Science Progress (2014), 97(1), 72 – 86
The Fukushima Daiichi nuclear accident
CHRISTOPHER J. RHODES
Fresh-lands Environmental Actions, 88 Star Road, Caversham, Berkshire RG4 5BE, UK
I remember vividly the event in 1986 when the Unit 4 reactor at Chernobyl1 exploded, since
I was working in Russia during the weeks following it. Largely, this was a preventable
occurrence, and was caused by a combination of circumstances, but principally through an
unscheduled and ill-conceived “experiment” involving the full withdrawal of the majority of
the control rods from the reactor, actually in defiance of standing rules and after deliberately
disabling safety systems. In part, the reason for the withdrawal of so many of the control rods
was an attempt to compensate for the loss of power caused by a build-up of xenon, which acts
as a neutron absorber. Various factors contributed to a loss of cooling water which heightened
the already unstable condition of the reactor, due to an increase in the production of steam in
the cooling channels (positive void coefficient). By this stage, there was nothing that could be
done to avert a calamity, since inherent positive feedback effects rendered the initial rise in
power unstoppable, leading to an overwhelming power surge, estimated to be 100 times the
nominal power output of the reactor.
There is much speculation as to how many deaths Chernobyl might eventually cause,
but the initial recorded number was 562 (including 47 “liquidators” and nine children who
died of thyroid cancer). Estimates of the ultimate number range from 4,0002 up to nearly
one million3 fatalities from radiation-induced cancers. Chernobyl is the third really serious
nuclear accident to occur in the civilian nuclear industry. There was very little information
made available within the USSR, and my Russian colleagues learned most about what had
happened from their counterparts in the West. I have mentioned “Chernobyl” to various of
my friends and acquaintances recently, and from this small survey it seems that no-one under
the age of about 50 is aware of even the name of the place, let alone what happened there.
Apparently, a worker at a Swedish nuclear power plant (NPP) set the alarms off when he
went into work on a Monday morning, having been hiking over the weekend. Naturally, this
was a surprise since someone working at an NPP might be expected to be contaminated by
exposure inside the installation, but in this case, the radioactive plume had contaminated
Sweden (and the NPP worker) along with much of Western Europe, which alerted that the
event had taken place. Along with Chernobyl, there have been major accidents at Three Mile
Island and Windscale (subsequently renamed Sellafield). That said, the nuclear industry has
a fairly impeccable safety record, albeit that the long-term storage of its waste remains an
To the above list of three, which occurred some decades ago, can now be appended the
Fukushima Daiichi nuclear accident4. In the latter instance, the tsunami following the Tōhoku
earthquake on 11 March 2011 resulted in failures of equipment and a loss-of-coolant event,
with nuclear meltdowns (overheating and damage to the reactor core, with melting of fuel
rod components and the potential for escape of radionuclides), and the egress of radioactive
isotopes, commencing on 12 March 2011. Fukushima and Chernobyl are the only NPP
accidents to measure Level 7 on the International Nuclear Event Scale5 (described below), and
it is estimated that the Fukushima accident has released6 10 – 30% of the amount of radiation
resulting from that at Chernobyl, although the emissions continue, and it is not clear how and
when they may be stemmed entirely. The Fukushima NPP7 had six separate boiling water
reactors which were made by General Electric (GE) and maintained by the Tokyo Electric
Power Company (TEPCO). Reactor 4 had been de-fuelled when the incident took place, and
reactors 5 and 6 were in cold shutdown with the intention of a planned maintenance effort.
When the earthquake hit, reactors 1 – 3 were automatically shut down by the insertion of control
rods, i.e. a SCRAM event. Emergency generators then came into play to provide power for
the electronics and coolant devices, which operated until the tsunami struck, 50 minutes after
the quake itself. In consequence of its coastal location, the NPP had a 10 metre high seawall,
but this was overwhelmed by the height of the tsunami at 13 metres, so that water quickly
flooded the low-lying rooms in which the emergency generators were housed. Consequently,
the diesel generators failed, as accordingly did the pumps that had circulated cooling water
through a Generation II reactor, as is necessary to prevent the fuel rods from melting down
following the SCRAM event. It is believed that, inside reactor 1 within about three hours
the water level fell to the top of the fuel (6.00 pm) and to the bottom of it about 1.5 hours
later (7.30 pm). As a consequence, severe heating of the exposed fuel occurred (to perhaps
2,800 °C) so that the central portion began to melt, and after 16 hours (7.00 am the following
day) most of it had dropped into the water at the bottom of the reactor pressure vessel (RPV)8.
RPV temperatures have fallen steadily thereafter. Full meltdowns occurred in reactors 1 – 3.
