Nuclear Power and the Energy Crisis

P. E. HODGSON is Senior Research Fellow Emeritus
in Physics at Corpus Christi College, Oxford.

The previous article in this series drew
attention to the energy crisis that faces
the world today. Energy is essential to maintain
and increase our standards of living. The
demand for it is also increasing due to the
world’s rising population. At the same time
the available sources of energy are proving
inadequate to satisfy the demand: oil production
will soon peak and then start to fall; coal
and the other fossil fuels are serious polluters;
hydroelectric power is limited by geography,
and wind, solar, and the other renewable
sources are unable to deliver energy in
the huge quantities required. This combination
of rising demand and falling supply is the
basis of the energy crisis. If that were all that
could be said, there would be no possibility of
resolving the crisis. There is, however, another
source—the nucleus of the atom.

In 1939 it was found that when the nuclei
of certain heavy elements such as uranium
are irradiated by neutrons they became unstable
and split into two pieces, a process
known as fission. The fission fragments fly
apart with great energy and also emit more
neutrons. These neutrons can enter nearby
uranium nuclei and cause them to fission,
resulting in a chain reaction and a large
release of energy. This energy release can be
controlled and used to drive a turbine to
generate electricity.¹

Many nuclear reactors have now been
built, and are making a growing contribution
to world energy supplies. They have,
however, encountered bitter opposition for a
variety of reasons that will be discussed below.
The question we have to face is whether
nuclear power can provide the solution to the
energy crisis, or whether nuclear reactors
pose such a threat that they should be phased
out as soon as possible. This question can be
tackled by applying the same criteria as those
already used to evaluate the other energy
sources, namely capacity, reliability, cost,
safety and effects on the environment.

The Capacity of Nuclear Power

Nuclear power reactors each have an output
similar to coal power stations, namely around
1000 MW. There are now about 440 nuclear
reactors worldwide delivering about 2,500
TWh per year, around a fifth of world
electricity consumption. The numbers of
nuclear power stations built in each country
depends on its natural resources, principally
coal and oil. France, which lacks these resources
and is unwilling to become dependent
on imports, generates about eighty percent
of its electricity from nuclear reactors. It
is unlikely to rise higher than this because
nuclear reactors take time to get started and
therefore cannot react quickly when there is
a sudden demand. They are best suited to
supply the base load, supplemented by other
methods of generation (such as gas power
stations) to handle the fluctuations in demand.

Many other countries generate around
fifty percent of their electricity from nuclear
power, and now nuclear has outstripped coal
in Western Europe. There is thus no doubt
that nuclear power stations are able to provide
a large contribution to the world’s
energy needs.

It has been objected that this program,
while possible in principle, is unable to solve
the energy crisis because of the limited supplies
of uranium. At present the rate of
uranium use is seventy thousand tonnes per
year, whereas the known economically recoverable
sources of uranium amount to over
three million tonnes, sufficient for about
forty-five years. In addition, there are about
twelve million tonnes of highly probable
deposits. If eventually there is a uranium
shortage the price will rise, increasing the
number of economically-recoverable deposits.
Since the cost of fuel is a small part of the
overall costs of reactors, this will have very
little effect on the price of the electricity
generated.

The present reactors are thermal reactors
that burn uranium-235, which constitutes
only 0.7 percent of natural uranium. The
remaining 99.3 percent consists of uranium-
238 that can be burnt in fast reactors. Prototypes
have shown that these reactors can be
built, although at present they are uneconomic.
If the uranium price rises to the level
that they become economical, they can take
over, increasing the amount of energy obtainable
from uranium by a factor of about
sixty. Since it is also possible to use the fissile
element thorium, which is even more abundant
than uranium, there is thus no danger
that nuclear reactors will ever suffer from
shortage of fuel.

Reliability

Nuclear reactors are unaffected by the
weather and rarely suffer breakdowns. The
best reactors operate for over 90 percent of
the time and nearly all the remainder is for
planned maintenance, which is arranged for
periods of low demand. Nuclear reactors are
thus highly reliable.

Cost

Nuclear power stations are more costly to
build but cheaper to run than other power
stations, and therefore the cost of the electricity
produced depends strongly on the rate of
interest required on the initial capital expenditure.
The cost is also affected by the lifetime
of the reactor, which may be around fifty
years, and in that period the effects of inflation
may be very large. This makes it difficult
to give a precise figure for the cost of nuclear
power.

