sustainability profile
technology
lasts a long time
does no harm
leaves no change
breakthroughs needed
solar electricity
carbon sequestration
nuclear electricity
cellulosic biofuel
electric transportation
emissions
risk
of leaks
?
?
emissions radioactive
waste
lower-cost, high-efficiency
photovoltaics; third-generation
materials and nanostructures;
electricity storage
understanding chemical reactivity
in extreme environments and migration
through rocks; geological monitoring
and predictive modelling
materials for extreme environments
(high temperature, radiation flux
and corrosivity); geological
monitoring and modelling; new strategies
for chemically separating fission products
new methods for cellulosic
breakdown to sugar or fuel;
new catalysts for converting
carbon dioxide to fuel
higher energy density in batteries;
better catalysts, membranes and
electrodes in fuel cells; renewable
production of electricity and hydrogen
Making the grade One of the most important factors to consider when evaluating sustainable technologies is the scientific advances needed to
make them viable. This table is only a rough guide, since several currently unknown factors still need to be explored.
supercritical carbon dioxide are also needed, so that
we can anticipate where and how far it might travel over
the thousands of years it must remain underground.
The potential for contaminating an aquifer or finding
an escape route to the atmosphere must be thoroughly
understood for every sequestration site. Leakage is
indeed one of the biggest challenges. A sequestration
system with a leak rate of 1% per year exhausts all the
carbon dioxide stored in its first year of operation in
just a century – a blink of an eye on the timescale of
ocean–atmosphere dynamics. During release, heavy
carbon dioxide can displace lighter oxygen in low-lying
areas, possibly leading to the suffocation of people
and animals, as happened in a catastrophic incident at
Lake Nyos, Cameroon, in 1986.
From a sustainability perspective, sequestration allows us to use the Earth’s coal resources (which will last
longer than oil, though not as long as the Sun) with
reduced harm to the atmosphere. Storing carbon dioxide underground, however, carries potential risks
of contamination and leakage that are largely unexplored. Sequestration also leaves clear chemical
changes as coal is removed from the Earth and carbon
dioxide is injected.
lifetimes, reduces the number of nuclear plants that will
need to be built.
These increases in efficiency can be achieved by
operating reactors at higher temperatures (1000 K
instead of the current 650 K) and at neutron fluxes an
order of magnitude higher than the current values of
4 × 1013 n cm– 2 s– 1. However, at such high temperatures
and fluxes, chemical corrosion is an additional serious
challenge. Next-generation reactors will require a new
generation of “extreme materials” that can not only
survive, but also function under the triple extremes of
high temperature, high neutron flux and aggressive
chemical corrosion. Advanced ferritic steels hold
promise in these environments; developing them by
design rather than serendipitously will accelerate
deployment significantly.
The scientific challenge for next-generation extreme
materials – whatever their composition – is to understand their failure modes, and to prolong their useful
lifetimes by interrupting or arresting these failures.
Damage starts with atomic displacements that create
interstitials and vacancies, which then migrate and
aggregate to form clusters and ever-larger extended
structures. Eventually, the damage reaches macroscopic dimensions, leading to degradation of performance and failure. This problem is massively multiscale,
covering nine orders of magnitude in its spatial dimension, and neither experiment nor theory has yet captured this complexity in a single framework.
On the experimental side, in situ measurements of
neutron irradiation with atomic or nano-scale resolution are needed to observe the initial damage processes,
followed by coarser-grained experiments to capture
migration, aggregation and ultimately macroscopic
failure. The modelling challenge is equally dramatic:
The nuclear options
Like carbon sequestration, nuclear electricity keeps
greenhouse gases out of the atmosphere, and thus represents a step towards sustainability. Next-generation
reactors based on new materials could last longer than
reactors designed in the 1960s – typically 80 years or
more instead of 60 – and can turn 50% of the heat produced by fission into electricity, compared with 32%
for existing reactors. Higher efficiency also allows the
uranium supply to last longer; this, together with longer
Like carbon
sequestration,
nuclear
electricity
keeps
greenhouse
gases out of the
atmosphere,
and thus
represents a
step towards
sustainability
