Radioactive waste is a
waste
product containing
radioactive
material. It is usually the product of a nuclear process such as
nuclear fission. However, industries
not directly connected to the nuclear industry may produce
quantities of radioactive waste. The majority of radioactive waste
is "
low-level waste", meaning it
contains low levels of radioactivity per
mass
or
volume. This type of waste often consists
of used protective clothing, which is only lightly contaminated but
still dangerous in case of
radioactive contamination of a
human body through
ingestion,
inhalation,
absorption, or
injection.
The issue of disposal methods for nuclear waste was one of the most
pressing current problems the international nuclear industry faced
when trying to establish a long term energy production plan, yet
there was hope it could be safely solved.
A report giving the
Nuclear Industry's perspective on this problem is presented in a
document from the IAEA
(The
International Atomic Energy Agency) published in October
2007. It summarizes the current state of scientific
knowledge on whether waste could find its way from a deep burial
facility back to soil and drinking water and threaten the health of
human beings and other forms of life. In the United States, DOE
acknowledges progress in addressing the waste problems of the
industry, and successful remediation of some contaminated sites,
yet some uncertainty and complications in handling the issue
properly, cost effectively, and in the projected time frame. In
other countries with lower ability or will to maintain
environmental integrity the issue would be even more
problematic.
In the United States alone, the
Department of Energy
states there are "millions of gallons of radioactive waste" as well
as "thousands of tons of
spent
nuclear fuel and material" and also "huge quantities of
contaminated soil and water." Despite copious quantities of waste,
the DOE has stated a goal of cleaning all presently contaminated
sites successfully by 2025.
The Fernald
, Ohio
site for
example had "31 million pounds of uranium product", "2.5 billion
pounds of waste", "2.75 million cubic yards of contaminated soil
and debris", and a "223 acre portion of the underlying Great Miami
Aquifer had uranium levels above drinking standards." The
United States has at least 108 sites designated as areas that are
contaminated and unusable, sometimes many thousands of acres. DOE
wishes to clean or mitigate many or all by 2025, however the task
can be difficult and it acknowledges that some may never be
completely remediated.
In just one of these 108 larger designations,
Oak Ridge
National Laboratory
, there were for example at least "167 known
contaminant release sites" in one of the three subdivisions of the
site. Some of the U.S. sites were smaller in nature,
however, cleanup issues were simpler to address, and DOE has
successfully completed cleanup, or at least closure, of several
sites.
Claims exist that the problems of nuclear waste do not come
anywhere close to approaching the problems of fossil fuel waste. A
2004 article from the BBC states: "The
World Health Organization (WHO)
says 3 million people are killed worldwide by outdoor air pollution
annually from vehicles and industrial emissions, and 1.6 million
indoors through using solid fuel." In the U.S. alone, fossil fuel
waste has been linked to the death of 20,000 people each year. A
coal power plant releases 100 times as much radiation as a nuclear
power plant of the same wattage.
It is estimated that during 1982, US coal
burning released 155 times as much radioactivity into the
atmosphere as the Three Mile Island accident
.
The
World Nuclear
Association provides a comparison of deaths due to accidents
among different forms of energy production. In their comparison,
deaths per TW-yr of electricity produced from 1970 to 1992 are
quoted as 885 for hydropower, 342 for coal, 85 for natural gas, and
8 for nuclear.
The nature and significance of radioactive waste
Radioactive waste typically comprises a number of
radioisotopes: unstable configurations of
elements that
decay, emitting
ionizing radiation which can be
harmful to human health and to the environment. Those isotopes emit
different types and levels of radiation, which last for different
periods of time..
Physics
The radioactivity of all nuclear waste diminishes with time. All
radioisotopes contained in the waste have a
half-life - the time it takes for any radionuclide
to lose half of its radioactivity and eventually all radioactive
waste decays into non-radioactive elements. Certain radioactive
elements (such as
plutonium-239) in
“spent” fuel will remain hazardous to humans and other living
beings for hundreds of thousands of years. Other radioisotopes
remain hazardous for millions of years. Thus, these wastes must be
shielded for centuries and isolated from the living environment for
millennia. Some elements, such as
Iodine-131, have a short half-life (around 8 days
in this case) and thus they will cease to be a problem much more
quickly than other, longer-lived, decay products but their activity
is much greater initially. The two tables show some of the major
radioisotopes, their half-lives, and their
radiation yield as a proportion of the
yield of fission of Uranium-235.
The faster a
radioisotope decays, the
more radioactive it will be. The energy and the type of the
ionizing radiation emitted by a
pure radioactive substance are important factors in deciding how
dangerous it will be. The chemical properties of the radioactive
element will determine how mobile
the substance is and how likely it is to spread into the
environment and contaminate human bodies. This is further
complicated by the fact that many radioisotopes do not decay
immediately to a stable state but rather to a radioactive
decay product leading to
decay chains.
Pharmacokinetics
Exposure to high levels of radioactive waste may cause serious harm
or
death. Treatment of an
adult animal with
radiation
or some other
mutation-causing effect, such
as a cytotoxic anti-
cancer drug, may cause cancer in the animal. In humans it has
been calculated that a 5
sievert dose is
usually fatal, and the lifetime risk of dying from radiation
induced cancer from a single dose of 0.1 sieverts is 0.8%,
increasing by the same amount for each additional 0.1 sievert
increment of dosage. Ionizing radiation causes deletions in
chromosomes. If a developing organism such as an
unborn child is irradiated, it is possible a
birth defect may be induced, but it is
unlikely this defect will be in a
gamete or a
gamete forming
cell. The incidence of
radiation-induced mutations in humans is undetermined, due to flaws
in studies done to date.
