p. 625. Nuclear safety
- Maxwell Irvine
‘ Nuclear safety’ explains the risks associated with the use and production of nuclear power and responds to some of the concerns frequently raised. We can rule out the possibility of a nuclear explosion: nuclear power stations do not have weapons-grade fuel on-site. The automatic shut-down of reactors is a result of fail-safe engineering — if the reactor begins to operate outside its design parameters it closes itself down. It was precisely the lack of fail-safe engineering that resulted in the Chernobyl disaster. The safety record of nuclear power stands favourable comparison with any other global industry of a similar scale.
All human activity has associated risk. Before the Industrial Revolution, apart from war, these risks were largely personal. After industrialization, the ramifications of risk are much more widely spread.
The assessment of risk can be based on the analysis of experiential statistics or on a personal subjective basis which may, or may not, have a basis in fact. A large element in subjective risk assessment is fear of the unknown. Familiar activities will be assessed as having a lower risk associated with them than unfamiliar ones. The hazard factor can be high, but the risk can be mitigated by safety precautions.
Nuclear power deals with hazardous materials. It has its origins in a weapons programme that produced the most horrendous capacity for mass destruction. A major source of danger is radioactivity which, for most people, is an unfamiliar and mysterious phenomenon. Bad news headlines sell newspapers and the media frequently report nuclear incidents in more alarmist language than other more frequent industrial accidents would attract. The horrors of Chernobyl would seem to confirm people's worst fears.
The aim of our discussion of ‘nuclear safety’ is to explain the risks and to present them in perspective.
p. 63The hazards of nuclear power begin with the mining of uranium. As with all mining, there are the usual hazards augmented by concerns about the radioactive nature of uranium. In nature, uranium occurs in relatively low concentrations, and thus mining it requires very large volumes of rock to be processed. Most uranium is from open pit mines. Following the exposure of the ore by drilling and blasting, it is extracted via loaders and trucks. In the form of solid ore, the low concentration ensures that there is no direct radiation hazard. However, following extraction and drilling, dust can be inhaled, and its accumulation in the body presents a serious health hazard. Workers should wear face masks at all times. The fact that they spend much of their time in enclosed cabins and vast quantities of water are used to suppress the airborne dust levels greatly reduces the exposure to radiation.
Deep-mined uranium presents a more serious risk. Uranium is an alpha particle emitter and its radioactive decay chain produces radon-222. Radon is an inert radioactive gas with a half-life of 3.8 days. As a gas, radon can be inhaled and its alpha decay is known to be carcinogenic. The problem does not exist in open-pit mining where dangerous accumulations of radon do not occur due to natural ventilation. Underground, in deep pits, accumulations can be hazardous unless adequate ventilation is installed.
Early miners of uranium were reported to have developed small cell carcinoma and some American Navajos, who mined uranium in the south-west USA, were awarded compensation in 1990 under the US Radiation Exposure Compensation Act. In 2008, Areva attracted criticism for not alerting mineworkers at its uranium mine in northern Niger to the health hazards, and air, soil, and water were found to be contaminated.
Nearly 45,000 tonnes of uranium are mined annually. More than half comes from the three largest producers, Canada, Kazakhstan, and Australia. Significant amounts are also obtained from Namibia, Russia, Niger, Uzbekistan, and the USA.
p. 64Before the Second World War, scientists researching the new nuclear sciences were not fully aware of the dangers that they faced and many were exposed to harmful amounts of radiation. During the Second World War, women who painted numerals on aircraft instruments with radioactive paint so that could be seen in the dark frequently licked their brushes in order to get a fine point. Several of these workers developed mouth cancers. After the war, the principal users of nuclear material were the military. Clearly not all the personnel understood the dangers inherent in the use of this material. Warheads of enriched uranium or plutonium were machined, as are other metals, on lathes and drills that leave fine particles in the oil that was used to cool the metal during this operation. The standard procedure for getting rid of machine oils was to simply burn it. In the case of nuclear filings, this resulted in plumes of radioactive dust that were carried from the states of Arizona and New Mexico on northerly wind streams to be deposited as far north as Utah. This resulted in cancers in sheep and humans. In a number of cases, ordinary soldiers were taken to witness nuclear weapons tests without being given the appropriate radiation protection, resulting in a number of claims for compensation. As these incidents were reported, they increased the public's concern about nuclear safety.
