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Fukushima I
The World’s First Triple Meltdown
We will be covering a large amount of content in varying degrees of
complexity. Some information is indeed highly complex and detailed.
The volume and type of information may be overwhelming at times.
Unfortunately, nuclear operations are themselves extremely
complicated, and understanding what has happened and is
happening at Fukushima necessitates covering “foundation
information” to provide context and reference.
While every effort has been made to keep to a reasonable level of
detail, please understand that the decision to include information
was made based on its necessity to understand the “macro view”
whilst avoiding unnecessary detail. There are many levels of
“micro view” beyond what we will cover today.
Questions are very welcome.
Overview 2 2
In the interests of focus, this presentation’s primary interest is in
what happens within a nuclear power generation facility. Thus, we do
not address what happens downstream to the electricity that is
produced. The processes of distribution and consumption are
themselves highly detailed, and there was concern that this would
inject unnecessary confusion. Truly, the concepts behind the power
grid are a lesson all their own.
I will be happy to explain those concepts either individually or as a
standalone presentation.
Overview 3 3
Today, we will explore:
•How nuclear fission works, fuel is assembled, and a typical nuclear
power plant like Fukushima I is configured.
•The emergency systems used to stop a reactor in trouble
•What sequence of events led to the accidents at Fukushima I
•What has happened within the reactors
•The definition and implications of a nuclear meltdown
•What measures have been taken at Fukushima I and their efficacy
•What radioactive materials have been released, how much radiation
“is around,” and what it can mean to persons exposed
•The various misconceptions about Fukushima and nuclear
accidents in general
•The likelihood of a similar accident occurring here
Fukushima Facts 4
Construction started: 1967-1973
Commissioned (online): 1971-1976
Reactors: 6
Reactor type(s): Boiling water
Reactor manufacturer(s): GE,
Toshiba, Hitachi
Owner/Operator: Tokyo Electric
Power Co. (TEPCO)
Containment version: Mark I
Previous incidents (1971-2010): 3 Japan Ministry of Land, Infrastructure and Transport, 1975
BWR facts 5
•Typically abbreviated BWR
•Simplest design – “Tea kettle” principle
•Two coolant loops: one primary (core)
one secondary (cooldown)
•Uses light water as coolant
•Like any thermal power plant, including coal and
oil, water is heated to produce steam. That steam
is used to drive (spin) a turbine, which is
connected to a generator. The generator converts
that rotating mechanical energy into electrical
energy.
Fission primer 6
•Reactors generate heat, and thus energy,
through nuclear fission – the splitting of atoms.
•A nuclear chain reaction is made possible by the
fissile properties of nuclear fuel:
235U
236
141Ba
92Kr
Nuclear fuel primer 7
•U235 is the fission fuel of the reactor, but only
about 3%-4% of the fuel is
fissionable (3-4% purity)
•U238 outnumbers U235 significantly and does
not fission. Instead, it captures neutrons, slowing
the reaction to a manageable level.
•Neutrons must also be slowed to be useful; many
neutrons coming off of a fission reaction are
generally moving too fast to “stick” to another
U235. Thus, something to slow the neutrons,
called a moderator, is required. In many reactors,
this is a combination of zirconium alloy (which is
neutron-transparent) and water.
Fuels 8
•Most nuclear power plants rely on uranium oxide
fuel
•Uranium oxide powder is pressed with a
binding agent then fired in a kiln to produce a
non-porous ceramic with a high melting point
•Fukushima I Unit 3 was converted to use MOX
fuel.
•Short for Mixed OXide, MOX is a combination
of uranium and plutonium – usually from
dismantled nuclear weapons. The usual ratio is
7% plutonium to 93% uranium. MOX is very
toxic and highly dangerous in the event of an
accident.
