Re: "Nuclear energy 'not the solution to global warming"

On Apr 4, 1:40 am, "Alex Terrell" <alexterr...@xxxxxxxxx> wrote:
On 2 Apr, 17:02, dave.walt...@xxxxxxxxxxx wrote:





On Apr 2, 7:16 am, "bill" <ford_prefec...@xxxxxxxxxxx> wrote:

On Mar 31, 6:41 pm, dave.walt...@xxxxxxxxxxx wrote:

On Mar 31, 2:18 pm, "bill" <ford_prefec...@xxxxxxxxxxx> wrote:

Honestly, hydrogen is *useful* now, just not as a transportation
fuel or energy storage medium :) It's used in every oil refinery, it
can easily be added to the NG grid up to 10% without any particular
problemss. I'm a little sceptical about the idea of a mode switching
pmbr reactor, due to the fact that I really can't see how you'd
'switch out' central elements of the hottest loop in the reactor
without badly degrading the efficiency and more importantly the
reliability of the reactor. Of course, just because I can't see how
doesn't mean it can't be done :)- Hide quoted text -

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The problem is not with the reactor, which would run flat out at 100%
rated power. The problem is with gas flow to the turbine. This is the
limiting factor (as it is with all steam turbines). By the use of in-
reactor divertor valves, the hot, inert helium would,during the day
and peak, run out to the high temperature gas turbine, making power.
As load decreases, helium can be diverted to a standard heat exchanger
(high or low pressure, it doesn't matter) to make superheated steam.
The power to the generator would decrease as more of the hot He is
routed to make process steam heat for H2 orther production. At a
certain point...designated the lower load limit of the gas turbine,
the turbine/generator would trip off line as it is designed to in
order to avoid a reverse power or 'motoring' of the generator.

David

Right, it's those "in-reactor divertor valves" that worry me.
They add complexity and failure points. There are already more than
enough of those in a nuclear reactor.

This may be a WILDLY off-base suggestion, but what about using
the primary loop water from a PWR system as the superheated steam in a
coal cracking plant? I realize that the worry is that *over time* the
primary loop water becomes radioactive, but does that not imply that
cycling it out *often* would extend the life of the reactor and reduce
the rad-waste disposal bill?- Hide quoted text -

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Yeah, but the don't use divertor valves in nuke plants at all, only in
combined cycle GTs. But it's theorectical only right now until the S.
African's get their rolling and the Chinese do the same. They are only
proposals. But...Bill, keep in mind that all the new Gen III plants
have on average 35% less pipe, less cable, less pumps, and 60% fewer
valves to start! The PBMR of the IV Geneation have even fewer as it's
a much simpler cycle.

The problem with the PWRs is that they don't get hot *enough* for
process heat so they are not designed to off-load thermal energy this
way. But...they are going to do this now in Canada with their CANDUs.
Of course for coke production, er, gas-from-coke/coal, yes, they could
do this in theory. I mean, even with PBMRs, they don't *need* the
diverter ralves, rather they are fixed bleed off of helium for
electricity and a fix % for a heat exchanger. One could in theory do
this with the secondary loop of a PWR. But the *primary loop*!?!?! I
don't know, I know the BWRs do this directly and end up radiating the
turbine. Interesting.
Dav id

Okay, after a deal of pondering, I have come to the conclusion
that while it should be perfectly technically feasible to build a
"dual mode" reactor like what you're talking about, it is highly
inadvisable on a wide variety of levels.
1) Adding complexity to a reactor, especially in the hottest
loops increases the chances of a failure, and the training and
opportunity for human errors.
2) Hydrogen is not a safe material to have around. in a lot of
ways it's more dangerous than the nuclear material itself. Having a
complicated chemical process involving explosive materials on-site
with a nuclear power plant, including many components under the
containment itself is probably inadvisable.
3) adding the components will increase the size of the
containment that is required, driving up the cost of the plant.
4) it's a WHOPPING security hole. delivery of the coal,
etcetera will involve a lot more floor traffic at the nuclear site.

For these reasons and a bunch of others, I think it's probably
better to pay carnot on that particular heat.- Hide quoted text -

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Bill, the PBMRs are they are *now* planning, are not designed for "in
plant" H2 production. The schemse that I've seen have a seperate
facility where the heat produced is piped *off facility* a seperate H2
production cracking unit. They don't have to be within explosive
distance of the PBMR.

David

There's some more herehttp://www3.inspi.ufl.edu/icapp06/highlights/pdf/Shiozawa.pdf

There's no reason why the chemical works can't be several hundred
metres from the nuclear plant.

This also implies no switching of the primary helium flow, just a heat
exchanger to take variable amounts of heat to the thermo chemical
process. I would have expected the heat exchanger to look bigger.- Hide quoted text -

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That looks about right for the size of the heat exchanger in relation
to the reactor itself. Well laid out presentation.

Something to note: the whole thing is built underground.The idea is
that not only is this safer, but it makes decommisioning a lot less
expensive...essentially the core is removed, basic decontamination is
completed (but not as complete as in an above ground plant) and then
the whole plant is simply sealed and left as is.

David

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