Nuclear Radiation and Health Effects

(Updated December 2012)

• Natural sources account for most of the radiation we all receive each year. 
• The nuclear fuel cycle does not give rise to significant radiation exposure for members of the public, and even in two major nuclear accidents radiation has caused no harm. 
• Radiation protection standards assume that any dose of radiation, no matter how small, involves a possible risk to human health. This deliberately conservative assumption is increasingly being questioned. 

Radiation is energy in the process of being transmitted, which may take such forms as light, or tiny particles much too small to see. Visible light, the ultra-violet light we receive from the sun and from sun-beds, and transmission signals for TV and radio communications are all forms of radiation that are common in our daily lives. These are all referred to as 'non-ionizing' radiation.

Radiation particularly associated with nuclear medicine and the use of nuclear energy, along with X-rays, is 'ionizing' radiation, which means that the radiation has sufficient energy to interact with matter, especially the human body, and produce ions, i.e. it can eject an electron from an atom.

X-rays from a high-voltage discharge were discovered in 1895, and radioactivity from the decay of particular isotopes was discovered in 1896. Many scientists then undertook study of these, and especially their medical applications. This led to the identification of different kinds of radiation from the decay of atomic nuclei, and understanding of the nature of the atom. Neutrons were identified in 1932, and in 1939 atomic fission was discovered by irradiating uranium with neutrons, and this led on to harnessing the energy released by fission.

Types of radiation

Nuclear radiation arises from hundreds of different kinds of unstable atoms. While many exist in nature, the majority are created in nuclear reactions^a. Ionizing radiation which can damage living tissue is emitted as the unstable atoms (radionuclides) change ('decay') spontaneously to become different kinds of atoms.

The principal kinds of ionizing radiation are:

Alpha particles

These are helium nuclei consisting of two protons and two neutrons and are emitted from naturally-occurring heavy elements such as uranium and radium, as well as from some man-made transuranic elements. They are intensely ionizing but cannot penetrate the skin, so are dangerous only if emitted inside the body.

Beta particles

These are fast-moving electrons emitted by many radioactive elements. They are more penetrating than alpha particles, but easily shielded – they can be stopped by a few millimetres of wood or aluminium. They can penetrate a little way into human flesh but are generally less dangerous to people than gamma radiation. Exposure produces an effect like sunburn, but which is slower to heal. Beta-radioactive substances are also safe if kept in appropriate sealed containers.

Gamma rays

These are high-energy beams much the same as X-rays. They are emitted in many radioactive decays and are very penetrating, so require more substantial shielding. Gamma rays are the main hazard to people dealing with sealed radioactive materials used, for example, in industrial gauges and radiotherapy machines. Radiation dose badges are worn by workers in exposed situations to detect them and hence monitor exposure. All of us receive about 0.5-1 mSv per year of gamma radiation from cosmic rays and from rocks, and in some places, much more. Gamma activity in a substance (e.g. rock) can be measured with a scintillometer or Geiger counter.

X-rays are also ionizing radiation, virtually identical to gamma rays, but not nuclear in origin.

Cosmic radiation consists of very energetic particles, mostly protons, which bombard the Earth from outer space.

Neutrons are mostly released by nuclear fission (the splitting of atoms in a nuclear reactor), and and hence are seldom encountered outside the core of a nuclear reactor. Thus they are not normally a problem outside nuclear plants. Fast neutrons can be very destructive to human tissue.

Units of radiation and radioactivity

In order to quantify how much radiation we are exposed to in our daily lives and assess potential health impacts as a result, it is necessary to establish a unit of measurement. The basic unit of radiation dose absorbed in tissue is the gray (Gy), where one gray represents the deposition of one joule of energy per kilogram of tissue.

However, since neutrons and alpha particles cause more damage per gray than gamma or beta radiation, another unit, the sievert (Sv) is used in setting radiological protection standards. This unit of measurement takes into account biological effects of different types of radiation. One gray of beta or gamma radiation has one sievert of biological effect, one gray of alpha particles has 20 Sv effect and one gray of neutrons is equivalent to around 10 Sv (depending on their energy). Since the sievert is a relatively large value, dose to humans is normally measured in millisieverts (mSv), one-thousandth of a sievert.

