Briefing
Nuclear Meltdowns:
Chernobyl, Three Mile Island
and Fukushima Daiichi
C
oncerns regarding the safety of nuclear energy, particularly after the
meltdowns at Three Mile Island and Chernobyl, have hindered its
continued development over the past few decades. However, increasing
energy demand and fears of climate change have led to
a “nuclear renaissance” in which states have
increasingly pursued nuclear power as a carbon-free
warming, and it emits numerous hazardous air
pollutants that likely result in thousands of deaths
annually. Furthermore, around the globe thousands of
energy source.1 Given the evolving nuclear crisis at the
Fukushima Daiichi nuclear plant, the future of nuclear
energy is once again in doubt because of concerns
about safety and health risks. When discussing the
potential hazards of nuclear power, it is useful to bear
in mind the cost of burning fossil fuels, such as coal.
The burning of coal is a primary contributor to global
coal miners die each year in mine accidents.2 Thus, the
death toll from fossil fuels is higher than that of nuclear
power.
CF-11-02-TC
This issue brief explores the nuclear meltdowns at the
Three Mile Island, Chernobyl and Fukushima Daiichi
plants.
THREAT CONVERGENCE | THE FUND FOR PEACE
Nuclear Meltdowns: Chernobyl, Three Mile Island and Fukushima Daiichi
Three Mile Island, United States
T
he incident at the Three Mile Island nuclear power plant, located near
Harrisburg, Pennsylvania, began on March 28, 1979. Three Mile Island’s
new Unit 2 reactor was operating at 97% power when a
restored and a massive release of radiation was averted.7
mechanical malfunction increased the temperature of the
primary coolant, triggering an automatic shutdown of the
Significant confusion and panic gripped the public during the
reactor.3 As pressure began to build within the reactor, a relief
Three Mile Island crisis, with government officials and the
valve opened. This valve should have closed when pressure
media speculating over whether a full-scale meltdown would
returned to normal levels, but it did not, and plant operators
received no signal indicating that the valve was still open. As
occur. The situation within the reactor had sufficiently
stabilized by the evening of March 28th. However, on March
a result, cooling water flowed out of the open valve, causing
30th, the plant’s auxiliary building released radiation in an
the reactor to overheat.4
effort to relieve pressure on the reactor and ensure that
coolant would continue to flow to the core, which increased
Operators were unable to properly diagnose the problem
public anxiety and scrutiny. Pennsylvania’s governor, Richard
because there was no instrument measuring the level of
coolant in the reactor core. Instead, the operators relied on the
L. Thornburgh, consulted with the Nuclear Regulatory
Commission and advised young children and pregnant
level of the pressurizer, which was high, and assumed that
women to evacuate areas within five miles of the plant.8
coolant levels were normal. Based on this reading, the
operators reduced the flow of coolant to the reactor,
exacerbating the problems of the overheating core.5
Despite the release of some radiation during the crisis, to date
no deaths or significant illnesses can be attributed to the crisis
at Three Mile Island. The crisis ranked 5 out of 7 on the
As the core continued to overheat, the zirconium cladding
encasing the nuclear fuel pellets ruptured and the pellets
International Nuclear Event Scale. The average increase in
radiation exposure to the surrounding population is believed
began to melt. However, the meltdown had not yet breached
to have been very low, potentially less than an individual
the walls of the containment shield, which would have led to a
would receive from an x-ray scan.9 However, this low level of
6
massive leak of radiation. Eventually, after a series of failed
attempts to stop a full meltdown, an operator decided to turn
exposure was only possible because the crisis was primarily
contained. Public outrage over the potential danger of nuclear
on the pumps, bringing coolant water back through the
power led to stricter federal regulation, increasing costs and
reactor to cool the core. Due to the lack of information about
what was really going on in the core, the decision was
contributing to the waning of nuclear power within the
United States.
effectively a stab in the dark. Nevertheless, stability was
Chernobyl, Ukraine
T
he Chernobyl disaster began on April 26, 1986, during a safety test prior to
a routine maintenance shutdown of the Chernobyl plant’s Unit 4 reactor.
