term Retention
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KKL-FCVS
Filtered Containment Venting System Scheme
Weir Wall
Suppression Pool
Containment
Drywell
Reactor Pressure Vessel
XK10N010
FCVS
Shield Wall
M M
LC11XK10S002
11XK10S001
XK20N001
ExhaustChimney
ZQ00B100
XK11B001
XK12B001
XK10N001
Stack
XK10B001
VENTStack
LOXK12S004
LCXK10S005
TC70S034
Suppression Pool
Cleaning System
Make-Up Water
System(UD)
Fire Water
System(UJ)
XK10S006
XK10S007
UJ70S067
UD70S098XK10Z006
LOXK11S004
XK10S301
Room ZC22R103
Roof of Reactor Auxiliary Building
ZC22R140
XK10S107
Local Operating Position
ZC24R102
Room ZC10R126
XK11S002
XK12S009
XK10S207
XK10S206
FT11XK10F002
FIP11XK10F002
PI11YY10P011
PIP11YY10P011
PI21YY00P011
PI21YY10P011
PRP21YY10P011
PI11YY10P011
• Scrubber construction ensures 5 sec residence time allowing for Iodine reaction to complete • 12 radial branches equipped with nozzles (92 nozzles per filter) expand the gas-steam mixture
into aerosol-carrying bubbles
Sodium thiosulfate is flashed into filter tanks on system initation due to pressure difference
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Layout Clean gas to stack
Gas from Containment
Shielded local control room
Filter Tanks Designer: Sulzer / EWI Rupture Disc Pressure [bara]: 3.1 Operating Pressure [bara]: 2.55
Comissioning: 1993 Max Flow [kg/s]: 20.66 Nominal flow [kg/s]: 13.77
Drain to Radwaste
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FCVS Efficiency
Activity release (“source term”) after postulated core melt accident
Noble gases Cesium + Iodine
Without Filter (“Fukushima”)
Noble gases
Cesium + Iodine
With FCVS Filter (“KKL”)
Temporary Iodine Resuspension
Decon Factor Iodine: 100 Decon Factor Aerosols: 1000
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Simulation: 1 Year Committed Dose
10 mSv limit
10 mSv limit
100 mSv limit
1 mSv limit
1 mSv limit
Without Filter (“Fukushima”) With FCVS Filter (“KKL”)
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Radiological Impact of Loaded Filters: Direct radiation very well shielded by surrounding buildings. Filter Inventory: 1E18 Bq ( 3E7 Ci)
Skyshine related Exposure on Site: <10 mSv/h (1 % of Stack Exhaust Exposure)
Operator Control Room: 30 mSv/h
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Problems with Existing Configuration: Possible Hydrogen Explosion
• Hazard of Explosion due to Hydrogen Input into Stack
• Calibration of Rad Monitor not easy due to difficult Geometry
Stack Flow Direction
Radiation Monitor
Exhaust «Plume»
Exhaust Line from Filters to Stack
H2 H2
H2
H2
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Difficulties with Source Term Estimation • Sampling not possible, very high Dose Rates of Samples and
inside Stack • Radiation Monitor is measuring Dose Rate [mSv/h], resp. [R/h] • Conversion Factor Dose Rate to Source Term
• [mSv/h] [Bq/h], resp. [R/h] [Ci/h] • Conversion Factor is depending on Energy of Nuclide-
Mixture and Stack Ventilation Rate: Depending on Accident Conditions and elapsed Time (rad. Decay).
• Conversion Factor is averaged for many different Accident Conditions over first 8 hours: 5E11 (Bq∙h/Sv∙m3)
• Stack Flow my be not well defined under Accident Conditions
• Radiation Monitor needs to be relocated FCVS| 2014 ALARA Symposium | J. Hammer and A. Ritter 28
New Pipe Routing outside Stack, new Rad Monitor Location
• No Hydrogen Input into Stack: No Explosion Hazard
• New Location of Rad Monitor (inside or outside of Stack Wall)
• Easy Calibration due to well defined Geometry
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Filter Long Term Retention
Activity release (“source term”) after postulated core melt accident
Noble gases
Cesium + Iodine
With FCVS Filter (“KKL”)
Temporary Iodine Resuspension
With proposed Additives (Aliquat)
Change in Filter Chemistry under Consideration: Long Term Retention of Organic Iodine (CH3I) possible
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Conclusions
• Filtered Containment Venting System were implemented 20 years ago in all Swiss NPP
• FCVS turned out to be very helpful in the Post-Fukushima Safety Evaluations
• Improvements concerning Hydrogen, Earthquake Resistance, and Source Term Evaluation under way
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for more information please visit:
www.ensi.ch www.ifsn.ch
www.kkl.ch
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Thank you for your attention!