The disposal of nuclear waste is a pressing
problem for society worldwide.
By
Dr. Nitish Priyadarshi
Geologist.
76,circular road, Ranchi , India
Email:
nitish.priyadarshi@gmail.com
The nuclear disaster in Fukushima , Japan
Harnessing the power of the atom has propelled humanity
forward at an astonishing rate since the dawn of the Nuclear Age. However, the
proper disposal and storage of nuclear waste leaves an incomplete equation.
Nuclear waste comes from nuclear power reactors and byproducts of
military-grade bombs. This waste can come in the form of spent nuclear fuel
rods or even toxic sludge. Perhaps the greatest danger of nuclear energy is the
long-term investment in waste disposal that will be passed to future
generations.
For more than 50 years, waste from nuclear power stations
has been accumulating into what is now the most dangerous rubbish dump in the
world. But we are still very far from coming up with a permanent, safe solution
for the disposal of radioactive material.
Seven years ago, there were around 250,000 tonnes of highly
radioactive waste worldwide. Towards the end of 2010, the International Atomic
Energy Agency (IAEA) estimated it to be 345,000 tonnes, and in 2022, 450,000 tonnes.
What are we going to do with it all.
According to another report, a typical nuclear power plant
in a year generates 20 metric tons of used nuclear fuel. The nuclear industry
generates a total of about 2,000 - 2,300 metric tons of used fuel per year.
Over the past four decades, the entire industry has produced about 67,500 metric tons of used nuclear fuel. If used fuel assemblies were stacked end-to-end and side-by-side, this would cover a football field about seven yards deep.
Over the past four decades, the entire industry has produced about 67,500 metric tons of used nuclear fuel. If used fuel assemblies were stacked end-to-end and side-by-side, this would cover a football field about seven yards deep.
A recent study found that, on average, people in Britain
live about 42km (26 miles) away from one of more than 30 radioactive waste
sites, including power plants and military bases, in the UK.
Half-a-century after launching the nuclear programme, India has
finally begun working on a “deep geological repository” to permanently store
its nuclear waste.
Over the next five years, scientists are going to study a set of physical and geological parameters required for setting up the nuclear waste storage facility before zeroing in on its location.
The options vary from underground storage in rocky centralIndia to plains where the storage
may be housed inside layers of clay.
Over the next five years, scientists are going to study a set of physical and geological parameters required for setting up the nuclear waste storage facility before zeroing in on its location.
The options vary from underground storage in rocky central
Sixteen nuclear reactors produce about 3% of India ’s
electricity, and seven more are under construction. Spent fuel is
processed at facilities in Trombay near Mumbai,
at Tarapur on the west coast north of Mumbai, and
at Kalpakkam on the southeast coast of India . Plutonium will be used in a
fast breeder reactor (under construction) to produce more fuel, and other waste
vitrified at Tarapur and Trombay. Interim storage for 30 years is
expected, with eventual disposal in a deep geological repository in crystalline
rock near Kalpakkam.
In 1997, IAEA members proposed certain criteria for nuclear
waste disposal. It should be done, “wherever possible”, in those countries that
have produced the waste. Further, it should avoid “imposing undue burden on
future generations”.
But at present, “no country has a geological site for the
interim and permanent storage of spent fuel rods,” complain experts of the
IAEA.
Radioactive wastes come in many different forms including
the following:
1. protective clothing of people in contact with radioactive
materials
2. the remains of lab animals used in experiments with
radionuclides
3. cooling water, used fuel rods, and old tools and parts
from nuclear power plants
4. mill tailings from uranium-enrichment factories
5. old medical radiation equipment from hospitals and
clinics
6. used smoke detectors which contain radioactive
americium-241 sensors
How does nuclear waste get to you?
The planet's water cycle is the main way radiation gets
spread about the environment. When radioactive waste mixes with water, it is
ferried through this water cycle. Radionuclides in water are absorbed by
surrounding vegetation and ingested by local marine and animal life. Radiation
can also be in the air and can get deposited on people, plants, animals, and
soil. People can inhale or ingest radionuclides in air, drinking water, or
food. Depending on the half life of the radiation, it could stay in a
person for much longer than a lifetime. The half life is the amount of time it
takes for a radioactive material to decay to one half of its original amount.
