Chapter 38: Comparison Risks

This chapter was published on “Inuitech – Intuitech Technologies for Sustainability” on October 4, 2012.

Perhaps one nuclear accident could be regarded as too many from a safety perspective simply because nuclear energy continues to be considered as an antagonistic technology not only by some politicians but also by many members of the public.  Nevertheless, from a realistic point of view, there were only four nuclear accidents in the world history of nuclear energy which covers a period of more than fifty years.  It’s important to recognize that each nuclear accident was treated as a unique opportunity by the regulatory organizations around the world to improve means of preventing and mitigating the consequences of accidents by the application of the concept of defence-in-depth, in which consecutive and independent levels of protection are used to minimize or eliminate harmful effects that could be caused to people and the environment.

The objectives of defence in depth, according to the International Atomic Energy Agency (IAEA), are to:

  • Compensate for potential human and component failures:
  • Maintain the effectiveness of the barriers by averting damage to the plant and to the barriers themselves; and
  • Protect the public and the environment from harm in the event that these barriers are not fully effective.

Here is a brief summary of the nuclear accidents:

1.      The Three Mile Island Accident (USA):

Aerial view of Three Mile Island nuclear plant near Harrisburg, Pa., scene of a nuclear accident, Thursday, March 28, 1979. The plant started leaking radioactive steam contaminating the area. (AP Photo)

Source: Britanica

The very first nuclear accident, Three Mile Island, was occurred on March 28, 1979 due to the fact that the operators were unable to diagnose properly to the unplanned automatic shutdown of the reactor.  Some radioactive gas was released a couple of days after the accident but not enough to cause any dose above background levels to local residents.  There were no injuries or adverse health effects from the Three Mile Island.

2.      The Chernobyl Daiichi Accident (USSR):

The Chernobyl accident was occurred on April 25, 1986 and it was the result of a flawed reactor design that was operated with inadequately trained personnel.  The resulting steam explosion and fires released at least 5 percent of the radioactive reactor core into the atmosphere and downwind.  Two Chernobyl plant workers died on the night of the accident, one later, and a further 28 people died within a few weeks as a result of acute radiation poisoning.


The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCLEAR) says that apart from increased thyroid cancers, “There is no evidence of a major public health impact attributable to radiation exposure 20 years after the accident.”  Resettlement of areas from which people were relocated is ongoing.

3.       The Tokaimura Criticality Accident (Japan):

The Tokaimura Criticality accident was occurred on September 30, 1999 and according to the IAEA, the cause of the accident was “Human error and serious breaches of safety principles”.  As a result of this accident, three workers received high doses of radiation in a small Japanese plant preparing fuel for an experimental reactor.  The accident was caused by bringing together too much uranium enriched to a relatively high level, causing a “criticality” (a limited uncontrolled nuclear chain reaction), which continued intermittently for 20 hours.

Source: thenation

A total of 119 people received a radiation dose over 1 mSv from the accident, but only the three operators’ doses were above permissible limits. Two of the doses proved fatal; and

4.      The Fukushima Daiichi Accident (Japan):

Following a major earthquake, a 15-metre tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors, causing a nuclear accident on March 11, 2011. All three cores largely melted in the first three days.  The accident was rated 7 on the INES scale, due to high radioactive releases in the first few days. Four reactors are written off – 2719 MWe net.  After two weeks the three reactors (units 1-3) were stable with water addition but no proper heat sink for removal of decay heat from fuel. By July they were being cooled with recycled water from the new treatment plant. Reactor temperatures had fallen to below 80C at the end of October, and official “Cold Shutdown Condition” was announced in mid-December.  Apart from cooling, the basic ongoing task is to prevent release of radioactive materials, particularly in contaminated water leaked from the three units.


There have been no deaths or cases of radiation sickness from the nuclear accident, but over 100,000 people had to be evacuated from their homes to ensure this. Government nervousness has delayed their return.

According to the report published by the Nuclear Energy Agency (NEA) on the subject of “Comparing Nuclear Accidents Risks with those from other Energy Resources”, comparison of real accident statistics for severe accidents (Defined as those resulting in 5 or more prompt fatalities) with the theoretically calculated accident statistics of nuclear power plants show that contrary to many people’s perception, nuclear energy presents very much lower risks.

