Teški akcidenti u nuklearnim elektranama

Nesreća u NE Fukushima
Davor Grgić
Okrugli stol HAZU
Zagreb, 05.04.2011.
NE Fukushima-Daichi
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Nekad i sad
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3
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NE Fukushima Daiichi
1 JST (5:46 UTC)
March 11, 2011, 14:46
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Inicirajući događaj:
Potres:
3
4 9,0 Richtera
•Magnituda potresa (u epicentru):
•Intenzitet potresa: IX stupanj po Mercaliju
Tsunami:
•Visina vala: 14 m
•Vrijeme dolaska do EN: t0+55 min
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EES Honshu
•3 konekcije sjever-jug, 1GW
•Nakon potresa obustava HE i TE
•Automatska obustava 14 reaktora
na 4 NE lokacije
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Lokacije BWR elektrana
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NE Fukushimi Daiichi – stanje reaktora
Jedinica / reaktor br.
1
Snaga/snaga na pragu NE [MWe]
460
439
784
760
1100
1067
Termička snaga reaktora [MWt]
1380
2381
3293
Vrsta nuklearnog reaktora
Vendor
BWR-3
BWR-4
BWR-5
Start (god)
1971
1974,1976,1978,1978
1979
Vrsta kontejnmenta
Mark 1
Mark 1
Pogonski status reaktora u
trenutku pojave potresa
GE
2
3
4
5
GE/TH, TH, HIT, TH
U pogonu 
automatska
obustava
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GE-TH
Mark 2
Van pogona
(planirani
remont)
Izvor: TEPCO, 11. ožujka 2011.
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Što se dogodilo u Fukushimi?
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NE izdržala potres 11. ožujka
– Magnituda potresa (u epicentru): 9,0 Richtera
– Intenzitet potresa: IX stupanj po Mercaliju
Sustavi za obustavu ispravno odradili u trenutku potresa
NE stavljena u stanje sigurne obustave
Normalno započelo hlađenje reakt. jezgre
Presudne su posljedice tsunamija
– 55 min nakon potresa
– Projektna/stvarna visina vala: 5,7 m / 14 m
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Gubitak vanjskog napajanja i diesel-generatora
Nemogućnost odvođenje ostatne topline za
– Gorivo u reaktoru
– Gorivo u bazenu (istrošeno)
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Kronologija ukratko
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Problemi s hlađenjem, eksplozija vodika i oslobađanje radioaktivnosti
iz:
– Reaktora 1
– Reaktora 3
– Reaktora 2
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Oštećenje bazena za ING jed. 4, vatra i oslobađanje radioakt.
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Pregrijavanje bazena za ING jed. 3 i oslobađanje radioakt.
Stabiliziranje stanja uz hlađenje morskom vodom u reaktorima 1-3 uz
nejasan stupanj oštećenja jezgre
Pokušaji vanjskog hlađenja bazena s ING u R-3 i R-4 uz znatan
stupanj oštećenja goriva
Uspostava napajanja, pokušaj pokretanja sigurnosnih sustava
Ispusti radioaktivnosti u zrak i vodu
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Kako radi nuklearna elektrana?
Tlakovodni (PWR) vs. kipući reaktor (BWR)
Tlakovodni reaktor (PWR)
- NE Krško
Kipući reaktor (BWR)
- NE Fukushima Daiichi
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BWR Mark-1 kontejnment
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BWR-3 koncept
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The Fukushima Daiichi Incident
1. Plant Design
Reactor Service Floor
(Steel Construction)
Concrete Reactor Building
(secondary Containment)
Fresh Steam line
Main Feedwater
Reactor Core
Reactor Pressure Vessel
Containment (Dry well)
Containment (Wet Well) /
Condensation Chamber
Spend Fuel Pool
The Fukushima Daiichi Incident
2. Accident progression
11.3.2011 14:46 - Earthquake
 Magnitude 9
 Power grid in northern Japan fails
 Reactors itself are mainly
undamaged
SCRAM
 Power generation due to Fission
of Uranium stops
