[Global Change: 779] Re: Nuclear Power is Not the Answer
Kooiti MASUDA <masuda <at> jamstec.go.jp>
2006-10-04 08:44:53 GMT
I have not read that book, but I think "Nuclear power is not the
answer" myself.
I think that discussing CO2 emission is not a good way to evaluate
nuclear power. More generally, we should not evaluate enviromental harm
of human activity with CO2 emission alone.
I think that advertisements by some nuclear lobbyists that nuclear
power does not emit CO2 is as wrong as denial of CO2-global-warming by
some fossil fuel lobbyists. Fossil fuel is used for mining and
trasportation at least, and also for refinery and waste management
probably.
But it is very uncertain whether those energy demands are met by
electricity produced by nuclear power plants in the future. And the
question is about the long-term effects. Thus the answer to the
question of CO2 emission of the whole stream of nuclear power
generation is inherently uncertain. It may be a good academic problem,
but a bad basis for policy making.
On the other hand, evaluation of costs in monetary terms is fragile,
too. Its uncertainty is large due to how to take account of
inhomogeneous inflation, and to the notorious discount rate.
Since a nuclear power plant is essentially a heat engine, the best
basis of evaluation would be thermodynamics. This is my opinion which
has been influenced by several Japanese physicists, material engineers
and economists who discussed at "The Society for Studies of Entropy".as
well as elsewhere. (Incidentally, one of the founders of this thought
recently advocates strong denial of CO2-global-warming and I think that
is flawed, Other members do not agree with this advocacy. This issue
does not affect their common criticism on nuclear power.)
I do not think that anyone has yet done comprehensive analysis of
entropy balance in the stream of nuclear power generation. But the
idea can be reflected in several points.
First, nuclear reaction makes higher temperature than the ambient air
or water, and the energy flow through the difference of temperature
makes a heat engine work. But, strong level of radiation makes choice
of materials for the reactor body and for the working fluid very
limited. Usually water is used as the working fluid, and thus the
high-end temperature of heat engine is limited around 300 deg. Celcius,
much lower than around 1000 deg. C achievable in gas turbines.
(Experimentally, liquid metal natrium (sodium) is used as the working
fluid, but it is well known that natrium reacts with water very
strongly. I doubt that complete insulation could be kept
operationally.) The smaller difference of temperature makes the
efficiency of the heat engine much less than the case of engines heated
by combustion. And the problem of waste heat is larger (though
sometimes production of warm water is welcomed).
Second, concentration of uranium, and uranium 235 in particular, is not
very high in the ore. Many processes are needed to make the
concentration sufficient for the power plant (but unsuitable for
bombs). Most of the processes are against the natural tendency of
diffusion and thus require low-entropy resources. Also, huge mass of
wastes is left at mines and at the refinery. Most of them are
radioactive though probably of low level. We need some resources to
make sure that they do not harm people in the place and the
environment. (Maybe the task is forgotten and we are making harm to the
people around uranium mines.)
Third, the used fuel is mixure of almost all possible elements and
isotopes, and many of them are radioactive. Some of them have strong
radioactivity, and some of them have long life. If we separate them,
handling of each element may be easier. But to separate is to decrease
entropy that requires low-entropy resources. Also the process must be
done under high radiation. Some elements are in gas phase in the
ambient temperature and it is almost impossible to prevent escape of
those elements to the environment. There is choice not to separate.
Then, we need to maintain large mass of wastes (though smaller than
wastes at mines) whose radioactivity is both very high initially and
long-lasting, for thousands of years.
Thus I think that thermodynamic cost (requirement of low-entropy
resources) of the nuclear energy stream is high. I am not sure
whether or not the cost overwhelms the low-entropy energy that the heat
engine produces. But I think it is enough to discourage development of
nuclear power as a way of mitigation of enviromnental degradation.
There are also problems related to justice and liberty in human
society, but I postpone that discussion to the next occasion.
Ko-1 M.
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