Here are some examples of severe energy related accidents (Other than nuclear energy):

  • More than 2,500 people are killed every year in severe energy related accidents and this figure is increasing as energy demand increases; and
  • Between 1969 and 2000 there were 2,259 and 3, 713 fatalities in the coal and oil energy chains respectively in the Organization for Economic Co-operation and Development (OECD) countries, and 18,017 and 16,505 fatalities in non-OECD countries.  Hydropower was responsible for 29,924 deaths in one incident in China.  In contrast, there has only been one severe accident in nuclear power plants over this period of time (Chernobyl) which resulted in 31 fatalities.

Deutsche Bank Group, DB Climate Change Advisors, published a report, The 2011 Inflection Point for Energy Markets – Health, Safety, Security, and the Environment, on May 2, 2011.  This report described the fuel sources and documented the attributes of each source with the focus on safety, health, security, and the environment which could serve as meaningful background information before proceeding to conduct a comparative analysis of the accidents.   Slide1

Out of all the attributes listed under each energy source, only the following seven attributes are considered to be positive:

  • Coal – Security – Relatively Abundant;
  • Nuclear – Security – Very Limited Feedstock;
  • Nuclear – Environment – Emissions Free;
  • Gas – Security – Relatively Abundant;
  • Gas – Environment – Relatively Low SOX/NOX and Carbon Emissions;
  • Renewables – Security – Wind/Solar: Very Limited Material Feedstock; and
  • Renewables – Environment – Low/Zero Emissions. 

Here is how the report described each fuel source with the focus on safety, health, security and the environment:

1.      FUEL SOURCE – OIL:

While oil ranks very high with regard to environmental concerns due to the large amounts of carbon and other emissions that occur during combustion of this fuel, oil is also the fuel that causes the most energy security anxiety as so many countries are dependent on it for their energy requirements.  In particular, the transportation sector is a very large consumer of energy around the world, and this sector tends to be highly dependent on oil derived petroleum, with few or no substitutes available.  Many countries are also reliant on oil as a key source of power generation.  Yet, a substantial portion of oil reserves are located in particularly unstable regions, and 41 percent of oil production comes from members of the Organization of the Petroleum Exporting Countries (OPEC).  With regard to human health and safety, oil is similarly a fuel of high concern due to the particulates, sulfur, nitrogen oxides, carbon monoxide, and greenhouse gases emitted during combustion, due to explosions at some oil rigs, and due to political violence against oil workers in some producing countries;


Coal ranks very high with regard to health and environmental concerns due to the emissions of sulfur and nitrogen oxides, particulates, heavy metals, and greenhouse gases from coal plants, and the resultant negative implications for human health and the environment.  These effects are particularly apparent in countries with less stringent air emissions standards.  It is estimated in the US that pollution from coal-fired power plants result in the premature deaths of more than 13,000 people a year.  Coal also ranks high with regard to safety risks, given the safety issues involved in storing highly contaminated coal ash or sludge and also due to mining accidents, which are particularly prevalent in countries with less stringent mining safety regulations.

Coal mining deaths have reduced to less than 50 per year in the US over the past two decades but in China, for example, there were over 2,433 coal mining deaths in 2010.  China remains the country with the highest number of fatalities from coal mining in the world despite a nearly 50 percent decline from 4,746 deaths in 2006.  Although coal ranks high with regard to human health and safety concerns, coal is not generally a fuel that endangers substantial energy security concerns as coal reserves are relatively abundant and tend to be located in particularly stable countries – more than 38 percent of global reserves are located in the US and Australia, with a combined 340 years of future extraction capacity based on the current rates of production.  Coal is also relatively risk-free to transport, as it is not an explosive fuel and does not carry the risk of spills, unlike oil, for example;


Similarly to coal, there is an abundance of gas reserves in politically stable countries – particularly the US – with strong export potential.  In Europe, reliance on gas for power generation is considered more risky due to geo-political concerns, given that Russia holds the vast majority of gas reserves in the region.  However, the fuel is being increasingly transported between countries and regions in liquid form (Liquefied Natural Gas or LNG).  Relative to other fossil fuels, natural gas is also not considered to be a particularly risk fuel source in terms of health or environmental concerns due to its relatively lower emissions of greenhouse gases (Although this has recently been an issue of some debate.), and other pollutants, and established extraction procedures.  In terms of safety, however, gas-induced explosions (e.g. Pipeline leaks, LNG tank explosions.) pose a significant risk element for natural gas as a fuel source – there has been an upward trend in frequency of gas-related accidents both in the European Union (EU) and in non-OECD countries over the last thirty years.  More recently, hydro-fracking processes for extraction of shale gas also caused some environmental, health, and safety concerns with regard to contamination of water resources and the creation of underground fissures, although these risks have not yet been fully evaluated;


