BBC News - Standby power scare story

[danielf]

Originally Posted by zinglebarb

I live on a council estate and tbh I wouldnt be to bothered if they built one here

Let me guess... It might cheer the place up a bit?

Originally Posted by danielf

Let me guess... It might cheer the place up a bit?

nah its a happy estate i live here you see

[danielf]

Originally Posted by zinglebarb

nah its a happy estate i live here you see

Good on ya

[Anonymouse]

Originally Posted by Damien

Wind farms and other such types of power do not generate a lot. We need nuclear

Need? Debatable.

If we could be sure that the design was safe, if we could be sure regular maintenance was carried out by independent authorities and if we could trust the government not to cut staff and maintenance to minimum levels, then it might be more feasible. However, correct me if I'm wrong, but those are bloody big 'if's!

Actually...does anyone here know why a lot of people who object to nuclear power do so? The reason I'm against it is not because of nuclear waste, or leakage. There is a far more serious objection, namely the actual design of the proposed reactors. For anyone not interested in physics, now's the time to switch threads...

Leaving aside the 'breeder' reactors (these can, in theory, reprocess 'spent' nuclear fuel and transmute it into different isotopes, i.e. new fuel, but in practice they aren't very efficient), there are, for practical purposes, two types of reactor: Advanced Gas-cooled and Pressurised Water Reactors. What happens inside a nuclear reactor core is this: in the fuel (uranium, thorium or plutonium), nuclei are continually, spontaneously undergoing nuclear fission, i.e. disintegrating into two more or less equal parts. This is because the laws of physics are such that certain ratios of protons to neutrons in a nucleus create instability; the nucleus has too much energy and must shed it somehow. Various particles are given off in the process, and that reduces the energy because the particles are ejected at high velocities, i.e. they have a lot of kinetic energy. But the most important particles in this context are neutrons emitted when uranium nuclei decay - because those neutrons can cause other nuclei to decay. These in turn emit more neutrons, which cause more nuclei to decay, and so on.

If you ensure that neutrons can't escape from the mass, by encasing it in a beryllium reflector, the result is a chain reaction - in other words, you've made and detonated an atomic bomb. It's not as simple as that, of course; you have to provide shaped charges to create implosion, to force two halves of the critical mass together in exactly the right way - this was, for a while, the major stumbling block for the Manhattan Project. But that's it in principle. Left to itself, uranium doesn't spontaneously explode, because the vast majority of the neutrons escape from the mass before they can cause any more nuclei to disintegrate. This is why a nuclear reactor can't - it literally cannot - become an atom bomb - even though the total mass of nuclear fuel is more than enough, there is no beryllium reflector in a nuclear core. The reaction still occurs, obviously, but at a steady pace instead of, as in an A-bomb, in microseconds or less, because enough neutrons escape from the mass to prevent a sustainable chain reaction.

On the other hand, you don't want too many neutrons to escape, else the reaction will proceed at too slow a pace to generate useful heat. So you introduce a moderator, a substance which absorbs some neutrons, but not too many. Depending on the design, either you raise or lower fuel rods into the moderator (depending on whether you want the reaction rate to decrease or increase), or you lower/raise control rods into the core to reduce or increase the rate of nuclear fission. If the rate increases, so does the heat generated.

(I'm coming to the point, honest!)

The coolant circulating around and through the core is of course heated by it; the hot coolant is drawn off to a heat-exchanger; cold coolant is pumped back in, and so on. The heat energy thus obtained is used to create high-pressure steam; this in turn drives a turbine, which produces electricity. All well and good so far. The kicker comes when you consider the major difference between the AGR and the PWR...

In an AGR, the moderator is usually bricks of graphite, and the coolant is generally sodium vapour or carbon dioxide. But in a PWR, the coolant - pressurised water - is also used as the moderator. Still doesn't sound like a problem, does it? And in fact a PWR is a lot simpler in design and cheaper to build.

But what happens if the coolant system breaks down?

With an AGR, the moderator is still in place - you can't lose that. So if the coolant system breaks down - despite multiple safety backups - it'll take the core about 16 hours to heat up to the point where there's serious danger, so that gives you plenty of time to find and correct the problem or, at worst, shut down the reactor by simply dropping the fuel rods all the way into the moderator; that halts the reaction, since virtually all the emitted neutrons are absorbed by the graphite.

But with a PWR, you lose both coolant and moderator. The result is that a) the reaction can proceed as fast as you like because there's no moderator to stop it doing so, and b) the core starts heating up very fast. In short, you have, not 16 hours, but more like 2 minutes, to do something. After that, the core will become so hot it will simply start melting down through the Earth, and nothing known to our science can stop it - doubtless many of you have now recognised this as the China Syndrome scenario. It hasn't happened...yet.

