Der Reaktorunfall von Fukushima - Ursachen, Hintergründe und Konsequenzen - F. Schäfer, P. Tusheva, S. Kliem Institut für Sicherheitsforschung - HZDR
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Der Reaktorunfall von Fukushima
Ursachen, Hintergründe und Konsequenzen
© TEPCO (Tokyo Electric Power Company)
F. Schäfer, P. Tusheva, S. Kliem
Institut für Sicherheitsforschung
HZDR Kolloquium, 21. November 2011The Tohoku (Honshu) Earthquake/Tsunami
11th of March 2011 at 14:46 h local time (6:46 h CET)
• Initiating event: earthquake magnitude 9.0 (design basis 8.2), epicenter
~150 km (east) from Sendai
• Water displacement: ~40 km3
• Maximum height of the tsunami
wave: 23 m
• Approx. 40-50 min later, several
waves up to 14 m high drown the
site of Fukushima NPP
• Impact: tragedy, destruction of the
surroundings (incl. electrical grids)
• Approximately 27000 people died
and 320000 temporarily evacuated
Source: atw 56/2011
Source: Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), VGB Power Tech,
TEPCO, Japan Nuclear Energy Safety Organization (JNES), Nuclear and Industrial Safety Agency (NISA)
Slide 2
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Tohoku (Honshu) Earthquake/Tsunami
Earthquake/Tsunami has led to:
• Shut-down of nuclear power plants at 4
sites (11 units) and numerous
conventional power plants Onagawa
• Loss of external power supply and finally
total loss of AC power supply at Fukushima Daiichi
Fukushima Daini
Fukushima I NPP (Station Blackout)
• Severe damages at 4 reactor units, Tokai
partial core melt, release of radioactivity
TEPCO
Source: VGB
The Fukushima accident and its progression into a severe one was
mainly caused by the consequences of the tsunami.
Slide 3
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Fukushima I Nuclear Power Plant
Overview Source: TEPCO
Unit 5 Unit 6
Protection
wall
Cooling water
Unit 4 Unit 2
Unit Reactor / Cont. Manufacturer Put into operation Power
Unit 3 Unit 1
1 BWR-3 / Mark-I GE 1971 460 MWel
2 BWR-4 / Mark-I Toshiba,GE 1974 784 MWel
3 BWR-4 / Mark-1 Toshiba 1976 784 MWel
4 BWR-4 / Mark-1 Hitachi 1978 784 MWel
5 BWR-4 / Mark-1 Toshiba 1978 784 MWel
6 BWR-5 / Mark-1 Toshiba,GE 1979 1100 MWel
Operating by TEPCO Periodic inspection outage (at time of the earthquake)
Slide 4
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deBackground Information
Boiling Water Reactor
Reactor building Control rods for
reactor shut down Turbine
Reactor
Spent fuel
neutron (therm.)
storage tank
U-235 Generator
U-236 Containment
Barium Krypton
Heat
removal
A B Condenser system
neutrons (fast)
Feed water
system
Source: E.ON
Nuclear Fission Heat Turbine Generator Electricity HWZ ca. 30 a
In an abnormal transient or accident the reactor will shut down
automatically injection of the control rods.
But, after shut down the fission products continue to produce heat …
Slide 5
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deBackground Information
Decay Heat Removal
Containment Reactor building /
After reactor shut down the residual thermal turbine hall
power (decay heat) has to be removed!
Containment
Reactor isolation valve
Steam
Heat source Heat sink
Turbine
Condenser
Fukushima I Units 2-4 - Pel = 784 MW Pth = 2350 MW Relief/safety
valve
Water
Radioactive decay (decay heat) Feedwater or
storage tank
Turbine Residual heat
driven removal
pump Pressure suppression
~6 % after shut down, ~2.5 % after 1 hour
and continuously decreasing … pool
A closed cycle for heat removal and water injection into the reactor pressure vessel is
an essential requirement to cool the reactor core!
After a Station Blackout only systems powered by batteries or those working on passive
principles are available!