Some estimates of the cost of nuclear
power compared with those of other energy
sources were given in the previous article.
Such comparisons are affected by many
factors, but on the whole, they show that
nuclear costs are similar, or perhaps rather
less, than those of coal. This comparison takes
no account of the huge and unquantifiable
costs of global warming and climate change
due to the carbon dioxide emitted from coal
power stations. The carbon dioxide emissions
from nuclear power stations are less than
one percent of those from coal power stations.

The decommissioning of nuclear reactors
after they have reached the end of their useful
life has to be carried out with great care due
to the large amounts of radioactivity they
contain. The fuel rods are easy to remove,
and much of the building and parts of the
reactor are not radioactive and can also be
removed easily. This leaves the highly radioactive
reactor core which can either be
allowed to decay for many decades before
dismantling or could be sealed and buried
under a mound of earth. Dismantling the
core greatly increases the cost, since it must
be carried out by remote control. This cost
can easily be covered by setting aside a small
fraction of the profits during each year of the
reactor’s life. As a reactor can operate for
fifty years or more this accumulates sufficiently
to cover the cost of decommissioning.
It has been estimated that the cost of
decommissioning is about 0.05 p/kWh for
pressurized water reactors.

Safety

The safety of nuclear reactors can be
quantified in the same way as the other
sources as one death per thousand megawattyears.
The deaths are attributable to normal
causes, such as those incurred in building,
and are unrelated to specifically nuclear
causes. This is less than all other sources
except for natural gas. Negative public perception
of safety is more influenced by rare
and spectacular accidents rather than by such
statistics. Thus in the years from 1969 to
1986 there have been one hundred eightyseven
mining disasters, three hundred thirtyfour
oil well fires, nine dam bursts, and one
severe nuclear accident at Chernobyl, which
is discussed below.

Environmental Effects

Nuclear reactors have four principal effects
on the environment, first by emitting
carbon dioxide, second by taking up valuable
land, third by producing waste, and
fourth by emitting radioactivity.

The amounts of carbon dioxide emitted
by various power sources in grams per kWh
are nuclear: 4, wind: 8, hydro: 8, geothermal:
79, gas: 430, oil: 828, and coal: 955.
Other estimates give similar figures. These
show that the fossil fuels—gas, oil, and coal—
are the greatest emitters, and the other
sources—nuclear, wind, and hydroelectric—
emit less than about one percent of their
amounts.

The land areas occupied by the various
types of power stations in square meters per
megawatt are nuclear: 630, oil: 870, gas:
1500, coal: 2400, solar: 100,000, hydro:
265,000 and wind: 1,700,000.

The radioactivity emitted by various
power sources in man-sieverts per gigawattyear
are coal: 4.0, nuclear: 2.5, geothermal:
2, peat: 2, oil: 0.5 and gas: 0.03. These are
all extremely small amounts, and it is noteworthy
that coal power stations emit more
radioactivity than nuclear power stations.
This is because coal contains small but significant
amounts of uranium, and a small
fraction of this is emitted into the atmosphere.
The amounts of uranium vary with
the type of coal, and the above figure is a
world average obtained by the International
Atomic Energy Agency.

Every year, a nuclear power reactor produces
about four cubic meters (m³) of high
level radioactive waste, 100 m³ of intermediate-
level waste, and 530 m³ of low-level
waste. The total amount of high-level waste
produced in Britain from 1956 to 1986 was
about 2000 m³, about the same volume as an
average house. This is very small compared
with the vast amounts of poisonous chemical
waste produced by the manufacturing industries,
much of which is buried in the sea
or emitted into the atmosphere.

The low- and intermediate-level nuclear
waste can safely be buried in deep trenches,
but the high-level waste requires special
attention. As the uranium or plutonium is
burnt in the nuclear reactor, the products of
fission accumulate in the fuel rods until they
absorb so many neutrons that they prevent
the reactor from working. To avoid this,
spent fuel rods are continually removed from
the reactor and replaced by new ones. The
spent fuel rods are taken to the reprocessing
plant where the uranium and plutonium are
separated and used to make new fuel rods.
The remaining portion contains the highly
radioactive fission fragments, The first step
in the disposal of this high-level waste is to
store it in tanks above ground for a few
decades so that most of the radioactivity from
the short-lived nuclei decays. Then the remainder
is concentrated and fused to form a
glassy or ceramic substance. For extra safety
this is placed in stainless steel containers and
then buried far below the surface in a stable
geological formation. There is then no chance
that the fission products will escape and cause
harm. This has been checked by a detailed
study sponsored by the European Union.
Eventually, over the years, the radioactivity
of the fission fragments will decay until it is
similar to that of the surrounding rocks.