Depending on the decay mode and the
pharmacokinetics of an element (how the
body processes it and how quickly), the threat due to exposure to a
given activity of a
radioisotope will
differ. For instance
iodine-131 is a
short-lived
beta and
gamma emitter but because it concentrates in the
thyroid gland, it is more able to cause
injury than
caesium-137 which, being water
soluble, is rapidly excreted in urine. In a similar way, the
alpha emitting actinides and
radium are considered very harmful as they tend to
have long
biological half-lives
and their radiation has a high linear energy transfer value.
Because of such differences, the rules determining biological
injury differ widely according to the radioisotope, and sometimes
also the nature of the chemical compound which contains the
radioisotope.
Goals of waste management
The main objective in managing and disposing or destruction of
radioactive (or other) waste is to protect people and the
environment. This means isolating, diluting, or destroying
(transmutating) the waste so that the rate or concentration of any
radionuclide returned to the
biosphere is
harmless. To achieve this the preferred technology to date has been
deep and secure burial for the more dangerous wastes;
transmutation, long-term retrievable
storage, and removal to space have also been suggested. Management
options for waste are discussed below.
Radioactivity by definition reduces over time, so in principle the
waste needs to be isolated for a particular period of time until
its components have decayed such that it no longer poses a threat.
In practice this can mean periods of hundreds of thousands of
years, depending on the nature of the waste involved.
Though an affirmative answer is often taken for granted, the
question as to whether or not we should endeavor to avoid causing
harm to remote future generations, perhaps thousands upon thousands
of years hence, is essentially one which must be dealt with by
philosophy.
Sources of waste
Radioactive waste comes from a number of sources. The majority of
waste originates from the nuclear fuel cycle and nuclear weapons
reprocessing. However, other sources include medical and industrial
wastes, as well as naturally occurring radioactive materials (NORM)
that can be concentrated as a result of the processing or
consumption of coal, oil and gas, and some minerals, as discussed
below.
Nuclear fuel cycle
Front end
Waste from the front end of the
nuclear fuel cycle is usually alpha
emitting waste from the extraction of uranium. It often contains
radium and its decay products.
Uranium dioxide (UO
2)
concentrate from mining is not very radioactive - only a thousand
or so times as radioactive as the
granite
used in buildings. It is refined from
yellowcake (U
3O
8), then
converted to
uranium
hexafluoride gas (UF
6). As a gas, it undergoes
enrichment to increase the
U-235 content from 0.7% to about 4.4% (LEU). It
is then turned into a hard
ceramic oxide
(UO
2) for assembly as reactor fuel elements.
The main by-product of enrichment is
depleted uranium (DU), principally the
U-238 isotope, with a U-235 content of ~0.3%.
It is stored, either as UF
6 or as
U
3O
8. Some is used in applications where its
extremely high density makes it valuable, such as the keels of
yachts, and
anti-tank shell. It
is also used (with recycled plutonium) for making
mixed oxide fuel (MOX) and to dilute highly
enriched uranium from weapons stockpiles which is now being
redirected to become reactor fuel. This dilution, also called
downblending, means
that any nation or group that acquired the finished fuel would have
to repeat the (very expensive and complex) enrichment process
before assembling a weapon.
Back end
The back end of the nuclear fuel cycle, mostly spent
fuel rods, contains
fission products that emit beta and gamma
radiation, and
actinides that emit
alpha particles, such as
uranium-234,
neptunium-237,
plutonium-238 and
americium-241, and even sometimes some neutron
emitters such as
californium (Cf). These
isotopes are formed in
nuclear
reactors.
It is important to distinguish the processing of uranium to make
fuel from the
reprocessing of
used fuel. Used fuel contains the highly radioactive products of
fission (see high level waste below). Many of these are neutron
absorbers, called
neutron poisons in
this context. These eventually build up to a level where they
absorb so many neutrons that the chain reaction stops, even with
the control rods completely removed. At that point the fuel has to
be replaced in the reactor with fresh fuel, even though there is
still a substantial quantity of
uranium-235 and
plutonium present.
In the United States, this used fuel is
stored, while in countries such as the Russia
,United Kingdom
, France
, Japan
and India
the fuel is
reprocessed to remove the fission products, and the fuel can then
be re-used. This reprocessing involves handling highly
radioactive materials, and the fission products removed from the
fuel are a concentrated form of high-level waste as are the
chemicals used in the process.
While these countries reprocess the fuel
carrying out single plutonium cycles, India is known to
be the only country in the world planning multiple plutonium
recycling schemes.. This has two distinct advantages, the
reprocessed fuel is rendered unusable for weapons development, and
high fuel efficiency can be achieved.
For their plutonium
generating reactors, India has realized
a burn-up almost 4 times as high as the typical fuel efficiency of
normal commercial nuclear reactors.
Fuel composition and long term radioactivity
Activity of U-233 for three fuel
types
Total activity for three fuel
types
Long-lived radioactive waste form the back end of the fuel cycle is
especially relevant when designing a complete waste management plan
for
spent nuclear fuel (SNF).
When looking at long term radioactive decay, the actinides in the
SNF have a significant influence due to their characteristically
long half-lives. Depending on what a
nuclear reactor is fueled with,
the actinide composition in the SNF will be different.
An example of this effect is the use of
nuclear fuels with
thorium. Th-232 is a fertile material that can
undergo a neutron capture reaction and two beta minus decays,
resulting in the production of fissile
U-233. The SNF of a cycle with thorium will
contain U-233, an isotope with a
half-life
of 1.59E5 years. Its radioactive decay will strongly influence the
long-term
activity curve of the
SNF around 10E5 years. A comparison of the activity associated to
U-233 for three different SNF types can be seen in the figure on
the top right.
