The
Intergovernmental Panel on Climate Change (IPCC) recently released its special report
on climate change with a clarion call for immediate action to reduce greenhouse
emissions.[i]
That has been clear for a long time, and the dire consequences of climate
change are now expected to be felt as soon as 2030. The urgency is mainly
because as a society we have been late in taking action.
The world also
needs lots of energy, particularly electricity, for the well-being of its
citizens. Unfortunately, the one source of clean electricity, nuclear power,
has been off the table for many in the “environmental” movement. Readers of
this blog know that I am a strong proponent of nuclear power. In my last post,
I pointed out three reasons for supporting nuclear power: near-zero carbon
emissions, fewest fatalities per unit of electricity, and the smallest
environmental footprint. This post deals with several of the what-about
questions I am asked online or after my talks.
What about the waste?
One question that
I get asked most often has to do with the issue of “waste.” So, let’s talk
about it. First, spent nuclear fuel is not “waste,” it is a resource for future
nuclear plants. Importantly, the spent fuel is a solid; totally contained inside
a steel rod. It is not something that is released to the environment. Contrast
that with coal-fired power plants that emit billions of tons of gases and
particulates into the air and equally large quantities of solid wastes, which
can end up in streams and waterways.
Figure 1. Detail showing uranium pellets inside fuel rods and assembly of fuel rods.
To begin with the
nuclear fuel consists of ceramic pellets of uranium oxide enriched in U-235,
the fissile isotope. The isotopic composition of the fuel pellets is about 4%
U-235 and the remaining 96% is U-238. After two years in service, the fuel
pellets still contain about a quarter of the U-235. Also present are the
fission products and 2% Pu isotopes. Between the remaining U-235 and Pu
isotopes, about 50% of the original fuel value is still in the rods when they
are removed from service. Two main reasons for retrieving the rods are that
after about 2 years in the reactor core some of the cladding materials develop cracks
and defects, and accumulation of fission products like cesium, iodine, strontium
and barium, interfere with the maintenance of neutron balance.
The fuel
assemblies are then withdrawn and stored under water. About 20 feet of water is
needed to cool the rods and provide adequate shielding from the radiation.
After 10 years under water, the highly radioactive fission products in have
decayed to a point that the rods may be stored on site in dry concrete casks
with passive air cooling. The spent fuel may alternatively reprocessed to
recover the fissile elements (uranium and plutonium), and fashioned into
pellets as is the practice in several countries like France, Japan, Russia. Because
reprocessing could lead to opportunities for siphoning off plutonium and thus
to proliferation of nuclear weapons, this practice was stopped in the US in
1980s. I will discuss the issue of proliferation later in this post, but let’s
continue with the discussion of “waste.”
Figure 2: Storage of spent fuel in dry casks poses no radiation hazard.
Second, the total
amount of spent fuel is tiny. According to the International Atomic Energy
Agency, the total amount of spent fuel produced by all the nuclear power plants
over the last 70 years is 370,000 tons.[ii]
About 120,000 tons of it has been reprocessed. The total volume of all the
spent fuel is 22,000 cubic meters, which would fill one football field (100
yards by 55 yds) to a depth of 13 feet! It is a small amount of “waste,”
considering all the carbon-free electricity these plants have generated.
Storing the spent
fuel in deep geological wellbores is technically feasible. As demonstrated in
Finland there are no technological
barriers to deep well storage, although there remain political barriers. In the United States, Yucca Mountain in Nevada
was proposed as a repository, but after years of back and forth, the plans were
abandoned. No politically acceptable site has yet been identified. To get
around the political deadlock, Deep Isolation—a California company, started by daughter
and father Elizabeth and Richard Muller, is proposing a modular and inexpensive
option. Their solution exploits recent advances in fracking technologies to
drill mile-deep wells with tilted horizontal holes to store the spent near the
nuclear plants.[iii] Until
such time as this or some other innovation is developed, on-site storage of the
spent fuel in dry casks remains a perfectly viable option.[iv]
Besides, on-site storage would make it easy to retrieve fuel for future fast
reactors.
What about fuel supply?
Another question I
often face is that there isn’t enough uranium to power the expanded nuclear
fleet. At the current rate of consumption (56,000 tU/yr), global supply of reasonably assured resources (RAR) of uranium
at $80/tU could last about 40 years, but if the nuclear fleet were to be
expanded substantially, these resources would not last very long. The thing to
note is that apart from uranium RAR
there is a much larger uranium resource base, which is accessible at higher
price. Doubling the price of uranium ore from $80/ton to $160/ton would greatly
increase the supply of uranium while raising the cost of electricity by only a
fraction of a cent per kWh, because each ton of U produces 1.2 TWh of
electricity. With more than adequate supplies in hand, current market
conditions do not favor efforts to explore other sources of uranium, but with
appropriate price signals these secondary sources could become part of the RAR.
Nuclear weapons
are another significant source of uranium. Under the megatons-to-megawatts
program, many nuclear warheads are being dismantled. The highly enriched
uranium and plutonium of the warhead is diluted with depleted uranium to make mixed
oxide (MOX) fuel suitable for nuclear power plants. Further, if we replace the
current practice of using the fuel in a once-through mode by reprocessing waste
fuel, the current supply of uranium could last several-fold longer. Finally, if
we develop breeder technologies to use thorium the supply of fissile fuels
would be virtually inexhaustible.
What about nuclear proliferation?