Fueling 9
Uranium Oxide
Fuel
Pellet
Ceramic (UO2)
(Typical)
Typically
approximately 1cm
tall by 0.75cm
diameter
DOE
Zirconium Alloy
Cladding
(Zirconium, Tin, and
Niobium)
Fuel
Rod
(Sizes vary by design)
Fuel
Bundle
(Quantities
vary by
design)
DOE
Fuel
Group
(Quantity and configuration
vary by design)
Neutron-Absorbent
Control Rod
(typ. Boron Carbide)
Placement, configuration,
quantity and composition vary
by design.
Control rods
Core dynamics 17
Plant overview 18
VAPOR
CONDENSATE
COOLING
TURBINE
TOWER
CORE
PRIMARY LOOP SECONDARY LOOP
Physical layout 19
1. Reactor pressure vessel
2. Drywell
3. Suppression Pool
4. Containment Building
5. Spent Fuel Pool
(Supporting equipment such as
pumps, steam and water lines,
steam turbines, and generators
not shown.)
Defense in depth 20
CORE
Suppression Systems 21
Overview
Multiple systems exist to help
cool an overheating reactor. ADS
Collectively, they are called
the ECCS – Emergency Core Main Feed
Cooling System. HPCI LPCI
HPCS LPCS
They consist of a series of
SLCS
water sprays and injection
pipes.
In order, they are:
HPCI
HPCS
ADS
LPCS
LPCI
SLCS
HPCI 23
ADS
Essentially delivers
pressurized water via pipe to Main Feed
the pressure vessel. HPCI LPCI
HPCS
Goal: Increase reactor water LPCS
SLCS
level.
HPCS 24
ADS
A pressurized spray of water
above reactor vessel pressure Main Feed
used to directly cool the fuel HPCI LPCI
elements. HPCS LPCS
SLCS
Goal: Decrease fuel
temperature.
ADS 25
ADS
Pressure release valves and
piping used to vent Main Feed
pressurized steam and gas HPCI LPCI
from the pressure vessel into HPCS LPCS
the suppression pool.
SLCS
Goal: Decrease reactor
pressure to enable functioning
of low-pressure systems.
LPCS 26
ADS
Delivers direct spray of water
at low pressure onto fuel rods. Main Feed
Capable of higher flow rate HPCI LPCI
than HPCS. HPCS LPCS
SLCS
Goal: Decrease fuel
temperature.
LPCI 27
ADS
Delivers massive amounts of
water at low pressure into the Main Feed
pressure vessel. HPCI LPCI
HPCS
Goal: Flood the reactor core. LPCS
SLCS
This is the biggest response
possible. LPCI is designed to
literally flood the core and can
deliver at least 40,000 gallons
per minute of water to the
core…provided there is power
to the pumps.
SLCS 28
ADS
Injection of neutron absorbent
solution, such as boron, into Main Feed
the reactor to douse fuel HPCI LPCI
elements. HPCS LPCS
SLCS
Goal: Absorb free neutrons
and “poison” the reactor.
If the SLCS is activated, the
reactor is ruined and will
require replacement.
However, by this point, it’s
assumed that a critical failure
has already occurred.
SCRAM 29
Defined
In an emergency, reactors are designed to be able
to shut down quickly.
This procedure is called a scram.
Its purpose is to stop the nuclear chain reaction as
much as possible, isolate sections of the system,
and place the reactor into a safe configuration.
In the event of a scram, several things happen
quickly under automatic control.
Scram procedure 31
1. Main Steam Isolation Valve (MSIV) closes
Prevent exit of radioactive materials from
core. Turbines slow, generators stop.
2. Bypass line opens
Direct steam into heat exchanger for
condensation and cooling
TURBINE
3. Feedwater pumps to full
Direct steam into heat exchanger for
condensation and cooling CORE
4. Continue cooling core
Using external power, keep
feedwater pumps running to cool
the core.
Segue 32
As with all reactor systems, there are backups and
safeties even for the scram procedure. Safe reactor
design requires that, above all else, the reactor
should be able to reach a safe condition.
