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TRANSCRIPT
The Fukushima Daiichi AccidentBy Sergio Peraza
Fukushima Daiichi Nuclear Power PlantA brief description 1)
Fukushima Daiichi Units 1-4
Fukushima Daiichi Nuclear Power Plant construction started July 25, 1967
First reached criticality on Oc-tober 10, 1970On March 26, 1971, Unit 1 started its first commercial op-eration In 2011, there were six BWR units8 units were planned to be finished by 2017. Units 7 & 8 ABWR projects were cancelled in April 2011
1) Fukushima Daiichi. IAEA/PRIS. 2013
Fukushima Daiichi Acci-dent
A brief description
1) The Fukushima Daiichi Accident Report by General Direc-tor.. IAEA, 2013
Fukushima Daiichi Nu-clear Power Plant is lo-cated 260 km north of Tokyo.
14:46 earthquake 9.0 Richter Scale15:26 tsunami wave ar-rived
The epicenter of the Great East Japan earthquake and the nuclear power
plants nearby 1)
Friday March 11, 2011
Fukushima Daiichi AccidentUnits Status
1) The Fukushima Daiichi Accident Report by General Direc-tor. IAEA, 2013
2) Technical Volume 1/5 description and Context of the Acci-dent. IAEA, 2013
Units 1, 2, and 3 operating at full powerUnit 4 unloaded
Units 5 and 6 scheduled for main-tenance and refuel-ing
An aerial view of the Fukushima Daiichi NPP 1)
Unit
Power (MWe) Status2)
1 460 Operating
2 784 Operating
3 784 Operating
4 784 Outage
5 784 Outage
6 1,100 Outage
Fukushima Daiichi ReactorsBWR Characteristics
1) Public domain image by U.S. NRC
Water is used as both moderator and coolant
Water is allowed to boil in the core pro-ducing steam
Steam is directly fed to the turbine to gen-erate electricity (steam cycle)Control rods are in-serted from the bottom of the core
LWR: BWR Animated Diagram of Boiling Water Reac-
tor (BWR)1)
Fukushima Daiichi ReactorsBWR Evolution 1)
ECCS: Emergency Core Cooling SystemESBWR: Economic Simplified BWR
BWR Version
First Com-mercial
Operation Date
Representative PlantCharacteristics
BWR/1 1960Dresden 1
Initial commercial size BWRDual Cycle
BWR/2 1969
Oyster CreekPlants purchased solely on economicsLarge direct cycle Forced circulation Variable speed pumps for circulation flow control
BWR/3 1971
Dresden 2Internal jet pumps applicationImproved ECCS: spray and flood ca-pability
BWR/4 1972 Vermont YankeeIncrease power density
1) Boiling Water Reactor Simulator with Passive Sate Systems. User Manual, IAEA. October 2009
Fukushima Daiichi ReactorsBWR Evolution Cont. 1)
BWR Version
First Com-mercial
Operation Date
Representative PlantCharacteristics
BWR/5 1977Tokai 2Improved ECCSValve flow control
BWR/6 1978
CofrentesCompacts control roomSolid-state nuclear system protection system
ABWR 1996
Kashiwazaki-Kariva 6Reactor internal pumps Fine-motion control rod drives Advanced control room, digital and fiber optic technology Improved ECCS: high/low pressure flooders
ESBWR Under Review Natural circulationPassive ECCS
1) Boiling Water Reactor Simulator with Passive Sate Systems. User Manual, IAEA. October 2009
ECCS: Emergency Core Cooling SystemESBWR: Economic Simplified BWR
Fukushima Daiichi ReactorsBWR Evolution Cont. 1)
1) Fukushima Dai-ichi Units 1-6 U.S.NRC May, 2012
Drywell
Suppression Chamber
Drywell Head
Typical Volumes
Drywell: 1.2 million galTorus Air: 0.9 million galTorus Water: 0.8 million gal
Fukushima Daiichi ReactorsBWR Construction
Reactor Pressure Vessel Dimensions
70 feet tall18 feet inside diameter 7 inch thick carbon steel
1) Fukushima Dai-ichi Units 1-6 U.S.NRC May, 2012
Fukushima Daiichi ReactorsBWR Reactor Assembly
Two phases:
Steam generation occurs in a direct cycle with steam separators and dryers in-side the reactor pressure vessel. Operating tempera-ture is 288°C; steam pres-sure ~ 7 MPaThe reactor (steam dome) pressure is controlled by turbine inlet valves and turbine bypass valves
BWR/6 Reactor Assembly 1)
1) U.S. NRC, General Electric, Sandia Laboratories
a sub-cooled liquid phase in the non-boiling region
saturated steam-water mixture in the boiling region
https://www.youtube.com/watch?v=i92VHLRUGeE
1) Battle to stabilize the Fukushima Daiichi reactors. Joseph Miller. March 30, 2011
The core: fuel bundles (assemblies) contain fuel rods ar-ranged in a N × N square lattice, with enriched uranium fuel ~ 2% to 5% U- 235 2).
