Risk in perspective:
Radiation, reactor accidents,
and radioactive waste
an interview with Bernard Cohen
by Jay Lehr
"If all the country's electricity were
generated by nuclear power plants, the health risk would be equivalent to the
risk faced by a regular smoker who smokes one extra cigarette every 10 years;
or by an overweight person who increases his weight by 0.03 ounces; by
crossing a street one extra time every 20 weeks; by increasing the national
speed limit from 55 mph to 55.02; or by using a sub-compact car rather than a
mid-size car one day every 10 years."
Dr. Bernard Cohen is professor emeritus of
physics and of environmental and occupational health at the University of
Cohen's best-known scientific work has been in
nuclear reactions and the structure of the atomic nucleus. Widely recognized
as one of the world's leading experts on nuclear energy and human health,
Cohen has conducted research on such topics as the hazards of plutonium
toxicity, risk analysis of radioactive wastes, radon in U.S. homes,
perspective on risks in society, and health effects of low-level
His work has led to prestigious national awards,
from the American Physical Society, Health Physics Society, and American
Nuclear Society. He has published some 300 papers in scientific journals, is
the author of six books, and has published roughly 75 papers in popular
A popular speaker in his field, Cohen has
presented about 650 invited talks in 47 states, six Canadian provinces, six
Australian states, seven Japanese prefectures, and 24 other countries in
Europe, Asia, and South America. He has conducted nearly 100 radio and 50
television appearances, including shows with Barbara Walters, William Buckley,
Charlie Rose, Geraldo Rivera, and Rolanda.
Lehr: You are
internationally known for your work in radiation, health, and physics. What do
you consider your first significant research breakthrough?
Cohen: The early part of my
career was devoted to experimental research in basic nuclear physics, a highly
successful worldwide program that brought our understanding of how protons and
neutrons behave in nuclei up to a par with our understanding of how electrons
behave in atoms. For my contributions to this enterprise, I received the 1981
American Physical Society Bonner Prize, the only award for research in nuclear
My best-known research in radiation and health
- Hazards from plutonium toxicity--an extensive
analysis of the total eventual consequences of plutonium dispersal (about 20
eventual deaths per pound dispersed in the most effective way);
- Probabilistic risk analysis of buried wastes
from electricity generation--showing that coal burning wastes will cause
thousands of times as many deaths as nuclear wastes;
- Risks in our society--showing that nuclear
power risks are completely trivial in perspective with other risks we
routinely accept, and showing society spends thousands of times more per
death averted to avoid nuclear risks than to avoid others.
- Radon in homes--measurement techniques,
surveying methods, correlations with house and occupant characteristics,
geographical variations, and correlation with lung cancer mortality.
For this and other research I received the 1992
Health Physics Society Distinguished Scientific Achievement Award, the 1995
American Nuclear Society Walter Zinn Award, and the 1995 American Nuclear
Society Special Award.
Lehr: How did America's
exaggerated fear of nuclear energy and radioactivity first develop, and how
have the fires of fear been fanned over the past two decades?
Cohen: Nuclear power was
going through an explosive growth period in the early 1970s. At the same time,
environmental activism was developing, leading to the formation of numerous
politically oriented environmental groups.
To compete for dues-paying members and financial
support from foundations, these new environmental groups were looking for
issues that would attract public interest. They focused on nuclear power, for
- It was an industry sponsored by very large
corporations, an enemy the environmentalists were generally accusing of
putting profits ahead of public safety, etc.
- It was related to fearful nuclear
- It was developed with very extensive analyses
of potential environmental impacts, and those analyses were widely available
in publications. All the environmentalists had to do was omit the fact that
the impact analyses showed very small probabilities of environmental harm.
The environmental groups reported dangers "may happen," implying that they
Lehr: Who were the leaders
of these environmental groups?
Cohen: The leaders were often
veterans of the anti-Vietnam war protests looking for a new cause; they had
developed good connections with the media. They had little interest in
science, except as a tool for promoting their political goals. Ralph Nader
united them into a well-coordinated political force to oppose nuclear
Lehr: Did the news media
play a significant role?
Cohen: Yes. Like the
environmental groups, the media found such issues as potential nuclear
accidents and radiation exposures attractive to their audiences, and readily
featured the materials supplied to them by these groups.
The great majority of scientists favor nuclear
power, but they have little access to the media and thus have a difficult time
getting their message to the public. Once an issue gets into the political
arena, science inevitably takes a back seat, so the public is left
In spite of all this, polls show that a sizable
majority of the U.S. public favors nuclear power. Still, the opposition is far
more vocal, and far more politically powerful.
Lehr: What has your research
shown about the relationship between radiation and risks to human health?
Cohen: There is a great deal of
accurate information on how high doses of radiation can cause cancer, from the
Japanese A-bomb victims, from therapeutic uses of radiation in medicine, from
occupational exposures, etc. But when it comes to radiation in the
environment, and the risk that poses to human health, nearly all important
questions involve very much lower doses.
To estimate the effects of low-level radiation,
it was conventional to assume the risk is simply proportional to the dose,
called the linear-no threshold (LNT) hypothesis. For example, the LNT
hypothesis assumes that the risk from 1 unit of exposure is 1/1000 of the risk
from 1,000 units of exposure.
