Uranium and radiation

 

Key Points

·        Everybody, everyday is exposed to low levels of radiation with no health effects.

·         People who receive large doses of radiation in a short period or accumulated large doses over a longer period may suffer effects on their health.

·         People who work at uranium mines and nuclear power plants are exposed to slightly more radiation than the general public but are unlikely to suffer ill-health as a result.

·         People who live near uranium mines or nuclear power plants or near the roads and railway lines along which uranium is transported are unlikely to suffer ill-health just because they live near places where uranium is used or transported.

·         An accident in the transport of uranium is unlikely to lead to health effects.

·         As in all workplaces, people who work at uranium mines or nuclear power plants are protected from radiation by principles and practices that minimise occupational health and safety risks.

·         Those same principles and practices determine how uranium is transported to protect the public.

·         Uranium mining companies take precautions to protect the communities of which they are neighbours from the effects of radiation.

·         While mistakes are made from time to time, these practices are very effective.

·         Radiation needs to be managed, not feared. 


Atoms are the basic units of matter of which all things are composed.

Most atoms remain what they are forever. Oxygen atoms, for example,  are always oxygen atoms.

But some atoms change from one thing to another.   Atoms which change in this way are called ‘radioisotopes’ or ‘radionuclides’ and the process of change they go through is called ‘radioactive decay’ or ‘radioactivity’.

When a radioisotope decays, it gives off a particle. These particles are also known as ‘rays’. There are three kinds, alpha, beta and gamma rays.

When a radioisotope decays, it is going through the process of changing from one kind of atom to another.   It may become many different kind of atoms before it finally stops decaying, before it ceases being radioactive, before it finally becomes the atom that it will then always be.

The time taken for half the atoms in a radioactive substance to decay fully is called a half-life. Radioactive substances that have short half-lives emit particles or rays relatively quickly; others with long half-lives are slower to emit particles or rays.

Short half-lives are associated with higher levels of radioactivity, while longer half-lives indicate lower levels of radioactivity.

When the rays or particles are emitted, they may strike other substances, producing electrically-charged particles called ions. If they strike living things, like human bodies, they may produce ions that cause biological changes.

This is what worries people about radiation: that it may cause harmful changes in their bodies.

Mostly, the rays or particles will not cause that harmful change: because they do not enter the body, as is the case with alpha radiation, which is stopped by the skin; or because, in the case of beta and gamma rays or particles, barriers between a person and the source of the radiation are put in place; or because people simply live a long way from the source of the radiation.

In any case, the body can repair the impact of radiation in the same way that it repairs itself in the case of other factors affecting the functioning of the human body or its health.

As it happens, people come into contact with radiation every day in their lives.   The sun is a source of radiation; medical procedures like x-rays intend that radioactivity is transmitted through the body; there is even radioactivity in coffee.

Of course, it is hard to avoid all the natural or background radiation that comes from the sun. And people may choose to take the very small risks from radioactivity in medical procedures and the even smaller risk with coffee.

The level of background radiation varies from place to place in the world.   Some places may experience background radiation up to 100 times the average background radiation.

There is no evidence of different health consequences of these differing levels of background radiation. 

Exposure to radiation is measured in sieverts (Sv). A sievert is the measure of biological effect of radiation exposure from any source. The most common measure used is the millisievert (mSv), one-thousandth of a sievert.

Some examples of radiation exposures and their effects are as follows:

·         Exposure of 10,000 millisieverts in a short time period would cause immediate illness and death within weeks

·         Exposure of 1000 millisieverts in a short time period would cause immediate illness but would be unlikely to cause death in a normally healthy person

·         Exposure of 1000 millisieverts over a long time period is unlikely to cause early health effects but leads to a measurable risk of cancer in the long term

·         Exposure of 20 mSv a year averaged over 5 years would not cause early health effects and is unlikely to lead to long term health effects

·         Exposure of 1.5 to 3.5 mSv a year is the background radiation exposure. There is no evidence of harmful health effects of such exposures.

Naturally occurring uranium has a long half-life and is mildly radioactive.   Workers in Australian uranium mines receive an exposure of less than 3 mSv per year in addition to background radiation.

A national register of the doses individual uranium workers receive during the course of their careers in the industry is now being established.

People who live in the vicinity of uranium mines in Australia receive an exposure of around 0.04 to 0.05 mSv per year in addition to background radiation.  

The uranium used in nuclear power plants, uranium that has been made into fuel for that purpose, is radioactive. The used fuel, what is left after the uranium is used in a nuclear power plant, is radioactive. Equipment and facilities used in mining uranium and in nuclear power plants may become radioactive. Workers involved in the nuclear industry receive an exposure of 1 mSv per year in addition to background radiation.

The average exposure to radiation for an individual from all artificial sources (medical, military, accidental, occupational) is 0.6 mSv per year. The average exposure to radiation for an individual from all natural sources is 2.4 mSv per year.

Four kinds of practices are adopted to protect people – whether workers or members of the public - from exposure to identified sources of radiation.

Of course, most people do not live near nor work in the uranium or nuclear industries nor use radioactive materials nor are exposed to radiation beyond background and no special protections are required for them in their everyday lives.

But for people who work in the uranium industry or the nuclear industry or in medical occupations using radioactive materials or who are exposed to radiation as part of medical treatment, the four practices followed are:

·         Limiting the time people are exposed to radiation

·         As the intensity of radiation decreases with distance, keeping people away from the source of radiation

·         Shielding people from the source of radiation by barriers made from lead, concrete or water

·         Containing radioactive materials and isolating them from the environment.

In effect, these are the principles that underpin the practices used in occupational health and safety where radiation is concerned; and which are used to protect local communities from radiation.

Governments are guided in their regulation of radiation by the work of the International Commission on Radiological Protection (ICRP).

The Commission recommends that the maximum permissible occupational exposure above background should be 20 mSv per year averaged over 5 years. For the public, the maximum permissible exposure above background is 1 mSv per year averaged over 5 years. That is the law adopted in Australia and which the uranium industry meets.

The assumption behind the regulation of radiation is that the risk of harmful health effects from radiation is directly proportional to the exposure; in the jargon of the industry, this is called the ‘linear no-threshold hypothesis (LNT)’.

There is some debate over the robustness of the hypothesis; and there is an alternative hypothesis that radiation may be beneficial at low doses. There is, however, insufficient evidence to overturn the LNT or to confirm the alternative hypothesis.

Adopting the LNT assumption for the purpose of regulation is, in effect, to take the view that the risks that accompany the low levels of radiation exposure in uranium mining and the nuclear industry are outweighed by the benefits.

In fact, the LNT hypothesis is adopted by the ICRP. It bases its recommendations on three principles:

·         Justification. No practice should be adopted unless it has a net benefit.

·         Optimisation. All exposures should be kept as low as possible.

·         Limitation. The exposure of individuals should not exceed the limits recommended.

By allowing uranium mining and nuclear power, governments accept the net benefit approach recommended by the ICRP.

Sources:

International Commission on Radiological Protection 

 United Nations Scientific Committee on Atomic Radiation

Radiation Workers Handbook 

 

May 2010