What went wrong 33
The two accidents
The Fukushima I incident actually involved two
separate, but linked, accidents:
1. Loss Of Outside Power (LOOP)
2. Loss Of Coolant Accident (LOCA)
Of these, it is the LOOP accident that is at the root
of the problem. From the LOOP, all other problems
followed.
LOOP steps 35
CORE
Scram
CORE
LOOP
CORE
Gen
CORE
Sequence overview
Electrical Grid Power Lost during earthquake due to
(Utility Power) damage.
Diesel generators
Destroyed by tsunami.
(Backup generators)
Designed to last only eight hours.
Lead-Acid Batteries
Exhausted. Unable to cool reactor
(Emergency batteries)
independently long-term.
No additional supplies
Cooling system failure.
available
LOCA 40
Decay heat 41
Many people do not understand how, if the control rods are
inserted and the reactor turned “off,” the reactor continues to
generate heat.
All fissile materials are radioactive, meaning they are
constantly undergoing decay and giving off particles. Some of
these particles are neutrons, which stimulate decay in other
atoms, and so on until all atoms decay down to lead.
Radioisotope thermoelectric generators (RTGs) use this heat
to produce power on space probes. Shown
here is a pellet of plutonium. It is glowing
red-hot from the heat of its own decay.
Reactor fuel is no different.
Decay heat problems DOE 42
Decay heat
contributed to
damage in two
locations:
The reactor cores
The spent fuel ponds
Reactors like
Fukushima 1-4 can
require up to
72,000 gallons of
water per day for
3-4 days to cool
decay heat.
Results 43
LOCA results
With core cooling systems offline, several things
began to happen:
1. Core fuel began to overheat
2. Zirconium-alloy fuel rod cladding began
overheating
3. Excess steam was generated as remaining
coolant boiled off, driving up core pressure
4. Hydrogen gas began to evolve and accumulate
Thus, each failure created additional problems
(a “cascade scenario”).
Hydrogen evolution 45
1. Fuel begins overheating due to
failure to remove decay heat by
inadequate or completely missing
coolant.
2. What coolant is left is rapidly
converted to steam. Pressure within
the vessel rises.
3. The overheated zirconium fuel
cladding reacts with the steam:
Zr + 2 H2O → ZrO2 + 2 H2 + Heat
Hydrogen gas is produced and
begins to accumulate.
Hydrogen sequence 46
Thus, hydrogen gas
was generated in the
core.
This caused the
pressure inside the
reactor’s pressure
vessel to rise to
dangerous levels,
beyond capacity of the
safety systems.
To avert a pressure
vessel rupture, the
decision was made to
vent steam from the
core
Contd 47
Hydrogen was vented
into the drywell, but
began to disperse
through the building
when flare systems
failed. As a buoyant
gas, it collected in the
space above the
reactor, within the
building shell but
outside containment.
This is where the first
hydrogen explosion
occurred, blowing the
top off of the building
shell.
Segue 48
This same sequence occurred at reactors 1, 2, and 3 at
Fukushima I.
Officially, hydrogen is the cause of all of the explosions at the
reactors. If this is true, it means that the Zircaloy fuel rod
cladding has been at extremely high temperature for days as
it continues to produce large amounts of hydrogen.
Consequently, this means that all three reactors have almost
certainly suffered meltdown.
Meltdown 49
Defined
The word “meltdown” is frequently misused by the public.
A meltdown does not mean a loss of containment, nor does it
mean an explosion. A meltdown can result in either or both of
these, but does not necessarily involve either.
In technical terms, a “meltdown” occurs when enough
thermal energy builds up in the core to cause the fuel
assembles to pass their melting point and begin
to melt down.
That’s all.
Of course, that is bad by itself, and is indicative of a severe
breakdown, but is not a catastrophe for the wider
environment.
TMI 51
NRC
JRC image
Cooling a Meltdown NRC graphic 52
Cooling a reactor that is undergoing meltdown is difficult. It’s
the mashed potato problem: since the fuel is now in a lump,
the outsides will cool while the inside remains very hot. This
can cause fuel to form globular lumps within the core.