Some materials have half-lives of more than 1,000 years!
On 26th June 1954, 110 km from Moscow , the first civil nuclear reactor of
the world supplied current in the grid. At the end of 2011, in 31 countries
where nuclear power is produced, there were 435 reactors in use, 104 in the US alone. They
meet 15 per cent of the world’s electricity demand, though the national ratios
vary. While France generates almost three-quarters of its own
electricity through nuclear power and also exports the surplus, India ’s figure is 3 per cent, and even USA ’s
only 20 per cent. But however small the total amount of nuclear energy may be,
the consequences are colossal.
Nuclear fission and decay not only produces radiation but
also heat. This heat is used in power plants to generate electricity. The core
of the fuel rods in the reactors must heat
up to about 1,200 degree centigrade. When they are worn out, they are
lifted with a remote-controlled crane into a cooling pond, where they are
stored for many years.
If the heat dissipation fails and the rods heat to over
2,500 degree centigrade, there is a risk of nuclear meltdown, which is what
happened in March 2011 in Fukushima in Japan .
New ideas for repositories have kept cropping up, some as
absurd as the one patented in 1956 by a physicist from Munich, who proposed
that waste containers be airdropped over
Antarctica, which would then melt into the depths of the ice on their own. This
proposal was discussed in trade conferences for many years.
For this option containers of heat-generating waste would be
placed in stable ice sheets such as those found in Greenland and Antarctica . The containers would melt the surrounding ice
and be drawn deep into the ice sheet, where the ice would refreeze above the
wastes creating a thick barrier. Although disposal in ice sheets could be
technically considered for all types of radioactive wastes, it has only been
seriously investigated for high-level waste (HLW), where the heat generated by
the wastes could be used to advantage to self-bury the wastes within the ice by
melting.
The option of disposal in ice sheets has not been
implemented anywhere. It has been rejected by countries that have signed the
1959 Antarctic Treaty or have committed to providing a solution to their
radioactive waste management within their national boundaries. Since 1980 there
has been no significant consideration of this option.
American scientists even considered shooting the waste into
the Sun. the proposal was rejected as too unsafe and too expensive. To send a
load of just half a kilo into the earth’s orbit would cost 10,000 dollars. And
in USA ,
more than 70,000 tonnes of highly radioactive material is already in storage.
The objective of this option is to remove the radioactive
waste from the Earth, for all time, by ejecting it into outer space. The waste
would be packaged so that it would be likely to remain intact under most
conceivable accident scenarios. A rocket or space shuttle would be used to
launch the packaged waste into space. There are several ultimate destinations
for the waste which have been considered, including directing it into the Sun.
The high cost means that such a method of waste disposal
could only be appropriate for separated high-level waste (HLW) or spent fuel
(i.e. long-lived highly radioactive material that is relatively small in
volume). The question was investigated in the United States by NASA in the late
1970s and early 1980s. Because of the high cost of this option and the safety
aspects associated with the risk of launch failure, this option was abandoned.
No doubt that’s why a final burial inside the earth is
considered the safest option. Natural and technical barriers should ensure that
no radiation leaks out. The waste can be sequestered in steel containers,
embedded in a concrete sarcophagus, which is further surrounded by
heat-resistant stone, and buried under hundreds of metres of rock.
Deep borehole concepts have been developed (but not
implemented) in several countries, including Denmark ,
Sweden , Switzerland and USA for HLW and spent fuel.
Compared with deep geological disposal in a mined underground repository,
placement in deep boreholes is considered to be more expensive for large
volumes of waste. This option was abandoned in countries such as Finland and USA . The feasibility of disposal of
spent fuel in deep boreholes has been studied in Sweden , in order to check whether
deep geological disposal remains the preferred option. The borehole concept
remains an attractive proposition under investigation for the disposal of
sealed radioactive sources from medical and industrial applications.
Although burial and long-term storage remain the best
solutions for nuclear waste disposal, geologic processes pose a significant
danger to these repositories. In reality, our limited ability to accurately
predict moving fault lines, earthquakes, and volcanic eruptions is the true
danger. The likelihood and possible location of future earthquakes is the
initial concern when selecting a disposal site. On the other hand, flooding and
groundwater pose their own geologic threat to underground disposal sites.