The most serious reactor failure in the UK occurred at the Windscale site in the north of England. When the Second World War ended, the USA closed its nuclear weapons programme to all other countries, including its partners in the Manhattan Project. The UK embarked on its own nuclear weapons programme and built two graphite piles at Windscale in order to produce plutonium. At the time, relatively little was known about the consequences of exposing graphite to intense neutron fluxes apart from the fact that the graphite was degraded (see Chapter 3).
The Hungarian physicist Eugene Wigner had studied the effects of neutron degradation of graphite and shown that it could lead to the release of energy, causing hot spots in the graphite. To stop p. 65↵the graphite degradation threatening the structural stability of the core and to prevent a build-up of Wigner heating, the graphite was periodically heated to 250°C to promote annealing of the neutron-induced cracks. The fission process generated considerable heat and the pile was cooled by a high flow rate of cold air. The cooling system was not designed to deal with the heat required for the annealing process.
In October 1957, Windscale Pile 1 began to overheat. The fuel for the reactor was metallic uranium which, unlike the uranium oxide used in modern reactors, combusts at high temperature. To cool the reactor down, the operators turned up the flow of cooling air, not realizing the some of the graphite and uranium was already alight. The fresh air turned the core of the pile into a blast furnace. When it was realized what was happening, the air was turned off and replaced by carbon dioxide, but the supply was insufficient to check the fire. Finally, the fire was extinguished by water. The use of water was problematic; if the temperature was too high, the heat could cause the water to dissociate into oxygen and hydrogen, and a build-up of hydrogen could have led to an explosion that would have spread components of the pile widely over the surrounding countryside. This did not occur. Nevertheless, there was a significant release of radioactivity into the surrounding area, and it has been estimated that more than 200 people may have been affected.
The civil nuclear power programme gives rise to concerns about hazards to the general public, including the possibility of an explosive incident, either from plant failure, terrorist attack, or other external event at a power station, resulting in the widespread distribution of highly radioactive material through the air, water, and soil, the theft of radioactive material allowing terrorists the possibility to make an atomic bomb or a dirty bomb (i.e. a conventional bomb clad in a blanket of highly radioactive material that is scattered in the blast), and leaks of radioactive p. 66↵material from a nuclear installation (a power plant, reprocessing facility, or a waste depository).
First, we can absolutely rule out the possibility of a nuclear explosion; nuclear power stations do not have weapons-grade fuel on site.
The designs of nuclear installations are required to be passed by national nuclear licensing agencies. These include strict safety and security features. The international standard for the integrity of a nuclear power plant is that it would withstand the crash of a Boeing 747 Jumbo Jet without the release of hazardous radiation beyond the site boundary.
While there are clearly examples of rogue state removal of reactor core material from which to produce weapon-grade material, this is not a trivial process. It does, however, give rise to concerns about the proliferation of nuclear weapons. To meet these concerns, the Nuclear Non-Proliferation Treaty was opened for signature in 1968. Currently, 189 countries are signatories to the treaty. Of them, only the five permanent members of the UN Security Council (the USA, UK, France, Russia, and CPR) have nuclear weapons. North Korea initially signed the treaty, but withdrew in 2003 when it exploded its own nuclear bomb. Only three other recognized sovereign states are not signatories – India, Pakistan, and Israel. India and Pakistan have tested nuclear weapons, and Israel has a policy of secrecy regarding its nuclear weapons programme. The safety of the world with regard to the threat of nuclear weapons thus rests with the UN Security Council and the influence that it can bring to bear on member states. The test case for this is the UN discussions with Iran over its uranium-enrichment programme.
It is unrealistic to believe that a terrorist cell could attack a nuclear power station and remove material from an operating reactor core. There must be a fear that a terrorist organization could steal, p. 67↵or buy, from a rogue operator weapon-grade material from the stockpiles of plutonium from Cold War weapons that have been decommissioned. The safe remedy is the rapid utilization of these stockpiles in the manufacture of reactor fuels or permanent disposition in secure storage.
In 2003, the IAEA (International Atomic Energy Agency) reported that there were no detrimental health effects or adverse environmental impacts from short- or long-term exposure to depleted uranium weapons material.