There have been several hydrogen explosions9 reported, beginning on 12 March, in Unit
1; and finally on 15 March, in Unit 4. It is reckoned that the reaction between water and the
heated zirconium-clad fuel in reactors 1 – 3 produced of the order of one tonne of H2 gas in each
case, which on release and admixture with air achieved an explosive concentration in units 1
and 3. Unit 4 also filled with hydrogen, resulting in explosions at the top of each unit, i.e. in
their upper secondary containment building8. So far, no one has died as a result of radiation
exposure from Fukushima, while some 18,500 fatalities have occurred from the earthquake
and the subsequent tsunami per se. There is speculation (as over Chernobyl) as to how many
cancer related deaths there will be in consequence of accumulated radiation exposures in the
years to come, and one estimate10 is that there will be 130 fatalities and 180 additional cancer
cases, mostly in the most heavily contaminated areas of Fukushima. However, the World
Health Organization (WHO) has concluded that the according health impacts are likely to be
below detectable levels11. In 2013, the WHO produced a report suggesting that girls exposed
as infants to radiation (presumably from radioactive iodine) have a 70% increase in their
risk of developing thyroid cancer12. I recall that after Chernobyl, 131I could be detected using
a radiation detector placed against the neck, and close to the thyroid gland of individuals in
Belarus, Ukraine and Russia, which permitted estimates of the degree of radiation exposure
to be made. In the Fukushima Prefecture region, abnormal thyroid glands were identified in
around one-third of children4, which does seem a rather high proportion. While 44 children in
the region have been diagnosed13 with cancers of the thyroid, it is not clear if this is caused by
exposure to radioactive materials from the Fukushima NPP. The Chernobyl incident appeared
to ring-in the death knell for the nuclear industry, and yet a more positive view of it has
been taken in recent years, in part as a strategy to avoid carbon-emissions from fossil-fuel
fired power plants. Fukushima has, to some degree, revoked this renewed support, and as
the radioactive emanations continue from the NPP, the voice of dissent is likely to become
2. The Fukushima Daiichi nuclear power plant itself
With a total output of 4.7 GW, the Fukushima I (Daiichi) nuclear power plant7 was on the list
of the world’s 15 largest NPPs, consisting of six light water, boiling water reactors (BWR).
Unit 1 is a 439 MWe type (BWR-3) reactor. It was constructed in July 1967 and began its
commercial life on 26 March 1971, and could cope with a peak ground acceleration of
0.18 g (1.74 m s – 2) and a response spectrum which was factored upon the 1952 Kern County
earthquake. Both the 2 and 3 units are of 784 MWe type BWR-4, which began producing
electricity respectively in 1974 and 1976. The earthquake design of the reactors was in
the range 0.42 g (4.12 m s – 2) to 0.46 g (4.52 m s – 2): in the aftermath of the 1978 Miyagi
earthquake [ground acceleration 0.125 g (1.22 m s – 2) for 30 seconds)], the critical parts of
the reactor were found to have suffered no damage. Unit 3 ran using a mixed-oxide fuel as
from September 2010. Nuclear reactors produce thermal energy (heat), which is normally
used to turn liquid water into steam and drive a turbine for generating electricity, typically
through the fission of 235U, although one-third approximately of the power output of an NPP
arises from the fission of 239Pu: the latter being produced in situ by neutron absorption into
238U. Even once the nuclear chain reaction has been switched off, the reactor emits heat from
the decay of unstable fission products; hence, in the period immediately following shutdown,
6% of the heat is still produced as when the reactor was fully running14. Over several days,
this falls to cold shutdown levels. The fuel rods themselves typically require another several
years of cooling in water before they can be put safely into dry cask storage containers15. To
achieve this cooling, water must be circulated over the fuel rods in the reactor core and in the
spent fuel pond. High pressure pumps are used to move water through the reactor pressure
vessel and into heat exchangers – the latter transfer heat to a secondary heat exchanger via the
essential service water system, and finally the hot water is moved to cooling towers on-site or
pumped out to the sea. To add context to the need for cooling water, we may note that if the
water in the Unit 4 spent fuel pool had been at its boiling point, the residual heat was sufficient
to evaporate some 70 tonnes of it per day15. Zirconium alloys are solid solutions of zirconium
or other metals, and are commonly known by their trademark Zircaloy. These have particular
advantages16 in the fabrication of the internal components of nuclear reactors: i.e. a very low
absorption cross-section of thermal neutrons, along with a high degree of hardness, ductility
and corrosion resistance. Zirconium alloys are employed as cladding for fuel rods, especially
in water reactors. Nuclear-grade zirconium alloys consist of > 95 wt % of zirconium with
< 2% of tin, niobium, iron, chromium, nickel and other metals, the presence of which enhances
mechanical properties and resistance to corrosion. At temperatures of the order of 300 °C,
typical for reactor operation, Zircaloy is practically inert; however, at temperatures > 500 °C,
Zircaloy reacts exothermically with steam to produce free H2 gas, and this is thought to be the
origin of the hydrogen explosions that occurred at Fukushima.