Sizewell A is a PWR. The proposed Sizewell B, if it's ever built, will be. Three Mile Island was a PWR - and compared to what could have happened, they were lucky. As for Chernobyl, which in fact was not a PWR, that was not a meltdown but a burn-down, i.e. the graphite core actually caught fire - and graphite burns at a very high temperature. I can't remember exactly why it happened, but I seem to recall reading they were trying some experimental - and not officially approved - procedure. We all know what happened then.

Nuclear power should be a viable alternative to fossil fuels. Despite the risks, it should be relatively safe. But it isn't. Just because PWRs are cheap does not mean they should be built - at the very least, they should have a separate moderator in the core to eliminate the risk of meltdown. I don't even want to think of what it would mean to the UK to have one happen here, on this relatively small island. And the scenario laid out in The China Syndrome - namely the power station's owners cutting corners by only doing weld tests every few years instead of every 6 months as they should have been doing - is all too horribly plausible...especially given our government's track record re skimping on safety procedures.

Sorry for the long and possibly boring post, but it used to be a pet subject of mine - a long time ago I had an ambition to be a nuclear physicist, and so I learned as much about nuclear fission as I could...and then I read about Kerr-McGee and Karen Silkwood.

[Stuart]

I don't know how accurate it is, but I bought a power consumption meter from Maplin and did some tests.. My TV (Sony Wega 28 inch) consumed 118-130 watts while on, and between 0 and 2 watts in standby.

[littld]

Originally Posted by Anonymouse

Need? Debatable.

Just wanted to thank you for such an informative post.

I for one feel much better informed.

My opinion is that all current means of getting power cause damage - even solar and wind. If nothing else, the resources used making the things, the chemicals involved etc.

Perhaps the least damaging are the geothermal means - heat from a few feet in the earth harnessed fairly easily.

Otherwise, I'm with the other people who think we need to include nuclear.

Originally Posted by Anonymouse

After that, the core will become so hot it will simply start melting down through the Earth, and nothing known to our science can stop it - doubtless many of you have now recognised this as the China Syndrome scenario. It hasn't happened...yet.

For those of us who have no idea what the "China Syndrome" is - perhaps you could explain why this is bad, won't it just vanish into the depths of the earth, never to be seen again ?

Originally Posted by Paul M

For those of us who have no idea what the "China Syndrome" is - perhaps you could explain why this is bad, won't it just vanish into the depths of the earth, never to be seen again ?

you could just watch the film http://www.imdb.com/title/tt0078966/

[Aragorn]

Originally Posted by Paul M

For those of us who have no idea what the "China Syndrome" is - perhaps you could explain why this is bad, won't it just vanish into the depths of the earth, never to be seen again ?

Or look in Wiki

[idi banashapan]

Originally Posted by greencreeper

Thieving chav types took my answer machine - ripped out the wiring first. Also took the NTL cable modem. They just think "nice" and take it. Years of inbreeding for you.



Probably about 40/60

lol

---------- Post added at 11:54 ---------- Previous post was at 11:53 ----------

Originally Posted by danielf

Perhaps they thought it held all the answers?

lol to that one too!!!

[DaggaDagga]

Big companies need to be forced to cut their energy consumption. The lunatic company I work for has a policy of leaving all dektops (2000+) on all the time.

As the IT department script upgrades etc for next reboot anyway, it's completely pointless.

So we have many kilowatts of PCs doing nothing, plus the air con fighting against the heat. Plus piles of other equipment in addition to the PCs.

I've made suggestions to the management, who did precisely nothing. Obviously the cost of electricity isn't enough incentive for them to do anything about it.

Against this kind of waste, installing energy efficient bulbs is almost pointless.

Originally Posted by homealone

everyone should read Ringworld

http://www.sfsite.com/~silverag/ringworld.html

or Orbitsville by Bob Shaw
http://www.amazon.co.uk/gp/product/0...lance&n=266239

[AndrewJ]

Originally Posted by zinglebarb

yeah but they aint that dangerous are they.If they go bang an area dies in for thousands of years.If we keep burning fossil fuels then eventually the global warming will destroy a good portion of the planet. We can send the waste from these stations into space and let people a few million miles away worry about it

Their is a logic there I admire Zingle.

[greencreeper]

Originally Posted by Felinix_Devotion

Their is a logic there I admire Zingle.

Until the "people" a long way away turn up seriously ****ed off. I say send Zingle to negotiate

[AndrewJ]

Originally Posted by greencreeper

Until the "people" a long way away turn up seriously ****ed off. I say send Zingle to negotiate

He would just upgrade their computer system and they would go home happy playing Quake 5,000,001