 Heat generation due to radioactive
Decay of Fission Products
• After Scram
• After 1 Day
• After 5 Days
~6%
~1%
~0.5%
Ostatna toplina
Fukushima I -1 decay pow er
6
5.5
5
Fukushima I -1 decay pow er
80
4
3.5
3
2.5
PLOT FER V1W 18:04:48, 13/03/11
Decay power (% of nominal)
4.5
2
1.5
70
1
.5
0
50
0
1
2
3
4
5
6
7
Time (day)
40
PLOT FER V1W 18:02:07, 13/03/11
Decay power (MW)
60
30
20
10
0
0
1
2
3
4
Time (day)
5
6
7
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The Fukushima Daiichi Incident
2. Accident progression
Containment Isolation
 Closing of all non-safety related
Penetrations of the containment
 Cuts off Machine hall
 If containment isolation succeeds,
a large early release of fission
products is highly unlikely
Diesel generators start
 Emergency Core cooling systems
are supplied
Plant is in a stable save state
The Fukushima Daiichi Incident
2. Accident progression
11.3. 15:41 Tsunami hits the plant
 Plant Design for Tsunami height of
up to 5.7m
 Actual Tsunami height 14m
 Flooding of
• Diesel Generators and/or
• Essential service water
building cooling the
generators
Station Blackout
 Common cause failure of the
power supply
 Only Batteries are still available
 Failure of all but one Emergency
core cooling systems
The Fukushima Daiichi Incident
2. Accident progression
Reactor Core Isolation Pump still
available
 Steam from the Reactor drives a
Turbine
 Steam gets condensed in the
Wet-Well
 Turbine drives a Pump
 Water from the Wet-Well gets
pumped in Reactor
 Necessary:
• Battery power
• Temperature in the wet-well
must be below 100°C
As there is no heat removal from
the building, the Core isolation
pump cant work infinitely
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Containnment
spray
Potencijalni vanjski
izvor vode
Parovod
HP
ubrizgavanje
Pojna voda
Recirkulacijske
crpke
Izmjenjivač
topline
Bitna voda
(SW)
Containnment
spray
Crpke LP
sistema
Crpke sustava za
rasprsivanje vode u jezgri
Potencijalni vanjski
izvor vode
The Fukushima Daiichi Incident
2. Accident progression
Reactor Isolation pump stops
 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)
Decay Heat produces still steam in
Reactor pressure Vessel
 Pressure rising
Opening the steam relieve valves
 Discharge Steam into the Wet-Well
Descending of the Liquid Level in
the Reactor pressure vessel
The Fukushima Daiichi Incident
2. Accident progression
Reactor Isolation pump stops
 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)
Decay Heat produces still steam in
Reactor pressure Vessel
 Pressure rising
Opening the steam relieve valves
 Discharge Steam into the Wet-Well
Descending of the Liquid Level in
the Reactor pressure vessel
The Fukushima Daiichi Incident
2. Accident progression
Reactor Isolation pump stops
 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)
Decay Heat produces still steam in
Reactor pressure Vessel
 Pressure rising
Opening the steam relieve valves
 Discharge Steam into the Wet-Well
Descending of the Liquid Level in
the Reactor pressure vessel
The Fukushima Daiichi Incident
2. Accident progression
Reactor Isolation pump stops
 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)
Decay Heat produces still steam in
Reactor pressure Vessel
 Pressure rising
Opening the steam relieve valves
 Discharge Steam into the Wet-Well
Descending of the Liquid Level in
the Reactor pressure vessel
The Fukushima Daiichi Incident
2. Accident progression
Reactor Isolation pump stops
 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)
Decay Heat produces still steam in
Reactor pressure Vessel
 Pressure rising
Opening the steam relieve valves
 Discharge Steam into the Wet-Well
Descending of the Liquid Level in
the Reactor pressure vessel
The Fukushima Daiichi Incident
2. Accident progression
Measured, and here referenced
Liquid level is the collapsed level.