Ideally, melted core components will be contained by the
reactor pressure vessel. Should pressure vessel integrity be
lost while the reactor is still under pressure, the molten core
material will be blown out with force through the breach.
There is no evidence that this has happened at Fukushima I,
but the possibility exists.
ECCS failures 53
With all of the combined ECCS components, it is difficult to
see how Fukushima I went out of control. However, a series
of failures each contributed to the accident.
HPCI Power failure,
Torus overheat
HPCS Power failure,
Suppression pool burst at Unit 3
ADS Operated manually
LPCS Insufficient water,
Power failure
LPCI Insufficient water,
Pump failures
SLCS Questionably effective
The seawater option 54
The choice, therefore, to use seawater to cool the reactors
showed just how serious the accident already was.
Using seawater in a nuclear reactor means that the reactor
will never again be useable; it must be decommissioned and
scrapped.
By injecting seawater into the cores from the start, TEPCO
effectively implied that there was no way to save the plant
from the start, and that preventing a much larger disaster was
the only possible course of action; keeping the plant
operational was impossible regardless of any other outcome.
Reactor 3 55
Much has been made over the status of the Unit 3 reactor,
especially in light of the recently discovered evidence of
serious, uncontrolled leaks. But little has been said as to why
this is such a concern.
Reactor 3 is nearly identical in design to the other three
affected units. Recall, however, that it uses an unusual fuel
called MOX.
MOX, which contains plutonium, is significantly more toxic
and radioactive that standard uranium oxide fuel. Therefore,
even a small leak from a MOX-fueled reactor can have more
dire consequences than larger leaks from normal reactors.
Segue 56
Unsurprisingly, most public attention focuses on the state of
the reactors. We are conditioned by news, movies, and
games to look at a reactor’s core as the most dangerous
component, and the source of all potential trouble.
Unfortunately, this isn’t the case.
Spent fuel 57
Defined
As previously mentioned, even when a reactor is shut down,
the fuel continues to produce heat due to normal radioactive
decay.
Fuel is typically removed from a reactor when it reaches an
established level of “burn,” meaning that only a given
percentage of its starting reactivity remains.
This fuel, called “spent fuel,” must be stored underwater for a
period of 1-5 years as decay heat continues to be produced.
This storage location is called a spent fuel pool, or SFP. The
amount of fuel, its storage conditions, and even the geometry
of the fuel bundles must all be carefully considered and
maintained to avoid criticality, or the resumption of a fission
chain reaction.
Fuel pools 59
DOE
TMI 60
The fuel stored in an FSP must remain immersed in water,
and that water requires constant cooling.
If the water is not cooled, it is heated to the boiling point and
begins to boil off. The steam will be radioactive.
DOE
Should the water boil down or leak
out to the point where the fuel
rods become exposed, the rods
will begin to overheat, just as they
would in the reactor. However, the
SFP is not sealed like the reactor
pressure vessel, meaning that
radiation can escape far more
easily.
Trying anything 61
Defined
The failure of the ECCS created a nearly unprecedented
problem.
Operators and engineers have tried numerous procedures to
bring the problems at Fukushima to a close. Each procedure
targeted a specific problem and had varying degrees of
success.
Pressure venting 63
Pressure Venting
Target: Reactor Cores, Units 1-3
Purpose: Relieve reactor core pressure, enable use of
low-pressure cooling systems
Success: Successful, but released radiation.
This was a classic Catch-22. On the one hand, high and
climbing core pressure not only prevented injection of
low-pressure water, but also threatened to burst
containment systems. But venting steam and gas
released radioactive materials. In the end, there really
was no other option, though; the pressure had to be
released or the risk of a far greater catastrophe
increased.
Seawater 64
Seawater Injection
Target: Reactor Cores, Units 1-3
Purpose: Adding water for cooling
Success: Not bad, better than doing nothing.