Slide 6
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Fukushima I Nuclear Power Plant
Overview
Reactor building Reactor service floor Spent fuel
storage pool
Browns Ferry Nuclear Power Plant, Alabama
BWR with 1065 MWel., General Electric (GE)
Source: Wikipedia / Tennessee Valley Authority
Biological
shield (Primary)
Containment
Wetwell
(pressure
suppression
pool, KOKA)
Source: Wikipedia
Slide 7
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Fukushima I Nuclear Power Plant
Components and Safety Systems
Slide 8
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Fukushima I Nuclear Power Plant
Components and Safety Systems
Contain- N2
ment Wetwell
(KOKA)
Slide 9
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Fukushima I Nuclear Power Plant
Components and Safety Systems
Reactor building
Spent fuel storage pool
Contain- N2
ment Wetwell
(KOKA)
Slide 10
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Fukushima I Nuclear Power Plant
Components and Safety Systems
Reactor building
Spent fuel storage pool
Spent fuel storage
pool cooling Isolation
M
Condenser
Core cooling systems
(active / passive)
Contain- N2
ment Wetwell
(KOKA) Wetwell cooling and
Auxiliary cooling
Slide 11
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Fukushima I Nuclear Power Plant
Components and Safety Systems
Reactor building
Spent fuel storage pool
Spent fuel storage
pool cooling Isolation
M
Condenser
Core cooling systems
(active / passive)
Contain- N2
ment Wetwell
(KOKA) Wetwell cooling and
Auxiliary cooling
G
Emergency power supply
(Network supply,
Emergency diesel
generators)
Slide 12
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Fukushima I Nuclear Power Plant
Components and Safety Systems
Reactor SCRAM
Reactor building
Containment-Isolation
Turbine trip
Spent fuel storage pool
Spent fuel storage
pool cooling Isolation
M
Condenser
Pressure limitation/
Pressure reduction Core cooling systems
(active / passive)
Contain- N2
ment Wetwell
(KOKA) Wetwell cooling and
Auxiliary cooling
G
Emergency power supply
(Network supply,
Emergency diesel
generators)
After SCRAM the emergency core cooling system and the auxiliary cooling system must cool the reactor core!
Slide 13
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Fukushima I Nuclear Power Plant
Residual Heat Removal / Core Cooling Systems
Depressurization
(Venting)
Condensate Active systems:
Turbine driven storage tank
Condensation
pool
pumps (HPCI) • Low pressure injection
system (core spray system)
• Low pressure coolant
Feedwater injection system (LPCIS),
special mode of operation for
„Isolation
Condenser“ Core spray system RHR-system
• Residual heat removal (RHR)
system
N2
Passive systems:
Main • High pressure coolant
Safety and circulation
loop
injection system (HPCIS),
relief valves
pumps powered by steam
turbines
• Passive heat removal from
Boron-injection RHR the core (1 isolation
system condenser) on Unit 1
• Reactor core isolation cooling
system (RCICS), powered by
Pressure suppression pool (PSP) steam turbines
PSP cooling system !
Source: Gesellschaft für Anlagen und Reaktorsicherheit (GRS mbH)
Slide 14
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Accident
After the earthquake Units 1-3 were automatically shut down by the reactor
protection system, Units 4-6 were in periodic inspection outage.
• Reactor shutdown and turbine trip loss of house load power supply
• Loss of external power supply (damage to
Reactor
electrical grids, shut down of other plants) Steam
• Containment isolation
Relief/safety
valve
• Start of the emergency diesel generators Water
• Start of the emergency core cooling
systems (active + passive*) PSP
• Depressurization of the reactor circuit and
decay heat removal to the pressure Turbine Residual heat
removal
driven pump
suppression pool +
Active emergency
core cooling
Before the tsunami has drown the site, Fukushima I NPP was in a stable
and safe state.
* Isolation condenser had been disconnected very early (not the best idea)!