3. International Nuclear and Radiological Event Scale (INES)
The INES5 is approximately logarithmic (Figure 1), in similarity with the Beaufort scale used
to describe relative wind force, and the moment magnitude scale for the comparative power
of earthquakes. Hence, each successive level indicates a 10-fold severity over the previous
one. Since the INES level can only be ascribed after the event has occurred (and this requires
some degree of interpretation), rather than during it, it has only limited use to guide disaster-
aid deployment, which is one of its criticisms. A description of the different levels follows,
along with selected examples of incidents to which each category has been assigned. The
INES extends from Level 0, indicating an abnormal situation with no safety consequences,
and ends at Level 7, which refers to an accident/incident from which there is widespread
contamination, and accordingly serious health and environmental outcomes.
3.1 Level 7: Major accident
Impact on people and environment:
• Major release of radioactive material with widespread health and environmental effects
requiring implementation of planned and extended countermeasures.
There have been two such events to date:
• Chernobyl disaster (Soviet Union), on 26 April 1986 a power surge during a test
procedure resulted in a criticality accident, leading to a powerful steam explosion and
fire that released a significant fraction of core material into the environment, resulting
in a death toll of 56, in addition to 4,000 additional cancer fatalities (official WHO
estimate) resulting from radiation exposure.
• Fukushima Daiichi nuclear disaster (Japan), a series of events beginning on
11 March 2011.
Figure 1 Pyramid representation of the INES scale for the classification of nuclear events (see text).
Image credit: Silver Spoon.
3.2 Level 6: Serious accident
Impact on people and environment:
• Significant release of radioactive material likely to require implementation of planned
There has been just one such event to date:
• Kyshtym disaster at Mayak Chemical Combine (M.C.C.) (Soviet Union), on 29
September 1957. A failed cooling system at a military nuclear waste reprocessing
facility caused a steam explosion with a force equivalent to 70 – 100 tonnes of TNT.
About 70 – 80 tonnes of highly radioactive material was released into the region. It is
thought that at least 22 villages were affected, although there is no population data.
3.3 Level 5: Accident with wider consequences
Impact on people and environment:
• Limited release of radioactive material likely to require implementation of some
• Several deaths from radiation.
Impact on radiological barriers and control:
• Severe damage to reactor core.
• Release of large quantities of radioactive material within an installation, with a high
probability of significant public exposure. This could arise from a major criticality
accident or fire.
• Windscale (United Kingdom), 10 October 1957. Annealing of graphite moderator at a
military air-cooled reactor caused the graphite and the metallic uranium fuel to catch
fire, releasing radioactive pile material as dust into the environment.
• Three Mile Island accident near Harrisburg, Pennsylvania (United States), 28 March
1979. A gradual loss of coolant occurred, with a partial meltdown. Although radioactive
gases were released into the atmosphere, no casualties have been attributed to this
• Goiânia accident (Brazil), 13 September 1987. An unsecured radioactive source
containing caesium chloride was stolen from an abandoned hospital by thieves who
were unaware of its nature and sold to a scrap dealer. As a result, 249 people became
contaminated, of whom four died.
3.4 Level 4: Accident with local consequences
Impact on people and environment:
• Minor release of radioactive material unlikely to result in implementation of planned
countermeasures other than local food controls.
• At least one death from radiation.
Impact on radiological barriers and control:
• Fuel melt or damage to fuel resulting in more than 0.1% release of core inventory.
• Release of significant quantities of radioactive material within an installation with a
high probability of significant public exposure.
• Sellafield (United Kingdom): five incidents occurred during the period 1955 – 1979.
• SL-1 Experimental Power Station (United States): 1961, reactor reached prompt
criticality, killing three operators.
• Saint-Laurent Nuclear Power Plant (France): 1969, partial core meltdown; 1980,
• Buenos Aires (Argentina): 1983, a criticality accident occurred during fuel rod
replacement which killed one operator and injured two others.
• Jaslovské Bohunice (Czechoslovakia): 1977, contamination of a reactor building
• Tokaimura nuclear accident (Japan): 1999, three inexperienced operators at a
reprocessing facility caused a criticality accident, two of whom died.
3.5 Level 3: Serious incident
Impact on people and environment:
• Exposure in excess of 10 times the statutory annual limit for workers.
• Non-lethal deterministic health effect (e.g., burns) from radiation.
Impact on radiological barriers and control:
• Exposure rates of more than 1 Sv h – 1 in an operating area.
• Severe contamination in an area that would not be anticipated by the design, with a low
probability of significant public exposure.
Impact on defence-in-depth (the practice of having multiple, redundant, and independent
layers of safety systems for the single, critical point of failure: the reactor core):
• Near accident at a nuclear power plant with no safety provisions remaining.
• Lost or stolen highly radioactive sealed source.
• Misdelivered highly radioactive sealed source without adequate procedures in place
to handle it.
• THORP plant Sellafield (UK), 2005.
• Paks Nuclear Power Plant (Hungary), 2003. Fuel rod damage in cleaning tank.
• Vandellos Nuclear Power Plant (Spain), 1989; fire destroyed many control systems;
the reactor was shut down.