This fuel is more difficult to rank, given that the probability of a nuclear accident is very low, but the health, safety, security (In terms of loss of power generation) and environmental and public acceptance implications are extremely severe and long-term, and are also extremely expensive to remedy.  In the case of Fukushima or another nuclear accident then, nuclear is very risky with regard to health, safety, security, and the environment.  By contrast, nuclear under a “business as usual” scenario is a medium to high risk with regard to health, safety, and the environment – nuclear workers will experience some radiation exposure, there is a chance of an accident (Minor or major), and the spent fuel is highly radioactive and difficult to dispose of, posing some environmental and security risks.  In terms of security of domestic energy supply though, nuclear is viewed as a very attractive fuel source (Particularly in countries with few natural fossil fuel resources) as it relies on very small quantities of uranium feedstock to produce electricity.  This explains why nuclear has been so popular in countries with few domestic fossil energy resources such as Japan and France; and


5.1          Renewables – Hydro:

There have been a few incidents of hydro dams being breached in recent decades, with some fatalities – The Banqiao dam failure in China in 1975 is the most infamous and deadly incident – with an estimated 30,000 people killed as a result of heavy rainfall, poor communications, and mismanagement.  In addition, construction of large dams (For example, the highly controversial Three Gorges Dam in China) has been criticized for population development and ecological damage for flooding very large areas – although this is far less of an issue with small hydro, which now accounts for the majority of new hydro build opportunities.  Hydro is also associated with excessive water usage, preventing upstream management of fish, and some fish-kill – the latter can occur if insufficient flow is maintained out of the dam (Flow is regulated in the US, for example), and as a result of fish passing through a dam’s turbines.  In general, if correctly designed, regulated, maintained, and efficiently operated, hydro (Particularly small hydro) should be a very low risk form of generation in terms of health, safety, security, and the environment, given the simple technological design, the lack of feedstock required (Once the dam is built), the water “consumed” is actually being stored and then released and the zero emissions from generation;

5.2  Renewables – Wind:

With regard to safety and security, wind ranks very low due to the negligible mortality rate involved in construction of wind components and wind farms, and the fact that once installed wind energy requires virtually no additional material inputs (Apart from occasional replacement of components), minimizing any commodity price or import risk.  The environmental impact of wind farms is also low, although there is some bird-kill associated with this technology – the US fish and Wildlife Service estimated 440,000 birds are killed by wind blades each year in the US, and that is likely to increase as the prevalence of wind farms increases.  It should also be noted, however, that up to 500 million birds are killed each year by domestic cats in the US, given an indication of the risk of wind blades relative to other bird-kill factors.  In addition to bird-kill, some scientists have cited human health concerns for residents living in close proximity to wind farms, arguing that the constant vibrations can cause heart disease, tinnitus and sleep deprivation due to disruption or abnormal stimulation of the inner ear vestibular system;

5.3        Renewables – Solar:

Solar energy ranks very low with regard to health, safety, and security concerns for similar reasons as for wind.  Once operating, solar is also a zero-emission source of energy, so the only environmental concerns are those associated with the manufacturing solar photovoltaic (PV) wafers, cells and modules, and excessive water usage in the process of generating Concentrated Solar Power (CSP or Solar Thermal).  The latter can generally be overcome by installation of dry cooling systems at the CSP plant, with estimated water use reductions of up to 90 percent.  With regard to solar PV manufacturing, there are two dominant types of PV cells – thin-film and silicon.  The process of producing electronic – grade silicon for solar cell production is fairly energy intensive, and cannot therefore be considered zero emissions.  Of greater concern to some, however, is the waste product generated during thin-film solar production – cadmium telluride is one of several materials used to convert sunlight into electricity in thin-film modules, and is a higher toxic metal.