The becquerel (Bq) is a unit or measure of actual radioactivity in material (as distinct from the radiation it emits, or the human dose from that), with reference to the number of nuclear disintegrations per second (1 Bq = 1 disintegration/sec). Quantities of radioactive material are commonly estimated by measuring the amount of intrinsic radioactivity in becquerels – one Bq of radioactive material is that amount which has an average of one disintegration per second, i.e. an activity of 1 Bq.

 

Radioactivity of some natural and other materials 

 

Older units of radiation measurement continue in use in some literature:
1 gray = 100 rads
1 sievert = 100 rem
1 becquerel = 27 picocuries or 2.7 x 10^-11 curies
One curie was originally the activity of one gram of radium-226, and represents 3.7 x 10¹⁰ disintegrations per second (Bq).

The Working Level Month (WLM) has been used as a measure of dose for exposure to radon and in particular, radon decay products^b.

Since there is radioactivity in many foodstuffs, there has been a whimsical suggestion that the Banana Equivalent Dose from eating one banana be adopted for popular reference. This is about 0.0001 mSv.
 

Routine sources of radiation 

Radiation can arise from human activities or from natural sources. Most radiation exposure is from natural sources. These include: radioactivity in rocks and soil of the Earth's crust; radon, a radioactive gas given out by many volcanic rocks and uranium ore; and cosmic radiation. The human environment has always been radioactive and accounts for up to 85% of the annual human radiation dose.

Radiation arising from human activities typically accounts for up to 15% of the public's exposure every year. This radiation is no different from natural radiation except that it can be controlled. X-rays and other medical procedures account for most exposure from this quarter. Less than 1% of exposure is due to the fallout from past testing of nuclear weapons or the generation of electricity in nuclear, as well as coal and geothermal, power plants.

Backscatter X-ray scanners being introduced for airport security will gives exposure of up to 5 microsieverts (μSv), compared with 5 μSv on a short flight and 30 μSv on a long intercontinental flight across the equator, or more at higher latitudes – by a factor of 2 or 3. Aircrew can receive up to about 5 mSv/yr from their hours in the air, while frequent flyers can score a similar increment^c. On average, nuclear power workers receive a lower annual radiation dose than flight crew, and frequent flyers in 250 hours would receive 1 mSv.

The maximum annual dose allowed for radiation workers is 20 mSv/yr, though in practice, doses are usually kept well below this level. In comparison, the average dose received by the public from nuclear power is 0.0002 mSv/yr, which is of the order of 10,000 times smaller than the total yearly dose received by the public from background radiation.

 

Natural background radiation

Naturally occurring background radiation is the main source of exposure for most people, and provides some perspective on radiation exposure from nuclear energy. The average dose received by all of us from background radiation is around 2.4 mSv/yr, which can vary depending on the geology and altitude where people live – ranging between 1 and 10 mSv/yr, but can be more than 50 mSv/yr. The highest known level of background radiation affecting a substantial population is in Kerala and Madras states in India where some 140,000 people receive doses which average over 15 millisievert per year from gamma radiation, in addition to a similar dose from radon. Comparable levels occur in Brazil and Sudan, with average exposures up to about 40 mSv/yr to many people.

Several places are known in Iran, India and Europe where natural background radiation gives an annual dose of more than 100 mSv and up to 260 mSv (at Ramsar in Iran, where some 200,000 people are exposed to more than 10 mSv/yr). Lifetime doses from natural radiation range up to several thousand millisievert. However, there is no evidence of increased cancers or other health problems arising from these high natural levels.  The millions of nuclear workers that have been monitored closely for 50 years have no higher cancer mortality than the general population but have had up to ten times the average dose. People living in Colorado and Wyoming have twice the annual dose as those in Los Angeles, but have lower cancer rates.

Radon gas has decay products that are alpha emitters. People everywhere are typically exposed to around 0.2 mSv/yr, and often up to 3 mSv/yr, from inhaled radon without apparent ill-effect^d. However, in industrial situations its control is a high priority.