Slide 15
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Accident
Tsunami waves after ~40-50 min
Flooding of the diesel generators / the batteries
Flooding of the essential service water building cooling the generators
Loss of emergency power supply in Units 1-5
Source: atw 56/2011
Reactor building Consequence of the tsunami:
Failure of the diesel generators and
Failure of the cooling systems
∼ 40m
Turbine building Site level 10 m (13 m Daini) Tsunami
14m
Protection wall
Venting duct 5.7m (5.2m Daini)
See level
Cable duct
Intake
Emergency diesel generator
Contaminated water
Slide 16
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Accident
• Simultaneous occurrence of external hazards and multiple failures of safety
systems in neighboring units has lead to:
Total loss of power supply and a long-term Station Blackout
Reactor
• For a limited time core cooling by
remaining ‘passive’ systems was available
Relief/safety
and effective (turbine driven pumps) valve
• Failure of the battery supported systems
of Units 1-3 (measurement systems, core
PSP
cooling systems, valves)
• Decreasing reactor water level leads to
Turbine Residual heat
increasing temperatures and later on to driven pump removal
+
core damage Active emergency
core cooling
• Emergency measures to feed the reactor and to depressurize the reactor
circuit / the containment were not effective or performed with delay
Source: www.grs.de
Slide 17
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Accident
• Core damages of Unit 1-3; release of H2 caused by Zr-water-reaction (the
reactor cores of Units 1-3 partly melted in the first three days!)
• Pressure reduction and venting to reduce the load to the containment
• Hydrogen explosion at the upper part of the reactor building of Unit 1+3,
explosion inside of the containment of Unit 2 and explosion at Unit 4
• Injection of borated and unborated (see-) water in the reactor and in the
containment; use of mobile pumps, helicopters, water cannon trucks …
Source: TV
Source: Spiegel Online / AFP/ JIJI PRESS
Core, pressure suppression pool and
spent fuel cooling, ex-vessel cooling
of the reactor pressure vessel
Slide 18
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Accident
Units 1-3, Main Events
Accident sequence following tsunami
Unit 1 Unit 2 Unit 3
Loss of AC power + 51 min + 55 min + 52 min
Loss of cooling + 1 hour + 71 hours + 36 hours
Water level down to top of
+ 3 hours + 74 hours + 37 hours
fuel
Core damage starts + 5 hours + 87 hours + 62 hours
Fire pumps with fresh water + 15 hours + 42 hours
+ 24 hours + 87 hours + 68 hours
Hydrogen explosion
service floor suppression chamber service floor
Fire pumps with seawater + 28 hours + 78 hours + 46 hours
Off-site electrical supply + 10 days
Fresh water cooling + 12-13 days
Source: http://world-nuclear.org/info/
Slide 19
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deThe Accident
Measurements
! ! ! !
Many instruments failed, data could not be downloaded and accessed remotely to assist
diagnosis and remedial action.
Slide 20
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deConsequences
Source: TEPCO
INES Classification
International nuclear
and radiological event
scale (INES, IAEA)
Slide 21
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deConsequences
Source: TEPCO
Slide 22
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deConsequences
Source: TEPCO
Unit 1 from above Unit 1 South direction
9th of September 2011 8th of October 2011
Slide 23
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deConsequences
Source: TEPCO
Unit 3 Unit 3 from above
29th of September 2011 24th of September 2011
Slide 24
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deConsequences
Radiation in the Environment
• Radioactive Cs detected in air
samples 20 km beyond from the
power plant (09.2011)
• I, Cs, Sr in the environment (air,
soil, river, drinking water, …)
• Soil: Pu-238, Pu-239, Pu-240
• Doses of 12 mSv/h outside
(release by explosion,
depressurization, fire)
• Units 1-4 high values (500 mSv/h)
and highly contaminated water
• In Germany for personnel:
20 mSv/y (10 µSv/h at 2000 h
working hours)
Slide 25
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deStatus of the Fukushima I NPP (17.11.2011)
Unit 1 Unit 2 Unit 3
Core Damaged
Partially damaged and
RPV structural integrity Unknown Unknown
leaking
PCV structural integrity Damage and leakage suspected
Core cooling Cooling with the alternative system created after the tsunami
Nitrogen in the PCV gas injection into the PCV
RPV bottom temperature 37 °C (below 100 °C) 69 °C (below 100 °C) 69 °C (below 100 °C)
Temperature inside the PCV 39 °C 70 °C 59 °C
Most spent fuels not
Fuel integrity in SFP Unknown Unknown
damaged
SFP cooling Function recovered Function recovered Function recovered
All Units are shut down and safe cooling has been established.
