Nuclear Power and Green Hydrogen
After the serious accident at Chernobyl
in 1986 that made the Russian citys name synonymous with disaster,
nuclear power was on the nose in the US and Australia.
But in other countries, theyve been able to
make it work. In France, for instance, about 75 percent of electricity is
generated from nuclear power. Worldwide, it provides 17% of our energy.
The US has not brought a new plant online since 1996 yet still generates
788.6 billion kilowatt-hours (KWh) yearly almost 20% of the US total
All technologies start out crawling before they can walk or even run.
The nuclear scientists have been working on the safety problems and
already may have solved them.
Danger aside, what makes nuclear power attractive? Its
cheaper than other forms of power generation. Its easy to build compact
plants that generate hundreds if not thousands of megawatts something
wind and solar can never hope to match. See the chart below to compare
energy generation costs.
Compared with coal, still used to produce 50% of the US electricity needs,
nuclear is clean. It creates no greenhouse gases. Its waste, although
highly toxic, is very compact and when handled correctly, quite safe.
Uranium, the fuel reactors use, is widely available in the continental US
and Canada. Australia has the largest known reserves. This makes it
unlikely rogue states can affect supply. Stable supply means lower
long-term costs especially when compared with oil and gas fired plants
which are now producing about 20% of US electricity.
Reactor designs such as the Canadian CANDU can be very safe and
less expensive to build than most reactors in use today. One drawback to
this design, unfortunately, is its ability to produce weapons grade
plutonium as a by-product. On the plus side, it can use unenriched uranium
about .07% uranium 235. Regular plants require between 2% and 7% uranium
235 in reactor fuel to run properly.
Physicists and engineers at Beijing's Tsinghua University have made the
first great leap forward in a quarter century, building a new nuclear
power facility: a pebble-bed reactor (PBR) sometimes also known as a
Pebble Bed Modular Reactor (PBMR). This reactor is small enough to be
assembled from mass-produced parts and cheap enough for emerging
economies. Its safety is a matter of physics, not operator skill or
reinforced concrete. This reactor is meltdown-proof.
What makes it so safe is the fuel: instead of conventional fuel rods made
of enriched uranium, PBRs use small, pyrolytic graphite coated pebbles
with uranium cores. As a PBR reactor gets hotter, the rapid motion of
atoms in the fuel decreases probability of neutron capture by U-235 atoms.
This effect is known as Doppler Broadening. Nuclei of heated uranium move
more rapidly in random directions generating a wider range of neutron
speeds. U-238, the isotope which makes up most of the uranium in the
reactor, is much more likely to absorb the faster moving neutrons. This
reduces the number of neutrons available to spark U-235 fission. This, in
turn, lowers heat output. This built-in negative feedback places a
temperature limit on the fuel without operator intervention.
PBRs use high-pressure helium gas, not water, for cooling. Reactors have
been run dry without cooling gas. Result: they simply stabilize at a
given temperature lower than the pebbles shell melting point. No
meltdown can occur.
PBR from www.pbmr.co.za
South Africa may have the most modern PBR on the drawing board. With the
help of German scientists acknowledged leaders in the field - they have
planned to build several reactors within the next five years. Images in
this article come from their design.
The reactor core is a bin of uranium fuel pebbles. Each tennis ball-sized
pebble is rotated and/or checked for reactivity by removing them from the
bottom of the funnel shaped reactor core. Spent pebbles are replaced by
adding new ones at the top of the stack. Used ones that are still reactive
also go to the top of the bin. The reactor can be re-fuelled without
stopping power production not possible in conventional rod reactors
which requires a full shut down.
Pebbles, because of their round nature, allow the cooling gas to be
introduced at the bottom and pass freely through the stack. The heated gas
is removed to perform work like spinning a turbine to generate electricity
then recycled in a closed loop back to the reactor core.
PBRs use helium, which has high thermal conductivity and inertness
(fireproof and noncorrosive) for cooling. This makes them more efficient
at capturing heat energy from nuclear reactions than standard reactor
designs. The ratio of electrical output to thermal output is about 50%.