While the addition of seawater into the reactor cores
did drive temperatures down somewhat, it created new
problems. First, the reactors are now hopelessly
contaminated and cannot be reused. Seawater has also
increased corrosion problems and has destroyed
several cooling pumps. Additionally, accumulation of
salt left behind when the water evaporated has created
a new thermal blanket around the fuel, making cooling
more difficult.
Boric acid 65
Boric Acid Injection
Target: Reactor Cores, Units 1-3
Purpose: Introduce neutron absorber to “poison” fuel
Success: Unknown.
Boric acid solution has been part of the critical
response menu for decades, but has never really been
applied in a situation like this. There is currently no
hard data one way or the other for its effectiveness, but
it can’t hurt to add borax to the cooling water.
Aerial water 66
Helicopter Water Bombing
Target: Spent Fuel Pools, Units 3 and 4
Purpose: Cool unshielded, unwatered spent fuel
Success: Failure.
News reports implied that helicopters were dumping
water “into the reactors,” but the targets were the
spent fuel pools, which had gone dry in some cases,
and nearly so in others. Due to high radiation levels,
helicopters had to do their drops at high altitude, and
very little water actually hit the pools, not nearly
enough to do any good.
Water cannons 67
Water Cannons
Target: Spent Fuel Pools, Units 2-4
Purpose: Cool unshielded, unwatered spent fuel
Success: Somewhat, better than nothing.
Hitting the spent fuel pools with ground-based riot
police and fire-department water cannons is difficult at
best, but some water has gone into the cooling pools.
The problem now facing responders is that the SFP on
Unit 4 is not holding water, leading to the belief that the
pool has cracked or otherwise developed a leak.
Entombment 68
Entombment
Target: Reactor Buildings, Units 1-4 definite,
Units 5 and 6 possible
Purpose: Seal contaminated site
Success: Planned.
Ultimately, it is likely safest to construct a permanent
“sarcophagus” similar to the one shielding
Chernobyl-4 around, at minimum, Fukushima I 1-4.
Units 5 and 6 also sustained damage, but not nearly as
much. Their fate is open to question.
Segue 69
In the meantime, there have been significant releases of
radiation from the site.
These releases have come from various sources and have
been of varying compositions and levels of intensity.
Radiation releases 70
Defined
Radioactive materials escaped containment at Fukushima I in
three ways:
•Deliberate venting
•Containment failures/explosions
•Fire
Venting 72
When reactor pressure
climbed to dangerous
levels, the decision was
made to vent pressurized
steam and gas from the
reactor to avoid rupturing
containment.
This is similar to what was
done at TMI. But, while TMI
only vented once, all of the
Fukushima reactors have
vented many times each.
Containment failure 73
It is probable that the
series of explosions
(hydrogen or otherwise)
have damaged the
containment. Specifically,
the containment plugs may
be dislodged or damaged.
Additionally, Unit 3’s
suppression pool pressure
readings have been at
atmospheric for days,
indicating the suppression
torus has ruptured and
vented.
Fire 74
In almost all nuclear
accidents to date, the
worst contamination is
caused by fire. This
includes Chernobyl.
A fire in the reactor core is
unlikely unless the damage
is far more severe than
reported. Instead, fires in
the spent fuel are far more
likely, and have the
potential to be a far bigger
disaster by releasing huge
amounts of radioactive
material.
Segue 75
While this explains how radioactive materials may have
escaped, understanding what radiation is and what it does is
equally important to understanding the impact of these
events.
Types of Radiation 76
Ionizing radiation takes four forms.
Alpha particles (2 protons, 2 neutrons) Can be stopped by any
Alpha emitted at high speed. rudimentary shielding, including
α Causes severe genetic damage.
Particularly harmful when ingested.
human skin and plain paper.
Electrons and positrons emitted at Requires heavier shielding, but
Beta high speed. aluminum foil is sufficient.
β Can cause moderate genetic damage
and burns.
Can create incidental gamma radiation
(positron annihilation).
