perm filename NUCLEA[1,VDS]1 blob sn#243734
filedate 1976-10-21 generic text, type C, neo UTF8
COMMENT ⊗ VALID 00006 PAGES
C REC PAGE DESCRIPTION
l. Controversy. Power pl. in operation. Proposed San Joaquin.
2. Energy demands. Energy crisis.
Population growth-> en. growth.
Present rates. Nuc. power, assume to increase dras. in use.
3. Nuc. Power use...problems ....as well as thermal pollution.
II. THERMAL POLLUTION
1. Waste heat. Reasons: Carnot, etc.
2. Stats on runoff. Projected needs for cooling water.
3. A limit to heating.
4. Develop ways of decr. the amt. of heat either by using the
heat or transfer of heat to atmos.
Must get it out of rivers, etc. Into oceans---only so many
ocean plants though. Inland states.
III. A NUCLEAR REACTOR
1. Picture of plant.
2. Efficiencies. Fossil fuels vs. reactor. Diff. reactor
effic. reasons why. steam vs. gas turbines.
3. Actual magnitude of thermal discharges.
IV. COOLING WATER IN WATERS
1. Transfer of heat to air---ways. Equations. Mixing vs.
plumage. Rates of dissipation and their dependencies.
2. Design of cooling water rejection structures.
3. Rivers vs. Lakes, etc. vs oceans.
V. HEAT REJECTION TO AIR
1. Take heat out of water into air.
2. Four methods.
3. Problems of these.
4. Problem remains of ineffic. usage of energy.
VI. PHYSICAL-CHEMICAL EFFECTS OF TH. POLL.
2. Thermal Strat.
3. Others..Chapter 4 of IAEA.
V. BIOLOGICAL EFFECTS OF TH. POLL.
VI. ACTUAL CASES
1. No problems so far....
VII. BENEFICIAL USES OF WASTE HEAT
1. It is feasible. Economics.
2. Use fossil fuel plant findings. Look ahead and apply to
nuc. power sys.
Fossil f. on way out. Need nuc. plan. now.
As well as municipal plan.
3. Weigh benefits.
4. Low vs. High quality heat.
5. Urgent...research now. Time span to develop ideas.
VIII. SOME USES OF WASTE HEAT.
IX. . SPEACIAL USE
1. Sewage disposal.
1. Energy conservation.
2. Effic. use of W.H. Need planning now.
3. Cannot continue to waste two-thirds of energy.
4. Money vs. Environment.
The majority of power plants today operate by employing the
team cycle. Pressurized hot steam drives a turbine, which turns the
uel energy into mechanical energy. This energy is then converted into
lectrical energy, which is thus in a form which is easy to distribute
to the consumers of electricity. However, not all of the fuel heat is
converted into mechanical energy in the turbine. A substantial amount
of the heat is in fact simply lost as rejected heat, usually on the
order of about 67% of the heat. This heat, known as waste heat, because
at present there is no use for it (competetively speaking), is pumped
out of the nuclear power plant after it has been condensed in the steam
condensers. The steam is condensed either directly or indirectly with
cold cooling water. Because of this extra steam which must cooled, the
problem of thermal pollution comes about.
The relatively poor efficiency of a power plant, then , is the
major cause for this type of pollution. Why is there so much energy
being wasted? The reason is because there is a thermodynamical limit
on the conversion of random heat energy to organized energy. This is a
limit imposed upon us from nature, and cannot be argued with! The maximum
efficiency of any machine is summed up by the following Carnot equation:
MAXIMUM EFFICIENCY = 1-T(1)/T(2). T(1) is the temperature of the gas
which leaves the system, and T(2) is the temperature of the gas which
enters the system. Thus, we can see that we want a very high entering
temperature and a very low leaving temperature. T(1), in a nuclear
reactor, is limited by the temperature of the cooling water, and T(2) is
limited by the nuclear fuel or the temperature capacity of the metals
which must enclose this heat. Let us take T(2)to be 843 degrees Kelvin
and T(1) to be 3O3 degrees Kelvin. By using the equation, this would be
an efficiency of 64%. In fact, this is the theoretical maximum efficiency
with a perfect gas. Steam is not a perfect gas, and its efficiency is much
less because of it.