The actual liquid level lies higher
due to the steam bubbles in the
liquid
~50% of the core exposed
 Cladding temperatures rise, but still
no significant core damage
~2/3 of the core exposed
 Cladding temperature
exceeds ~900°C
 Balooning / Breaking of the
cladding
 Release of fission products form
the fuel rod gaps
The Fukushima Daiichi Incident
2. Accident progression
~3/4 of the core exposed
 Cladding exceeds ~1200°C
 Zirconium in the cladding starts to
burn under Steam atmosphere
 Zr + 2H20 ->ZrO2 + 2H2
 Exothermal reaction further
heats the core
 Generation of hydrogen
• Unit 1: 300-600kg
• Unit 2/3: 300-1000kg
 Hydrogen gets pushed via the
wet-well, the wet-well vacuum
breakers into the dry-well
The Fukushima Daiichi Incident
2. Accident progression
at ~1800°C
[Unit 1,2,3]
 Melting of the Cladding
 Melting of the steel structures
at ~2500°C
[Block 1,2]
 Breaking of the fuel rods
 debris bed inside the core
at ~2700°C
[Block 1]
 Melting of Uranium-Zirconium
eutectics
Restoration of the water supply
stops accident in all 3 Units
 Unit 1: 12.3. 20:20 (27h w.o. water)
 Unit 2: 14.3. 20:33 (7h w.o. water)
 Unit 3: 13.3. 9:38 (7h w.o. water)
The Fukushima Daiichi Incident
2. Accident progression
Release of fission products during
melt down
 Xenon, Cesium, Iodine,…
 Uranium/Plutonium remain in core
 Fission products condensate to
airborne Aerosols
Discharge through valves into water
of the condensation chamber
 Pool scrubbing binds a fraction of
Aerosols in the water
Xenon and remaining aerosols
enter the Dry-Well
 Deposition of aerosols on surfaces
further decontaminates air
The Fukushima Daiichi Incident
2. Accident progression
Containment
 Last barrier between Fission
Products and Environment
 Wall thickness ~3cm
 Design Pressure 4-5bar
Actual pressure up to 8 bars
 Normal inert gas filling (Nitrogen)
 Hydrogen from core oxidation
 Boiling condensation chamber
(like a pressure cooker)
Depressurization of the
containment
 Unit 1: 12.3. 4:00
 Unit 2: 13.3 00:00
 Unit 3: 13.3. 8.41
The Fukushima Daiichi Incident
2. Accident progression
Positive und negative Aspects of
depressurizing the containment
 Removes Energy from the Reactor
building (only way left)
 Reducing the pressure to ~4 bar
 Release of small amounts of
Aerosols (Iodine, Cesium ~0.1%)
 Release of all noble gases
 Release of Hydrogen
Gas is released into the reactor
service floor
 Hydrogen is flammable
The Fukushima Daiichi Incident
2. Accident progression
Unit 1 und 3
 Hydrogen burn inside the reactor
service floor
 Destruction of the steel-frame roof
 Reinforced concrete reactor
building seems undamaged
 Spectacular but minor safety
relevant
Način ventiliranja kontejnmenta
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Ispuštanje i izgaranje vodika
Shapiro-Moffette dijagram pokazuje mogućnost zapaljenja u ovisnosti
o koncentraciji vodika, zraka i pare
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The Fukushima Daiichi Incident
2. Accident progression
Unit 2
 Hydrogen burn inside the reactor
building
 Probably damage to the
condensation chamber
(highly contaminated water)
 Uncontrolled release of gas from
the containment
 Release of fission products
 Temporal evacuation of the plant
 High local dose rates on the plant
site due to wreckage hinder further
recovery work
No clear information's why Unit 2
behaved differently
The Fukushima Daiichi Incident
2. Accident progression
Current status of the Reactors
 Core Damage in Unit 1,2, 3
 Building damage due to various
burns Unit 1-4
 Reactor pressure vessels flooded
in all Units with mobile pumps
 At least containment in Unit 1
flooded
Further cooling of the Reactors by
releasing steam to the atmosphere
Only small further releases of
fission products can be expected
Posljedice plavljenja kontejnmenta
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NAPREDOVANJE TEŠKE NESREĆE
događaj
Tipična vremena (hr)
Inicijalni kvar
0.0
Faze akcidenta
1. Gubitak rashladnog sredstva
Gubitak rashladnog sredstva
2.0
Otkrivanje jezgre
Oksidacija Zr
2. Pregrijavanje jezgre i taljenje
Oštećenje obloge goriva
Taljenje jezgre
Premještanje taljevine
4.0
Oštećenje reakt. posude
3. Gubitak integriteta reaktorske posude
4. Odziv zaštitne zgrade
Ostaci rastopljene jezgre izlaze iz
reakt. posude u zaštitnu zgradu
Poplavljivanje ostataka
rastopljene jezgre
Porast tlaka u zaštitnoj zgradi zbog
isparivanja
Interakcija rastopljene jezgre s
betonom
Porast tlaka u zašt. zgradi zbog
isparivanja i nekondenzibilnih plinova