In July 2007, Tokyo Electric Power Company's Kashiwazaki-Kariwa nuclear power station was hit by a earthquake registering 6.8 on the Richter scale. Operators were first alerted by a fire in an electrical transformer room. At the time, four of the plant's seven reactors were operating, and they all automatically shut down. The spent fuel from the reactors was stored in water pools. Twelve hours after the shock, operators were alerted to contaminated water leaking from the storage pools through cracks. In all, 315 gallons of contaminated water entered the ocean. The radiation leakage was estimated at one-billionth of Japan's legal limit. The plant was closed for nearly two years while safety checks were carried out.
In August 2009, the Chubu Electric Power Company's Hamaoka plant near Nagoya was hit by a 6.5-magnitude earthquake. Two operating reactors shut down automatically and a third was closed for routine maintenance. It is reported that there was a temporary increase of radioactivity in one of the reactors but no radioactive leakage. Post-shock investigations revealed 39 problems, including malfunctions of neutron monitor and auxiliary transformer operations.
In both Japanese incidents, the automatic shut-down of the reactors was as a result of fail-safe engineering. These require the reactors to be engineered according to ‘fail-safe’ principles. p. 68↵That is, if the reactor begins to operate outside its design parameters for whatever reason – human error or faulty equipment – it closes itself down. The two most widely reported incidents in the history of nuclear power had demonstrated the essential need for this feature to be implemented in all reactor designs.
On 29 March 1979, a reactor at Three Mile Island, Pennsylvania, went out of control. For the next week, it was the headline news in every paper across the world. Again, speculation was rife. Unless the reactor was brought under control, the pressure vessel would rupture and a plume of radioactive gas would roll across the state, resulting in thousands of deaths. It did not happen. A popular bumper sticker of the time read ‘more people were killed at Chappaquiddick [Chappaquiddick is where an aide to Senator Edward Kennedy was drowned] than at Three Mile Island’. In this regard, the fail-safe engineering of Three Mile Island reactor behaved according to its specification.
The importance of the ‘fail-safe’ principle was highlighted seven years later at Chernobyl in the Ukraine, then part of the USSR. The totalitarian Soviet regime did not encourage a questioning of those in authority. Where in the West protest groups are often an irritation to the establishment, but can freely challenge orthodoxy and influence policies, protests in the USSR could lead to banishment to the Gulags. At Chernobyl, the authority of the reactor operators was not questioned when they began an illegal reactor experiment in May 1986. The reactor began to run out of control and the lack of fail-safe engineering resulted in all the worst fears of Three Mile Island being realized. A build-up of hydrogen, a cause of concern during the Windscale fire, led to an explosion that blew the plant apart, with a large release of radioactivity. Two people died in the initial blast and 29 died from the immediate radiation burst. A further 200 people were treated for radiation burns and sickness. There was a great fear that exposure to the radiation would harm a much larger population for p. 69↵decades to come. Now, 20 years later, the impact appears to be less severe than originally feared, with fewer than 60 deaths directly attributable to the incident. The public harm appears to be limited to fewer than 2,000 cases of adolescent thyroid cancer, which is normally curable. It is true that the land once used for agriculture remains unsafe for food production and that this is a long-term consequence of the incident.
In both cases, the accidents were due to human failure. At Three Mile Island there were no injuries and the only losers were the reactor operators, for whom it was a financial disaster. We now know that the cause of the incident was the consequence of greed and the US tax regulations. If the plant operators could commission the plant by 31 December, they would get a full year's tax allowance. Thus the plant was rushed into service before every component had been fully checked and the staff fully trained. The incident was triggered by a combination of a faulty component and an inexperienced human response. The impact on the public perception of the dangers of nuclear power was increased by the Jane Fonda film The China Syndrome, a fictional version of a Three Mile Island type of event, released just a few days before its actual occurrence. Nearly 30 years were to elapse before proposals for new nuclear plants in the USA were to appear. At Chernobyl, an unauthorized experiment at a commercial nuclear station that was not fail-safe engineered resulted in disaster.