The argument against the use of cadmium in thin-film solar production is that the modules could potentially could catch fire and release toxic substances or that once the modules have outlived their useful life these substances could be released during disposal.  However, cadmium is a by-product of zinc mining and thus a waste material at the start, so advocates argue that thin-film modules are sequestering cadmium for at least 20 years (Average lifetime of a solar module).  In addition, thin-film solar companies have been working to develop recycling programs to re-use the cadmium removed from solar modules in nickel-cadmium batteries.  The environmental risk of thin-film solar and CSP plants (Without dry cooling plants) are thus issues of environmental concern and have been characterized as medium;

5.4          Renewables – Bioenergy:

Bioenergy covers a range of different forms of energy, including biomass and biogas power, and biofuels.  With regard to the environment, biomass power is generally characterized as carbon-neutral as the feedstock is usually waste product (e.g. Wood Pellets) that would otherwise decay naturally and release carbon.  There are, however, some other emissions including particulates, nitrogen and sulfur oxides – although these are considerably lower from biomass burning than fossil fuels.  Biogas generally reduces emissions as it involves capturing and generating power from methane emissions during the organic decomposition of animal or agricultural waste.  Biofuels in particular, “first generation” biofuels (In the US, this is typically corn ethanol), have been the most controversial form of bioenergy with regard to the environment and security due to the huge quantities of water consumed in producing these fuels, the relatively low energy return on energy invested, and as corn ethanol diverts a food-source (As opposed to be waste product) towards fuel production.  These technologies are therefore ranked as medium with regard to environmental concerns.  With regard to health, safety, and security concerns, they are ranked as very low as there are negligible adverse of health or safety effects from producing power or fuel from bioenergy, and the feedstock tends to be locally sourced; and

5.5           Renewables – Geothermal:

Traditional geothermal technologies are touted for their provision of secure, baseload power, and the health and safety risks of geothermal drilling and operations are low.  The only real concern with geothermal is associated with enhanced geothermal systems (EGS), a new “generation” of geothermal technologies whereby developers deliberately fracture hot rock formations with high-pressure water blasts to access geothermal heat.  This process has been associated with some induced seismic activity – for example, an EGS project in Basel, Switzerland, caused a 3.4 magnitude earthquake in 2006, was subsequently shutdown by the Swiss authorities after studies determined the project would trigger earthquakes and cause millions of dollars of damages each year.  And a California, US-based EGS project named AltaRock received considerable negative press coverage in 2009 due to perceived seismic risk from the project – The company commissioned an induced seismicity evaluation in an attempt to ally public safety concerns, but the project was subsequently called off anyway due to local concerns, combined with operational problems and cost over-runs.

The following graph (Figure: 38-02) sets out a matrix for looking at the key fuel sources in the electricity market against the criteria of health, safety, security, and the environment in terms of risk.  These overall risk ratings are driven by the preceding considerations, but are not a quantitative, but qualitative synthesis.Slide2Severe accidents in the energy sector have been identified as one of the main contributors to manmade disasters. Based primarily on the historical experience, the Paul Scherrer Institute (PSI) carries out extensive analyses of severe accidents in the energy sector. The work covers severe accident risks in fossil energy chains, i.e. coal, oil, natural gas and Liquefied Petroleum Gas (LPG), as well as hydropower and nuclear.

In 1998, an Energy Related Severe Accident Database (ENSAD), a highly comprehensive database on severe accidents with emphasis on the energy sector, was established by PSI. The historical experience represented in this database was supplemented by probabilistic analyses for the nuclear energy, to carry out a detailed comparison of severe accident risks in the energy sector. The database allows performing comprehensive analyses of accident risks, which are not limited to power plants but cover full energy chains, including exploration, extraction, processing, storage, transports and waste management.

Since then, the ENSAD database and the analysis have been much extended, not only in terms of the data as such but also what concerns the scope of applications. The main objectives of this activity are:

  • To carry out comparative assessment of severe accidents in the energy sector; and
  • To assess the external costs associated with severe accidents within the various energy chains.

Thus, the results can support policy decisions and serve as an essential input to the evaluation of sustainability of specific energy systems. Lack of estimates of external costs of non-nuclear accidents was earlier identified as one of the major limitations of the state-of-the-art of externality assessment. Uses of the database for engineering purposes are feasible but have not been fully exploited until now.