Public exposure to natural radiation^e 

 

Crews of nuclear submarines have possibly the lowest radiation exposure of anyone, despite living within a few metres of a nuclear reactor, since they are exposed to less natural background radiation than the rest of us, and the reactor compartment is well shielded.  Film badge data shows average of 0.3 mSv/yr.
 

Limiting exposure

Public dose limits for exposure from uranium mining or nuclear plants are usually set at 1 mSv/yr above background.

In most countries the current maximum permissible dose to radiation workers is 20 mSv per year averaged over five years, with a maximum of 50 mSv in any one year. This is over and above background exposure, and excludes medical exposure. The value originates from the International Commission on Radiological Protection (ICRP), and is coupled with the requirement to keep exposure as low as reasonably achievable (ALARA) – taking into account social and economic factors.

Radiation protection at uranium mining operations and in the rest of the nuclear fuel cycle is tightly regulated, and levels of exposure are monitored.

There are four ways in which people are protected from identified radiation sources:

• Limiting time. In occupational situations, dose is reduced by limiting exposure time.
• Distance. The intensity of radiation decreases with distance from its source.
• Shielding. Barriers of lead, concrete or water give good protection from high levels of penetrating radiation such as gamma rays. Intensely radioactive materials are therefore often stored or handled under water, or by remote control in rooms constructed of thick concrete or lined with lead.
• Containment. Highly radioactive materials are confined and kept out of the workplace and environment. Nuclear reactors operate within closed systems with multiple barriers which keep the radioactive materials contained.

Standards and regulation of radiation exposure

Radiation protection standards are based on the conservative assumption that the risk is directly proportional to the dose, even at the lowest levels, though there is no actual evidence of harm at low levels, below about 100 mSv/yr. This assumption, called the 'linear no-threshold (LNT) hypothesis', is recommended for radiation protection purposes only, such as setting allowable levels of radiation exposure of individuals. LNT was first accepted in 1958 and 1959 by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the ICRP as a philosophical basis for radiological protection, stating outright that “Linearity has been assumed primarily for purposes of simplicity, and there may or may not be a threshold dose”.

LNT cannot properly be used for predicting the consequences of an actual exposure to low levels of radiation and it has no proper role in low-dose risk assessment. For example, it suggests that, if the dose is halved from a high level where effects have been observed, there will be half the effect, and so on. This would be very misleading if applied to a large group of people exposed to trivial levels of radiation and could lead to inappropriate actions to avert the doses.

Much of the evidence which has led to today's standards derives from the atomic bomb survivors in 1945, who were exposed to high doses incurred in a very short time. In setting occupational risk estimates, some allowance has been made for the body's ability to repair damage from small exposures, but for low-level radiation exposure the degree of protection may be unduly conservative.

The International Commission on Radiological Protection (ICRP) set up in 1928 is a respected source of recommendations and guidance on radiation protection, and its recommendations are widely followed by national health authorities.

The International Atomic Energy Agency (IAEA) has published international radiation protection standards since 1962. It is the only UN body with specific statutory responsibilities for radiation protection and safety. Its Safety Fundamentals are applied in basic safety standards and consequent Regulations.  However, the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) set up in 1955 is the most authoritative source of information on ionizing radiation and its effects.

In any country, radiation protection standards are set by government authorities, generally in line with recommendations by the ICRP, and coupled with the requirement to keep exposure as low as reasonably achievable (ALARA) - taking into account social and economic factors. The authority of the ICRP comes from the scientific standing of its members and the merit of its recommendations.

The three key points of the ICRP's recommendations are:
• Justification. No practice should be adopted unless its introduction produces a positive net benefit.
• Optimisation. All exposures should be kept as low as reasonably achievable, economic and social factors being taken into account.
• Limitation. The exposure of individuals should not exceed the limits recommended for the appropriate circumstances.

National radiation protection standards are framed for both Occupational and Public exposure categories.
The ICRP recommends that the maximum permissible dose for occupational exposure should be 20 millisievert per year averaged over five years (ie 100 millisievert in 5 years) with a maximum of 50 millisievert in any one year. For public exposure, 1 millisievert per year averaged over five years is the limit. In both categories, the figures are over and above background levels, and exclude medical exposure*.