Why should we draw any comfort from such an explanation we have given for the incident at Chernobyl? Could a similar event not occur in the future with devastating consequences? It has to be stressed that the accident was completely avoidable if fail-safe engineering had been employed; the Chernobyl reactor would never have been licensed in North America or Western Europe. A nuclear plant in Finland originally of the Chernobyl design has been retro-fitted with fail-safe technology and continues to operate safely. The lessons to draw from these two incidents are p. 70↵that humans are fallible and that reactor designs should only receive licences for construction if they are adequately fail-safe designed. Indeed, they give great weight to the argument that national licensing of nuclear plant is an insufficient international safeguard. Since failure of a nuclear plant has the potential to produce damaging effects beyond the borders of the country in which it is operated, the licensing of the design should be subject to IAEA approval.
However, no matter how careful the planning or the regulatory framework, or how excellent the construction, not all risks can be eliminated. This was graphically illustrated when the east coast of Japan was struck by an earthquake and ensuing tsunami on 12 March 2011. The final total death toll was in the order of tens of thousands. Hundreds of thousands of people saw their homes and belongings totally destroyed, along with hospitals and schools. Large sections of the national infrastructure of road and rail systems and water and electricity supply suffered considerable disruption. There were major explosions and fires at gas and oil storage facilities. The final economic cost of this disaster is likely to top a trillion US dollars. Japan is one of the world?s largest economies, and the economic impact quickly spread across the globe. In the midst of all this destruction and chaos, concerns naturally arose about the impact on Japan?s nuclear power plants. We have already noted the earlier impact of earthquakes on the Kashiwazaki-Kariwa plant near Tokyo in 2007 and the Hamaoka plant near Nagoya in 2009. Both these earthquakes measured less than 7.0 on the Richter scale. The March 2011 quake measured 9.0 on the Richter scale and triggered a devastating tsunami.
There were 17 nuclear power sites in Japan operating 55 nuclear reactors, most of which were BWRs. Concerns quickly concentrated on the Fukushima-Dalichi plant north of Tokyo. The plant operated six BWRs built in the 1970s, and it was obvious that the cooling systems had been seriously compromised. As temperatures in the reactor cores rose, a number of explosions shook the p. 71↵plant, but the containment vessels remained intact. In addition to the fuel rods overheating, the highly radioactive spent fuel rods, kept in storage pools, started to heat as the pools lost water. Externally, water and electricity supplies to the plant had been cut. The authorities struggled to restore power and water supplies to the plant.
There was some radioactive leakage from Fukushima detected in Tokyo, and drinking water was briefly contaminated with radioactive iodine. Raised radioactivity levels were also detected in spinach crops and milk from farms close to the plant. The authorities moved rapidly to remove these products from the market, though experts concluded that these had posed negligible risk to human health.
An emergency 30-km exclusion zone was established around the site and, as a precaution, the region was evacuated, adding further to the difficulties arising from the nearly half-million refugees already rendered homeless by the earthquake and tsunami.
As with previous nuclear incidents, a full international enquiry was initiated and lessons will be learned. But the enquiry may take several years to complete. (The site of the Windscale fire is still being monitored 50 years after the event!)
Some sections of the media made comparisons with Chernobyl. It is relevant to compare the worst-case scenario at Fukushima with Chernobyl. The worst-case scenario was that a hydrogen-based explosion sufficiently powerful to destroy the already weakened containment vessel occurred. Because of the different construction of the two reactors, the blast would have been less strong than that at Chernobyl. The blast consequences for personnel in the reactor at the time of such an explosion were likely to be similar. However, the developments at Fukushima were fully monitored, and it may have been possible to evacuate all personnel before an explosion. While the long-term impact on personnel in the reactor buildings p. 72↵will take years to assess, and some fire-fighters were exposed to intense radiation levels, they were wearing the best radiation-protection garments available. The evacuation of the region around the site would have greatly reduced the radiation hazards to the local population. The Chernobyl explosion released a plume of radioactivity that was driven north and west by prevailing winds across the highly populated European continent. The plume was detected in Scandinavia. As a precaution, meat and dairy produce from contaminated grazing land was taken off the market. There has been no suggestion that anyone outside the Ukraine suffered harm from the radiation plume. A plume from a Fukushima explosion would naturally be driven eastwards over the Pacific Ocean and, although it might have been eventually detected on the west coast of North America, it would not have been harmful to humans.