Now, the thermal efficiency of a power plant is a measurement of
how much thermal energy from the fuel gets converted into useful electric
power. A modern fossil fuel plant has a thermal efficiency of 4O%, if it
uses a steam cycle with superheat. However, this is quite a high figure,
most fossil fuel plants today have an efficiency of about 35%. The efficiency
of nuclear plants is varied, as it is dependent upon the type of reactor.
The efficiency depends upon the ability of the reactor to deliver high
temperatures to the turbine inlet. A typical Light Water Reactor (LWR)
has a hot temperature of about 277 degrees Centigrade. With a 17 degrees
C. cold temperature, the efficiency is about 33%. Now, if a High Temperature
Reactor is used (HTR) the efficency is increased to 4O% because the hot
temperature can go up to 53O degrees C. Generally speaking, nuclear power
plants which use the steam cycle have low efficiencies and reject low-grade
heat (usually about 1O degrees C. higher). The gas turbines, on the other
hand, can produce very high-quality waste heat, which can be used much more
easily and effectively, while not causing hardly any loss to the electrical
generating capacity of the plant. A figure of 8O% overall thermal efficiency
is agreed upon to be possible if this waste heat from the gas turbine is
With an efficiency of 33% for a 3,OOO MW LWR, 2,OOO MW of heat is
dumped into the environment. With amounts of heat such as that, and with
many nuclear power plants, we can see where the temperature of the receiving
water could become quite high if the waste heat was to be directly dumped into
from the plant. This is called once through condenser cooling. By a rough
estimate, it is assumed that 1 GW of electrical capacity causes a body of
water to be raised about 1O degrees C. (Assuming a thermal efficiency of 33%),
and requires 5O cubic meters per second of cooling water. The EPA has limited
the temperature increase in receiving waters to 5 degrees C. Thus, we can see
that 1 GW will require 1OO cubic meters per second of cooling water to meet
these limits! The U.S. has a run-off of 53,OOO cubic meters per second, making
a limit of only 53O GW of power to be obtained from the nuclear power plants.
With our energy consumption at such high rates, and the predicted higher
consumption rates, this figure of 53O GW should be reached around 198O.
Therefore, it is obvious that this heat will have to be dissipated elsewhere
besides the runoff water if we want to continue using this type of power, or a
large percentage of it will have to.
So, we see that one of two steps can be taken with this waste heat.
Number one, we can return the cooling water directly into a body of water.
We have seen where this will not be feasible within a few years. The one
major exception to this is using seawater. Because the ocean is so vast,
the cooling water represents only an insignificant fraction. If properly
designed discharge pipes are used, there will be no deleterious effects on
the environment. However, there are only so many miles of shore-line. Of
course, we must also keep in mind aesthetic considerations...how many miles
of a beautiful coastline are we willing to part with for the sake of nuclear
power plants? And, of course, there are many inland states with no shores.
The second step then is to reject this heat into the air by various means,
which usually involves the use of cooling ponds or cooling towers. The
choice of which step to take for heat rejection is a function of economical,
environmental and technical factors. Essentially, it depends upon the local
conditions...how much available water is there?
Let us look into the actual effects of heat rejection to surface
a bit more. With proper design of water discharge structures, the detrimental
effect upon the ecology of the receiving water can be greatly reduced. The
waste heat is dissipated by a number of ways...heat is evaporated from a
water surface to the atmosphere by approximately 4O% evaporation, 3O% radia-
tion, 25% conduction and 5% advection.
What are some of the effects of increasing the temperature of
river water? Perhaps the most important effect is the decrease of oxygen
solubility at saturation. This is so because dissolved oxygen is an essential
element for aquatic life. High temperperatures can reduce the saturation
capacity for oxygen to such a great extent that fish will not be able to
By using cooling towers or cooling ponds, the problem of thermal
pollution may have been taken care of (depending upon the validity of
assumptions that thermal air pollution causing detrimental effects to the
environment will not occur). However, it is obvious that this energy in
the form of waste heat is simply being wasted. With energy costs and
possible future environmental problems, attempts should be made to utilize
effectively this heat energy.