* The most recent revision of the ICRP's recommendations were issued in 2007 (Publication 103) which replaced the 1990 recommendations (Publication 60) without making any changes to the dose limits for occupational or public exposure. These values are also implemented by the IAEA in their Basic Safety Standard.
 

Nuclear fuel cycle

The average annual radiation dose to employees at uranium mines (in addition to natural background) is around 2 mSv (ranging up to 10 mSv). Natural background radiation is about 2 mSv. In most mines, keeping doses to such low levels is achieved with straightforward ventilation techniques coupled with rigorously enforced procedures for hygiene. In some Canadian mines, with very high-grade ore, sophisticated means are employed to limit exposure. (See also information page on Occupational Safety in Uranium Mining.) Occupational doses in the US nuclear energy industry – conversion, enrichment, fuel fabrication and reactor operation – average less than 3 mSv/yr.

Reprocessing plants in Europe and Russia treat used fuel to recover useable uranium and plutonium and separate the highly radioactive wastes. These facilities employ massive shielding to screen gamma radiation in particular. Manual operations are carried by operators behind lead glass using remote handling equipment.

In mixed oxide (MOX) fuel fabrication, little shielding is required, but the whole process is enclosed with access via gloveboxes to eliminate the possibility of alpha contamination from the plutonium. Where people are likely to be working alongside the production line, a 25mm layer of perspex shields neutron radiation from the Pu-240. (In uranium oxide fuel fabrication, no shielding is required.)

Interestingly, due to the substantial amounts of granite in their construction, many public buildings including Australia's Parliament House and New York Grand Central Station, would have some difficulty in getting a licence to operate if they were nuclear power stations.

Accidental radiation exposure (nuclear and other)

Three Mile Island 

The March 1979 accident at Three Mile Island nuclear power plant in the USA caused some people near the plant to receive very minor doses of radiation, well under the internationally recommended level. Subsequent scientific studies found no evidence of any harm resulting from that exposure. In 1996, some 2,100 lawsuits claiming adverse health effects from the accident were dismissed for lack of evidence.  INES rating 5.
 

Chernobyl 

Immediately after the Chernobyl nuclear power plant disaster in 1986, much larger doses were experienced. Apart from the residents of nearby Pripyat, who were evacuated within two days, some 24,000 people living within 15 km of the plant received an average of 450 mSv before they were evacuated.  A total of 14,000 PBq of radioactivity (iodine-131 equivalent) was released.

In June 1989, a group of experts from the World Health Organization agreed that an incremental long-term dose of 350 mSv should be the criterion for relocating people affected by the 1986 Chernobyl accident. This was considered a "conservative value which ensured that the risk to health from this exposure was very small compared with other risks over a lifetime". (For comparison, background radiation averages about 150-200 mSv over a lifetime in most places.)

Out of the 134 severely exposed workers and firemen, 28 of the most heavily exposed died as a result of acute radiation syndrome (ARS) within three months of the accident. Of these, 20 were from the group of 21 that had received over 6.5 Gy, seven (out of 22) had received between 4.2 and 6.4 Gy, and one (out of 50) from the group that had received 2.2-4.1 Gy.¹ A further 19 died in 1987-2004 from different causes (see information page on Chernobyl Accident Appendix 2: Health Impacts).

Regarding the emergency workers with doses lower than those causing ARS symptoms, a 2006 World Health Organization report² referred to studies carried out on 61,000 emergency Russian workers where a total of 4995 deaths from this group were recorded during 1991-1998. "The number of deaths in Russian emergency workers attributable to radiation caused by solid neoplasms and circulatory system diseases can be estimated to be about 116 and 100 cases respectively." Furthermore, although no increase in leukaemia is discernible yet, "the number of leukaemia cases attributable to radiation in this cohort can be estimated to be about 30." Thus, 4.6% of the number of deaths in this group are attributable to radiation-induced diseases. (The estimated average external dose for this group was 107 mSv.)