Unlike Three Mile Island and Chernobyl, there is no suggestion of human failure in the operation of the Fukushima plant. At Three Mile Island, not all components of the reactor had been fully tested before operations began, and Chernobyl was not constructed to current fail-safe engineering standards and was the subject of an illegal experiment. At Fukushima, the design was to current safety standards, taking into account the possibility of a severe earthquake; what had not been allowed for was the simultaneous tsunami strike. It is recognized that human activity in regions of geological instability carries additional risk, and Fukushima serves as a timely reminder that the forces of Nature can still upset the best-laid plans of humankind.
While Fukushima dominated the headlines, the nuclear component of the tragedy that followed in the wake of the earthquake and tsunami in Japan represented a very tiny fraction of the cost, in both financial and human terms, of the disaster.
Nothing short of a human disaster can categorize the incident at Chernobyl. However, it should be seen in relation to other large-scale industrial activity. For example, in December 1984 the Union p. 73↵Carbide pesticide plant in the city of Bhopal in the Madhya Pradesh state of India released 42 tonnes of toxic gas. More than half a million people were exposed. Approximately 9,000 people died within the first 72 hours, and it is estimated that 25,000 have died since then from gas-related illness.
There have been many reports of minor incidents at nuclear installations, but none involving the loss of life associated with the nuclear aspect of the plants. At each stage, as the technology advanced, the limits on reportable incidents have been lowered. In the UK, most of these incidents have related to waste storage leaks at the Sellafield and Dounreay sites. Here, waste has been stored in temporary facilities awaiting political decisions on its final disposal. It seems incredible that it took 50 years from the opening of the first reactor to the commissioning by the UK government of the Committee on Radioactive Waste Management and its report.
One of the most alarming incidents was the report of cancer clusters around nuclear sites in the UK, most seriously at Sellafield. The cancer was of an unusual form in that it was among young children. It was proposed that the cause was due to radiation received by fathers working at the nuclear plant before the conception of their children. The reports had a devastating effect on many families. Detailed medical studies have revealed that the cancer clusters had nothing whatever to do with the nuclear nature of the plants but rather is an epidemiological feature of large-scale construction projects in rural areas where there are relationships between the incoming project workers and the local population. While the initial reports were world news, the more mundane explanation has received little publicity.
The effects of radiation are short-ranged and thus can only become more widespread if it is water soluble or airborne. These possibilities carry the additional hazard that the radioactive material can be ingested either from breathing contaminated air or drinking contaminated water. This hazard is amplified in the p. 74↵case of radioactive isotopes that chemically mimic elements that the body relies on for specific functions. Thus iodine is naturally concentrated in the thyroid gland. Radioactive isotopes of iodine are a by-product of fission and do exist in reactor cores, and, as we saw, the bulk of the radiation patients at Chernobyl were treated for thyroid cancers. A common precautionary measure, if there is thought to be the possibility of leak of radioactive material, is to give injections of iodine in advance to saturate the thyroid gland so that it does not accumulate the radioactive isotopes.
Another common nuclear fission product is radioactive strontium. Strontium is chemically similar to calcium, which the body concentrates in the bones. The bones are where blood is created, and thus dairy animals ingesting strontium-contaminated grass may produce milk, a common source of calcium for humans, which carries the risk of producing leukaemia. Indeed, the milk and meat of all grazing animals pose a potential hazard if the pasture has been contaminated by radioactive fallout. The prime concerns in decommissioning a nuclear plant and the safe storage of radioactive waste are to prevent radioactive dust entering the atmosphere and the prevention of radioactive contamination of water supplies.
Throughout discussions of these contentious issues, there are two topics that polarize the debate: is there a safe level of radioactivity that can be tolerated, and how long must the lifetime of the secure store be?
Radioactive strengths are measured in Becquerels (1Bq = 1 disintegration per second). In dealing with radioactive materials, a more practical unit, the Curie (1Ci = 3.7 x 1010Bq), is used. The biological impact of radioactivity depends not just on the number of radioactive emissions but also on their type (alpha, beta, gamma, neutrons) and energy; it also depends on the region of the body receiving the radiation; for this reason, radiotherapy is p. 75↵carefully focused on the source of cancer tumours. The severity of the biological impact is measured by the deposition of energy in Sieverts (1Sv = 1 Joule/kg =1m2/s2). For a normal adult human, whole-body exposure leads to the following effects
1Sv → nausea
2.5Sv → hair loss and haemorrhaging
3.5Sv → 50% chance of death within 30 days
6Sv → almost certain death
Radioactivity is a part of our natural environment. It comes to us from the Sun and the stars and from the rocks beneath our feet. Indeed, it is an essential component in the evolution of plants and animals. Natural radiation can randomly cause minor biological mutations. Most of these are short-lived and not passed down through the generations; some may produce cancers, and some produce genetic modifications that are passed to future generations. Successful mutations provide benefit to the individual and natural selection sees these mutations passed on.
