This will be published later this month in the journal, Science Progress, of which I am an editor, so this is a preview!:
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 9 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. At the time, there was very little information made available within the U.S.S.R., 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 fifty 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 in the hills, 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 unresolved dilemma.
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 March 11th, 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 March12th, 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-fueled when the incident took place, and reactors 5 and 6 were in cold shutdown in 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 by 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 March 12th, in Unit 1; and finally on March 15th, 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 familiarly strident.
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 March 26th,1971, and could cope with a peak ground acceleration of 0.18 g (1.74 m/s2) 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/s2) to 0.46 g (4.52 m/s2): in the aftermath of the 1978 Miyagi earthquake [ground acceleration 0.125 g (1.22 m/s2) 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 oC, typical for reactor operation, zircaloy is practically inert; however, at temperatures > 500 oC, 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.
International Nuclear and Radiological Event Scale (INES).
The INES5 is approximately logarithmic, similarly to 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 tenfold 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.
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 April 26th, 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 March 11th, 2011.
Level 6: Serious accident.
Impact on people and environment:
Significant release of radioactive material likely to require implementation of planned countermeasures.
There has been just one such event to date:
Kyshtym disaster at Mayak Chemical Combine (M.C.C.) (Soviet Union), on September 29th, 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.
Level 5: Accident with wider consequences.
Impact on people and environment:
Limited release of radioactive material likely to require implementation of some planned countermeasures.
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), October 10th, 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), March 28th, 1979. A gradual loss of coolant occurred, with a partial meltdown. Although radioactive gases were released into the atmosphere, this incident has not been attributed to casualties.
Goiânia accident (Brazil), September 13th, 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 4 died.
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, graphite overheating.
Buenos Aires (Argentina): 1983, a criticality accident occurred during fuel rod replacement which killed one operator and injured 2 others.
Jaslovské Bohunice (Czechoslovakia): 1977, contamination of a reactor building occurred.
Tokaimura nuclear accident (Japan): 1999, three inexperienced operators at a reprocessing facility caused a criticality accident, two of whom died.
Level 3: Serious incident.
Impact on people and environment:
Exposure in excess of 10x 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 in an operating area.
Severe contamination in an area not expected by 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 (United Kingdom), 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.
Level 2: Incident.
Impact on people and environment:
Exposure of a member of the public in excess of 10 mSv.
Exposure of a worker in excess of the statutory annual limits.
Impact on radiological barriers and control:
Radiation levels in an operating area of more than 50 mSv/h.
Significant contamination within the facility into an area not expected by 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.
Inadequate packaging of a highly radioactive sealed source.
Blayais Nuclear Power Plant flood (France), December 1999.
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.
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.
Low activity lost or stolen radioactive source, device or transport package.
(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) April 5th, 2012. An abnormal leak on the primary circuit of the reactor No. 2 was found in the evening of April 5th, 2012 after a fire in reactor No. 2 around noon was extinguished.
Gravelines (Nord, France), August 8th, 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.
Level 0: Deviation.
No safety significance.
June 4th, 2008: Krško, Slovenia: Leakage from the primary cooling circuit.
December 17th, 2006, Atucha, Argentina: Reactor shutdown due to tritium increase in reactor compartment.
13th February 2006: Fire in Nuclear Waste Volume Reduction Facilities of the Japanese Atomic Energy Agency (JAEA) in Tokaimura.
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 U.K. and France, advised their own nationals to consider leaving Tokyo, some 225 km away. The evacuation of Tokyo itself was considered, which would have jeopardized the future of the Japanese state. On March 12th, 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 March 14th and by March 16th to the west coast of the United States. 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 March 21st and mid-July, around 27 PBq of 137Cs entered the ocean, about 82% having flowed into the sea before April 8th.
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.
On July 8th, 2013, TEPCO found 9,000 Bq/L of 134Cs per litre and 18,000 Bq/L 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 make the contamination even more widespread, 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. On September 9th, 2013 a high level of β-radiation (3,200 Bq/L) 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.