The burnt fuels are thorium with reactor-grade plutonium (RGPu),
thorium with weapons-grade plutonium (WGPu) and
Mixed Oxide fuel (MOX). For RGPu and WGPu, the
initial amount of U-233 and its decay around 10E5 years can be
seen. This has an effect in the total activity curve of the three
fuel types. The absence of U-233 and its daughter products in the
MOX fuel results in a lower activity in region 3 of the figure on
the bottom right, whereas for RGPu and WGPu the curve is maintained
higher due to the presence of U-233 that has not fully
decayed.
The use of different fuels in nuclear reactors results in different
SNF composition, with varying activity curves.
Proliferation concerns
When dealing with uranium and plutonium, the possibility that they
may be used to build
nuclear weapons
is often a concern. Active nuclear reactors and nuclear weapons
stockpiles are very carefully safeguarded and controlled. However,
high-level waste from nuclear reactors may contain plutonium.
Ordinarily, this plutonium is
reactor-grade plutonium,
containing a mixture of
plutonium-239
(highly suitable for building nuclear weapons),
plutonium-240 (an undesirable contaminant and
highly radioactive),
plutonium-241,
and
plutonium-238; these isotopes are
difficult to separate. Moreover, high-level waste is full of highly
radioactive
fission products.
However, most fission products are relatively short-lived. This is
a concern since if the waste is stored, perhaps in
deep geological storage, over
many years the fission products decay, decreasing the radioactivity
of the waste and making the plutonium easier to access. Moreover,
the undesirable contaminant Pu-240 decays faster than the Pu-239,
and thus the quality of the bomb material increases with time
(although its quantity decreases during that time as well). Thus,
some have argued, as time passes, these deep storage areas have the
potential to become "plutonium mines", from which material for
nuclear weapons can be acquired with relatively little difficulty.
Critics of the latter idea point out that the half-life of Pu-240
is 6,560 years and Pu-239 is 24,110 years, and thus the relative
enrichment of one isotope to the other with time occurs with a
half-life of 9,000 years (that is, it takes 9000 years for the
fraction of Pu-240 in a sample of mixed plutonium
isotopes, to spontaneously decrease by half—a typical enrichment
needed to turn reactor-grade into weapons-grade Pu). Thus "weapons
grade plutonium mines" would be a problem for the very far future
(>9,000 years from now), so that there remains a great deal of
time for technology to advance to solve this problem, before it
becomes acute.
Pu-239 decays to
U-235 which is suitable
for weapons and which has a very long half life (roughly
10
9 years). Thus plutonium may decay and leave
uranium-235. However, modern reactors are only moderately enriched
with U-235 relative to U-238, so the U-238 continues to serve as
denaturation agent
for any U-235 produced by plutonium decay.
One solution to this problem is to recycle the plutonium and use it
as a fuel e.g. in
fast reactors. But in
the minds of some, the very existence of the
nuclear fuel reprocessing
plant needed to separate the plutonium from the other elements
represents a proliferation concern. In
pyrometallurgical fast reactors, the
waste generated is an actinide compound that cannot be used for
nuclear weapons.
Nuclear weapons reprocessing
Waste from
nuclear weapons
reprocessing (as opposed to production, which requires primary
processing from reactor fuel) is unlikely to contain much beta or
gamma activity other than
tritium and
americium. It is more likely to contain
alpha emitting actinides such as Pu-239 which is a fissile material
used in bombs, plus some material with much higher specific
activities, such as Pu-238 or Po.
In the past the neutron trigger for a bomb tended to be
beryllium and a high activity alpha emitter such
as
polonium; an alternative to polonium is
Pu-238. For reasons of national security,
details of the design of modern bombs are normally not released to
the open literature. It is likely however that a D-T
fusion reaction in either an electrically
driven device or a D-T fusion reaction driven by the chemical
explosives would be used to start up a modern device.
Some designs might well contain a
radioisotope
thermoelectric generator using Pu-238 to provide a longlasting
source of electrical power for the electronics in the device.
It is likely that the fissile material of an old bomb which is due
for refitting will contain decay products of the plutonium isotopes
used in it, these are likely to include
U-236
from Pu-240 impurities, plus some U-235 from decay of the Pu-239;
however, due to the relatively long half-life of these Pu isotopes,
these wastes from radioactive decay of bomb core material would be
very small, and in any case, far less dangerous (even in terms of
simple radioactivity) than the Pu-239 itself.
The beta decay of
Pu-241 forms
Am-241; the in-growth of americium is likely to be a
greater problem than the decay of Pu-239 and Pu-240 as the
americium is a gamma emitter (increasing external-exposure to
workers) and is an alpha emitter which can cause the generation of
heat. The plutonium could be separated from the
americium by several different processes; these would include
pyrochemical
processes and aqueous/organic
solvent
extraction. A truncated
PUREX type
extraction process would be one possible method of making the
separation.
Medical
Radioactive
medical waste tends to
contain
beta particle and
gamma ray emitters. It can be divided into two
main classes. In diagnostic
nuclear
medicine a number of short-lived gamma emitters such as
technetium-99m are used. Many of
these can be disposed of by leaving it to decay for a short time
before disposal as normal waste. Other isotopes used in medicine,
with half-lives in parentheses:
Industrial
Industrial source waste can contain
alpha,
beta,
neutron or gamma emitters. Gamma
emitters are used in
radiography while
neutron emitting sources are used in a range of applications, such
as
oil well logging.