The report also links the accident to an increase in thyroid cancer in children: "During 1992-2000, in Belarus, Russia and Ukraine, about 4000 cases of thyroid cancer were diagnosed in children and adolescents (0–18 years), of which about 3000 occurred in the age group of 0-14 years. For 1152 thyroid cancer patient cases diagnosed among Chernobyl children in Belarus during 1986-2002, the survival rate is 98.8%. Eight patients died due to progression of their thyroid cancer and six children died from other causes. One patient with thyroid cancer died in Russia."

There has been no increase attributable to Chernobyl in congenital abnormalities, adverse pregnancy outcomes or any other radiation-induced disease in the general population either in the contaminated areas or further afield.

Reports two decades after the accident make it clear that the main health effects from the accident are due to the evacuation of many people coupled with fear engendered, and thousands have died from suicide, depression and alcoholism. The 2006 Chernobyl Forum report said that people in the area suffered a paralysing fatalism due to myths and misperceptions about the threat of radiation, which contributed to a culture of chronic dependency. Some "took on the role of invalids." Mental health coupled with smoking and alcohol abuse is a very much greater problem than radiation, but worst of all at the time was the underlying level of health and nutrition. Psycho-social effects among those affected by the accident are similar to those arising from other major disasters such as earthquakes, floods and fires.
 

After the shelter^f was built over the destroyed reactor at Chernobyl, a team of about 15 engineers and scientists was set up to investigate the situation inside it. Over several years they repeatedly entered the ruin, accumulating individual doses of up to 15,000 mSv. Daily dose was mostly restricted to 50 mSv, though occasionally it was many times this. None of the men developed any symptoms of radiation sickness, but they must be considered to have a considerably increased cancer risk.  INES rating 7.
 

Fukushima 

The March 2011 accident at Fukushima Daiichi nuclear power plant in Japan released more radioactivity than Three Mile Island, but much less than Chernobyl, probably about 570 PBq (iodine-131 equivalent), and the effects are still being assessed. Certainly the main radiation exposure was to workers on site, and some 167 workers received doses over 100 mSv. Of these 135 had received 100 to 150 mSv, 23 150-200 mSv, three more 200-250 mSv, and six had received over 250 mSv - the limit set for emergency workers there, apparently due to inhaling iodine-131 fume early on. There were around 250 workers on site each day.  INES rating 7.

Current work of UNSCEAR is focused on assessing radiation exposure from the Fukushima accident, and its preliminary findings at the end of 2012 said that no radiation heath effects arising from it had been observed among the public or the workers. Thyroid doses in children were significantly lower than from the Chernobyl accident.
 

Goiania 

In 1987 at Goiania in Brazil, an old radiotherapy source stolen from an abandoned hospital caused four deaths, 20 cases of radiation sickness and significant contamination of many more. The teletherapy source contained 93 grams of caesium-137 (51 TBq) encased in a shielding canister 51 mm diameter and 48 mm long made of lead and steel, with an iridium window. Various people came in contact with the source over two weeks as it was relayed to a scrapyard, and some were seriously affected. The four deaths (4-5 Sv dose) were family and employees of the scrapyard owner, and 16 others received more than 500 mSv dose. Overall 250 people were found to have significant levels of radioactive material in their bodies.  INES rating 5.

Fleurus 

In March 2006 at the Institute for Radioelements (IRE) in Fleurus in Belgium a worker at a commercial irradiation facility received a high radiation dose of about 4.6 Sv from cobalt-60, resulting in severe health effects. INES rating 5.

In August 2008 about 45 GBq of iodine-131 was released through the stack of the Institute for Radioelements (IRE) in Fleurus, Belgium. The release occurred following the transfer of liquid waste from one tank to another. INES rating 3.

Stamboliysky

In June 2011 in Bulgaria, preparations for the recharging of a gamma-irradiation facility with cobalt-60 sources were being undertaken at Stamboliysky. A device already recharged with sources had been taken out, instead of an empty one due to personnel error. As a result, four workers were exposed to a powerful gamma radiation for approximately five minutes, giving them effective doses of over 1 Sv.   INES rating 3.
 

