Up to: Nuclear energy.

One of the biggest fears about nuclear energy is radiation. Here are some questions and answers.

Q. Is the radiation involved in nuclear energy harmful?

A. Yes. If you were in with the fuel rods, while a nuclear power plant was generating energy, or even if it had generated electricity in the past, you would die very quickly. The radiation is stopped by shielding before it reaches the rooms inside the plant.

Q. What about the radiation emitted from the plant?

A. There is a trivial amount of radiation emitted from an operating nuclear plant.

Q. What do you mean by trivial?

A. Here's a catalog of risks.

Hazards to life from Bernard Cohen, L.A. Times June 4, 1978 Risk days of life expectancy lost by taking the risk Riding in cars (10,000 miles/yr) 200 Not using seat belts 50 Driving small cars 50 Smoking one pack/day 2200 Overeating by 200 calories/day 400 Being one pound overweight 30 One diet drink/day 2.5 Fire 30 Drowning 40 Being poisoned 20 Choking on food 12 Being asphyxiated 7 Struck by falling object 6 Electrocution 6 Lightning 6 Being bitten by an animal or insect 0.3 Being murdered 90 Consuming nuclear electricity (if it were all nuclear) 0.05 Consuming electricity from coal 15 Air pollution (all sources) 25 Being male rather than female 2700 Remaining unmarried 1800 Working as a coal miner 1500 Q. How could Cohen know that the amount of radiation emitted by nuclear power plants is so small?

A. How much radiation is emitted is part of the design of every plant and is monitored by radiation detectors both inside and outside the plant. There is now plenty of evidence from the 400 nuclear power plants operating in the world.

You might disagree with Cohen about how frequent accidents that emit more radiation are likely to be, but there is a lot of evidence on that also. An accident in which two people died in Japan was billed as the worst nuclear accident since Chernobyl. For an energy source, that is extremely good - only two dead worldwide in 13 years.

Q. How could Cohen know that the effects of radiation are so small? Isn't all ionizing radiation harmful?

A. Cohen is presuming yes, although there is some statistical evidence that very small amounts might be helpful to health. Hardly anyone, including Cohen takes this very seriously, because no-one has suggested a plausible helpful biological effect of ionizing radiation.

1996 May note: The evidence that small amounts of radiation are somehow good for you is accumulating. Here is an article by Jay Lehr about that referring to a recent study by Cohen.

1997 January note: Here's a Japanese study with some experimental results on the hormetic effects of small amounts of radiation.

Hundreds, or more likely thousands, of studies have been made of animals exposed to radiation and people exposed to radiation accidentally, in connection with work, from where a person lives, in war or for medical purposes. Health effects are looked for.

Very small amounts of radiation do not produce measurable health effects. However, since the main harmful effect expected is cancer, and there is plenty of cancer anyway, very small increases in the amount of cancer would not be detected.

Therefore, the effects of small amounts of radiation have to be estimated. The most conservative estimate is the linear hypothesis that the amount of damage from small amounts of radiation is proportionately smaller than the damage from large amounts. There is good evidence that this is too conservative, but I believe this is what Cohen used in the above table.

Q. What are the other causes of human exposure to radiation?

  1. Cosmic rays. These come from outer space and are only partly stopped by the atmosphere. The higher the altitude, the more cosmic rays. Naturally, scientists looked to see if cancer rates were larger in high altitude places. They aren't.

  2. From rocks. Many rocks and soils, especially those containing granite, are more radioactive than most rock. There is an area in India where a mineral called monazite containing thorium is very radioactive. There is no measurable health effect from this either.

    In the 1970s or 1980s it was noticed that the radioactive gas radon was prevalent in basements in areas where the underlying rock is granite. According to EPA rules, many places have more than EPA considers safe, and EPA advocates mitigating it, e.g. by sealing basements. Bernard Cohen compared death rates from lung cancer in elderly women (who rarely had smoked) in counties where there is lots of granite with the death rates where the underlying rock does not emit radon. He found no increase, suggesting that the linear hypothesis exaggerates by at least a factor of 4.

  3. From potassium in the blood. Potassium is essential for life, but it contains a small fraction of a radioactive isotope. It would be difficult, but perhaps not impossible to tell whether this natural radiation within the body contributes to cancer.

  4. The largest average human exposure to radiation is from medical X-rays.

  5. As part of radiation treatments for cancer, people are sometimes exposed to radiation up to where they get acute radiation sickness. If they survive the treatment and survive the cancer, they don't seem to get additional cancer from the treatment.

Here's a table from the School of Public Health at the University of Michigan. They present much more information.

Annual Effective Dose Equivalent


Radon 200 2.0 55%
Cosmic 27 0.27 8%
Terrestrial 28 0.28 8%
Internal 39 0.39 11%
Total Natural 300 3 82%


Medical X ray 39 0.39 11%
Nuclear medicine 14 0.14 4%
Consumer products 10 0.1 3%


Occupational 0.9 <0.01 <0.3
Nuclear Fuel Cycle <1 <0.01 <0.03
Fallout <1 <0.01 <0.03
Miscellaneous <1 <0.01 <0.03
Total Artificial 63 0.63 18%
Total Artificial and
360 3.6 100%

Q. What about the depleted uranium used in tank shells in the Gulf War and in Kosovo?

There have been accusations from Iraq and supported by Ramsay Clark and other people who find evil in everything the US does. Here's their most vigorous accusation: Depleted Uranium: Metal Of Dishonor

Here's a fact sheet from the World Health Organization, an agency of the United Nations, on depleted uranium.. The study links to a yet more detailed WHO study with references.

Q. Isn't plutonium the most poisonous substance known?

A. This is a considerable exaggeration.

Plutonium can kill you in two ways - apart from blowing you up with a bomb. If you ingest it in an absorbable form, it goes to the bones, and the radiation is bad for you. It is also a heavy metal poison like lead. Second if you breathe plutonium dust into your lungs, you can get lung cancer.

However, Bernard Cohen, who knows about radiation hazards, has offered to eat a gram of plutonium oxide, e.g. a piece about the size of a penny. Plutonium oxide is not absorbable in the human gut, and Cohen says it will go right through the intestinal tract. He also offered to breathe a liter of air with plutonium oxide dust particles of a size to remain suspended in the air for one minute. He calculated that the risk he would be undergoing was equivalent to that of a six months sabbatical in Denver. At 5,000 feet Denver gets a lot more cosmic radiation than Pittsburgh.

Q. Who is this Bernard Cohen anyway?

A. He is Professor of Physics at the University of Pittsburgh and has been active in the Health Physics Society. This is the professional society concerned with monitoring human exposure to radiation. He has an article reporting on the statistical relation between the prevalence of cancer and the geological likelhihood of significant radon. I believe his recent study is reported in the 1997 January issue of the journal Health Physics, but I haven't looked up the paper.

Here's a link to another FAQ (not mine) on radiation with links to several relevant home pages.

Here's a table of sources of radiation exposure from the Harvard Radiology Department.

Sources of Radiation Exposure to the Average American
Radon 55%
X-ray Exams 11%
Natural Internal 10%
Terrestrial 8%
Cosmic rays 8%
Nuclear Medicine 4%
Commercial Products 3%
Other less than 1%

See also fact sheets from the International Atomic Energy Agency.

The Center for nuclear Technology and Society at Worcester Polytechnic Institute maintains an active site.

See also my page on the Chernobyl accident.

Up to: Nuclear FAQ

Up to: Sustainability FAQ

Send comments to mccarthy@stanford.edu. I sometimes make changes suggested in them. - John McCarthy

The number of hits on this page since 1996 Feb 17.