According to a Final Report on Severe Accident Risks including Key Indicators, published in January 2011, here is an overview of energy chains and technologies, and the data sources and assumptions used for the comparative analysis based on ENSAD (In addition to other criteria, the main criteria was used to include accidents with at least five fatalities): Slide3

Here is a graphical representation of Accidents and Fatalities  for Fuel Source – Oil:Slide4Here is a graphical representation of Accidents and Fatalities for Fuel Source – Natural Gas:Slide5Here is a graphical representation of Accidents and Fatalities for Fuel Source – Nuclear:Slide6Here is a graphical representation of Accidents and Fatalities for Fuel Source – Renewable:Slide7Here is an overview of the accidents and fatalities for all sources of energy, covering from 1970 to 2008 with the only exception where oil accidents for China were included only from 1994 to 1999:Slide8Here is a graph representing the total accidents and fatalities: Slide9The conclusions based on the studies conducted by the NEA specialist committees on nuclear safety, the Committee on Nuclear Regulatory Activities and the Committee on the Safety of Nuclear Installations, are listed below (The data about the accidents and fatalities included in these conclusions reflects the tables and graphs presented previously):

1.      Comparative Analysis of Severe Risks in the Energy Sector:

  • Even though nuclear power is perceived as a high-risk, comparison with energy sources shows far fewer fatalities;
  • Between 1970 and 2008 (1994 to 1999 for China in case of Coal), there were 1,999 severe accidents with 54,986 fatalities in the coal, oil, natural gas, and renewables around the world.  By comparison the one severe accident at Chernobyl killed 31 people.  The accident at Fukushima Daiichi didn’t qualify as severe accident simply because there were no deaths involved with this accident; and
  • The latent fatalities following the Chernobyl accident are estimated to be between 9,000 and 33,000 over the next 70 years.  By comparison, OECD estimates of the latent deaths from particulates in air pollution were at a level of 960,000 for the year 2000 alone, with about 30 percent (288,000) of this pollution attributed to energy sources.2.

2.    Trends in Predicted Sever Accident Risks:

  • The predicted frequency of a severe nuclear power plant accident followed by a large radioactivity release has reduced by a factor of 1,600 between the original designs of early Generation I reactors and Generation III/III+ plants being built today.  However, the safety performance of these earlier plant designs has also improved by that upgrades over subsequent years; and
  • In the early 1960s, an accident that resulted in severe core damage may have led to a large radioactivity release: However, engineering improvements mean that the probability of a release to the environment from a Generation III/III+ reactor is about ten times less than that of core damage.

3.     Public confidence in Nuclear Operations:

  • While nuclear power remains a contentious issue, public confidence in nuclear power evolves slowly but there is a correlation between awareness of the technology and trust;
  • Public opinion polls show a strong correlation between trust in regulators and trust that nuclear plants can be operated in a safe manner; it is clear that trust in regulatory bodies is crucial to gaining support for nuclear energy programmes; and
  • Openness and transparency in government decisions about the use of nuclear power and in the licensing process are vital elements in improving public confidence.

The Generation IV International Form (GIF) was established in 2000 with the focus to identify and select six nuclear energy systems for further development, ensuring these systems will excel in safety and reliability, and will have a very low likelihood and degree of reactor core damage.  These objectives will be, achieved by: Increasing the use of inherent safety features, robust designs, and transparent safety features that can be understood by non-experts; and Enhancing public confidence in the safety of nuclear energy.  Depending on their respective degrees of technical maturity, the Generation IV systems are, expected to become available for commercial introduction in the period between 2015 and 2030 or beyond.


  1. Chapter 34 – Nuclear Energy – Safety – Accidents – Three Mile Island;
  2. Chapter 35 – Safety – Accidents – Chernobyl;
  3. Chapter 36 – Nuclear Energy – Safety – Accidents – Tokaimura Criticality;
  4. Chapter 37 – Nuclear Energy – Safety – Accidents – Fukushima Daiichi;
  5. NEA – Comparing Nuclear Accident Risks with Those from Other Energy Sources;
  6. The 2011 Inflection Point for Energy Markets – Health, Safety, Security, and Environment;
  7. ENSAD – Energy Related Severe Accident Database;
  8.  SECURE;
  9. Security of Energy Considering its Uncertainty, Risk, and Economic Implications; Inuitech – Chapter 6 – Generation III Advanced Nuclear Reactors – Part 1; and
  10. Chapter 8 – Generation IV Advanced Nuclear Reactors.

Chapter 39