It has been suggested that the radiation
emitted from nuclear power stations increases
the number of cases of leukaemia in the area.
It has also been suggested that this radiation is
responsible for long-tem genetic effects. These
possibilities are discussed below.

Nuclear Radiations

One of the main differences between
nuclear and other power stations is the presence
of nuclear radiation. The fission fragments
produced when the uranium nuclei
split are highly radioactive and emit alphaparticles
and beta and gamma rays until
finally a stable nucleus is formed. There are
many different nuclei among the fission
fragments, and the rates of emission vary
from a small faction of a second to many
thousands of years. These decay rates are
characterized by a half-life, which is the time
taken by the radioactivity of a sample of a
particular type of nucleus to decay to half its
initial value.

When it passes through the human body,
nuclear radiation can break up the complicated
molecules inside the cells, releasing
reactive radicals that can cause more damage.
If the level of radiation is small, few cells
are affected; they are soon replaced and no
harm is done. If, however, the radiation
level is high, serious damage will be caused,
and cancers may develop during the following
years. In the case of massive whole-body
irradiation, death can also take place. It is
vital, of course, to specify just what we mean
by low and high levels of irradiation, and this
will be done later.

The three types of nuclear radiation have
different effects on the human body. Alphaparticles
are helium nuclei and, since they
are doubly charged, they lose energy rapidly
and ionize strongly and are very destructive.
Their short range means that they are harmful
only if the radioactive material is inside
the body. The beta rays are energetic electrons,
and the gamma rays are short-wavelength
electromagnetic radiation. They can
both penetrate far inside the human body.

Nuclear radiation can easily be detected
by very sensitive instruments that can record
the passage of a single particle, so it is possible
to detect the presence of extremely small
amounts of radioactive substances. This enables
us to learn how they move through the
atmosphere, the oceans, and our own bodies.
This property has proved to be extremely
useful in medical research.

When considering the effects of nuclear
radiation on people, it is necessary to take
account of the different sensitivities of the
different organs of the body. This is done by
defining the rem, which is the dose given by
gamma radiation that transfers a hundred
ergs of energy to each gram of biological
tissue, and for other types of radiation it is the
amount that does the same biological damage.
A new unit, the Sievert, has now been
defined as 100 rem.

Nuclear radiation is often feared because
it is unfamiliar and can cause great damage
to living organisms without our being aware
that anything untoward is happening. The
damage only appears afterwards, sometimes
very long afterwards, when it is too late to do
anything about it. Our senses warn us of
many dangers, such as excessive heat and
some poisonous gases, and we can take
avoiding action. Nuclear radiation is not
alone in being invisible; many poisonous
gases such as carbon monoxide have no
smell, and we don’t know that a wire is live
until we touch it and receive an electric
shock.

When nuclear radiation was first discovered,
it was welcomed with enthusiasm, and
to some extent this was justified. In the form
of X-rays it improved medical diagnosis and
treatment, and bottles of health-giving mineral
waters were advertised as radioactive. It
was only much later, when pictures were
released of the radiation damage to the
victims of Hiroshima and Nagasaki, that the
public image of nuclear radiation switched
to one of fear.

Undoubtedly this reaction has gone too
far. Nuclear radiation is indeed dangerous in
large amounts, but so are fire and electricity.
Properly used, nuclear radiation has numerous
beneficial applications in medicine, agriculture,
and industry. Like so many of
God’s gifts, it can be used for good or evil.

Nuclear radiation is not new; it did not
first enter the world with the experiments of
Henri Becquerel or Madame Curie. It has
been on the earth since the very beginning.
Many rocks and minerals, such as the pitchblende
refined by Madame Curie to produce
the first samples of radium, are naturally
radioactive and emit radiation all the time.
The nuclei formed by such radioactivity
include radon, a gas that seeps up through the
soil and enters our homes. The natural radioactivity
of the earth varies greatly from one
place to another, depending on the concentration
of rocks containing uranium. In
addition, the earth is bathed in the cosmic
radiations from outer space, and they are
passing through our bodies all the time.
Cosmic rays are attenuated as they pass
through the atmosphere and so they are
more intense at the top of a mountain than at
sea level. There are radioactive materials in
our own bodies, such as a rare isotope of
potassium. Thus the human species has
evolved through millions of years immersed
in nuclear radiation. This natural radioactivity
is important for estimating the hazards
of nuclear radiation in general, since if the
additional source emits radiation at a level
far below that of the natural radiation it is
unlikely to be injurious to health.