• Fukushima Daiichi Nuclear Power Plant (Japan), 2013. In a further incident of the
Fukushima Daiichi nuclear disaster, 300 tonnes of heavily contaminated water had
leaked from a storage tank.
3.6 Level 2: Incident
Impact on people and environment:
• Exposure of a member of the public to a radiation dose in excess of 10 mSv.
• Exposure of a worker to above the statutory annual limits.
Impact on radiological barriers and control:
• Radiation levels in an operating area in excess of 50 mSv h – 1.
• Significant contamination within the facility into an area that would not be expected
by the design.
Impact on defence-in-depth:
• Significant failures in safety provisions but with no actual consequences.
• Found highly radioactive sealed orphan source, device or transport package with safety
provisions intact. (An “orphan” is the term given to a radioactive source that has been
• Inadequate packaging of a highly radioactive sealed source.
• Blayais Nuclear Power Plant (France), December 1999. Flood.
• Ascó Nuclear Power Plant (Spain) April 2008. Radioactive contamination.
• Forsmark Nuclear Power Plant (Sweden) July 2006. Backup generator failure; two
were online but fault could have caused all four to fail.
• Gundremmingen Nuclear Power Plant (Germany) 1977. Weather caused short-circuit
of high-tension power lines and rapid shutdown of reactor.
• Shika Nuclear Power Plant (Japan) 1999. Criticality incident caused by dropped
control rods, covered up until 2007.
3.7 Level 1: Anomaly
Impact on defence-in-depth:
• Overexposure of a member of the public in excess of statutory annual limits.
• Minor problems with safety components with significant defence-in-depth remaining.
• A lost or stolen radioactive source, device or transport package of low radioactivity.
• (Arrangements for reporting minor events to the public differ from country to country.
It is difficult to ensure precise consistency in rating events between INES Level 1 and
Below scale/Level 0).
• Penly (Seine-Maritime, France), 5 April 2012. An abnormal leak on the primary circuit
of the reactor No. 2 was found in the evening of 5 April 2012 after a fire in reactor No.
2 around noon was extinguished.
• Gravelines (Nord, France), 8 August 2009. During the annual fuel bundle exchange in
reactor 1, a fuel bundle snagged. Operations were stopped, the reactor building was
evacuated and isolated in accordance with operating procedures.
• TNPC (Drôme, France), July 2008. Leak of 18,000 litres (4,000 imp gal; 4,800 US gal)
of water containing 75 kilograms (165 lb) of unenriched uranium into the environment.
3.8 Level 0: Deviation
• No safety significance.
• 4 June 2008: Krško, Slovenia. Leakage from the primary cooling circuit.
• 17 December 2006: Atucha, Argentina. Reactor shutdown due to tritium increase in
• 13 February 2006. Fire in Nuclear waste volume reduction facilities of the Japanese
Atomic Energy Agency (JAEA) in Tokaimura.
4. Estimated severity of the Fukushima NPP incident
In the case of the Fukushima nuclear accident, a provisional INES rating of 7 has been
given (Chernobyl also scored 7, and Three Mile Island, 5). Estimates of the total amount of
intermediate and long lived radionuclides that egressed from the Fukushima Daiichi NPP are
of the order of 10 – 30% of the release from Chernobyl. It is thought that Fukushima has so far
released ca 15 PBq8,17 of 137Cs, which is the activity of 4.6 kilograms of the radionuclide. In
comparison, Chernobyl released 85 PBq of 137Cs18, or 26 kg worth. The radionuclide release,
including 137Cs, 90Sr, 241Am and various Pu isotopes, which emanated from the Fukushima
NPP were strongly mitigated by the reactors being housed in concrete containment vessels,
unlike at Chernobyl, where the fated Unit 4 reactor had no containment. While it is the most
biologically hazardous isotope, the half-life of 131I is only about 8 days, meaning that after
10 half-lives (80 days) practically all of it has decayed to the stable isotope 131Xe, which is
harmless; hence the time during which human exposure can occur is relatively short. 500 PBq17
of 131I were released from the Fukushima NPP, but 1,760 PBq18 of 131I from Chernobyl.
Concerns that a large-scale release of radioactivity from the Fukushima NPP might occur,
led to a 20 km exclusion zone being set up around the power plant19, and those living within
the 20 – 30 km zone were advised to remain indoors. As the reaction to fears over the spread
of radioactive contamination escalated, some countries, including the UK and France, advised
their own nationals to consider leaving Tokyo, some 225 km away. The evacuation of Tokyo
itself was considered, which would have jeopardised the future of the Japanese state. On 12
March, radioactive materials were first detected by a CTBTO (Preparatory Commission for the
Comprehensive Nuclear-Test-Ban Treaty Organization) monitoring station in Takasaki, Japan,
some 200 km distant from the NPP. The path of the radioactive isotopes (131I, 134Cs, 137Cs) could
be tracked20 to eastern Russia on 14 March and by 16 March to the west coast of the USA. Within
one month, radioactive materials were recorded by CTBTO stations in the southern hemisphere,
e.g. those in Australia, Fiji, Malaysia and Papua New Guinea. As already noted, it has been
reckoned that the total amount of radioactive materials released from the Fukushima NPP is
about 10 – 30% that released from the Chernobyl NPP accident, and the area of contamination is
about one-tenth that of Chernobyl. The French Institute for Radiological Protection and Nuclear
Safety reported21 that, between 21 March and mid-July, around 27 PBq of 137Cs entered the
ocean, about 82% having flowed into the sea before 8 April. The Kuroshio Current on the
Fukushima coast is one of the world’s strongest, and has transported the contaminated waters
far into the Pacific Ocean, causing the radioactive materials to become highly diluted. It is
thought that the consequences for marine life from radioactivity will be fairly minor. The human
health impacts are discussed in more detail later, but are also expected to be minor.