Effects of radiation

Our knowledge of radiation effects derives primarily from groups of people who have received high doses. The risk associated with large radiation doses is relatively well established. However, the risks associated with doses under about 200 mSv are less obvious because of the large underlying incidence of cancer caused by other factors. Radiation protection standards assume that any dose of radiation, no matter how small, involves a possible risk to human health. However, available scientific evidence does not indicate any cancer risk or immediate effects at doses below 100 mSv a year. At low levels of exposure, the body's natural repair mechanisms seem to be adequate to repair radiation damage to cells soon after it occurs.

 

The main expert body on radiation effects is the UN Scientific Commission on the Effects of Atomic Radiation (UNSCEAR), set up in 1955 and reporting to the UN General Assembly. It involves scientists from over 20 countries and publishes its findings in major reports. The UNSCEAR 2006 report is the latest dealing with the Effects of Ionising Radiation.  Another valuable compendium of statements and scientific papers was published in June 2012 by the American Nuclear Society: Low-level Radiation and its Implications for Fukushima Recovery (57 MB).

In 2012 UNSCEAR reported to the UN General Assembly on radiation effects. It had been asked in 2007 “to clarify further the assessment of potential harm owing to chronic low-level exposures among large populations and also the attributability of health effects” to radiation exposure. It said that while some effects from high acute doses were clear, others were not, and could not be attributed to exposure, and that this was especially true at low levels. “In general, increases in the incidence of health effects in populations cannot be attributed reliably to chronic exposure to radiation at levels that are typical of the global average background levels of radiation.” Furthermore, multiplying very low doses by large numbers of individuals does not give a meaningful result regarding health effects. UNSCEAR also addressed uncertainties in risk estimation relating to cancer.
 

 

 

Epidemiological studies continue on the survivors of the atomic bombing of Hiroshima and Nagasaki, involving some 76,000 people exposed at levels ranging up to more than 5,000 mSv. These have shown that radiation is the likely cause of several hundred deaths from cancer, in addition to the normal incidence found in any population^g. From this data the ICRP and others estimate the fatal cancer risk as 5% per sievert exposure for a population of all ages – so one person in 20 exposed to 1,000 mSv could be expected to develop a fatal cancer some years later. In Western countries, about a quarter of people die from cancers, with smoking, dietary factors, genetic factors and strong sunlight being among the main causes. Radiation is a weak carcinogen, but undue exposure can certainly increase health risks.

In 1990, the US National Cancer Institute (NCI) found no evidence of any increase in cancer mortality among people living near to 62 major nuclear facilities. The NCI study was the broadest of its kind ever conducted and supported similar studies conducted elsewhere in the USA as well as in Canada and Europe.

In the UK there are significantly elevated childhood leukaemia levels near Sellafield as well as elsewhere in the country. The reasons for these increases, or clusters, are unclear, but a major study of those near Sellafield has ruled out any contribution from nuclear sources. Apart from anything else, the levels of radiation at these sites are orders of magnitude too low to account for the excess incidences reported. However, studies are continuing in order to provide more conclusive answers.

The health effects of exposure both to radiation and to chemical cancer-inducing agents or toxins must be considered in relation to time. We should be concerned not only about the effects on people presently living, but also about the cumulative effects of actions today over many generations. Some radioactive materials which reach the environment decay to safe levels within days, weeks or a few years, while others continue their effect for a long time, as do most chemical cancer-inducing agents and toxins. Certainly this is true of the chemical toxicity of heavy metals such as mercury, cadmium and lead, these of course being a natural part of the human environment anyway, like radiation, but maintaining their toxicity forever. The essential task for those in government and industry is to prevent excessive amounts of such toxins harming people, now or in the future. Standards are set in the light of research on environmental pathways by which people might ultimately be affected.

About sixty years ago it was discovered that ionizing radiation could induce genetic mutations in fruit flies. Intensive study since then has shown that radiation can similarly induce mutations in plants and test animals. However evidence of genetic damage to humans from radiation, even as a result of the large doses received by atomic bomb survivors in Japan, has not shown any such effects.

