Subtitle: Nuclear
plants are huge to reduce costs
In this series of
articles on the truth about nuclear power plants, one focus area is the
economics. Others include safety,
financing, water usage, different technologies, and a few more. This article addresses a part of the
excessive cost issue: why are nuclear power plants so huge? One description of these plants is “cathedrals”. For perspective, modern designs are approximately 1100 MWe
per reactor, however a French design has 1,600 MWe per reactor.
Another reason for the articles on nuclear
plant costs is the argument by nuclear proponents that the only reason the
plants cost so much is the opposition and lawsuits brought by anti-nuclear
groups. That is simply not true, as
these articles demonstrate. The very nature of a nuclear power plant design,
its inherent features as part of using nuclear fuel for heat, requires more
equipment, larger equipment, more costly alloys, longer construction times, and
attendant costs for equipment inflation and financing interest. Even without lawsuits, nuclear power plants
remain the highest cost plants for baseload power production. Several
studies reach the same conclusion on this point.
This article delves
into attempts to reduce costs by three aspects of economy of scale,
1) where bigger
is cheaper if a manufacturing process is based on a circle or sphere;
2) where mass
production reduces costs; and
3) where a learning curve makes future projects
more efficiently constructed, in theory, at least.
Those are three of the elements of gains due
to economy of scale. Each is addressed
in turn.
Economy of scale
based on a circle or sphere
This takes
advantage of the fact that a pipe or tube has a circular cross-section. A pipe with double the diameter can carry
four times the quantity compared to the original pipe. Also, if one doubles a sphere’s diameter, it
holds eight times the volume. These
basic facts of engineering are employed all over the world in process plants,
refineries, power plants, chemical plants, and any other process where fluids
are moved through pipes or stored in spheres.
To a lesser extent, material storage
in cylindrical tanks also achieve economy of scale as the tank diameter
increases.
Over time, nuclear
power plant designs have increased in output from 600 MW to 1000 MWe to 1200 MWe to 1600 MWe, all as measured in electrical output, MWe. These increases in size were attempts to
reduce costs through economy of scale. It
is appropriate to pause here, and consider that statement. If, as nuclear proponents assert, nuclear
power really is as cheap as 4 cents per kWh, or 6 cents, why would it be
necessary for successive designs to be bigger and bigger, trying to drive down
the costs of the power produced? The
very fact that modern designs are bigger than previous designs puts the lie to
the cheap power argument.
Since most of a
nuclear power plant has fluids, steam or water, flowing through a pipe or some
similar item based on a circular cross-section, the first economy of scale
applies. As examples, the major
equipment includes cylinders for the reactor vessel, steam generator, steam
condenser, and containment structure.
Steam turbines also are based on a horizontal cylinder. All the pipes, pumps, fittings, and valves
also are based on a cylinder. To
illustrate, a pipe carrying water at 7 feet per second, approximately 2 meters
per second, can convey 22 cubic feet per second. If the pipe diameter is doubled, with
velocity maintained at 7 feet per second, the water volume goes up by a factor
of four to 88 cubic feet per second. Similarly, if one wishes to double the plant
size, for example from 600 MWe to 1200 MWe, pipes can achieve double the flow
with an increased diameter of only 1.4 times the original size. If the initial pipe is 2 feet or 24 inches
in diameter, the pipe size that is required for double the flow is only 34
inches in diameter. This is significant
because a 34 inch pipe usually will not cost double that of a 24 inch pipe, but
will cost only about 30 percent more than the 24 inch pipe. The cost savings occur throughout the plant,
wherever equipment is based on a circular cross-section.
Similarly, the
third level of containment required by the NRC, the containment structure,
typically has a dome for the roof. A
dome is half of a sphere, and economy of scale applies here, too. The result is a plant with twice the
production capacity, but a containment structure that costs approximately 1.3
times that of a smaller, half-sized plant.