Electromagnetic radiation. Very high Very difficult to shield
Gamma energy. conventionally. Barium, lead,
γ Causes some genetic damage. and depleted uranium most
effective, but thick shielding is
often necessary.
Neutrons emitted at high speed. Water-dense materials make
Neutron Creates additional radiation emissions most effective shielding, but
upon striking matter. creation of incidental gamma
Destroys hydrogen bonds. radiation requires additional
protection.
Lethal at high levels.
Dosimetry
77
The SI unit for human radiation dosage is the Sievert (Sv).
Rather than reflecting just the sheer level of radioactivity, like
the Rad scale, the Sievert scale is concerned with radiation’s
effects on human bodies.
Sievert is also expressed using the metric equivalencies of
milli- (mSv, 10−3 Sv) and micro- (μSv, 10−6 Sv).
Thus:
1 Sv = 1,000 mSv = 100,000 μSv
In the United States, the rem is more commonly used though
it is not SI.
1 Sv = 100 rem
Dosage levels 78
The effects of radiation exposure increase with dose and
time:
•A short, low-level dose is often relatively non-harmful.
•A long, low-level dose can be mildly harmful.
•A short, medium-level dose can be mildly harmful.
•A long, medium-level dose can be hazardous.
•A short, high level dose is dangerous.
•A long, high level dose is deadly.
•A short, very high level dose is deadly.
Rad sickness 79
Acute Radiation Syndrome
Note: Effects are cumulative
Best / Worst
Dose ARS Prominent
Survival
Threshold Severity Effects Rates
1 Sv Nausea, headache, some present 100%
Mild
(1,000 mSv) “nuclear tan.” 95%
Bleeding (external and internal),
100%
2 Sv Moderate hair loss. At 3 Sv, skin loss
50%
begins.
Moderate shock, blood pressure
100%
6 Sv Severe instability, vomiting, diarrhea,
50%
disorientation.
Rapid incapacitation (less than
0%
8 Sv Extreme 10-15 minutes). Fever. Severe
Up to 48hrs
shock.
Convulsion. Seizure. Respiratory
30 Sv Off Scale arrest. Above 40 Sv, immediately 0%
fatal due to molecular disruption.
NIH, DOE
Dose samples 80
A banana (potassium) 0.1 μSv
Exposure
Single
Dental X-Ray 5 μSv
Chest CT Up to 18 mSv
Nuclear power plant
~1 μSv/year
emissions
Coal power plant
Exposure
~3 μSv/year
Ongoing
emissions
Average background
~2.5 mSv/year
radiation
Maximum Chernobyl level
4 Sv/min
(core area)
March 15 IAEA site 400 mSv/hr
reading (0.4 Sv/hr)
Fukushima
Exposures
Emissions during
10 mSv/hr
Unit 4 fire
Highest recorded 1 Sv/hr
radiation level (1,000 mSv/hr)
Types of Exposure 81
Radiative Contact Ingestion
α β γ α β γ α β γ
Principal Contaminants 82
In addition to simple particulates and chemical contaminants,
three radioactive particulates are confirmed to have escaped,
with the possibility of a fourth. Additionally, radioactive gases
have been vented.
The particulates are Iodine-131, Cesium-137, Strontium-90,
and potentially Plutonium-239.
I-131 83
Release
Confirmed
Beta emitter
Half-life: 8 days
Effects
Settles in thyroid, causing malignancy
or necrosis (in high doses). Higher risk for children.
Found In
Leafy vegetables (spinach), tap water
Preventive Measures
Iodine therapy (tablets)
CS-137 84
Release
Confirmed
Beta emitter
Half-life: 30.17 years
Effects
Uniform body distribution, with slightly higher concentrations
in muscles. Can result in malignancy and radiation poisoning
(radiation sickness) in significant doses.
Found In
Water, Particulate contamination
Mitigation Measures
Prussian blue chelation treatment
SR-90 85
Release
Confirmed
Beta emitter
Half-life: 28.8 years
Effects
Deposits in bones, similar to calcium. Causes leukemia
and/or osteomalignancies.