Presently, there is much research devoted to finding ways to use
this energy. The problem is finding low cost-high return use of it. The
economic factor is always very important. The important thing is that
utilizing this waste heat is feasible. Research must be accelerated, so
that provisions can be made for waste heat use in original designs of the
nuclear reactors. Plans should also be started now for integrating uses
of the heat into municipal structures, greenhouses, houses, or other such
The major concern of water pollution is of course the damage
to the ecological systems of rivers, lakes, and estuarine waters by the
increased temperature. The fish are very sensitive to temperture changes
in their waters, as they are unable to quickly regulate their body temp.
In general, each aquatic species can tolerate slight changes, but they
do not have the ability to adjust to an abnormal abrupt change of temp.
The particular reasons for this inability are varied.
An 18 degree F. increase in temperature causes the basic metabolic
rate of fish to double. This is in accordance with the Van't Hoff Principle
which states that the rate of chemical reactions increase with increased
temperatures. This principle is extremely important, because this increase
of metabolic rate includes the increased rate of respiration, which of
course increases the need for oxygen. At the same time, an increase in
water temperature directly correlates with a decrease of oxygen solubility,
a decrease in the river re-aeration rate and an increase in Biological
Oxygen Demand (BOD). All of this spells disaster for the fish. And, to
make matters even worse, the respiration difficulties are coupled with the
problem of the reduced hemoglobin affinity for oxygen, which means that
there will be a reduced efficiency of carrying oxygen to the tissues. These
two effects alone put the fish under severe stress.
Another serious problem occurs in the reproduction cycle of the fish.
Ususally, fish spawn in the Fall or Spring. The temperature of the waters
induce the seasonal development of the gonads. At the critical temperature,
the female deposits her eggs. For instance, estuarine shellfish such as
oysters and clams spawn within hours of the critical temp. With the temp.
being increased artificially through the waste heat, the hatching time of
fish are greatly effected. Atlantic Salmon have a normal hatch time of ll4
days at 36 degrees F., but only a 9O day period at 45 degrees F. This then
prevents normal development of the eggs. The tiny crustacean, Gammarus,
reacts to this in a strange way...at temperatures greater than 46 degrees F.,
the species lays only female offspring! D'Arcy W. Thompson has also established
the fact that accelerated stage development by warmth curtails the duration
of the life. Thus, the longevity of the fish are threatened by the increased
Fish are fortunately able to acclimate to temperature shifts, providing
that they are not too sudden. An example of this is shown by the reaction by
the largemouth bass. When they are transferred suddenly to 85 degree F. temp.
from 65-7O degree F. temps, 9O% of their eggs perish. However, if one gives
them enough time to adjust to the change, in this case 4O hours, only 2O% will
die. The fish, as a general rule, acclimate to elevated temperatures much more
quickly than they acclimate to decreased temperatures.
Realiing the importance of utilizing as much of this waste heat
effectively as we can, research is advancing rapidly in this field. The two
main considerations that must be taken into concern when developing uses for
the heat is in reducing adverse environmental effects and in creating an economic
gain for the power plants. The most important difficulty which limits the
development of the heat uses is the economic factor. Much progress has been
made in developing uses for the waste heat in areas such as aquaculture,
mariculture, agriculture, airport deicing, space heating, airconditioning,
and uses in many industrial processes. However, much more research is needed
to actually turn these ideas into realities. I have chosen two areas to
discuss in greater detail, that of using the waste heat for treating sewage
and for producing hydrogen with it.
Like most everything else, utilizing this waste heat energy involves
many problems besides the economic setbacks. One major problem deals with
the fact that most LWR produce low quality heat, usually the normal maximum
range being from 9O to 1OO degrees F, and in such hugh quantities. There is
a lot of heat, but being at such a low temperature, what can they do with it?