5. Groundwater contamination
On 8 July 2013, TEPCO found 9,000 Bq L – 1 of 134Cs per litre and 18,000 Bq L – 1 of 137Cs in a
sample taken from a well near to the coast, some 85 times greater than in a sample taken three
days previously22. TEPCO assumed that the radioactive leak stemmed from the incident itself
in 2011, but experts from the NRA (Nuclear Regulation Authority of Japan) considered that
other sources could not be ruled out. Due to the complexity of the array of pipes used to cool
the reactors and decontaminate the water used, leaks might occur anywhere. The groundwater
flows could easily be shifted which could spread the contamination even farther, and there
were also plans to pump groundwater. Since the reactor 2 and 3 turbine-buildings contained
5,000 and 6,000 m3 of highly radioactive water, and there were wells in direct contact with
the turbine-buildings, there was a distinct possibility that radioactive material could be
transferred into the ground/groundwater. The NRA had issued a nuclear disaster rating earlier,
in consequence of leaks that were detected in the surface water and top-soil near the leaking
tanks, with β-radiation levels as high as 2,200 mSv h – 1. On 9 September 2013, a high level
of β-radiation (3,200 Bq L – 1) was found in a groundwater testing well23 (not near a storage
tank), indicating that the groundwater upstream of the reactors had become contaminated. An
adjacent well was also found to be contaminated, though to lower levels, implying that the
contaminated water is not “contained” in any way, but can move through the ground.
6. Radioactive contamination of the ocean
On 22 July 2013, TEPCO admitted there had been a leak of radioactive water into the ocean,
and on 27 July, the company announced that, in a pit containing about 5000 m3 of water
adjacent to the reactor 2 building, there were massive levels24 of tritium (8.7 million Bq
L – 1) and particularly caesium, at 2.35 billion Bq L – 1. [Tritium is produced in an NPP by the
absorption of neutrons by boron, which is employed either as an intrinsic component of the
control rods, or is added to the coolant water to assist control of the nuclear chain reaction,
since it is a highly efficient neutron absorbing agent. Minor quantities of tritium may arise
when 235U fissions in the reactor core, or from neutron absorption by lithium or deuterium
oxide (“heavy water”) in the coolant water. Caesium, along with strontium, is a major fission
product of 235U]. Since there was still water flowing from the reactor into the turbine building
and into the pit, the NRA feared that there might be a further and more serious such radiation
leak. In August 2013, TEPCO admitted that up to 400 tonnes of contaminated water flows into
the Pacific Ocean every day25 and that probably 20 – 40 terabecquerels of tritium had entered
the ocean since May 20118. Alarming though this statistic sounds, it should be compared with
the 22 terabecquerels per year, that TEPCO was allowed to put into the sea according to its
regulations, but when exactly the tritium had begun to escape was not clear.8 Liquid glass
was injected into the soil to form a wall, rendering the soil impermeable to water, a task that
was completed on 9 August. The following day, TEPCO speculated that radioactive water
might be flowing over the top of the underground wall, which was some 1.8 metres below the
surface of the ground, according both to sea and groundwater measurements; the leakage was
not stemmed by groundwater pumping26. Around 1,000 tonnes per day of groundwater flow
was reckoned, of which ca 400 tonnes was flowing into the reactor buildings. Thus, a clear
potential mechanism existed for water to enter the ground via the complex maze of pipes and
tunnels that existed there27.
7. Leakage from storage tanks
Around 1,000 storage tanks have been set up within the 860-acre compound of the Fukushima
NPP, to hold 350,000 tonnes of radioactive water, of which 350 are of the flange type28.