Found In
Water, Particulate contamination
Mitigation Measures
None.
PU-239 86
Release
Very Possible
New leaks discovered
Alpha emitter on March 25th
Half-life: 24,000 years ±200
Effects
Inhalation or ingestion causes extreme risk of malignancy.
Lung cancer most common.
Found In
Water, Particulate contamination
Mitigation Measures
None.
Gases 87
•Xenon: 133Xe and/or 135Xe, gaseous
•Nitrogen: Several possible isotopes, gaseous
•Argon: 37Ar and/or 39Ar, gaseous
Has affected 88
•Vegetables (spinach, broccoli, cauliflower, turnips)
•Milk
•Tap water
•Seawater
•Surrounding land (evacuation zone increased to 30km, “stay
indoors” zone changed to required
evacuation on March 25th.)
•Ships at sea – USCG inspections have found elevated
radiation levels on ships that were up to
400km away from the site…to the east.
What will happen 89
Intro
Even assuming that nothing else goes wrong from this point
on, there are several likely outcomes from the accidents at
Fukushima I.
Reactors 91
Condition: Contain core materials that have at
least partly if not completely melted
down. Badly contaminated by
seawater. Highly radioactive.
Possibly ruptured by repeated
explosions.
Probable Fate: Defueled as much as possible (if
possible at all), then abandoned.
The reactor pressure vessels are both full of highly
radioactive debris and are most likely damaged by
explosions. Even if they were not, seawater
contamination would prevent reuse.
Turbines 92
Condition: Almost certainly warped. Radioactive
contamination from normal operation.
Probable Fate: Abandonment.
Steam turbines operate at high speed. Consequently,
even the slightest warp (a thousandth of a millimeter)
can cause dangerous vibrations that can destroy the
turbine and injure workers.
To prevent this, hot turbines are kept on a “turning
gear” until they cool. Like a rotisserie, the turbines are
spun at low speed to prevent gravity-induced warpage.
Since there was no power to turn the turbines, they
simply stopped while hot, and have almost definitely
warped very badly.
Generators 93
Condition: Unknown. Possibly contaminated by
radioactive debris.
Probable Fate: Salvage.
The generators, housed in buildings separate from the
reactor cores, may have escaped significant damage
from the accident. Provided that they haven’t been
contaminated, they could be broken down for transport
elsewhere.
This assumes, however, that no earthquake, structural,
fire, or water damage has already affected them.
Units 5&6 94
Condition: Reportedly stable.
Probable Fate: Uncertain.
Units 5 and 6 were not in operation at the time of
the quake and tsunami, and have, according to
reports, remained stable since. Units 5 and 6 are
housed in a separate building from Units 1
through 4. Barring the discovery of damage
during inspection, and provided that the
buildings are not heavily contaminated, the
reactors may be put back into service.
On March 20th, the announcement was made
that the plant would be closed, but it was not
made clear if Units 5 and 6 were included in that
statement.
Site 95
Condition: Known to be heavily contaminated in
some places. Severe structural
damage to many buildings.
Probable Fate: Entombment.
Defueling of the TMI-2 reactor was possible due to the
nature and degree of damage. In all likelihood, it will be
prohibitively dangerous to try to defuel Fukushima I
Units 1-4.
Once the cores are cooled, they will probably be sealed
in concrete, then the buildings themselves sealed
inside steel and concrete containment structures.
This plan has had vocal approval from several
scientists, such as Michio Kaku.
Misconceptions 96
Condition: Emergency pumps, vehicles, and other
equipment have definitely been
contaminated.
Probable Fate: Decontamination where possible,
entombment where not.
Objects near high radiation become
radioactive themselves due to
neutron absorption. From the SL-1
explosion in Idaho in 1963 to
Chernobyl in 1986, the fact that
objects can be unsalvageably
contaminated has been encountered
repeatedly.
If decontamination is economically not viable, any contaminated
equipment will likely be sealed in with the reactors.