Unit 4: - no fuels loaded, no damage
- SFP desalination of the pool water, most spent fuels not damaged
- SFP cooling: function recovered
Slide 26
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deTschernobyl and Fukushima Accidents Compared
• No containment • Containment
• Graphite moderated and water cooled • Water moderated and water cooled
• Uncontrolled power excursion • Hydrogen explosions following a station blackout
• Full destruction of the reactor building with loss of emergency core cooling
• Release of radio-nuclides, also Sr-90 and • Release of radio-nuclides with one magnitude less
Pu-isotopes than Tschernobyl (much less Pu)
• Accident was a consequence of design • Insufficient protection against external hazards
flaws and human errors
Slide 27
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deSevere Accident Management
Processes, Phenomena
• Core heat-up due to decay of fission products
• Core material oxidation (by steam)
In-vessel phase
• At about 900 °C steam-zirconium reaction, hydrogen generation
• Cladding failure, fission products release and transport (Cs-137, I-131)
• Liquefaction and melting of core materials core degradation loss of core
geometry slumping of the molten materials in the RPV lower plenum
Ex-vessel phase
• Containment: continuous release of H2, CO, CO2 and steam
• Hydrogen deflagration/detonation, challenges to the containment
Corium
Source: TEPCO
Source: CORA-Experiments at FZK, GRS
Slide 28
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deSevere Accident Management
Core Status at Fukushima I
TEPCO Analysis (23.05.2011):
• Bottom RPV temperatures: within 100 °C - 170 °C, stably cooled
• Water level top fuel: 3 hours after SCRAM
• Water level bottom fuel: 4.5 hours after SCRAM
• Pellets melted down to the RPV bottom rather soon after the tsunami Unit 1
• Central part started to melt: 16 hours after SCRAM
• Fallen into water in the RPV bottom
• Units 2 and 3 analysed cases: fuel also melted to some degree
Unit 3
?
Source: TEPCO
Slide 29
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deSevere Accident Management
Possible Countermeasures
• Reactor circuit depressurization (manual)
• Water injection into the reactor pressure vessel (from feed water system,
storage tanks, fire extinguisher system, …)
• Flooding of the reactor pressure vessel compartments
• Management of combustible gasses like H2 (recombiners, igniters)
• Management of containment temperature, pressure and integrity (containment
spray and venting systems)
Positive und Negative Aspects of Depressurizing the Containment
• Removes energy from the reactor building, reduction of the pressure
• Release of small amounts of aerosols (I, Cs), hydrogen (flammable)
Slide 30
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deSevere Accident Management
Countermeasures in the Preventive / Mitigative Domain
BWR PWR
Reactor circuit depressurization Primary side bleed and feed
Feeding from pressure suppression pool Secondary side bleed and feed
or feed water system/storage tank In-vessel retention by ex-vessel cooling
Slide 31
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deSevere Accident Management
Passive Safety Systems / Concepts
Source: AREVA NP
Loviisa (Finnland), WWER-440 ice-condenser EPR, Core catcher KERENA, Passive systems are
designed to cool the reactor for
approx. 3 days without electrictiy
Slide 32
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deLessons learned from Fukushima
• Consequences of natural hazards were obviously underestimated
• Insufficient protection of the emergency power and service water systems
• Protection of fuel assembly storage pools insufficient
• Safety review for Station Blackout and seismic evaluation needed
• Diverse power supply systems, diverse sources for water delivery
• Role of passive safety systems, they must work in a real passive manner and
without electricity to open valves
• Backup systems for reactor parameters monitoring
• Revision of Severe Accident Management Guidelines and countermeasures for
specific “rare” events
• Training
Slide 33
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deConsequences after the Fukushima Accident
Germany and the ‘Energiewende’
Before the Fukushima accident: ‘Atomgesetznovelle’:
• 17 NPPs in operation (11 PWR, 6 BWR) • 4 BWR-69 and 4 older PWR have been
• Total power: ~ 21.5 GWel shut down
• ~23% of the installed power and ~ 48% • In operation: 2 BWR-72 and 7 PWR of 3rd
of the base load and 4th generation
• ~150 Mio t/y CO2 emission avoided • ~ 8.5 GWel has been lost
• Shut down of remaining NPPs till 2022
• ‘Novellierung’ des EEG …
Slide 34
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deConsequences after the Fukushima Accident
Germany and the ‘Energiewende’
• BMU: Reduktion der Treibhausgasemissionen bis zum Jahr 2020 gegenüber 1990 um 40%
• EU-2020: 20% erneuerbare Energie, 20% Energieeinsparung, 20% weniger CO2!