Fukushima Daiichi ReactorsBWR Fuel assemblies 1)
Unit 1: 400 as-sembliesUnits 2-5: 548 as-sembliesUnit 6: 740 as-sembliesEach assembly has 72 fuel rods con-taining the ura-nium oxide fuel within zirconium alloy cladding
2)http://www.tepco.co.jp/en/nu/fukushima-np/outline_f1/index-e.html
https://www.youtube.com/watch?v=6LIu7bhRDXE
BWR Control Design 1) Fukushima Daiichi Reactors
1) ABWR Seminar-Reactor, Core & Neutronics LE Fen-nern April 13, 2007
Fukushima Daiichi Reactors
1) Dynamic Behavior of BWR Massachusetts Institute of Technology Department of Nuclear Science and Engineer-ing. Class of Engineer-ing of Nuclear Systems
BWR Power Control 1)
Power controls: control rods and recirculation flow controlControl rods control the
power level using com-pacted boron carbide
The recirculation flow is con-trolled by a change in water density using a pump
The recirculation flow is controlled by a change in wa-ter density using a pump
BWR Control Rods 1) Fukushima Daiichi Reactors
1) Dynamic Behavior of BWR Massachusetts Institute of Technology Department of Nuclear Science and Engi-neering. Class of Engineering of Nuclear Systems
Fukushima Daiichi ReactorsBWR Power Control
Control rods control power level using compacted boron carbide
1) BWR Description. Jacopo Buongiorno. CANES.
Control Blade 1) Four Bundle Array 2)
2) ABWR Seminar-Reactor, Core & Neutronics LE Fennern, 2007
Power in fresh fuel assembly of conventional de-sign as adjacent control rod is withdrawn toward
bottom1)
1) BWR/6 General Description of a Boiling Water Reactor. GE Nu-clear Energy
Fukushima Daiichi ReactorsBWR Power Control
Control rods control power level using compacted boron carbide
Systems for cooling the coreUnit 1
Isolation condenser 1)
1) The Fukushima Daiichi Accident Report by General Direc-tor.. IAEA, 2013
Unit 2-6 Systems for cooling the core
Reactor core isolation cooling 1)
1) The Fukushima Daiichi Accident Report by General Direc-tor.. IAEA, 2013
Fukushima Daiichi ReactorsBWR
Boiling water reactors at Fukushima Daiichi NPP 1)
1) The Fukushima Daiichi Accident Report by General Direc-tor.. IAEA, 2013
Earthquake Scenario The development (History)
Earthquake at 14:47
When the earthquake hit the coast, control rods were in-serted into the reactors, but temperature and pressure in-creased due to the decay heat.Off-site power was lost
Emergency Diesel Generator (EDG) turned on automatically. On-site power was activated
1) The Fukushima Daiichi Accident Report by General Di-rector.. IAEA, 2013
Unit 1 at Fukushima Daiichi NPP 1)
Tsunami Scenario The development (History)
Tsunami at 15:27
The EDG was dis-abled; on-site power was lost
Waves went over the sea wall (designed for 4.5m), flooding the lower part of the plant.
Unit 1: Operators unable to operate the IC (cooling rate)
Units 2 and 3: RCIC designed to op-erate for 8 h. It just cooled down some of the steam.
Units 1-5 experi-enced station
blackout during the first 10-15 minutes after the flooding
Variation of tsunami wave impact, runup1)
1) Coastal Engineering Committee Of Japan Society Of Civil Engi-neers, The 2011 off the Pacific coast of Tohoku Earthquake In-formation (30 March 2012), Coastal Engineering Committee, JSCE
https://www.youtube.com/watch?v=vggzl9OngaM
Meltdown Scenario The development (History)
Meltdown Scenario Units 1, 2, and 3
Water evaporated
Temperature increased to 2300°C
Fuel was exposed
Radioactive steam
Core melted to the bottom of the vessel
1) https://www.youtube.com/watch?v=YBNFvZ6Vr2U
Meltdown Scenario for Units 1-3 1)
Estimated conditions of the RPVs and PCVs of Units 1–3 February 2014
Meltdown Scenario The development (History)
Meltdown Scenario Units 1, 2, and 3
RPV: Reactor Pressure VesselPCV: Primary Contain-ment Vessel
ExplosionsThe development (History)
Operators decided to release gas into the atmos-phere Hydrogen leakage occurred through pass-ways and accumulated into the reactor building Reactor buildings for Units 1, 3, and 4 exploded due to the con-centration of hydrogen
H formation 2)
ExplosionsThe development (History)
Unit
Amount, Kg
1 890
2 460
3 810
Amount of H gen-erated1)
1) Yanez J, et al., An analysis of the hydrogen explosion in the Fukushima-Daiichi accident,International Journal of Hydrogen Energy (2015), http://dx.doi.org/10.1016/j.ijhydene.2015.03.154
The main sources of hydrogen are the oxidation of Zircaloy by steam, the radiolysis of water, the reaction between water and boron car-bide and the interaction of the molten core with the concrete of the contain-ment
2) https://www.youtube.com/watch?v=YBNFvZ6Vr2U
ExplosionsUnits 1-4
https://www.youtube.com/watch?v=YBNFvZ6Vr2U
https://www.youtube.com/watch?v=YarjI1FwsuA
http://skeptics.stackexchange.com/questions/9522/is-fukushima-reactor-no-4-on-the-verge-of-catastrophic-failure-that-will-destro
Spent fuel poolUnits 1-4
All units had lost their cooling system.