In addition to this natural radiation, we
are exposed to radiation from medical diagnosis
using X-rays, medical treatment, atomic
bomb tests, and the nuclear industry. Estimates
of the radiation exposure in the United
Kingdom due to all these sources (in millirem
per year) are 186 mrem for natural radiations,
including 50 mrem for radon, and 53
mrem for man-made irradiation, nearly all
due to medical treatment and diagnosis.
That for medical purposes is quite high, but
in the long term what is important is the
average exposure over a long time weighted
by the age distribution of those exposed.
This is because the effects of radiation at
levels typical of medical uses do not appear
for many years so that the irradiation of
young people before the end of their reproductive
age is more serious than that given to
older people. Since the larger part of the
medical irradiation is received during the
treatment of cancers, which more often
afflict older than younger people, the dangers
to health due to medical irradiation are
not so great as might appear.

Nearly half the radiation exposure due to
the natural background is attributable to
radon. This is a radioactive gas formed by
the radioactive decay of uranium. In regions
where the soil contains uranium the radon
seeps upwards into the atmosphere or into
our homes where it collects unless the house
is well-ventilated. Radon decays with the
emission of alpha-particles and when breathed
in can irradiate the inside of the lung, causing
lung cancer. According to the National
Radiation Protection Board a radon gas
concentration level of 200 Becquerels/m3,
equivalent to an effective dose of 10 mSv per
year, is the level at which action should be
taken to reduce the level. This involves
creating a cavity under the floors and pumping
out the radon at a cost of up to £1000.
Many local authorities are now recommending
that such action be taken.

Before doing this, however, it is necessary
to establish the relation between the
level of exposure and the probability of lung
cancer. Many studies worldwide, in Canada,
China, Finland, France, Germany, Japan,
Sweden, and the USA have failed to establish
any positive correlation and, indeed, in
three of these studies, there was an inverse
relationship. Other studies² find that the
increased risk of lung cancer due to a lifetime
dose of 100 Becquerels/m3 is about 0.1
percent and twenty-five times greater for
smokers. The data used in this study were
consistent with a linear dose relationship but
do not exclude different behavior at very
low exposures. The validity of this assumption
is discussed in more detail below. It thus
seems that, particularly for non-smokers, the
level of irradiation due to radon is so low that
when compared with other much greater
hazards it is difficult to justify such expensive
precautions.

Radioactive isotopes have many medical
applications. If, for example, we want to
know how salt is taken up by the body, we
can feed a patient with some salt that contains
a very small amount of a radioactive isotope
of sodium. This emits radiation that can be
detected by a counter outside the body, and
so we can follow the progress of the sodium
as it is absorbed. The amount of radiosodium
needed is so small that it does no harm to the
patient. In this way radioisotopes provide a
valuable diagnostic tool. Radioisotopes can
also be used for treatment. For example, it is
known that iodine tends to concentrate in
the thyroid gland. If therefore we want to
treat cancer of the thyroid we can feed the
patient with radioiodine, and it will go to the
thyroid gland and irradiate the tumor, without
appreciably affecting the rest of the
body.

The powerful nuclear accelerators that
are used to explore the structure of the
nucleus and to produce new unstable particles
can also be used to irradiate tumors.
The radiation emitted by radium and other
natural sources has the disadvantage that it is
relatively low in energy and so can penetrate
only a small distance into the body. In
addition, the radiation comes out in all
directions equally. If we want to treat a
tumor deep inside the body we need a way
of irradiating the tumor that minimizes the
irradiation of the surrounding healthy tissue.
The only way to do this is to have a collimated
beam of radiation of sufficient energy
to penetrate the body, and such beams are
produced by accelerators. During the treatment,
the patient is rotated so that the beam
always passes through the tumor but irradiates
a particular part of the surrounding
healthy tissue for only a small part of the
time. This is a difficult technique, but with
great care it can be used successfully. Many
nuclear accelerators such as that at Faure in
South Africa are used partly for medical
treatment and partly for nuclear research.