Wooded areas are being cleared to make room for more tanks. On 19 August 2013, two
“hotspots” of water were found near a 1,000 tonne cylindrical, steel, flange type storage tank,
which were emitting 80 million Bq L – 1, which it was later shown had leaked 300 tonnes
of water. The radiation level at the surface of one of the puddles was measured at100 mSv
h – 1, which is sufficient to give a year’s annual dose to a German radiation worker in just
12 minutes. The incident was provisionally rated by the NRA as a Level 1 “anomaly” on
the seven-level INES scale, but this was revised up to Level 3 on 28 August, and reported
to the IAEA (International Atomic Energy Agency). On 2 September, it was reported that
radiation near another tank was measured at 1,800 mSv h – 1, which was18 times higher29
than the initially reported 100 mSv h – 1, but this discrepancy arose because that latter was
the maximum reading possible on the equipment initially employed. A more sophisticated
radiation-meter was necessary, that could record much higher levels, to determine the correct
dose rate. TEPCO started cleaning the draining ditch at the north side of the leaking tank on
9 September. By 12 September, it became clear that levels of tritium were increasing in a
test well some 20 metres north from the leaking storage tank30: 8 September, 4,200 Bq L – 1;9
September, 29,000 Bq L – 1; 10 September, 64,000 Bq L – 1; 11 September, 97,000 Bq L – 1. On
12 September, a β-radiation level of 220 Bq L – 1 was measured in a drainage ditch, some
150 metres from the coast, leading directly into the ocean, an increase by a factor of 12 in
the previous two days. Given that this contamination from the leaking tank was located some
130 metres west from the planned frozen wall, there is some question as to how effective this
strategy will be in diverting contaminated water to the sea31.
8. Reactor stabilisation and clean-up operations
The reactor units involved in the Fukushima Daiichi nuclear accident are located in mutually
close proximity, which has contributed to chain-reaction events, causing hydrogen explosions
of sufficient force to blast the roofs of the buildings in which the reactors were housed and water
draining from the spent-fuel pools. Thus it was necessary to try to deal with core meltdowns
at three reactors and exposed fuel pools at three units, simultaneously32. A “roadmap” has
been released by the Japanese government which indicates that for the complete clean-up and
decommissioning of the NPP, and its environs will take up to 40 years33. Toshiba are more
optimistic, and think they can do the job in just 10 years34, and for comparison it took some
14 years to clean up Three Mile Island. This was a different kind of event, however. The
Tokyo Electric Power Company (TEPCO) began using unmanned heavy machinery on 10
April 2011 to remove debris from around the reactors 1 – 4, and on 17 April 2011 the company
put forward the broad basis of a plan which included reaching “cold shutdown in about six to
nine months, and indeed shutdown was achieved on 11 December 2011. Although cooling was
no longer required, it was still necessary to control large water leaks. On 5 May 2011, workers
were able to enter the reactor buildings and began to install filtration systems to remove
radioactive materials from the air, so that other workers could install water cooling systems; on
16 August, the company said it had installed desalination equipment in the spent fuel pools35.
The latter were temporarily cooled using seawater, but TEPCO warned of the risk that this
might corrode the walls of the pools and pipes made of stainless steel. The Prime Minister of
Japan, Yoshihiko Noda is quoted as saying that his government might have to spend 1 trillion
yen ($13 billion)36 to clean up those vast areas that are radioactively contaminated from the
Fukushima accident. It was believed that 29 million cubic metres of soil might need to be
disposed of and removed from a large area in Fukushima, and four nearby prefectures, for
which hydrothermal blasting was one of several techniques that were considered. However,
the contamination proved to be only superficial37, and while the crops grown in 2011, the
year that the accident had occurred in, were contaminated, those now grown in the area are
considered safe to be consumed by humans. The majority of caesium was detected in the
vegetation and litter layer of the forest and, accordingly, the preferred method of disposal is
incineration. Overall, this might be thought of as a kind of phytoremediation38 strategy since
it can reduce contamination levels by a factor of 10 and is a very low-tech method. However,
there is a risk from the resulting ash which is accordingly contaminated with caesium ending
up in the atmosphere, with potential health risks. Burning in situ is probably not an option, but
removing the plant material to be burned in a special incinerator fitted with suitable fine-ash
filters might prove feasible.
9. Roadmap for scrapping the nuclear reactors
At a session of the Fukushima Prefectural Assembly, which was investigating the accident at
the Fukushima NPP, on 7 September 2011 the TEPCO president, Toshio Nishizawa announced
that the four damaged reactors would be scrapped. On 9 November, a schedule was drawn
up for scrapping the damaged reactors, by an expert panel from the Japanese Atomic Energy
Commission. The approach chosen was partly based on prior experience in dealing with the
Three Mile Island accident, in 1979, although at Fukushima there had been three practically
simultaneous meltdowns on the one site, and so a considerably greater problem prevailed. The
following main points were identified:
• The overall process will take around 40 years33.
• First the containment vessels must be repaired and filled with water to absorb the
• The reactors should be in a state of stable cold shutdown.
• In another three years, the transfer of all spent fuel from the four damaged reactors to
a pool inside the compound could be started.
• After 10 years, work could begin to remove the melted fuel from inside the reactors.
10. Decontamination of regions neighbouring Fukushima
On 10 October 2011, the Japanese government produced a revised decontamination plan,
which involves removing topsoil and washing down buildings, and all areas at which radiation
levels > 1 mSv yr – 1 were measured would be cleaned. Previously it had been intended only to
act where in the case of levels of > 5 mSv yr – 1.