The test sought to determine if enough energy could be
an extremely unstable state. Protocol called for the reactor to
generated to continue the cooling of the reactor if the station
lost power. Inadequate safety protocol, operator error, and a
be stabilized at approximately 700-1000 MWt prior to the test,
but power had fallen to 30 MWt before stabilizing at 200 MWt.
poor system design precipitated the disaster that followed.
To compensate, the operators withdrew the number of control
rods to eight, although the minimum Operating Reactivity
The test was largely deemed an electrical operation without
nuclear implications. Thus, the operators did not understand
Margin mandated fifteen rods.11 When the test commenced, a
massive energy surge caused fuel fragmentation and rapid
that the test could jeopardize the safety of the reactor.10 The
steam production, which damaged fuel channels, jammed
shutdown of the reactor commenced while the reactor was in
control rods, and quickly led to a steam explosion that
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Threat Convergence
Nuclear Meltdowns: Chernobyl, Three Mile Island and Fukushima Daiichi
released fissile materials. A second explosion followed
Europe. Vast portions of Ukraine, Belarus, and the Soviet
seconds later, ejecting graphite and fuel that caught fire,
contributing to the main release of radioactivity.12 The Unit 4
Union were evacuated, and as many as 336,000 people were
permanently resettled. Approximately 60% of the fallout is
reactor had no containment shell, so once the explosions
believed to have landed in neighboring Belarus.15 By July
occurred radioactive materials were immediately released into
1986, 22 plant workers and 6 firemen had died due to acute
the surrounding environment.13
radiation poisoning.16 Additionally, 112 plant workers and
emergency responders were diagnosed with acute radiation
Two workers were killed in the explosions. Over the next day
poisoning that was not fatal. As of 2006, 19 of those who
and a half, 200-300 tons of water per hour was injected into
what remained of the reactor core, although this was
survived radiation poisoning had passed away, but
apparently none of these deaths were due to radiation-related
discontinued to prevent the flooding of other reactors. Over
causes. The hundreds of thousands of individuals involved in
the next eight to nine days, helicopters dumped
approximately 5,000 tons of sand, lead, clay, boron and
recovery operations have also experienced a slightly higher
rate of leukemia and cataracts which may be attributable to
dolomite onto the burning core to put out the fire and limit the
radiation exposure.17 The surrounding population was also
14
release of radioactive materials.
impacted by the radiation fallout, although death toll
The accident at Chernobyl is considered the worst nuclear
approximations vary widely. According to the United Nations
Scientific Committee on the Effects of Atomic Radiation, milk
power disaster in history, ranked 7 out of 7 on the
was contaminated with Iodine-131 in the fallout zone. This
International Nuclear Event Scale. The fire from the graphite
and fuel released a plume of radioactive fallout that spread
contamination was primarily responsible for a large spike in
thyroid cancer in the surrounding population.18
across the region, impacting the Soviet Union and the rest of
Fukushima Daiichi, Japan
O
n March 11, 2011, a 9.0 magnitude earthquake struck off the eastern coast
of Japan’s largest island, Honshu, triggering a massive tsunami that
killed thousands, and
have occurred at reactors 1 and 2. In addition, the containment
substantially damaged infrastructure. The earthquake was the
largest recorded in Japan in 140 years and created a situation
vessel at reactor 3 is believed to have been damaged.
Although progress has been made in restoring electricity to
that the Fukushima Daiichi nuclear power plant, located on
the plant, radiation levels remain extremely high and several
the Japanese coastline, was not designed to handle.19 The
pumps may be damaged, ensuring that challenges will
nuclear plant’s sensors recognized the powerful earthquake,
which triggered an automatic shutdown of the plant’s
continue to hinder attempts to restore the plant’s normal
cooling operations.21
inundated coastal
communities,
reactors. Substantial power was needed to continue cooling
the reactors and spent fuel pools to prevent a meltdown.