In a plant or animal cell the material (DNA) which carries genetic information necessary to cell development, maintenance and division is the critical target for radiation. Much of the damage to DNA is repairable, but in a small proportion of cells the DNA is permanently altered. This may result in death of the cell or development of a cancer, or in the case of cells forming gonad tissue, alterations which continue as genetic changes in subsequent generations. Most such mutational changes are deleterious; very few can be expected to result in improvements.

The relatively low levels of radiation allowed for members of the public and for workers in the nuclear industry are such that any increase in genetic effects due to nuclear power will be imperceptible and almost certainly non-existent. Radiation exposure levels are set so as to prevent tissue damage and minimize the risk of cancer. Experimental evidence indicates that cancers are more likely than genetic damage.

Some 75,000 children born of parents who survived high radiation doses at Hiroshima and Nagasaki in 1945 have been the subject of intensive examination. This study confirms that no increase in genetic abnormalities in human populations is likely as a result of even quite high doses of radiation. Similarly, no genetic effects are evident as a result of the Chernobyl accident.

Life on Earth commenced and developed when the environment was certainly subject to several times as much radioactivity as it is now, so radiation is not a new phenomenon. If we ensure that there is no dramatic increase in people's general radiation exposure, it is most unlikely that health or genetic effects from radiation will ever become significant.

Low-level radiation risks

 

A lot of research has been undertaken on the effects of low-level radiation. Many of the findings have failed to support the so-called linear no-threshold hypothesis. This theory assumes that the demonstrated relationships between radiation dose and adverse effects at high levels of exposure also applies to low levels and provides the (deliberately conservative) basis of occupational health and other radiation protection standards.

Some evidence suggests that there may be a threshold below which no harmful effects of radiation occur. However, this is not yet accepted by national or international radiation protection bodies as sufficiently well-proven to be taken into official standards.

A November 2009 technical report from the Electric Power Research Institute in USA drew upon more than 200 peer-reviewed publications on effects of low-level radiation and concluded that the effects of low dose-rate radiation are different and that "the risks due to [those effects] may be over-estimated" by the linear hypothesis⁴. "From an epidemiological perspective, individual radiation doses of less than 100 mSv in a single exposure are too small to allow detection of any statistically significant excess cancers in the presence of naturally occurring cancers. The doses received by nuclear power plant workers fall into this category because exposure is accumulated over many years, with an average annual dose about 100 times less than 100 mSv". It quoted the US Nuclear Regulatory Commission that "since 1983, the US nuclear industry has monitored more than 100,000 radiation workers each year, and no workers have been exposed to more than 50 mSv in a year since 1989."  A 2012 US study exposing mice to low-dose rate radiation for an extended period showed no signs of DNA damage, though a control group receiving the same dose acutely did show damage. This test on live animals confirms other work and epidemiological studies suggesting that people exposed to 1000 mSv/yr at low dose rate will not suffer adverse health effects.

In addition, there is increasing evidence of beneficial effect from low-level radiation (up to about 10 mSv/yr). This 'radiation hormesis' may be due to an adaptive response by the body's cells, the same as that with other toxins at low doses. In the case of carcinogens such as ionizing radiation, the beneficial effect is seen both in lower incidence of cancer and in resistance to the effects of higher doses. However, until possible mechanisms are confirmed, uncertainty will remain. Further research is under way and the debate continues. Meanwhile standards for radiation exposure continue to be deliberately conservative.

Further Information 

Notes 

a. Three of the main radioactive decay series relevant to nuclear energy are those of uranium and thorium. These series are shown in the Figure at www.world-nuclear.org/uploadedImages/org/info/radioactive_decay_series.png [Back]

b. One 'Working Level' (WL) is approximately equivalent to 3700 Bq/m³ of Rn-222 in equilibrium with its decay products. Exposure to 0.4 WL was the maximum permissible for workers. Continuous exposure during working hours to 0.4 WL would result in a dose of 5 WLM over a full year, corresponding to about 50 mSv/yr whole body dose for a 40-hour week. In mines, individual workers' doses are kept below 1 WLM/yr (10 mSv/yr), and typically average half this. [Back]