Naturally occurring radioactive material (NORM)
Processing of substances containing natural radioactivity; this is
often known as NORM. A lot of this waste is
alpha particle-emitting matter from the decay
chains of
uranium and
thorium. The main source of radiation in the human
body is
potassium-40 (
40K). There is a natural background
radioactivity that life systems are built to resist. Most rocks,
due to their components, have a certain, but low level, of
radioactivity.
Coal
Coal contains a small amount of radioactive
uranium, barium, thorium and potassium, but, in the case of pure
coal, this is significantly less than the average concentration of
those elements in the
Earth's crust.
However, the surrounding strata, if shale or mudstone, often
contains slightly more than average and this may also be reflected
in the ash content of 'dirty' coals. The more active ash minerals
become concentrated in the
fly ash precisely
because they do not burn well. However, the radioactivity of fly
ash is still very low. It is about the same as black
shale and is less than
phosphate rocks, but is more of a concern because
a small amount of the fly ash ends up in the atmosphere where it
can be inhaled.
Oil and gas
Residues from the
oil and
gas industry often contain radium and its
daughters. The sulphate scale from an oil well can be very radium
rich, while the water, oil and gas from a well often contains
radon. The radon decays to form solid
radioisotopes which form coatings on the inside of pipework. In an
oil processing plant the area of the plant where
propane is processed is often one of the more
contaminated areas of the plant as radon has a similar boiling
point as propane.
Types of radioactive waste
Removal of very low-level waste
Although not significantly radioactive,
uranium mill
tailings are waste. They are byproduct material from the
rough processing of uranium-bearing ore. They are sometimes
referred to as 11(e)2 wastes, from the section of the U.S. Atomic
Energy Act that defines them. Uranium mill tailings typically also
contain chemically-hazardous heavy metals such as
lead and
arsenic.
Vast mounds of uranium
mill tailings are left at many old mining sites, especially in
Colorado
, New
Mexico
, and Utah
.
Low level waste
(LLW) is generated from hospitals and industry, as well as
the nuclear fuel cycle. It comprises paper, rags, tools, clothing,
filters, etc., which contain small amounts of mostly short-lived
radioactivity. Commonly, LLW is designated as such as a
precautionary measure if it originated from any region of an
'Active Area', which frequently includes offices with only a remote
possibility of being contaminated with radioactive materials. Such
LLW typically exhibits no higher radioactivity than one would
expect from the same material disposed of in a non-active area,
such as a normal office block. Some high activity LLW requires
shielding during handling and transport but most LLW is suitable
for shallow land burial. To reduce its volume, it is often
compacted or incinerated before disposal. Low level waste is
divided into four classes, class A, B, C and GTCC, which means
"Greater Than Class C".
Intermediate level waste (ILW) contains higher
amounts of radioactivity and in some cases requires shielding. ILW
includes
resins, chemical
sludge and metal reactor
fuel cladding, as well as contaminated
materials from reactor decommissioning. It may be solidified in
concrete or bitumen for disposal. As a general rule, short-lived
waste (mainly non-fuel materials from reactors) is buried in
shallow repositories, while long-lived waste (from fuel and
fuel-reprocessing) is deposited in
deep underground facilities. U.S.
regulations do not define this category of waste; the term is used
in Europe and elsewhere.
High level waste
(HLW) is produced by
nuclear
reactors. It contains
fission
products and
transuranic elements
generated in the
reactor core. It is
highly radioactive and often thermally hot. HLW accounts for over
95% of the total radioactivity produced in the process of nuclear
electricity generation. The
amount of HLW worldwide is currently increasing by about 12,000
metric tons every year, which is the equivalent to about 100
double-decker busses or a two-story structure with a footprint the
size of a basketball court.
Transuranic waste
(TRUW) as defined by U.S. regulations is, without regard
to form or origin, waste that is contaminated with alpha-emitting
transuranic radionuclides with
half-lives greater than 20 years, and concentrations greater than
100
nCi/g (3.7
MBq/kg), excluding High Level Waste. Elements that
have an
atomic number greater than
uranium are called transuranic ("beyond uranium"). Because of their
long half-lives, TRUW is disposed more cautiously than either low
level or intermediate level waste. In the U.S. it arises mainly
from weapons production, and consists of clothing, tools, rags,
residues, debris and other items contaminated with small amounts of
radioactive elements (mainly plutonium).
Under U.S. law, Transuranic waste is further categorized into
"contact-handled" (CH) and "remote-handled" (RH) on the basis of
radiation dose measured at the surface of the waste container. CH
TRUW has a surface dose rate not greater than 200
mrem per hour (2
mSv/h), whereas RH TRUW has a surface dose rate
of 200
mrem per hour (2
mSv/h) or greater. CH TRUW does not have the very high
radioactivity of high level waste, nor its high heat generation,
but RH TRUW can be highly radioactive, with surface dose rates up
to 1000000
mrem per hour
(10000 mSv/h).
The United States currently permanently
disposes of TRUW generated from nuclear power plants and military
facilities at the Waste Isolation Pilot Plant
.
Management of waste
Of particular concern in nuclear waste management are two
long-lived fission products, Tc-99 (half-life 220,000 years) and
I-129 (half-life 17 million years), which dominate spent fuel
radioactivity after a few thousand years. The most troublesome
transuranic elements in spent fuel are Np-237 (half-life two
million years) and Pu-239 (half life 24,000 years). Nuclear waste
requires sophisticated treatment and management in order to
successfully isolate it from interacting with the
biosphere. This usually necessitates treatment,
followed by a long-term management strategy involving storage,
disposal or transformation of the waste into a non-toxic form.