• No-entry zones and evacuation zones designated by the government would be the
responsibility of the government.
• The rest of the areas would be cleaned by local authorities.
• In areas with radiation levels > 20 mSv yr – 1, decontamination would be done step by step.
• Within 2 years, radiation levels between 5 and 20 mSv yr – 1 should be reduced to 60%.
There has been opposition to the plan by cattle-farmers in the Iwate Prefecture who
feared that the sale of cattle would fall, once the area had been labelled as contaminated, and
similarly the tourist industry in the city of Aizuwakamatsu were of the opinion that tourism
would be discouraged there. On the other hand, those living in regions with readings of
< 1 mSv yr – 1 complained that they would not receive a funded decontamination programme39.
There are many associated problems, in terms of ruined local economies and according to
one survey, one third of former residents of a lush village called Litate, resplendent in its
fresh produce, never want to return there, while half would prefer to be compensated so they
can move to farm elsewhere in Japan.
11. Building an “ice-wall”, and increasing the storage capacity for
Under the orders of the Japanese government, TEPCO commenced its plans to construct
an “ice-wall” around the reactor buildings to limit the influx of groundwater to them40. The
wall will be 1.4-km long and will be created by sinking pipes into the ground, through which
freezing fluid is circulated, gradually forming a barrier of permafrost 30 m deep, down to
the bedrock, thus forcing the water to drain into the sea instead. It is thought that this should
be finished during the first half of the Japanese fiscal year 2015 (i.e. from 1 April, 2015 to
31 March 2016). $470 million has been pledged for the project by the Japanese government,
including $150 million to reduce contamination of the stored water to a level at which it can
be dumped at sea. The International Atomic Energy Agency is has approved the strategy.
Such an ice wall is not a new idea, since they have been used extensively in the USA, e.g. to
secure mine shafts and contain contamination. TEPCO has also been instructed to build tanks
with a total capacity of 800,000 tonnes (up from the 330,000 tonnes capacity that existed at
the end of May 2012) to store radioactive water, which are expected to be completed by the
end of the 2016 fiscal year.
12. Disposal of materials and safe extraction of caesium
A study41 was reported on the “safe incineration of contaminated wastes while restricting
the release of volatile caesium to the atmosphere”, which involved the construction of a
modified incinerator to enable the combustion of a variety of contaminated materials while
minimising the release of toxic substances into the atmosphere, including caesium. From
the incinerated materials was derived wood ash (from evergreen trees and deciduous trees)
household garbage ash, and sludge ash, which needed to be decontaminated of its caesium
concentration before it could be disposed of. The simplest method would be dissolving the
caesium out with water, and it was found that by using a 1 : 25 ash : water ratio, and mixing
for 10 minutes, at 40 °C, about 93% of the caesium originally present was removed. Since
toxic heavy metal cations were removed simultaneously during the process, the ash was
clean enough to be put back into the environment. Similar results were found for household
ash. Sludge ash proved much more difficult to handle than the other two, and due to the
presence of clay particles, which tended to retain the caesium more strongly, necessitating
the use of 0.5 M nitric or sulfuric acids in the ratio 1 : 100 (ash : acid), mixed for one hour,
at 95 °C, which resulted in the removal of 82.3% of the caesium originally present in the
13. Impacts on health
Although around 18,500 people died from the earthquake and tsunami, there were no deaths
from short-term radiation exposure. Any future deaths from cancer as a consequence of the
Fukushima accident are estimated to be statistically insignificant. Just 0.1% of the 110,000
clean-up workers at Chernobyl have so far developed leukaemia, which cannot entirely be
ascribed to the accident itself. Using a linear no-threshold model (LNT model), workers from
Stanford University suggest that an ultimate total of 130 cancer deaths might be expected
as a consequence of Fukushima10, although there is some dissent42 as to the validity of the
model which did not prove reliable in predicting the number of casualties from Chernobyl,
Hiroshima nor Nagasaki. In 2013, on the basis of the LNT model (which assumes that any
degree of radiation exposure will impact negatively on health) the WHO concluded that the
levels of exposure to those populations who were evacuated, were so low that no significant
health effects should be expected11. The WHO further concluded that for those living in the
vicinity of the Fukushima NPP the risk of developing thyroid cancer is increased by 70%,
and of breast cancer by 6%, for females exposed as infants. Males exposed as infants were
reckoned to have a 7% higher than average risk of leukaemia. The lifetime absolute baseline
chance of developing thyroid cancer in females is 0.75%, which is raised to 1.25% by the
radiation-induced cancer chance, which is the source of the “70% greater risk” statistic12.