However, one
factor works against the gains afforded by economy of scale. That factor is the low steam pressure and
temperature produced in a modern nuclear reactor system. This requires that more steam must be
circulated to produce the same amount of power.
Therefore, all equipment must be larger: reactor, steam generators,
steam turbines, condensers, pipes, pumps, cooling towers, everything except the
generator and electrical transmission equipment. This is due to the low-pressure, saturated
steam that is inherent in the PWR design.
The steam has no superheat and cannot use supercritical pressures due to
risk of large pipes bursting, or the pipes must have prohibitively expensive
thick walls. There are proposals to
overcome this problem by burning natural gas in supplemental boilers to provide
superheat to the steam. However, nuclear
proponents are very much against natural gas and shudder at the thought that
their nuclear power plant must allow natural gas on the premises.
Economy of scale
from mass production
In this aspect of
economy of scale, the cost of each unit of production decreases where a large
number of units are produced. This is a
very old concept, perhaps starting with the assembly line and manufacturing
cars. Certainly, the concept applies in
many manufacturing processes. For
nuclear power plants, with only approximately 400 plants in the entire world,
built over several decades, there has never been much opportunity to achieve
mass production. One reason for this
has been the lack of standardized designs.
If each design is unique, the unique parts must each have its own
design, drawings, manufacturing process that may require special jigs, possibly
its own transportation system, installation system, etc. This
includes the major equipment such as the reactor, steam generator, steam
condenser, steam turbine, power generator, auxiliary systems, containment
structure, and other items. The cost of
each plant, therefore, suffers from a lack of mass production. In the US, this problem has long been
recognized and an attempt was made to standardize the design of new plants. The Westinghouse AP-1000 design is supposed
to solve the unique design aspect, so that each new plant will use the same
design. This has yet to occur, as the
first such plants are currently under construction in Georgia at the Vogtle
power plant. These are, by definition,
first-of-a-kind in the US. The Vogtle
plant has many drawbacks and serious issues, which will be addressed in one or
more future articles. It is notable
that the Vogtle plant is building two reactors adjacent to each other, where
there is at least a minimal opportunity to employ a small form of mass
production. However, building two of an
item is not much better than building only one.
It requires building many items to reduce costs substantially.
Economy of scale
from a learning curve
The cost
reductions from a learning curve applies to the second and subsequent projects,
which attempt to apply the lessons learned from building the first
project. This aspect of economy of scale
works fairly well at times, but only when the lessons learned are effectively
transferred to the subsequent projects.
In some cases, even when the lessons are communicated, the subsequent
project has unique aspects that cannot apply the lessons. Different geography, site conditions, climate
and weather, all are examples of potential reasons why lessons cannot be
applied. There may also be different
construction companies with different business philosophies, different
equipment used in construction, and many other reasons why lessons learned will
not be applied. As above, using the Vogtle plant as the
example, the two reactors are being built next to each other, and on a schedule
so that one plant should follow about two years behind the first. This will allow the second plant to take
advantage of lessons learned, from the learning curve experienced in building
the first plant.
Conclusion
Nuclear power
plants cost far too much to build due to their inherent design for use of
nuclear fuel. The plants are huge to try
to reduce the costs by economy of scale.
It can be seen
that nuclear power plants have attempted to reduce the very high costs of
construction by designing and building larger plants, by building multiple
reactors at the same site, and to apply lessons learned from recent plants to
the new plants. It is still an
interesting question, why should any of this be necessary if nuclear power
plants truly produce electric power at the lowest cost of any type of baseload
plant? Some nuclear advocates go even
further, with the assertion that nuclear plants can also be used as
load-following plants. If the costs of
nuclear power were truly as low as the advocates maintain, there would be no
reason ever to employ the well-known strategies of economy of scale.
Benefits and
drawbacks from building smaller, modular plants will be addressed in a future
article in the series.
Previous articles
in The Truth About Nuclear Power series can be found at the following links.
Roger E. Sowell, Esq.
Marina del Rey, California