Governments around the world are considering a range of waste
management and disposal options, though there has been limited
progress toward long-term waste management solutions.
Initial treatment of waste
Vitrification
A vitrification experiment for the
study of nuclear waste disposal
Long-term storage of radioactive waste requires the stabilization
of the waste into a form which will not react, nor degrade, for
extended periods of time. One way to do this is through
vitrification.
Currently at Sellafield
the high-level waste (PUREX
first cycle raffinate) is mixed with
sugar and then calcined. Calcination involves passing the waste through a
heated, rotating tube. The purposes of calcination are to evaporate
the water from the waste, and de-nitrate the fission products to
assist the stability of the glass produced.
The 'calcine' generated is fed continuously into an induction
heated furnace with fragmented
glass. The
resulting glass is a new substance in which the waste products are
bonded into the glass matrix when it solidifies. This product, as a
molten fluid, is poured into
stainless
steel cylindrical containers ("cylinders") in a batch process.
When cooled, the fluid solidifies ("vitrifies") into the glass.
Such glass, after being formed, is very highly resistant to
water.
After filling a cylinder, a seal is
welded onto
the cylinder. The cylinder is then washed. After being inspected
for external contamination, the steel cylinder is stored, usually
in an underground repository. In this form, the waste products are
expected to be immobilized for a very long period of time (many
thousands of years).
The glass inside a cylinder is usually a black glossy substance.
All this
work (in the United
Kingdom) is done using hot cell
systems. The sugar is added to control the
ruthenium chemistry and to stop the formation of
the volatile
RuO4
containing
radio ruthenium.
In the west, the
glass is normally a borosilicate
glass (similar to Pyrex), while in the
former Soviet
bloc it is
normal to use a phosphate
glass. The amount of fission products in the glass must
be limited because some (
palladium, the
other Pt group metals, and
tellurium) tend
to form metallic phases which separate from the glass. Bulk
vitrification uses electrodes to melt soil and wastes, which are
then buried underground. In Germany a vitrification plant is in
use; this is treating the waste from a small demonstration
reprocessing plant which has since been closed down.
Ion exchange
It is common for medium active wastes in the nuclear industry to be
treated with
ion exchange or other
means to concentrate the radioactivity into a small volume. The
much less radioactive bulk (after treatment) is often then
discharged. For instance, it is possible to use a
ferric hydroxide floc to remove radioactive metals from aqueous mixtures
[6343]. After the radioisotopes are absorbed
onto the ferric hydroxide, the resulting sludge can be placed in a
metal drum before being mixed with cement to form a solid waste
form. In order to get better long-term performance (mechanical
stability) from such forms, they may be made from a mixture of
fly ash, or
blast
furnace slag, and
portland cement, instead of normal
concrete (made with
portland cement, gravel and sand).
Synroc
The Australian
Synroc (synthetic rock) is a
more sophisticated way to immobilize such waste, and this process
may eventually come into commercial use for civil wastes (it is
currently being developed for U.S. military wastes).
Synroc was invented
by the late Prof Ted Ringwood (a geochemist) at the Australian
National University
. The Synroc contains
pyrochlore and cryptomelane type minerals. The
original form of Synroc (Synroc C) was designed for the liquid high
level waste (PUREX raffinate) from a
light water reactor. The main minerals
in this Synroc are hollandite
(BaAl
2Ti
6O
16),
zirconolite (CaZrTi
2O
7)
and
perovskite (CaTiO
3). The
zirconolite and perovskite are hosts for the
actinides. The
strontium
and
barium will be fixed in the perovskite.
The
caesium will be fixed in the
hollandite.
Long term management of waste
The timeframe in question when dealing with radioactive waste
ranges from 10,000 to 1,000,000 years, according to studies based
on the effect of estimated radiation doses.Researchers suggest that
forecasts of health detriment for such periods
should be
examined critically. Practical studies only consider up to 100
years as far as effective planning and cost evaluations are
concerned. Long term behavior of radioactive wastes remains a
subject for ongoing research projects.
Geologic disposal
The
process of selecting appropriate deep final repositories for high
level waste and spent fuel is now under way in several countries
(Schacht Asse
II
and the waste Isolation Pilot Plant) with the first
expected to be commissioned some time after 2010.
The basic
concept is to locate a large, stable geologic formation and use
mining technology to excavate a tunnel, or large-bore tunnel boring machines (similar to
those used to drill the Chunnel
from England to France) to drill a shaft 500–1,000
meters below the surface where rooms or vaults can be excavated for
disposal of high-level radioactive waste. The goal is to
permanently isolate nuclear waste from the human environment.
However, many people remain uncomfortable with the immediate
stewardship cessation of this
disposal system, suggesting perpetual management and monitoring
would be more prudent.
Because some radioactive species have half-lives longer than one
million years, even very low container leakage and radionuclide
migration rates must be taken into account. Moreover, it may
require more than one half-life until some nuclear materials lose
enough radioactivity to no longer be lethal to living things. A
1983 review of the Swedish radioactive waste disposal program by
the National Academy of Sciences found that country’s estimate of
several hundred thousand years—perhaps up to one million
years—being necessary for waste isolation “fully justified.”
Storing high level nuclear waste above ground for a century or so
is considered appropriate by many scientists. This allows the
material to be more easily observed and any problems detected and
managed, while decay of radionuclides over this time period
significantly reduces the level of radioactivity and associated
harmful effects to the container material. It is also considered
likely that over the next century newer materials will be developed
which will not break down as quickly when exposed to a high neutron
flux, thus increasing the longevity of the container once it is
permanently buried.