New York may be considered to be a hazardous city, but few would consider radiation from the granite of Grand Central Station, which exceeds the current safety limit imposed on the operators of nuclear power stations at the edge of their sites, to be a significant danger. Mountaineering is a hazardous activity, but the increase in radiation exposure with altitude is not a danger often considered.
Most people love the sunshine. At one level, it provides the heat and light that make our lives possible. We are all aware that overexposure presents a hazard in the form of sunburn or, in extremis, melanoma (skin cancer). However, we are also aware that protection can be effectively provided by a simple barrier cream. The beaches of the world attest to the confidence that most people have handling the dangers of solar radiation which arises from the nuclear activity in our Sun.
p. 76Cosmic rays interact with our atmosphere to produce a radioactive form of carbon (carbon-14, or radio carbon). This radioactive carbon is completely mixed with stable carbon-12 in our atmosphere and is taken up by plants during normal photosynthesis. Thus, all our food naturally contains radioactive material, as does the air we breathe. This is not a cause for concern. It may be that cosmic rays and their radioactive products do cause mutation in an individual cell, a process that has allowed evolution to occur, but the risk of serious health implications is negligible.
We have no choice but to live with this natural radioactive background. Our atmosphere protects us from most of the solar and cosmic radiation, and sunblockers and hats from the rest. Buildings in granite areas and built of granite may now be checked for ventilation to ensure that there is no accumulation of radon gas.
In setting ‘safe’ levels of radiation for human activity, this variable natural background is a useful yardstick. The worldwide average annual natural human dose from the natural background is 2.5mSv (2.5 x 10−3Sv), and varies from around 1mSv to a high of over 200mSv with location. This is to be compared with the human contribution from all nuclear activity (both military and civil) and other non-nuclear industries of 5μSv (5 x 10−6Sv).
The World Health Organization has declared that the largest human activity contributor to global radiation is not the nuclear industry but fly-ash from burning coal, which it estimates causes 350 deaths per year globally. The largest nuclear contribution comes from early above-ground testing of nuclear weapons. This contribution peaked at 0.15mSv in 1963 and is declining at a rate of 0.005mSv per year.
With regard to the question ‘what should the safe radiation limit for the general public be?’, there are those who hold that if there is any detectable source of radiation then this is p. 77↵unacceptable. As our capacity to measure lower and lower levels of radiation has increased, safety levels have steadily been lowered. National limits vary, but are currently set at around 10μSv/year, or about 1% of the regional variation in the natural background. In this debate there are no absolutes. The impact of radiation, both natural and produced by humans, is statistical in nature. It should be recalled that radioactive material never completely stops radiating. When we talk about the half-life of a source of radioactivity, we mean the time during which the level of radiation from that source halves. After several such periods, the level has fallen to such an extent that we consider it ‘safe’. All human activity carries a risk; the question is, to what extent should that risk be mitigated?
With regard to secure, safe radioactive waste disposal, the question is ‘how long must the HLW store be secure?’ Initially, the USA proposed 10,000 years. Currently, more stringent limits of a million years are being suggested. Again, there are no absolutes. A personal view is that looking back over human development in the past 10,000 years, I can have little concept of the world 10,000 years in the future, far less a million years.
The nuclear industry is rightly the most stringently controlled industry in the world. Incidents involving nuclear plant are widely reported. Many incidents at nuclear plants are due to engineering failures unconnected with the nuclear aspects of the site. A cull of all reported civil nuclear incidents worldwide reveals that, excluding the Chernobyl disaster, in the 1950s one nuclear plant worker in Yugoslavia developed leukaemia, in the 1980s two plant workers were killed in Argentina, and in 1999 two plant workers died in Japan. Despite the fact that the records may not be complete, principally due to the secrecy surrounding such incidents in the former USSR, the safety record of nuclear power stands favourable comparison with any other global industry of a similar scale.