Nuclear
proliferation is another reason people object to developing nuclear power
plants. The underlying assumption is that countries with nuclear power plants
will use their technology and facilities for developing nuclear weapons. This
assumption is not justified. There are many countries which have nuclear power,
but no plans to develop weapons. Argentina, Belgium, Canada, Japan, Germany,
South Korea, and Sweden are prime examples of nations in this category. Nor is
nuclear power a prerequisite of weapons development. USA and Soviet Union
developed weapons long before nuclear power plants were built.
The reason why
countries acquire nuclear weapons technology is largely geopolitical, and proliferation
is best addressed through political solutions. Countries acquire them primarily
as a deterrent against a more powerful neighbor. Other factors include national
pride and exercise of hegemony. France was concerned about Soviet weapons in
its neighborhood. It developed nuclear weapons despite protestations from the
Kennedy administration. Even assurance of a nuclear umbrella from the US did
not dissuade France from its path.
Uranium-based
nuclear weapon has a relatively straightforward gun design that shoots one
subcritical mass of uranium into another subcritical mass. Together the pieces exceed
the critical threshold and a nuclear explosion ensues. However, getting the
uranium fuel and enriching it to weapons grade (i.e., greater than 80% U-235)
is a substantial challenge. Recall that natural uranium has only 0.7% U-235. Fuel
grade uranium requires increasing the ore about 6 fold to between 3% and 5%
U-235. Enriching it to weapons grade requires an additional 20-fold enrichment,
something that requires access to a vast arrays of high speed centrifuges. Non-nuclear
nations could not follow this path surreptitiously as these facilities would be
readily detected and are also subject to sabotage through cyber-attacks—the U.S.
successfully set Iran back in its drive to acquire weapons grade uranium by
deploying the Stuxnet worm.
Plutonium-based
devices require Pu-239, which is present in the spent nuclear fuel. Chemical
extraction of plutonium is a relatively simpler process than enriching isotopes,
and hence the fear that countries could divert some of the spent fuel for
making a weapon. However, the construction of the plutonium device is much more
challenging and presents a major hurdle.[v]
Besides, the plutonium in spent fuel also contains other isotopes of plutonium,
notably Pu-240, which must be removed, or the device would simply fizzle.
Weapons-grade plutonium are best obtained from research reactors in which the
uranium is “burnt” for very short periods before reprocessing—a practice not
conducive to electrical power production.
What about dirty bombs?
Another concern is
the possibility of nuclear waste being used by terrorists to create a “dirty
bomb” which causes radioactive damage. The damage that a dirty bomb can really
create is one of fear of contaminating a vital area so as to cause mass
disruption. A dirty bomb will also cause a small increase of cancer risk for
the population as a whole, but it does not lead to immediate loss of life.
Terrorists are more likely to try something more spectacular, including
conventional bombs.
The hurdles for
making a dirty bomb are also significant for a terrorist organization. For
starters, amassing the radioactive material without killing themselves before
they can make the device is an insurmountable challenge for the terrorists.
While the radiation from the dirty bomb after
it has been exploded—and the radioactive materials dispersed—poses only a small
risk to the large population, in a concentrated form, as would be necessary for
the bomb, the radiation levels will be high enough to cause illness and death.
The terrorists could decide to make dirty bomb from
alpha-emitters, because they
can protect themselves against this non-penetrating radiation. For this type of
dirty bombs the radioactive materials can be obtained from a variety of medical
and other devices that have nothing to do with nuclear energy, and so this
threat is not reduced by turning off nuclear power plants.
There will always
be violent groups with grievances, and therefore the risk of having such a
group acquire a small fissionable bomb can be minimized with adequate
protection of important secrets and technology. The real risk would be from a
rogue nation providing a terrorist group with a small nuclear device and a
means for delivering it. A one-kiloton “suitcase” device does not wreak as much
damage as many conventional explosive charges do.
I do not mean to
take the threat of terrorist attacks using a nuclear device lightly, for it can
cause mass economic disruption. Ours is not a situation with easy choices, and
the growth of nuclear power is important for the energy security of the world.
This is a problem that needs a political solution. Greater involvement of the
IAEA and internationalization of the enrichment and fuel reprocessing is a path
proposed by ElBaradei, former Director General of the IAEA and winner of 2005
Nobel Prize for peace. Internationalization of fuel processing could provide
assurance to countries pursuing nuclear power that they will get the fuel for
their plants. Stable energy supplies is a deterrent of war. This scenario also
provides the safeguard that nuclear material is not being diverted to military
uses, because the material would be watched over by personnel from many
different countries.
[i] Summary for Policymakers of IPCC Special
Report on Global Warming of 1.5°C approved by governments; Press release. Oct.
8, 2018; http://www.ipcc.ch/news_and_events/pr_181008_P48_spm.shtml
[ii] Status
and Trends in Spent Fuel and Radioactive Waste Management, IAEA Nuclear Energy Series No. NW-T-1.14 (2018)
[iii] https://www.deepisolation.com/technology/
[iv] U.S.
Nuclear Regulatory Commission: https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/storage-spent-fuel.html
[v] In
order to successfully explode a plutonium bomb it is important to keep the Pu-239
from poisoning itself by its own neutrons. To achieve this, plutonium is
fashioned into a thin-walled sphere so that the neutrons mostly escape and are
not absorbed by the neighboring Pu atoms. In order to explode the device, the
Pu sphere has to be compressed together into one lump. This feat is achieved by
a process of implosion. A number of chemical explosives are set off around the
Pu sphere, and their shock wave compresses the sphere. The timing of the
explosions has to be very precisely controlled, or the nuclear device simply
fizzles.