Radioactive contamination of the Ocean
On July 22nd, 2013 TEPCO admitted there had been a leak of radioactive water into the ocean, and on July 27th, 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) and particularly caesium, at 2.35 billion Bq/L. [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 9th 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 tunnels27.
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 August 19th, 2013, two “hotspots” of water were found near a 1000 tonne cylindrical, steel, flange type storage tank, which were emitting 80 million Bq/L, 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, 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 August 28th, and reported to the IAEA (International Atomic Energy Agency). On September 2nd, it was reported that radiation near another tank was measured at1,800 mSv/h, which was18 times higher29 than the initially reported 100 mSv/h, 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 September 9th. By September 12th, it became clear that levels of tritium were increasing in a test well some 20 meters north from the leaking storage tank30: September 8th: 4,200 Bq/L; September 9th: 29,000 Bq/L; September 10th: 64,000 Bq/L; September 11th: 97,000 Bq/L. On September 12th, a β-radiation level of 220 Bq/L was measured in a drainage ditch, some 150 metres from the coast, leading directly into the ocean, an increase by a factor of twelve in the previous two days. Given that this contamination from the leaking tank was located some130 meters 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.
Reactor stabilization and cleanup operations
The reactor units involved in the Fukushima Daiichi nuclear accident are located in close proximity to one another: it is this that 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 and deal with core meltdowns at three reactors and exposed fuel pools at three units, all at the same time32. 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 April 10th, 2011 to remove debris from around the reactors 1─4, and on April 17th, 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 December 11th, 2011. Although cooling was no longer required, it was still necessary to control large water leaks. On May 5th, 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 August 16th, the company said it had installed desalination equipment in the spent fuel pools35. The latter were cooled using seawater for some while, 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 meters of soil might need to be disposed of and removed from a large area in Fukushima, and four nearby prefectures, for which hydrothermal blasting is one of several techniques that was 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 form 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.
Roadmap for scrapping the nuclear reactors
At a session of the Fukushima Prefectural Assembly, which was investigating the accident at the Fukushima NPP, on September 7th, 2011 the TEPCO president, Toshio Nishizawa announced that the 4 damaged reactors would be scrapped. On November 9th, 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 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 radiation.
The reactors should be in a state of stable cold shutdown.
Three years later, the transfer of all spent fuel from the 4 damaged reactors to a pool inside the compound could be started.
After 10 years, work could begin to remove the melted fuel inside the reactors.
Decontamination of regions neighbouring Fukushima.
On October 10th, 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/year were measured would be cleaned. Previously it had been intended only to act where in the case of levels of > 5 mSv/year.
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/year, decontamination would be done step by step.
Within two years, radiation levels between 5─20 mSv/year should be cut down 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 felt that tourism would be discouraged there. On the other hand, those living in regions with readings of < 1 mSv/year 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.
Building an “ice-wall”, and increasing the storage capacity for contaminated water.
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 April 1st, 2015 to March 31st 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, and they have been used extensively in the U.S., 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.
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 that enabled the combustion of a variety of contaminated materials while minimizing 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 to water ratio, and mixing for 10 minutes, at 40°C, about 93% of the originally present caesium 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 sulphuric 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 sludge.
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 Fukishima accident are estimated to be statistically insignificant. Just 0.1% of the 110,000 cleanup workers at Chernobyl have so far developed leukemia, and not all of these can 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 or 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 leukemia. 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. 44 children were newly diagnosed13 with thyroid cancer, and other cancers by August 2013, in the overall Fukushima prefecture area, but the 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─2005 in the Chernobyl region, there have been 9 fatalities, which implies a > 99% rate of survival44.
Energy policy implications
Only two of Japan's nuclear reactors were still running by March 2012; some of those shut-down had been damaged by the quake and tsunami. Although local governments had been authorized 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, and 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 stabilize 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 afoot plans 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 finalized in 2016, as a result of which 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 megawatts of solar panels a year50.
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 March 11th, 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 assembles 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. Bulletin of the Atomic Scientists. March 1, 1-13. http://www.jsmillerdesign.com/FukushimaPapers/Bulletin%20of%20the%20Atomic%20Scientists-2012-Funabashi-0096340212440359.pdf
(35) Kazuaki, N. "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.