A total of 44 children were newly diagnosed13 with thyroid cancer, and other cancers by
August 2013, in the overall Fukushima prefecture area, but any connection to radiation
exposure is presently unknown. Following the Chernobyl accident in 1986, a steady then
sharp increase in thyroid cancer rates was observed. Thus, there was nothing greater than the
baseline value (prior to the accident) of ca 0.7 cases per 100,000 people per year, prior to the
period 1989 – 1991, (i.e. 3 – 5 years following the accident) in both the children and adolescent
age groups43. Accordingly, if the same effect prevails for Fukushima, any increase in the
incidence of thyroid cancer is not to be expected to manifest itself until a similar period after
the accident occurred, in 2011 (i.e. during the years 2014 – 2016). Thyroid cancer responds
well to treatment (96% survival rate) and, for example, of the 4,000 cases of the disease in
children and adolescents diagnosed from 1989 to 2005 in the Chernobyl region, there have
been nine fatalities, which implies a > 99% rate of survival44.
14. Energy policy implications
Only two of Japan’s nuclear reactors were still running by March 2012; some of those that
were shut-down had been damaged by the quake and tsunami. Although local governments
had been authorised to re-start those reactors that were serviceable after routine maintenance,
it was local opposition that prevented this happening. An opinion poll held in June 2011,
found that almost three-quarters of a sample of 1,980 respondents were in favour of Japan
closing all 54 of its reactors and becoming a nuclear-free nation. As a result of the loss of
30% of its electricity generating capacity from nuclear, Japan has become far more reliant
on oil and coal. Immediately following the accident, power rationing was introduced in nine
prefectures served by TEPCO45. Major companies were asked by the Japanese government
to reduce their power consumption46 by up to 30%: some of whom moved their employees’
weekends to weekdays in an effort to stabilise demand for electricity46. It was reported in
October 2013, that nine Japanese electricity companies, including Tokyo Electric Power
Company, are outlaying more to cover the costs of imported fuel to the tune of ca 3.6 trillion
yen, or $37 billion, as compared with the year immediately preceding the accident 2010,
to compensate for the electricity that would previously have been provided by nuclear47.
One option is for Japan to become nuclear-free by switching to oil- and gas-based power
production, and yet this would cost tens of billions of dollars annually: and a soaring cost,
as the price of a barrel of oil is now above $100, and is expected to rise inexorably over the
coming years, and global conventional crude oil production declines.
Not surprisingly, there is an opinion, held by a number of analysts of energy policy, that
the way forward is for Japan to go all-out for renewable energy. It has been estimated that
Japan has a total of 324 GW of achievable potential in the form of onshore and offshore wind
turbines (222 GW), geothermal power plants (70 GW), additional hydroelectric capacity
(26.5 GW), solar energy (4.8 GW) and agricultural residue (1.1 GW)48. Accordingly, there
are plans afoot to construct a floating wind farm, as a pilot project, with six 2 MW turbines,
off the Fukushima coast49, and there is an ongoing evaluation phase, expected to be finalised
in 2016, so that consequently Japan may build up to 80 floating wind turbines off Fukushima
by 2020 49. An expansion of (photovoltaic) solar energy is expected too, and the company
Canadian Solar is looking to build a factory in Japan with a manufacturing capacity of
150 MW of solar panels per year50.
15. Fukushima nuclear clean-up enters critical phase
In November 2013, TEPCO began removing more than 1,500 fuel assemblies from the spent
fuel pool inside the No. 4 reactor51. The tank contains 1,331 spent and 202 fresh assemblies
weighing a total of 400 tonnes, and there are concerns that another earthquake, such as that of
magnitude 9.0, as occurred on 11 March 2011 could cause the fuel pool to collapse, with the
potential for a very serious leakage of radioactive material into the atmosphere. It is a tricky
procedure, however, especially if the assemblies come into contact with one another or are
exposed to the air. If the level of water in the tank were to drop significantly for some reason,
the fuel could begin to heat-up. Having been removed from the tank, the fuel rods are placed
in batches in dry casks, and these are then lowered to ground level and transported to a safer
storage site nearby. It is hoped that the task will be completed by the end of 2014.
6. Von Hippel, F.N. (2011) “The radiological and psychological consequences of the Fukushima Daiichi accident”.
Bulletin of the Atomic Scientists, 67, 27 – 36.
32. Funabashi, Y. and Kitazawa, K. (2012) Fukushima in review: a complex disaster, a disastrous response. Bull.
Atomic Scient. 1 March, 1 – 13. http://www.jsmillerdesign.com/FukushimaPapers/Bulletin%20of%20the%20
35. Kazuaki, N. (2012) Public mulls Noda’s definition of ‘safe’. Japan Times, 9 March 2012, p. 1.
38. Rhodes, C.J. (2013) Bioremediation and phytoremediation. Sci. Prog., 96, 417 – 427.
41. Parajuli, D. et al. (2013) “Dealing with the Aftermath of Fukushima Daiichi Nuclear Accident: Decontamination
of Radioactive Cesium Enriched Ash”. Env. Sci. Technol., 47, 3800 – 3808.
42. Normile, D. (2011). “Fukushima Revives the Low-Dose Debate”. Science, 332, 908 – 910.