Re: [asa] vast new gas supplies

From: Iain Strachan <igd.strachan@gmail.com>
Date: Thu Dec 10 2009 - 02:36:38 EST

On Thu, Dec 10, 2009 at 2:38 AM, David Clounch <david.clounch@gmail.com>wrote:

>
>
> On Tue, Dec 8, 2009 at 6:37 AM, Iain Strachan <igd.strachan@gmail.com>wrote:
>
>>
>>
>> On Mon, Dec 7, 2009 at 11:36 AM, David Clounch <david.clounch@gmail.com>wrote:
>>
>>> I think of it in terms of what is available. When will it be depleted
>>> and when will that sub-industry collapse, leaving humanity without energy?
>>> Of course there will be economic collapse long before actual depletion.
>>> Unless there are vast new sources of uranium we don't yet know about I don't
>>> see a long term answer to energy supply.
>>>
>>>
>> On the contrary, nuclear is an extremely long term answer to energy
>> supply. Existing fission reactors use only U-235, which is 0.7% of natural
>> uranium. As such it is a limited resource. But fast breeder reactors can
>> be used to convert the U-238 (99.3%) of natural uranium to the fissionable
>> product Pu-239.
>>
>
> Are there any governments proposing the usage of breeder reactors? My
> assumption is these styles of reactor are frowned upon because plutonium
> presents a huge waste storage problem. The other thing I don't know about
> is whether breeder technology is as safe in its operation as more
> conventional models.
>

I'm not aware that fast reactors pose a bigger waste problem than
conventional reactors.

I think there's something I should explain about fast breeders. The term
itself is a very confusion mis-nomer. At the time fast breeders were
proposed the anti-nuclear lobby went round with tee-shirts saying "The only
safe fast breeder is a rabbit". This misses the point completely. The
"fast" does not refer to the rate at which Plutonium is "bred", it refers to
the energy of the neutrons required and produced in the fission chain
reaction. In a conventional reactor these are low-energy "thermal"
neutrons, but in a Pu-239 reactor they are high energy of "fast" neutrons.

In fact conventional reactors "breed" plutonium as well - so much so that
there is a huge stockpile of Pu-239 that could in principle be used in a
fast reactor - there was of course a big drive to produce the stuff for the
weapons programme - I think the first atomic explosion (the Trinity test)
was a Plutonium device.

I heard from a physicist at Harwell that in an initial stage "Plutonium
economy" the breeding ratio for fast reactors would be set to less than 1 so
they would be net consumers rather than net producers of Plutonium.

As to the safety issue, there are headaches involved in that the reactor
runs at higher temperatures, and requires two levels of heat exchangers -
the primary heat exchangers being liquid sodium, and the secondary ones
being water. The British Prototype Fast Reactor (PFR) at Dounreay was
dogged with problems to do with the welds on the primary heat exchangers -
not that this was an insoluble problem - just that typically once the hard
physics was done, insufficient research funds were dedicated to solving the
conventional engineering problems. Clearly the thought of a mix of liquid
sodium and water coming together is a nightmare!

I think the real problem with the fast reactor program is the cost - short
termism means that it doesn't become economical to build them ... probably
until we desperately need them and it's getting on for too late.

Iain

> I think the anti-nuclear lobby will have a cow over breeders. Given these
> are the same folks that embrace AGW I expect a huge political warfare to
> take place before any widespread deployment of plutonium generators.
> Because of this I just ignore the presence/possibility of breeders as a
> solution.
>
> Seems to me a peak energy crisis is the real crisis, not a warming crisis.
>
>
> Look, we have been really good at putting particle pollutants in the air to
> increase the albedo of the planet to get a cooling effect. And we could do
> that deliberately. If the people who are so concerned over GW are serious
> they would be fighting the anti-pollution measures that are lowering the
> albedo. They would also be proposing nuclear if they were serious. Do they
> in fact do either? I suspect not. So I am very skeptical of everything.
> I am suspsicious of the real agenda behind the AGW movement.
>
>
>> According to Wikipedia there is enough U-238 around to be an energy supply
>> for five billion years, but I think this must be a mistake - I would have
>> put it at several thousand years.
>>
>> In addition it is possible to use U-233 that is bred from Thorium - an
>> element that is 3.5 times as common as uranium, as an intermediate term
>> solution.
>>
>> For the long term solution, one must look to Nuclear Fusion. Current
>> reactors are based on a D-T reaction which requires the breeding of Tritium
>> from Lithium - an abundant element, which according to Wikipedia would last
>> 3000 years if all the worlds energy came from this source. If it became
>> feasible in the future to have sustainable power from a D-D fusion reaction
>> then (again according to Wikipedia) there would be sufficient for 150
>> billion years.
>>
>> I wouldn't trust any of these figures, to be honest. For a better
>> estimate, consult David MacKay's book "Sustainable Energy without the Hot
>> Air", which is available on the web. However, Fusion is an extremely long
>> term solution, and it appears that, given Thorium and Fast breeder reactors,
>> that nuclear fission is almost certainly a sufficiently long medium-term
>> solution to allow the fusion solution to be developed.
>>
>> Iain
>>
>>
>> --
>> -----------
>> Non timeo sed caveo
>>
>>
>

-- 
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Non timeo sed caveo
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Received on Thu Dec 10 02:37:13 2009

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