Environmental Engineering Reference
In-Depth Information
create a competition for uranium provisions, compromising the nuclear plans of
the weaker countries. Other aspects of nuclear energy which could limit its
further development consist in very high investment costs and the feature of
guarantee the maximum efficiency only producing electric energy at constant
power, which would not be compatible with the typical absorption fluctuations
of the electric grid if electricity was totally produced by nuclear.
In comparison with the above critical concerns, the main advantages of nuclear
energy are constituted by very high specific energy (1 ton of U
3
O
8
can produce
about the same electricity obtainable from 14,000 tons of coal) and the substantial
absence of greenhouse gas emissions, even if some CO
2
generation has to be
considered for other operations connected to working of a nuclear plant, such as
extraction of uranium from U
3
O
8
ore and plant fabrication. These significant
advantages could better express their potentialities if nuclear power generation was
integrated with energy storage systems based on hydrogen as energy carrier. While
thermochemical routes to produce hydrogen from water feedstock by using nuclear-
produced heat have not yet reached the prototype phase, the electrolysis process
based on low-cost nuclear electricity appears in the short term as the best approach
to store the surplus of energy produced by the reactor and not required by grid in the
same site of the nuclear plant [
34
], so permitting overcoming of one of the limi-
tations of nuclear reactors for electricity generation, i.e. the working at constant
power in proximity of the base load. In the long term, high temperature electrolysis
could be coupled to thermochemical water splitting, both enabled by nuclear heat
(see
Sect. 2.1
). Regarding the transportation sector, recent studies have compared
different possibilities of using nuclear energy for production of energy carriers for
vehicles, i.e. electricity, hydrogen, and liquid fuels (both synthetic and biofuels)
[
31
]. In this case, the role of the nuclear energy in the production of liquid fuels
would consist in supplying heat and/or electrolitycal hydrogen for the coal gasifi-
cation and Fischer-Tropsch processes. These analysis have evidenced that the
availability of low cost and carbon-free energy carriers, such as electricity and
hydrogen nuclear-derived, could reduce the CO
2
emissions in the production of
liquid fuels by eliminating the combustion of fossil materials for the required heat
supplying and would be essential for the future development of both solutions
before considered as zero emission vehicles, i.e. BEVs and HFCEVs.
Regarding the economic implications of the different energy supply processes
before considered, in recent years the approach based on Energy Return On
Investment (EROI) is gaining always growing assents [
35
-
37
]. Expressed as
function of time the EROI can be defined as the ratio of the delivered end-user
energy, E
o
(t), to the energy invested for its delivery, E
c
(t) (all energy costs associated
with the fabrication of the plant, its management and dismantling), both quantities
being cumulative for the specified time t: EROI (t) = E
o
(t)/E
c
(t). Assuming the time
t equal to the whole life cycle of the plant, E
o
(t) can be calculated with sufficient
reliability and data are readily available, while E
c
(t) needs an approach based on the
life cycle analysis (LCA), which is often object of estimates not convergent. On the
other hand, although in societies based on free market the correlation between
money and energy should be always verified, it is unavoidable that some distortions