Rising groundwater can erode away containment zones and spread radioactive
waste into the water table.
Disposal at sea involves
radioactive waste being shipped out to sea and dropped into the sea in
packaging designed to either: implode at depth, resulting in direct release and
dispersion of radioactive material into the sea; or sink to the seabed intact.
Over time the physical containment of containers would fail, and radionuclides
would be dispersed and diluted in the sea. Further dilution would occur as the
radionuclides migrated from the disposal site, carried by currents. The amount
of radionuclides remaining in the sea water would be further reduced both by
natural radioactive decay, and by the removal of radionuclides to seabed
sediments by the process of sorption.
This method is not permitted by a number of
international agreements.
Researchers have short listed four kinds of rock for the
construction of such a repository.
- In
- In the
- In
The newest solution, sending the waste to the center of the earth, is the one solution combining safety, economy and permanence to nuclear waste disposal. At first glance, this seems impossible. There has never been a hole drilled in the earth's crust, so how can one be drilled to the center of the earth? The answer? Let the earth itself do the work through known subduction faults.
What is a subduction fault? This is an earthquake fault at the edge of a continental crust that is in collision with the adjoining oceanic crust. Since the continental crust is lighter than the oceanic crust, the latter deflects below the former when the two plates are colliding.
Permanent RadWaste Solutions has developed a process that utilizes a subduction fault for sending the waste to the center of the earth. This has the benefits of being permanent, no maintenance, much less expensive than other proposals, terrorist-proof, and no threat to people, fish, crabs or the environment.
To do this requires burying a
specially designed pressure-and-temperature-compensating submersible transport
vehicle (STV). It is to be buried in the sediments at a subduction fault.
Numerous options for long-term nuclear waste management have
been considered in the past. The table below highlights a number of these.
|
Ideas
|
Examples
|
|
|
·
Investigated in
·
Not currently planned to be implemented anywhere.
|
||
|
Disposal in outer
space (proposed for
wastes that are highly concentrated)
|
·
Investigated by
·
Investigations now abandoned due to cost and potential risks
of launch failure.
|
|
|
Deep boreholes
(at depths of a few kilometres) |
·
Investigated by
·
Not implemented anywhere.
|
|
|
Rock-melting
(proposed for wastes that are heat-generating) |
·
Investigated by
·
Not implemented anywhere.
·
Laboratory studies performed in the
|
|
|
·
Investigated by
·
Not implemented anywhere.
·
Not permitted by international agreements.
|
||
|
·
Implemented by
·
Not permitted by International agreements.
|
||
|
·
Investigated by
·
Not implemented anywhere.
·
Not permitted by international agreements.
|
||
|
Disposal in ice
sheets (proposed for
wastes that are heat-generating)
|
·
Investigated by
·
Rejected by countries that have signed the Antarctic Treaty or
committed to providing solutions within national boundaries.
|
|
|
Direct injection
(only suitable for liquid wastes) |
·
Investigated by
·
Implemented in
·
Investigations abandoned in
|
|
Other countries are also looking at waste in new ways in the
post-Fukushima world. Right now, worldwide, most spent fuel waste is
stored on the site of the facility that produced it, in spent-fuel pools and,
after it eventually cools, dry casks. Experts say dispersed storage is
expensive and that central storage would be more secure.
Few countries , apart from Sweden
and Finland ,
have moved forward on centralized disposal sites, deep in the earth, designed
to hold the waste permanently.
The disposal of nuclear waste is a pressing problem for
society worldwide. Potential health and safety concerns require that nuclear
waste be stored in a controlled and secure manner. The issue is further
complicated by the extremely long half life of radioactive materials, some of
which retain half of their dangerous properties 100,000 years after production.
The disposal and storage of nuclear waste is one of the major factors limiting
society's use of nuclear power as a widespread energy source.
There is no safe way of disposing of nuclear waste and one
of the most important lessons is not to create any more, which means until and
unless safe disposal method is identified we should not go for new nuclear
power plants.
Reference:
Kampe, J.A.D. and Bischoff, J. October 2012, Now What?. GEO,
(Indian Ed.)