Unit 1 contained very little spent fuel
Unit 4 contained the amount of 3 reactor cores: 1535 spent fuel assemblies Helicopters dropped sea water and fresh water was sprayed by water cannon trucks
A visual inspection by remote controlled camera has shown no significant damage to the used fuel pond of Fukushima Daiichi unit 4http://www.world-nuclear-news.org/RS_No_significant_damage_to_fuel_at_Unit_4_3004111.html
Surveying of the Area
Radiation dose rate mea-surement of nearly 12 mSv/h was recorded at the main gate at 09:00 on 15 MarchResidents within a 20–30 km radius of the Fukushima Daiichi NPP were required to take shel-ter indoors.Atmospheric release of I-131 was estimated to be 100-500 PBq Cs-137 was in the range of 6-20 PBq
The Fukushima Nuclear Accident and Crisis Management, 2012
Post Fukushima Daiichi NPP Accident
Lessons Learned
Mitigation Strategies: to enhance the capability to maintain plant safety during a prolonged loss of electrical power
http://www.nrc.gov/reactors/operating/ops-experience/japan-dashboard/mitiga-tion-strategies.html
The mitigation strategies are ex-pected to use a combination of cur-rently installed equipment (e.g., steam-powered pumps), additional portable equipment that is stored on-site, and equipment that can be flown in or shipped in from support centers
Post Fukushima Daiichi NPP Accident
Lessons Learned
Containment Venting System: to provide a re-liable hardened containment vent system for boiling water reactors (BWRs) with Mark I or Mark II containment designsThe NRC issued an order on March 12, 2012 requiring all U.S. nuclear power plants with the Fukushima-style con-tainment design to install a reliable, hardened vent that can remove heat and pressure before potential damage to a re-actor core occurs. This not only helps preserve the integrity of the containment building, but can also help delay reactor core damage or melting
The NRC issued an order on March 12, 2012 requiring all U.S. nuclear power plants to install water level instrumenta-tion in their spent fuel pools. The instrumentation must re-motely report at least three distinct water levels: 1) normal level; 2) low level but still enough to shield workers above the pools from radiation; and 3) a level near the top of the spent fuel rods where more water should be added without delay
Spent Fuel Instrumentation: to provide a reli-able wide-range indication of water level in spent fuel storage pools
http://www.nrc.gov/reactors/operating/ops-experience/japan-dashboard/mitiga-tion-strategies.html
Post Fukushima Daiichi NPP Accident
Lessons Learned
Flooding Hazard Reevaluation: to reanalyze potential flooding effects using present-day information to determine if safety upgrades are neededSeismic Reevaluation: to reanalyze potential seismic effects using present-day information to determine if safety upgrades are needed
Plant Walkdowns of Seismic and Flooding Protection Features: to inspect existing plant protection features against seismic and flood-ing events and correct any degraded condi-tionsEmergency Preparedness – Staffing and Communications: to assess staffing needs and communications capabilities to effectively re-spond to an event affecting multiple reactors at a sitehttp://www.nrc.gov/reactors/operating/ops-experience/japan-dashboard/mitiga-tion-strategies.html
Post Fukushima Daiichi NPP Accident
Lessons Learned
Station Blackout Mitigation Strategies: the eventual rule will ensures that if a plant loses power, it will have sufficient procedures, strategies, and equipment to cope with the loss of power for an indefinite amount of timeOnsite Emergency Response Capabilities: The NRC is rewriting its rules to strengthen and integrate the various emergency response ca-pabilities. The Mitigation of Beyond Design Basis Events rulemaking will establish stan-dards that ensure the plants can smoothly transition between the various procedures, keeping the plants' overall strategies coher-ent and comprehensive
http://www.nrc.gov/reactors/operating/ops-experience/japan-dashboard/mitiga-tion-strategies.html
Post Fukushima Daiichi NPP AccidentMore Lessons Learned
Design and Equipment
Equipment required to respond to a long-term loss of all AC and DC power and loss of the ultimate heat sink should be conveniently staged, protected, and maintained such that it is always ready for use if neededPlant modifications may be needed to ensure critical safety functions can be maintained during a multi-unit event that in-volves extended loss of AC power, DC power, and the ultimate heat sink
Post Fukushima Daiichi NPP Accident
Lessons Learned Sum-mary
http://www.nrc.gov/reactors/operating/ops-experience/japan-dashboard/mitiga-tion-strategies.html