Sea-based options for disposal of radioactive waste include burial
beneath a stable
abyssal plain, burial
in a
subduction zone that would slowly
carry the waste downward into the
Earth's mantle, and burial beneath a remote
natural or human-made island. While these approaches all have merit
and would facilitate an international solution to the vexing
problem of disposal of radioactive waste, they are currently not
being seriously considered because of the legal barrier of the
Law of
the Sea and because in
North
America and
Europe sea-based burial has
become taboo from fear that such a repository could leak and cause
widespread damage. Dumping of radioactive waste from ships has
reinforced this concern, as has contamination of islands in the
Pacific Ocean. However, sea-based approaches might come under
consideration in the future by individual countries or groups of
countries that cannot find other acceptable solutions.
Article 1 (Definitions), 7., of the 1996 Protocol to the Convention
on the Prevention of Marine Pollution by Dumping of Wastes and
Other Matter, (the London Dumping Convention) states:
- “Sea” means all marine waters other than the internal waters of
States, as well as the seabed and the subsoil thereof; it does not
include sub-seabed repositories accessed only from land.”
The proposed land-based subductive waste disposal method disposes
of nuclear waste in a subduction zone accessed from land, and
therefore is not prohibited by international agreement. This method
has been described as the most viable means of disposing of
radioactive waste, and as the state-of-the-art in nuclear waste
disposal technology.Another approach termed Remix & Return
would blend high-level waste with
uranium
mine and mill tailings down to the level of the original
radioactivity of the
uranium ore, then
replace it in inactive uranium mines. This approach has the merits
of providing jobs for miners who would double as disposal staff,
and of facilitating a cradle-to-grave cycle for radioactive
materials. However, this approach would be inappropriate for spent
reactor fuel in the absence of reprocessing, due to the presence in
it of highly toxic radioactive elements such as plutonium.
Transmutation
There have been proposals for reactors that consume nuclear waste
and transmute it to other, less-harmful nuclear waste. In
particular, the
Integral Fast
Reactor was a proposed nuclear reactor with a nuclear fuel
cycle that produced no transuranic waste and in fact, could consume
transuranic waste. It proceeded as far as large-scale tests but was
then canceled by the U.S. Government. Another approach, considered
safer but requiring more development, is to dedicate
subcritical reactors to the
transmutation of the left-over
transuranic elements.
An isotope that is found in nuclear waste and that represents a
concern in terms of proliferation is Pu-239. The estimated world
total of plutonium in the year 2000 was of 1,645 MT, of which 210
MT had been separated by reprocessing. The large stock of plutonium
is a result of its production inside uranium-fueled reactors and of
the reprocessing of weapons-grade plutonium during the weapons
program. An option for getting rid of this plutonium is to use it
as a fuel in a traditional Light Water Reactor (LWR). Several fuel
types with differing plutonium destruction efficiencies are under
study. See
Nuclear
transmutation.
Transmutation was banned in the United States
on April 1977 by President Carter due to the danger
of plutonium proliferation, but President Reagan rescinded the ban
in 1981. Due to the economic losses and risks, construction
of reprocessing plants during this time did not resume. Due to high
energy demand, work on the method has continued in the
EU. This has resulted in a practical nuclear research
reactor called
Myrrha in which transmutation is possible.
Additionally, a new research program called
ACTINET has
been started in the
EU to make transmutation
possible on a large, industrial scale.
According to
President Bush's Global Nuclear Energy Partnership (GNEP) of 2007,
the United
States is now actively promoting research on transmutation
technologies needed to markedly reduce the problem of nuclear waste
treatment.
There have also been theoretical studies involving the use of
fusion reactors as so called
"actinide burners" where a fusion reactor
plasma such as in a
tokamak, could be "doped" with a small amount of the
"minor" transuranic atoms which would be transmuted (meaning
fissioned in the actinide case) to lighter elements upon their
successive bombardment by the very high energy neutrons produced by
the fusion of
deuterium and
tritium in the reactor.
It was recently found
by a study done at MIT
, that only 2
or 3 fusion reactors with parameters similar to that of the
International Thermonuclear Experimental
Reactor
(ITER) could transmute the entire annual minor actinide production from all of the
light water reactors presently
operating in the United States
fleet while simultaneously generating approximately 1 gigawatt of power from each reactor[6344].
Re-use of waste
Another option is to find applications of the isotopes in nuclear
waste so as to
re-use them.
Already,
caesium-137,
strontium-90 and a few other isotopes are
extracted for certain industrial applications such as
food irradiation and
radioisotope
thermoelectric generators. While re-use does not eliminate the
need to manage radioisotopes, it may reduce the quantity of waste
produced.
The Nuclear Assisted Hydrocarbon Production Method, Canadian patent
application 2,659,302, is a method for the temporary or permanent
storage of nuclear waste materials comprising the placing of waste
materials into one or more repositories or boreholes constructed
into an
unconventional oil
formation. The thermal flux of the waste materials fracture the
formation, alters the chemical and/or physical properties of
hydrocarbon material within the subterranean formation to allow
removal of the altered material. A mixture of hydrocarbons,
hydrogen, and/or other formation fluids are produced from the
formation. The radioactivity of high-level radioactive waste
affords proliferation resistance to plutonium placed in the
periphery of the repository or the deepest portion of a
borehole.
A 1990 proposed type of breeder reactor called a
traveling wave reactor is claimed, if
it were to be built, to be able to be fueled by depleted uranium,
which is currently considered nuclear waste.