Oštećenje zaštitne zgrade
35.0
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Važnije temperature
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Tipična konfiguracija rastaljene jezgre
(TMI iskustvo)
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Sekvenca događaja u NE TMI-2 i
konačno stanje jzgre
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Inicijalni proračuni za reaktor 1
Depressurization and
termination of emergency water
injection
Peak core temperature (K)
{U-Zr}-O2 melting
Hydrogen generation rate –
(kg/s)
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Bazen za istrošeno gorivo
Gorivni elementi na lokaciji NE
Reaktor
1
2
3
4
5
6
Jezgra
400
548
548
-
548
764
SFP
toplina
292
0.3 MW
587
1.0 MW
514
0.7 MW
1331
3.0 MW
946
4.5 MW
876
1.5 MW
Načini spremanja istrošenog goriva na lokaciji:
U bazenu za istrošeno gorivo svakog reaktora:
4546 FAs u trenutku nesreće
8310 FAs max kapacitet
U zajedničkom bazenu (12m x 29m x 11m):
6291 FAs (03.2010)
6849 FAs max kapacitet
Suho skladištenje:
408 FAs
Godišnje potrebno pospremiti:
700 FAs (procjena)
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Time to Heatup and Boiloff SFP Inventory Down to 3 Feet Above
Top of Fuel (60 GWD/MTU)
Zr + O2 → ZrO2 oksidacija na zraku (1.2 107 J / kg )
Zr + 2 H 2O → ZrO2 + 2 H 2 oksidacija u pari (5.8 106 J / kg )
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Vrijeme potrebno da se gorivo zagrije do 900 oC
(moguće ispuštanje radioaktivnosti) u zraku
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The Fukushima Daiichi Incident
4. Spent fuel pools
Spend fuel stored in Pool on
Reactor service floor
 Due to maintenance in Unit 4 entire
core stored in Fuel pool
 Dry-out of the pools
• Unit 4: in 10 days
• Unit 1-3,5,6 in few weeks
 Leakage of the pools due to
Earthquake?
Consequences
 Core melt „on fresh air “
 Nearly no retention of fission
products
 Large release
The Fukushima Daiichi Incident
4. Spent fuel pools
Spend fuel stored in Pool on
Reactor service floor
 Due to maintenance in Unit 4 entire
core stored in Fuel pool
 Dry-out of the pools
• Unit 4: in 10 days
• Unit 1-3,5,6 in few weeks
 Leakage of the pools due to
Earthquake?
Consequences
 Core melt „on fresh air “
 Nearly no retention of fission
products
 Large release
The Fukushima Daiichi Incident
4. Spent fuel pools
Spend fuel stored in Pool on
Reactor service floor
 Due to maintenance in Unit 4 entire
core stored in Fuel pool
 Dry-out of the pools
• Unit 4: in 10 days
• Unit 1-3,5,6 in few weeks
 Leakage of the pools due to
Earthquake?
Consequences
 Core melt „on fresh air “
 Nearly no retention of fission
products
 Large release
It is currently unclear what is
amount of released radioactivity
from SFPs 3 and 4
The International Nuclear Event Scale
INES
Unit 1-3
Unit 4
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Neka promišljanja
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Elektrana je pokazala zavidnu otpornost na potres
Projektna zaštita od tsunamija neadekvatna za doživljene uvjete
Teška oštećenja na električnoj i ostaloj infrastrukturi
Neadekvatne i nepravovremene akcije u uvjetima prolongiranog
gubitka svih vanjskih napajanja
• Uvjeti teške katastrofe na i van lokacije utječu na strateško
planiranje sanacije stanja
• Izraziti problemi s ispustom vodika - eksplozije
• Međusobni utjecaj blisko smještenih jedinica na lokaciji
• Propust sanacije stanja bazena za ING dok je to još bilo
jednostavno izvedivo
• Uglavnom pravovremeni potezi na nivou off-site planiranja u
slučaju nesreće
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Reference
•
Matthias Braun, The Fukushima Daiichi Incident, PEPA4-G,
AREVA–NP GmbH
• Teški reaktorski akcidenti, Sigurnost nuklearnih postrojenja, FER,
Zagreb
• Tribina HND, Europski dom, Zagreb, 31.03.2011.
• Duane Arnold, Fukushima Daiichi Nuclear Plant Event Summary
and FPL/DAEC Actions, NEXTera Energy
• Michael Buck, Modelling of the Late Phase of Core Degradation in
Light Water Reactors, IKE Stuttgart, 2007
• Ludger Mohrbach, Tohoku-Kanto Earthquake and Tsunami on
March 11, 2011 and Consequences for Northeast Honshu Nuclear
Power Plants, VGB PowerTech
• Boiling Water Reactor (BWR) Systems, USNRC Technical Training
Center
• Chris Allison, Status report on ISS/SDTP activities related to
Japanese reactor accident analysis
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Hvala na pažnji!
Davor Grgić, davor.grgic@fer.hr
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