Sometimes it is difficult to know whether
the benefits of radiation outweigh the hazards.
Thus X-rays can detect cancers early
enough for effective treatment, and yet they
can also themselves cause cancers. A detailed
study of stomach tumors showed that for
young people the dangers outweigh the
benefits, whereas for older people the opposite
is the case.

There is widespread public anxiety about
the effects of nuclear radiation, particularly
concerning the genetic effects and the cases
of leukemia in children near nuclear installations.
The children of the survivors of the
atomic bombing of Hiroshima and Nagasaki,
who all received massive doses of radiation,
have been studied in detail by Professor S.
Kondo, who personally visited Nagasaki
soon after the bombing and saw the devastation.
He has studied the effects of the bombing
for forty years and has recorded the
indicators of genetic damage for 20,000
children of atomic bomb survivors exposed
to an average dose of 400 mS. The numbers
of the genetic indicators such as chromosome
abnormalities, mutations of blood proteins,
childhood leukemia, congenital defects,
stillbirths, and childhood deaths showed
no differences between the children of the
atomic bomb survivors and a control group.
There is thus no evidence of genetic damage
due to the atomic bombs.

To estimate the biological damage due to
a particular dose of radiation we must know
the relation between the two quantities. The
difficulty is that the doses that cause measurable
damage are hundreds of thousands of
times larger than the extra doses received by
people living around nuclear installations. It
is often assumed that there is a linear relation
between the two, so that the probability of
contracting cancer is proportional to the
dose. As it seems the safest assumption to
make, it is widely adopted in setting safety
standards. There is, however, no direct evidence
for this, and indeed there is much
contrary evidence.³ This is not unreasonable,
since the body has an innate capacity to
repair damage, and it is only when the
defenses of the body are overwhelmed by a
massive dose that harm occurs. Thus a dose
received over a long period is less harmful
than if it were received all at once.

A direct result of the linear dose assumption
is the setting of unreasonably strict limits
on permitted radiation exposure in many
industries, thus greatly increasing costs. This
leads to reluctance to accept vital
radiodiagnostic and radiotherapeutic irradiations,
and restricts the use of radiation in
industry and research. Adherence to these
exposure limits led to large-scale evacuation
from the region around Chernobyl, causing
much unnecessary distress and suffering.

It is also possible that small doses stimulate
the body’s repair mechanisms, so that small
doses are beneficial. This is supported by an
extensive study made by Frigerio et. al. at the
Argonne National Laboratory in 1973.⁴ They
compared the cancer statistics for the USA
from 1950 to 1967 with the average natural
background for each State, and found that
the seven States with the highest natural
background had the lowest cancer rates.
Unless there is some other explanation for
this result, it implies that the chance of
contracting cancer is reduced by 0.2 percent
per rem. Further evidence is provided by
“the higher life expectancy among survivors
of the Hiroshima and Nagasaki bombs; many
times lower incidence of thyroid cancer
among children under fifteen exposed to
fallout from Chernobyl than the normal
incidence among Finnish children; and a 68
percent below-average death rate from leukemia
among Canadian nuclear energy workers.”
⁵ Many studies on animals have given
similar results.

Furthermore, it is found that people living
in areas of high background radiation show
no evidence of detrimental effects; thus in
Kerala the life expectancy is seventy-four
years compared with fifty-four years for
India as a whole. Aircrews are exposed to
higher doses of cosmic radiation, and their
union asked for compensation. Studies of the
mortality rates of 19,184 pilots in the period
from 1960 to 1996 showed, however, that
they actually decreased with increasing dose.
The skin cancer rate was, on the other hand,
higher because of the time they spent lying
in the sun on tropical beaches. Such evidence
has been widely discounted because it
seems counter-intuitive.

In favour of the idea of a threshold dose,
it can be argued that the passage of a single
nuclear particle through a cell, the lowest
possible dose, can cause DNA double strand
lesions. Such lesions occur naturally at the
rate of about ten thousand per cell per day,
whereas exposure to radiation at the current
population exposure limit would cause only
two lesions per cell per day. Thus radiationinduced
lesions are insignificant compared
with those occurring naturally.