• BMU: ‘EEG-Gesetz’ Erhöhung des Anteils der Stromerzeugung aus erneuerbaren Energien
bis 2020 auf mindestens 35%, bis 2030 auf mindestens 50%, bis 2040 auf mindestens
65% und bis 2050 auf mindestens 80%
Bundesnetzagentur, Pressegespräch vom 27. Mai 2011:
„Die historisch einmalige zeitgleiche Abschaltung von 5.000 MW Leistung und das längerfristige
Fehlen von 8.500 MW Leistung bringen die Netze an den Rand der Belastbarkeit. … Die
Übertragungsnetzbetreiber sind daher gezwungen, das Marktergebnis durch gesteigerten Einsatz ihrer
Handlungsinstrumente wie Schalthandlungen, gegenläufige Handelsgeschäfte (Countertrading, …,
Redispatch) und andere Eingriffe in den Kraftwerkseinsatz (Anweisung zur
Blindleistungsbereitstellung, Verschieben von Revisionszeiten, Bereitstellung von Kraftwerken aus der
Kaltreserve, Einspeisemanagement der Erneuerbaren Erzeuger) zu korrigieren.“
„Damit wird das eigentlich anzustrebende, wettbewerblich strukturierte Marktergebnis durch einen
mehr oder weniger zentral gesteuerten planerischen Ansatz ersetzt. Das ist energiewirtschaftlich
zweifelhaft, ökonomisch ineffizient und ökologisch schädlich, …“
„… Ebenso wenig besteht Anlass, von der Mahnung Abstand zu nehmen, vorerst keine weiteren
Kraftwerke auf Grund politischer Überlegungen vom Netz zu nehmen bzw. solche Schritte erst nach
sorgfältiger Abstimmung mit den Übertragungsnetzbetreibern und der Bundesnetzagentur
einzuleiten.“
Slide 35
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deConsequences after the Fukushima Accident
Germany and the ‘Energiewende’ Speicherkapazität derzeit ~40 GWh
(Stromverbrauch Mai 2011 ~1440 GWh
?
Source: Bundesnetzagentur
Source: Konsequenzen eines Ausstiegs aus der Kernenergie
bis 2022 für Deutschland und Bayern, Prognos AG
Slide 36
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deConsequences after the Fukushima Accident
Germany and the ‘Energiewende’
EU-Stresstest … 2012
Slide 37
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deVielen Dank für Ihre Aufmerksamkeit!
Quellen für weitere Informationen:
http://fukushima.grs.de/
http://www.vgb.org/tohoku.html
http://www.tepco.co.jp/en/nu/fukushima-np/index-e.html
http://world-nuclear.org/info/fukushima_accident_inf129.html
http://www.jaif.or.jp/english/
http://www.nisa.meti.go.jp/english/index.html
http://www.jnes.go.jp/english/index.html
http://www.iaea.org/newscenter/focus/fukushima/
Slide 38
F.Schäfer, P. Tusheva, S. Kliem | Institut für Sicherheitsforschung | http://www.hzdr.deYou can also read