Space disposal
Space disposal is an attractive notion because it permanently
removes nuclear waste from the environment. However, it has
significant disadvantages, not least of which is the potential for
catastrophic failure of a
launch
vehicle. Furthermore, the high number of launches that would be
required — due to the fact that no individual rocket would be able
to carry very much of the material relative to the material needed
to be disposed of—makes the proposal impractical (for both economic
and risk-based reasons). To further complicate matters,
international agreements on the regulation of such a program would
need to be established.
[6345] This method would also be energy intensive and
thus is not necessarily economically feasible.
In the future, alternative,
non-rocket spacelaunch technologies
may provide a solution. It has been suggested that through the use
of a stationary launch system many of the risks of catastrophic
launch failure could be avoided. A promising concept is the use of
high power lasers to launch "indestructible" containers from the
ground into space. Such a system would require no rocket
propellant, with the launch vehicle's payload making up a near
entirety of the vehicle's mass. Without the use of rocket fuel on
board there would be little chance of the vehicle
exploding.
[6346]
One possibility involves encasing the waste in glassified form
inside a steel shell thick, which in turn is tiled with shuttle
tile to its exterior. If the launch vehicle fails just before
reaching orbit, the waste ball will safely re-enter the Earth's
atmosphere. The steel shell would deform on impact, but would not
rupture due to the density of the shell. Also, this would
potentially allow the waste to be shot into the Sun.
National management plans
Most countries are considerably ahead of the United States in
developing plans for high-level radioactive waste disposal. Sweden
and Finland are furthest along in committing to a particular
disposal technology, while many others reprocess spent fuel or
contract with France or Great Britain to do it, taking back the
resulting plutonium and high-level waste. “An increasing backlog of
plutonium from reprocessing is developing in many countries... It
is doubtful that reprocessing makes economic sense in the present
environment of cheap uranium.”
In many European countries (e.g., Britain, Finland, the
Netherlands, Sweden and Switzerland) the risk or dose limit for a
member of the public exposed to radiation from a future high-level
nuclear waste facility is considerably more stringent than that
suggested by the International Commission on Radiation Protection
or proposed in the United States. European limits are often more
stringent than the standard suggested in 1990 by the International
Commission on Radiation Protection by a factor of 20, and more
stringent by a factor of ten than the standard proposed by the U.S.
Environmental Protection Agency (EPA) for
Yucca Mountain nuclear waste
repository
for the first 10,000 years after closure.
Moreover, the U.S. EPA’s proposed standard for greater than 10,000
years is 250 times more permissive than the European limit.
Illegal dumping
Authorities in Italy are investigating a
'Ndrangheta mafia clan accused of trafficking
and illegally dumping nuclear waste.
According to a
turncoat, a manager of the Italy’s state
energy research agency Enea paid the clan to
get rid of 600 drums of toxic and radioactive waste from Italy,
Switzerland, France, Germany, and the US, with Somalia
as the destination, where the waste was buried
after buying off local politicians. Former employees of Enea
are suspected of paying the criminals to take waste off their hands
in the 1980s and 1990s. Shipments to Somalia continued into the
1990s, while the 'Ndrangheta clan also blew up shiploads of waste,
including radioactive hospital waste, and sending them to the sea
bed off the Calabrian coast. According to the environmental group
Legambiente, former members of the
'Ndrangheta have said that they were paid to sink ships with
radioactive material for the last 20 years.
Accidents involving radioactive waste
A number of incidents have occurred when radioactive material was
disposed of improperly, shielding during transport was defective,
or when it was simply abandoned or even stolen from a waste store.
In the
Soviet Union, waste stored in Lake Karachay
was blown over the area during a dust storm after the lake had partly dried
out. At Maxey Flat
, a low-level radioactive waste facility located in
Kentucky
, containment trenches covered with dirt, instead of
steel or cement, collapsed under heavy rainfall into the trenches
and filled with water. The water that invaded the trenches became
radioactive and had to be disposed of at the Maxey Flat facility itself. In other cases of
radioactive waste accidents, lakes or ponds with radioactive waste
accidentally overflowed into the rivers during exceptional storms.
In Italy, several radioactive waste deposits let material flow into
river water, thus contaminating water fit for domestic use.
In
France, in the summer of 2008 numerous incidents happened; in one,
at the Areva plant in Tricastin
, it was reported that during a draining operation
liquid containing untreated uranium overflowed out of a faulty tank
and about 75 kg of the radioactive material seeped into the
ground and, from there, into two rivers nearby;; in another case,
over 100 staff were contaminated with low doses of
radiation.
Scavenging of abandoned radioactive material has been the cause of
several other cases of
radiation
exposure, mostly in
developing
nations, which may have less regulation of dangerous substances
(and sometimes less general education about radioactivity and its
hazards) and a market for scavenged goods and scrap metal. The
scavengers and those who buy the material are almost always unaware
that the material is radioactive and it is selected for its
aesthetics or scrap value.
Irresponsibility on the part of the radioactive material's owners,
usually a hospital, university or military, and the absence of
regulation concerning radioactive waste, or a lack of enforcement
of such regulations, have been significant factors in radiation
exposures.
For an example of an accident involving
radioactive scrap originating from a hospital see the Goiânia
accident
.
Transportation accidents involving spent nuclear fuel from power
plants are unlikely to have serious consequences due to the
strength of the
spent
nuclear fuel shipping casks.
See also
References
- U.S. Department
of Energy Environmental Management - " Department of Energy Five Year Plan FY 2007-FY 2011 Volume
II." Retrieved 8 April 2007.