This involves problems such as transporting the heat to many different areas,
needing many pipelines, etc. Results have shown that from a 1,OOO MW plant,
4.4 miles of greenhouse could be heated. Another problem is that of timing.
When there is maximum heat discharge, will there be a maximum need for the
heat? It would be highly unlikely that the facility which uses this waste
heat could actually utilize the heat at the identical rate at which it is
being rejected by the power plant. Thus, back-up structures would be needed
to insure that the waste heat could always be disposed of at all times.
This back-up structure, known as a heat sink, would require a lot of high
capital costs, possibly making the usuage of the heat uneconomical, unless
the plant would be able to use once through heating with a nearby river. This
would have to be used as little as possible though to make sure that the waters
would not be overheated, in complying with strict EPA requirements. Another
problem deals with the transportation costs. Estimates for the pumping cost
of one million gallons per minute per ten feet for heat is $2OO,OOO per year.
This figure also includes the depreciation and maintenance costs for the pumping
facility itself. This is a huge amount of money, which must be taken into
account when developing uses for the heat. This is also a good reason for
building the power plants as near to the consumers as possible. The final
problem which I will mention (there are many more), deals with the predictability
of the availability of the waste heat. A nuclear power plant can shutdown
unpredictably, for various reasons, such as for maintenance or malfunctions.
This will of course cause many complications for the consumers who use the
heat, because they will not be able to rely upon the waste heat being available
at all times. Thus, we have seen many problems which must be reckoned with,
and taken into consideration when designing systems for waste heat use.
Whether or not the energy being produced in the nuclear plant is
in the form of electricity or waste heat, all of it must be rejected at
some later time. The problem is in releasing it to outer space without
causing horrible environmental effects as it travels through the biosphere
to get there. Since a nuclear reactor disperses it electrical energy quite
effectively, the problem is in disposing the waste heat in the cooling water,
because so much of the heat is concentrated, which causes the thermal problem.
Three main methods of have used to dissipate this heat: Once through cooling,
cooling towers, and cooling ponds, which I will discuss in greater detail in
the following paragraphs.
Briefly, I will summarize these three methods. The first, once-through
cooling, requires massive amounts of withdrawal water, which it heats up to
undesirable temperatures, and has a low consumption rate. The cooling towers
can either be wet or dry towers. Wet towers have little withdrawal, no heat
dumped into the water, but a high consumption rate. Dry towers use no withdrawal
waters, dump no heat, and have a very low consumption rate. This appears to be
the best choice, but the capital costs are by far the most costly.
The future use of nuclear power is presently causing much intense
controversy, as was shown in the 1976 Californian issue of the well known
Proposition l5. However, admist this controversy, there does not seem to be
any reduction in the usage of energy, which is extremely high. With a present
day increase rate of 7%, or 5% per capita in the U.S., per year, much energy
will be needed in the not too far away future. In l975, Americans used
blah blah blah amounts of energy, approximately blah percent being in the
form of electricity. The use was evenly divided into three major categories,
about one third for industry, onethird for whatever, and one third for residential
use. Oh blah. Redo this, find info. Pop. growth, toasters, fossil fuels down,
etc. Thus, with energy demands increasing at such high rates, and with
the present trends, we can assume that nuclear energy use will increase. In
fact, recent predictions indicate that by the year blah blah blah, so much
energy will be produced by nuc. power plants. Blah blah blah. I forgot to
include how many plants there are existing today and about the proposed blah
What are the benefits of using water as the reciving body for this
heat? Water as a dilution, dispersion and dissipation medium is four times
more efficient that air on a weight basis and forty two times more efficient
on a volume basis. The second major reason is that it is much less costly
than using structures such as cooling towers, etc. But, the benefits must
be compared with the potential ecological cost of ecological damage to the
The important thing to remember is the fact that the aquatic system
consists of a very delicately balanced ecosystem. The food chains in the
oceans consist of long food chains, as opposed to the relatively small food
chains on land. Man, then, must be very careful to avoid destroying any
link of this tightly woven food chain.
The dispersal of heat through receiving waters into the atomosphere
is a function of the current speed, the turbulence, the temp. difference,
the humidity, and the wind.