A new technique for evaluating the effects
of small doses of radiation has been developed
by Professor Feinendegen.⁶ His results
show conclusively that the linear dose assumption
is incorrect: at low doses there is an
additional quadratic term. Furthermore, a
Joint Report of the Academie des Sciences
(Paris) and of the Academie National de
Medicine concludes that estimates of the
carcinogenic effects of low doses of ionizing
radiations obtained using the linear assumption
could greatly overestimate those risks.⁷

The concern about nuclear radiation has
diverted attention from other threats to our
health. Radiation is responsible for only
about 1 percent of diseases worldwide, and
most of this comes from the natural background
and from medical uses. The nuclear
industry is responsible for less than 0.01
percent. The vast sums spent to reduce this
still further could be spent far more effectively
on simple disease prevention. It is
greatly in the public interest that these matters
should be treated as objectively as possible,
taking full account of the scientific
evidence. This would avoid much unnecessary
anxiety and enable the best decisions to
be taken concerning our future energy supplies.

Reactor Accidents

The two reactor accidents that have received
wide publicity are that at Three Mile
Island in 1979 and the much more serious
one at Chernobyl in 1986. The accident at
Three Mile Island was initially due to the
breakdown of the pumps circulating water in
the secondary cooling system. The standby
cooling systems failed to come into action,
and the reactor temperature rose. The automatic
safety system then shut down the
reactor, but the radioactive core still emitted
heat. The operators at first misinterpreted a
dial reading but eventually they brought the
reactor under control. A small amount of
radioactivity was emitted giving people
nearby a dose of about one millirem, which
is what they receive every day from natural
sources. During the incident several alarming
announcements were made to the public,
which naturally caused much distress. It was
a major financial disaster, and it took more
than ten years to remove the damaged reactor
at a cost of nearly a billion dollars.

The disaster at Chernobyl was immeasurably
worse. It happened by a combination of
bad design and operator irresponsibility. The
reactor was designed to produce weaponsgrade
plutonium as well as electrical power.
It was thermally unstable at low power, so
that overheating would cause further overheating,
with catastrophic consequences. The
operators were therefore instructed to raise
the power rapidly through this dangerous
region to ensure stable operation. Such a
design would never be accepted in the West.
On the fatal night the operators wanted to
find out what happened at low power. Fearing
that the safety circuits could shut the
reactor down before they finished their experiment
they switched then off. The power
rose rapidly, the graphite caught fire, the
cover was blown off, and radioactive materials
were discharged into the atmosphere
and deposited over much of Europe. Firemen
fought the blaze heroically; many received
lethal doses of radiation, and fifty-six
of them died.

There was, nonetheless, no evidence of
excess cases of leukemia or other types of
cancer among the hundreds of thousands of
workers employed in the clean-up after the
accident. Using the discredited linear dose
assumption a large increase in cancer victims
all over Europe due to the radioactivity
released into the atmosphere was predicted,
causing much public anxiety. For the same
reason large numbers of people were needlessly
evacuated from the region around the
reactor, causing much distress. Many countries
immediately lost faith in nuclear power
and opposed the construction of new nuclear
power stations. Since that time, more realistic
appraisals, especially by industrialists, have
convinced them of the necessity of nuclear
power, and many new power reactors are
being built or are planned.⁸ The reactors now
in operation are so designed that such accidents
can never happen again.

References:

1. P. E. Hodgson, Nuclear Power, Energy and
   the Environment. (London: Imperial College Press, 1999).
   This book contains many references to the topics discussed
   in this article.
2. Sir Richard Doll, H. J. Evans, and
   S. C. Darby, Nature 367.678.1994.
3. B. L. Cohen,
   “Validity of the Linear No-Threshold Theory of Radiation
   Carcinogenesis at Low Doses,” Nuclear Energy
   38.157.1999.
4. See also J. A. Simmons and D. E. Watt,
   Radiation Protection Dosimetry—A Radical Reappraisal. (Wisconsin:
   Medical Physics Publishing, 1999).
5. Lord
   Taverne, Speech in the House of Lords. SONE Newsletter
   No. 71.
6. Ludwig E. Feinendegen, lecture at the
   Conference on Nuclear Radiations and their Effects,
   Nagasaki, August 2004.
7. M. Tubiana and A. Aurengo,
   Nuclear Issues (October 2005), 3.
8. See Ref. 1, pp 81-94
   for discussion of Chernobyl. Further details in Nuclear
   Issues (October 2005).