- American Scientist Jan/Feb 2007
- Nuclear proliferation through coal burning —
Gordon J. Aubrecht, II, Ohio State University
- Nuclear Information and Resource Service, Radioactive Waste Project, retrieved September
2007
- Goldstein, Inge, and Martin Goldstein. How much risk?
Oxford University Press, 2002. ISBN 0195139941
- Gofman, John W. Radiation and human health. San
Francisco: Sierra Club Books, 1981, 787.
- Gofman, John W. Radiation and human health. San
Francisco: Sierra Club Books, 1981, 760-849.
- Depleted Uranium-FAQs, Janes
- Cosmic origins of Uranium
- Coal Combustion - ORNL Review Vol. 26, No. 3&4,
1993
- U.S. Geological Survey, Radioactive Elements in Coal and Fly Ash:
Abundance, Forms, and Environmental Significance, Fact
Sheet FS-163-1997, October 1997, retrieved September 2007
- Survey & Identification of NORM Contaminated
Equipment
- Marathon Resources Ltd :: Our Business :: Uranium
Industry :: Nuclear Waste
- Why WIPP?
- Vandenbosch, Robert, and Susanne E. Vandenbosch. 2007.
Nuclear waste stalemate. Salt Lake City: University of
Utah Press, 21.
- M. I. Ojovan, W.E. Lee. An Introduction to Nuclear Waste
Immobilisation, Elsevier Science Publishers B.V., Amsterdam,
315pp. (2005)
- See, for example, Paul Brown, 'Shoot it at the sun. Send it to Earth's core. What
to do with nuclear waste?', The Guardian, 14 April
2004.
- M. I. Ojovan, W.E. Lee. An Introduction to Nuclear Waste
Immobilisation, Elsevier, Amsterdam, 315pp. (2005)
- Removal of Silicon from High Level Waste Streams
via Ferric Flocculation
- World Nuclear Association, Synroc, Nuclear Issues Briefing Paper 21,
retrieved January 2009
- cited in in .
- .
- .
- .
- .
- International Atomic Energy Agency, Spent Fuel and High Level Waste: Chemical
Durability and Performance under Simulated Repository
Conditions, IAEA-TECDOC-1563, October 2007.
- Vandenbosch, Robert, and Susanne E. Vandenbosch. 2007.
Nuclear waste stalemate. Salt Lake City: University of
Utah Press, 10.
- Yates, Marshall. 1989. “DOE waste management criticized:
On-site storage urged.” Public Utilities Fortnightly 124
(July 6): 33.
- Sea-based Nuclear Waste Solutions
- Subductive Waste Disposal Method
- Utah Nuclear Waste Summary, by Tricia Jack,
Jordan Robertson, Center for Public Policy & Administration,
University of Utah
- Radioactive waste: The problem and its
management, by K. R. Rao, Current science, vol. 81, no. 12, 25
december 2001
- Remix & Return
- Transmutation being banned in the US since 1977
- National Policy Analysis #396: The Separations Technology
and Transmutation Systems (STATS) Report: Implications for Nuclear
Power Growth and Energy Sufficiency - February 2002
- http://www.gnep.energy.gov/pdfs/GNEP_SOP.pdf
-
http://www.heritage.org/Research/EnergyandEnvironment/upload/86845_1.pdf
- http://www.nuclearhydrocarbons.com/
- TR10: Traveling Wave Reactor, Technology Review,
March/April 2009
- Space Disposal of Nuclear Wastes Eric E. Rice Battelle Memorial Institute
- Vandenbosch, Robert, and Susanne E. Vandenbosch. 2007.
Nuclear waste stalemate. Salt Lake City: University of
Utah Press, 247.
- Vandenbosch, Robert, and Susanne E. Vandenbosch. 2007.
Nuclear waste stalemate. Salt Lake City: University of
Utah Press, 248.
- From cocaine to plutonium: mafia clan accused of
trafficking nuclear waste, The Guardian, October 9, 2007
- Mafia sank boat with radioactive waste:
official, AFP, September 14, 2009
- Strengthening the safety of radiation sources &
the security of radioactive materials: timely action, by Abel
J.González, IAEA Bulletin, 41/3/1999
- GlobalSecurity.org, Chelyabinsk-65/Ozersk, retrieved September
2007
- Report RAI.it, L'Eredità (in Italian), 2 November 2008
- Reuters UK, New incident at French nuclear plant, retrieved
March 2009
- The Guardian, Accidents tarnish nuclear dream, retrieved
March 2009
- Reuters UK, Too many French nuclear workers contaminated,
retrieved March 2009
- International Atomic Energy Agency, The radiological accident in Goiânia,
1988, retrieved September 2007
Further reading
- Babu, B.V., and S. Karthik, Energy Education Science and
Technology, 2005, 14, 93–102. An overview of
waste from the nuclear fuel cycle.
- Bedinger, M.S. (1989). Geohydrologic aspects for siting and
design of low-level radioactive-waste disposal [U.S.
Geological Survey Circular 1034]. Washington, D.C.: U.S. Department
of the Interior, U.S. Geological Survey.
- Fentiman, Audeen W. and James H. Saling. Radioactive Waste
Management. New York: Taylor & Francis, 2002. Second
ed.
- Hamblin, Jacob Darwin (2008). Poison in the Well: Radioactive
Waste in the Oceans at the Dawn of the Nuclear Age. Piscataway, NJ:
Rutgers University Press.
- Nuclear and Radiation Studies Board. ( NRSB)
Going the Distance? The Safe Transport of Spent
Nuclear Fuel and High-Level Radioactive Waste in the United
States [6347] ISBN 0-309-10004-6
External links
Top topics
Wikis
Quiz
Facts
Map
Search