However, the earthquake also knocked out main power to the
However, more radiation may have been leaked from the
spent fuel cooling ponds than the reactor cores. Spent fuel has
plant. With the loss of Fukushima’s primary power source,
an incredibly long half-life, thus making it dangerous for
backup diesel generators started and ran for just under an
hour before the tsunami hit the plant and knocked out this
thousands of years after its initial use in producing nuclear
energy. Once the fuel is spent, it is placed in on-site cooling
backup source of power. After the loss of the generators there
pools until it reaches a point where it will not overheat and
was insufficient power to fuel the plant’s cooling mechanisms.
melt, which would release dangerous levels of radiation. At
The crisis gradually escalated as the reactor and spent fuel
pools began to overheat.20
Fukushima, water levels in the reactor ponds became
depleted, causing the spent fuel to overheat and likely leak
radioactive
gas.
As
there
is
no
containment
shield
Seawater was pumped into the reactors in an attempt to cool
the cores. However, temperatures continued to rise and
surrounding the pools, the radiation would have been leaked
directly into the surrounding environment. On March 15,
pressure mounted, necessitating the release of hydrogen gas.
2011, the Unit 4 reactor pool caught fire and released
This led to explosions outside of reactors 1 and 3 that blew
hydrogen, likely resulting in the release of dangerous levels of
holes in the roof of the complex. Partial meltdowns, likely
leading to the release of radioactive materials, are believed to
radiation. Due to high radiation levels, emergency responders
attempted to refill the Unit 3 and Unit 4 pools from outside
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Threat Convergence
Nuclear Meltdowns: Chernobyl, Three Mile Island and Fukushima Daiichi
the facility using fire hoses and helicopters.22 To date, water
By the end of March 2011, the Fukushima Daiichi plant has
still needs to be pumped or sprayed into these pools in order
to cool them and prevent the leak of radiation.23
continued to release high levels of radiation, measured at 1000
millisieverts per hour. At this level, those exposed would be
vulnerable
to
temporary
radiation
sickness.26
The
Like all nuclear meltdowns, the damage from Fukushima
contaminated water which injured the three emergency
Daiichi will not be known for some time, although the death
toll from the crisis is expected to be far less than the
responders has slowed efforts to solve the crisis, and some of
it has leaked out to sea.27 Japan recently raised the rating of
devastation
tsunami.
the Fukushima crisis from 5 to 7 on the International Nuclear
Nevertheless, the nuclear crisis has triggered substantial fear
and apprehension amongst the Japanese people. The Japanese
caused
by
the
earthquake
and
Event Scale, the same ranking given to the Chernobyl disaster.
A ranking of 7 indicates “widespread health and
government has gradually expanded the scope of the
environmental effects” and the “external release of a
evacuation zone around the plant from a 12 mile radius to a 19
mile radius, covering approximately 139,000 individuals.
significant fraction of the reactor core inventory.”28 Japan’s
nuclear regulatory agency indicated that the amount of
However, the United States embassy has recommended the
radioactive materials released at Fukushima is approximately
evacuation of anyone within fifty miles of the plant, which
ten percent of the total released during the Chernobyl crisis.
would involve 2 million residents.24 Japanese officials have
urged citizens not to give their infants tap water in Tokyo and
However, an executive from Tokyo Electric Power Company,
which runs the Fukushima plant, indicated that radiation
surrounding areas after radioactive iodine was detected in the
leaks continue and the final total could eventually surpass
city’s drinking supplies.25 No cases of acute radiation
poisoning have been reported yet, although three workers
Chernobyl.29 Although the amount of radiation leaking from
the plant is likely declining, it appears as if the crisis at
have been hospitalized for radiation burns to their feet and
Fukushima is far from over.
legs when they stepped into radioactive water in the Unit 3
reactor.
References
For a full list of references from this briefing, please visit: www.fundforpeace.org/global/?q=cf-11-02-tc
About the Fund for Peace
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The Fund for Peace Publication CF-11-02-TC (11-04A) - Circulation: PUBLIC - Compiled by Ryan Costello
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Threat Convergence