c. At an altitude of 30,000 feet, the dose rate is 3-4 μSv per hour at the latitudes of North America and Western Europe. At 40,000 feet, the dose rates are about 6.5-8 μSv per hour. Other measured rates were 6.6 μSv per hour during a Paris-Tokyo (polar?) flight and 9.7 μSv per hour on the Concorde, while a study on Danish flight crew showed that they received up to 9 mSv/yr. [Back]

d. A background radon level of 40 Bq/m³ indoors and 6 Bq/m³ outdoors, assuming an indoor occupancy of 80%, is equivalent to a dose rate of 1 mSv/yr and is the average for most of the world's inhabitants. [Back]

e.
Range for cosmic and cosmogenic dose for sea level to high ground elevation.
Range for external terrestrial radiation depends on radionuclide composition of soil and building material.
Range for inhalation exposure depends on indoor accumulation of radon gas.
Range for ingestion exposure depends on radionuclide composition of foods and drinking water.
Source: Table 12 from Exposures of the Public and Workers from Various Sources of Radiation, Annex B to Volume I of the 2008 United Nations Scientific Committee on the Effects of Atomic Radiation Report to the General Assembly, Sources and Effects of Ionizing Radiation, available on the UNSCEAR 2008 Report Vol. I webpage (www.unscear.org/unscear/en/publications/2008_1.html) [Back]

f. A reinforced concrete casing was built around the ruined reactor building over the seven months following the accident. This shelter – often referred to as the sarcophagus – was intended to contain the remaining fuel and act as a radiation shield. As it was designed for a lifetime of around 20 to 30 years, as well as being hastily constructed, a second shelter – known as the New Safe Confinement – with a 100-year design lifetime is planned to be placed over the existing structure. [Back]

g. The actual doses received by atomic bomb survivors are uncertain. Also much of the radiation then was from neutrons, though gamma radiation is the prime concern for radiation protection. Some 65 years after the acute exposure it can be seen that cancer rate in the irradiated survivors is lower than the controls, and lower than in the Japanese population as a whole³. [Back]

References 

1. Table 11 from Exposures and effects of the Chernobyl accident, Annex J to Volume II of the 2000 United Nations Scientific Committee on the Effects of Atomic Radiation Report to the General Assembly, available on the UNSCEAR 2000 Report Vol. II webpage (www.unscear.org/unscear/en/publications/2000_2.html) [Back]

2. Health Effects of the Chernobyl Accident and Special Health Care Programmes, Report of the UN Chernobyl Forum, Expert Group "Health", World Health Organization, 2006 (ISBN: 9789241594172). [Back]

3. T. D. Luckey, Nuclear law stands on thin ice, International Journal of Nuclear Law, Vol 2, No 1, P 33-65 (2008) [Back]

4. Program on Technology Innovation: Evaluation of Updated Research on the Health Effects and Risks Associated with Low-Dose Ionizing Radiation, Electric Power Research Institute (EPRI), Palo Alto, California, USA, 1019227 (November 2009) [Back]

IAEA, Goiania accident: http://www-pub.iaea.org/mtcd/publications/pdf/pub815_web.pdf

 Nuclear submarines, radiation exposure: http://www.epa.gov/radtown/submarine.html

General sources

Prof Bernard L. Cohen, Validity of the Linear No-Threshold Theory of Radiation Carcinogenesis at Low Doses, presented at the 23rd Annual International Symposium of The Uranium Institute (now World Nuclear Association) held in London, UK in September 1998

Prof Zbigniew Jaworowski, Radiation Risk and Ethics, Physics Today, 52(9), p24-29 (September 1999)

Position Statements webpage and the Policy Papers webpage of the Health Physics Society (www.hps.org)

Health Physics Web Site of the University of Michigan (www.umich.edu)

UNSCEAR web site FAQs (http://www.unscear.org/unscear/en/faq.html#Effects+of+radiation+exposure)

UNSCEAR report from 59th session, May 2012, to UN General Assembly November 2012.

Merck Manual Radiation Exposure and Contamination (detailed)
(http://www.merckmanuals.com/professional/injuries_poisoning/radiation_exposure_and_contamination/radiation_exposure_and_contamination.html?qt=&sc=&alt=)