This LNT hypothesis is responsible for the notion
that any exposure to radiation, no matter how small, can cause
cancer. That notion, in turn, has led to widespread fear of all radiation. The
U.S. government holds to this position.
Lehr: Does research support
Cohen: In the past 10 years, a
large body of evidence has developed that indicates low-level radiation has
benefits that can protect people from developing cancer.
Low-level radiation increases production of
enzymes that repair the DNA damage that can initiate development of cancer.
Low-level radiation also increases the time available for this DNA repair,
stimulates the immune system to resist the growth of tumors, and enhances the
process by which potential cancer cells commit suicide (apoptosis).
Lehr: What research have you
conducted in this field?
Cohen: My contribution has been
to show there is a very strong and statistically indisputable tendency for
U.S. counties with high radon exposures to have low lung cancer rates, and for
counties with low radon exposures to have high lung cancer rates. These
findings run contrary to the prediction from LNT, based on the fact that very
high exposures to radon cause lung cancer.
My findings are not affected by corrections for
smoking prevalence, or by consideration of over 500 potential confounding
factors like socioeconomic variables, climate, ethnicity, etc.
Lehr: Where do the majority
of scientists now stand on the LNT hypothesis and low-level radiation?
Cohen: As a result of all
of this recent evidence, a large fraction of the involved scientific community
is convinced LNT grossly exaggerates the cancer risk from low-level radiation,
and that the net effect of the radiation exposures normally at issue may even
be to protect against cancer.
Lehr: What are the principal
issues hindering the public's understanding and acceptance of nuclear
Cohen: Many issues have been
raised by critics, and all of these are addressed at substantial length in my
books. The most important ones are (1) an irrational fear of radiation, (2)
greatly exaggerated concepts of potential reactor accidents, (3) failure to
understand the potential dangers of radioactive wastes, and (4) poor
recognition of the various risks we all face, and failure to keep them in
perspective. There are one or more lengthy chapters on each of these in my
Lehr: How do you respond to
the public's fear of radiation?
Cohen: This fear is fueled by
the popular idea that being hit by a single particle of radiation can cause
cancer. That fear is based on the linear-no threshold theory, which I accept
when dealing with the public.
In response, I point out that every one of us is
hit by 15,000 of these particles every second, and a typical diagnostic X-ray
hits us with about a trillion.
The reason we survive is that the probability for
one of these hits to cause cancer is just one chance in 30,000,000,000,000,000
(30 quadrillion): pretty good odds. Thirty quadrillion is 30 times the number
of hairs on all the heads of the current human population of the Earth.
[Editor's note: If you counted to 30 quadrillion, one second at a
time, it would take you roughly 1 billion years.]
This makes clear that the dangers of radiation
must be treated quantitatively. To do this I introduce the millirem, the units
in which we measure dose, and give examples of doses from natural radiation
and from nuclear power; the latter are obviously negligible by
Lehr: How do you address
fears of reactor accidents?
Cohen: People have the
impression that if anything goes wrong in a nuclear power plant, there is a
good chance a terrible accident will result. To counteract this, I explain and
illustrate the design principle of defense in depth.
If a pump fails or if a valve misfunctions, a
substitute pump or valve automatically takes over. If a whole system fails,
another system automatically takes over its function. If this fails, a third
system kicks in to mitigate the problem, etc. This explains why, after about
10,000 years of reactor operation, no one has ever been killed by an accident
in a U.S. type nuclear power plant.
Lehr: And what are we going
to do with the nuclear waste?
Cohen: We're going to convert it
into rocks and put it in the natural habitat of rocks, deep
We know all about how rocks behave. Using this
knowledge, we can show this buried waste will have trivial health impacts. In
fact, there are three different types of wastes from coal-burning, each of
which will cause more than a thousand times more deaths than the nuclear
wastes created in generating the same amount of electricity.
Lehr: How do you put risks
into perspective for people?
Cohen: One approach is to
give the number of days of lost life expectancy due to various risks. For
example, being poor reduces your life expectancy by 3,500 days; smoking, by
2,300 days; being 30 pounds overweight, by 900 days; motor vehicle accidents,
by 180 days; living near a nuclear power plant, by 0.4 days.
Another approach is to show the risk-equivalent,
for the average American, of having all of our electricity from nuclear
plants. For example, if all the country's electricity were generated by
nuclear power plants, the health risk would be equivalent to the risk faced by
a regular smoker who smokes one extra cigarette every 10 years; or by an
overweight person who increases his weight by 0.03 ounces; by crossing a
street one extra time every 20 weeks; by increasing the national speed limit
from 55 mph to 55.02; or by using a sub-compact car rather than a mid-size car
one day every 10 years.
Lehr: As a highly respected
senior scientist not known for his pithy sound bites on the evening news, how
would you like to participate in a broad public education program on these
Cohen: The highest priority
in my professional life now is to contribute to such an educational
I am always willing to speak to any audience that
will hear me, and I write papers for publication in journals. Four of the six
books I have authored, and about 80 of my 350 published papers, are aimed at
educating the general public. I am always open to suggestions for other ways
in which I can contribute.