Reactor Interior pebbles in red:
http:// www.eskom.co.za/ nuclear_energy/ pebble_bed/ pebble_bed.html
The high-temperature gas design also has a
silver lining it can produce hydrogen. Think about that fuel cell
vehicles need expensive-to-produce hydrogen to run on this reactor could
make hydrogen as a by-product.
Generation of hydrogen has been the biggest stumbling block to it adoption
as a clean fuel. Hydrogen, found primarily in water, is expensive to
extract as a gas. While the technical problems of handling, storage and
use as fuel are largely solved, the high energy cost to produce hydrogen
has made it an energy transport medium, not a source.
These new reactors run at high temperatures which are perfect for cracking
abundant water or helium gas into hydrogen which can then be used as a
green fuel burning hydrogen just produces water vapour.
PBRs could produce cheap hydrogen that could be piped to areas of need or
used in the local communities.
Plant sites are much smaller than traditional nuclear power plants. Their
modular design allows for smaller plants that can grow with needs. A
single PBR reactor would consist of one main building covering an area of
about 1,300 square meters less than half a football field. It would be
about 42m high (6 stories), some of it below ground level. Billion dollar
steel reinforced concrete containment vessels are not required any
coolant leak would be in the form of nonradioactive helium gas which would
quickly disperse with out causing any ill effects.
Internal functioning with cooling diagram:
Each PBR would produce between 100 and 200
MW small, in comparison to light and heavy water reactors which
typically product around 1,000 MW. But they could easily be scaled up by
Ten PBR reactors producing 1,100 MW would occupy an area of no more than
three football fields. Each PBR could serve about 30,000 to 40,000 homes.
Control rooms - much simpler than standard ones - would have a few PCs and
extra monitors instead of banks of valves and dials. Each control room
could monitor and manage up to 10 reactors.
One of the key features to this technology, especially important in China
where energy demand is exploding, is its modular nature. While
conventional reactors in operation today are all one of a kind although
many are based on the same designs PBR reactors could de built with
standard rail-movable components. When a new power plant is needed, they
simply load the parts on a train with a construction crew and can have it
delivering power in short order. Traditional plants in the US were sunk
principally by long construction times and cost overruns, not
Nuclear waste disposal has become a hot-button issue. Standard nuclear
waste is very radioactive for 10,000 years or more. It must be transported
to and stored in special containment facilities normally underground. It
can also be reprocessed but this is costly and technically difficult.
There are only 3 reprocessing facilities worldwide: Thorpe in England,
Cogema in France and Myakrt1 Chemical Combine in Russia. Far away from
most of the world that needs clean, inexpensive power.
Fuel pebbles have 4 caps of containment built in. Many authorities
consider pebbled radioactive waste stable enough it can be safely disposed
of in geological storage without any additional shielding or protection.
Even in tests where pebbles were exposed to very high heat without coolant
for long periods, they showed no outward damage. If one did manage to
break a pebble it would only release one tiny (0.05mm) uranium dioxide
particle. This particle is too heavy to be wind borne and so could not be
blown into other areas like the fallout from the explosion at Chernobyl.
PBR proponents state they plan to store all waste products on the plant
site avoiding costly and dangerous radioactive material movement.
Even with the long term radioactivity and highly toxic nature of nuclear
waste, some environmentalists are voicing support for nuclear energy.
James Lovelock, well known green activist and creator of the Gaia
hypothesis that Earth is a single self-regulating organism, published a
plea to phase out fossil fuels. Nuclear power, he argued, is the best
short term hope for averting climatic catastrophe:
"Opposition to nuclear energy is based on irrational fear fed by
Hollywood-style fiction, the Green lobbies, and the media.
Even if they
were right about its dangers - and they are not - its worldwide use as our
main source of energy would pose an insignificant threat compared with the
dangers of intolerable and lethal heat waves and sea levels rising to
drown every coastal city of the world. We have no time to experiment with
visionary energy sources; civilization is in imminent danger and has to
use nuclear, the one safe, available energy source, now, or suffer the
pain soon to be inflicted by our outraged planet." - From the London
Independent May, 2004
Nuclear power, shunned after so many years, may be ready for resurgence.
For some countries, like China, it may offer the only hope to meet its
energy needs of its billion plus population in the 21st century. Indeed,
they already have the first 10MW test reactor up and running.