Misconceptions 97
Defined
Few things seem to scare the public as much as the specter
of radiation and nuclear power. Largely this is because it is
not well understood.
This breeds many misconceptions.
Reactor v bomb 99
≠
British Nuclear Group Ltd.
A reactor cannot go “mushroom cloud” even in the worst
accident.
Reactor fuel-grade uranium is 3-4% pure.
Weapons-grade uranium is 90+% pure.
Chernobyl
Fuel doesn’t have enough “kick.” 100
The Chernobyl disaster
was caused by a massive
steam/hydrogen explosion
within the reactor itself that
blew apart the core. This
started a massive graphite
fire that caused much of
the radioactive release
from the plant and
worldwide contamination.
Everybody carries a little Soviet Ministry of Electrical Power and Electrification
piece of Chernobyl within
them.
Ronald Reagan 101
It is true that the USS Ronald Reagan was forced to move by
higher-than-normal radiation levels detected aboard ship. It is
also true that the radiation was caused by fallout from
Fukushima I. However, while the average dose equaled the
dose expected over a course of a full month, the ship is not
hopelessly contaminated and the crew is not considered at
risk.
Can it happen 102
Defined
The short answer is yes.
We have a number of nuclear power plants in seismic and
tsunami hazard zones. Thus, the potential exists for an
incident at one of these plants.
However, most American nuclear facilities adhere to higher
safety standards for construction and containment.
Furthermore, all facilities are required to have evacuation
plans and alert systems online, understood, and regularly
tested.
Most significantly, though, nuclear power plants in this
country use much more durable construction, adding several
layers to the Defense In Depth model.
US defense in depth 104
Containment Methodology
Fukushima I US Standard
1. Fuel rod cladding 1. Fuel rod cladding
(Zircaloy shielding) (Zircaloy shielding)
2. Reactor pressure vessel 2. Reactor pressure vessel
(15cm 316L stainless steel) (15cm 316L stainless steel)
3. Containment structure 3. Primary containment
(Incomplete, 1m thick concrete) (2.5cm steel plate)
4. Containment structure
(1.2-2.4m thick concrete,
complete shell)
5. Missile shield
(1m thick concrete)
Reactor map 105
DOE
In the United States, the Department of Energy has
licensed 104 reactors for operation.
35 are boiling water reactors similar to those at Fukushima I.
The rest, 69, are pressurized water reactors, or PWRs, which
employ still greater levels of safety redundancy.
TMI 106
Ultimately, nuclear power has distinct advantages and
disadvantages as a power source.
108
The only carbon emissions are from transport of ore and fuel,
as well as some processing steps.
Nuclear power plants do not affect air quality, contribute to
smog, or induce respiratory problems.
The total footprint of nuclear power is small: uranium mines
are not strip mines like coal; uranium ore is not hazardous
when spilled like oil; and nuclear fuel refineries are compact.
Nuclear power plants typically need refueling infrequently,
and even then only a third of the fuel is replaced.
By using MOX fuel, the nuclear proliferation risk of
dismantled weapons can be reduced by redirecting weapon
materials into power generation.
109
Generally, nuclear power has the ability to be very beneficial.
110
However, accidents at nuclear power plants are
disproportionately serious when compared to other thermal
plants. While oil and coal plants can suffer fires, the risk of
long-term harm is slight.
Only rare accidents like the TVA coal fly-ash slurry spill in
2008 cause “lump sum” releases. Combustion at these plants
does release harmful materials, but not in continuously high
levels.
Additionally, waste products from thermal plants are more
easily handled and remediated than waste from nuclear
power. A typical reactor produces up to 30 tons of high-level
radioactive waste per year, mostly as spent fuel. Even with
the best, as-yet un-fielded technology, waste will require
isolation from the environment for up to 300 years.
111
With currently approved handling procedures, nuclear waste
must be isolated for up to ten million years as it progresses
through the various stages of nuclear decay.
112
