A little bit of devil's advocate here but let me address each in turn:
skeptik wrote:clv101 wrote: Can someone remind me of the benefits of a major nuclear build programme (say 10GW)?
big reliable base load from each unit. You'd have to plant a lot of windmills for the equivalent.
Ouput does not vary with the weather, time of day or season.
The granularity of nuclear is a bad thing, requiring large amounts of transportation of electricity. Your point is that nuclear is reliable where as wind would not be? This is based on the misconception that wind is intermittent? I prefer the word variable since intermittent suggests it?s either there or it isn?t ? that isn?t the case.
UK wind availability could be considered better than a fixed base load since a recent study from Oxford University came to the conclusion it blows harder in the winter than the summer and blows harder during the day than the night so there is a degree of tracking of demand. They also said low wind speeds affect 90% of the country one hour in 5 years during winter and excessively high winds only occur one hour in 10 years. Also consider the rate of variation ? an hourly change exceeding 20% is only likely to happen in one hour per year with the most likely hourly change being less than 2.5%
skeptik wrote:
Clean in operation compared with Carbon fuelled electicity.
No poisonous fly ash, noxious flue gasses. Significantly less CO2 over a 40 year operation cycle.
Uranium Fuel pellets are comparatively compact and easy to transport. Less environmental impact - no pipelines, hugepiles of coal , oil spills.
It?s a dirty industry ? the uranium comes from uranium ore which is between 0.1 and 0.01% uranium therefore between 1000 and 10,000 tonnes of uranium ore have to be mined and milled for each single tonne of yellow cake. That?s only at around 0.7% U235 so needs enriching to between 2 and 4% for reactor use so you can see how the approx 100 tones of enriched uranium needed per year per reactor actually needs of the order of a million tonnes of rock to be mined. It?s also not just a case of mining and burning like coal, the extraction process involves sulphuric acid, nitric acid and other chemicals so after the uranium is extracted we?re left with thousands of tonnes of tailings which are chemically and biologically toxic, are larger in volume than the hole they came from and are radioactive with the decay products from uranium (things like thorium, protactinium, polonium and radium) which now ground up are freely dispersed on the wind.
It doesn?t end there though since the enrichment process is also problematic, it can be thought of as removing some U238 therefore increasing the concentration of U235 in what is left. Enrichment involves reacting the uranium oxide with hexafluoride which becomes a gas a little above room temperature. This gas can then be spun in centrifuges or diffused through porous membranes to separate U238 and U235. Most of the uranium exits the enrichment process as uranium hexafluoride (now waste); some of which is chemically converted into depleted uranium metal to be distributed back into the environment in the form of armour-piercing shells but most (some half a million tonnes now) is stored as uranium hexafluoride in a solid form in cool storage (requiring energy) to prevent gassing.
Nuclear is anything but CO2 free ? every process in the nuclear life cycle other than the actual fission produces CO2. Other green house gases are also produced in some processes. As the nuclear industry operates today it produces something like 16% the CO2 of a gas power station per kWh that isn?t telling the whole story though since the industry is living on borrowed time as it were in that the cycle isn?t closed. The energy (CO2) costs of decommissioning, waste storage, reinstating previously mined areas etc hasn?t been counted yet. The complete CO2 figure is closer to one third that of gas when a full analysis is carried out. The other climate change point is that halogenated compounds like freon-114 which has 10,000 times the greenhouse effect of CO2 are released during the process ? typically from solvents used in fuel processing.
skeptik wrote:
fuel comes from 'friendly' countries , not the middle east.
I?m not sure we have any idea where the fuel is going the come from ? the world?s largest producer recently signed their production away to China! Friendly or not there is no guarantee there will be the fuel available to power our new reactors and the rest of the world?s.
skeptik wrote:
Fuel use can be hugely extended using breeder technology. (Candu reactors can be used in a 'breeder mode' I read somewhere.. )
I?d like to add the word theoretically to that statement. It's a nice idea, based on the principle that U238 can absorb a fast neutron and eject an electron to become Pu-239, Pu-239 can even be used as the source of neutrons, the start up fuel.
But it's complicated with the fast-breeder (anything but fast!) cycle involving the three processes of breeding, reprocessing and fuel fabrication all having to work together. The breading process doesn't just produce Pu-239 from U238, it also produces Pu-241, americium, curium, rhodium, technetium, palladium and some other nasty stuff - this complicated mixture clogs equipment and a smooth-running breeding process has never been achieved on a large scale.
The reprocessing involves extracting the Pu-239 from this highly radioactive mixture, the radioactivity degrades the solvent again clogging the equipment with an outside chance of a critical mass of plutonium forming! The mixture is also hot and gasses - again large scale smooth-running of this process has never been achieved.
Fabricating the recovered plutonium into fuel is also tricky since large amounts of gamma and alpha radiation is given off meaning the whole process of fabrication, transportation and reactor refuelling has be to done by remote control - again a process yet to be achieved in a large scale smooth-running way. Worth remembering that U238/U235 fuel assemblies aren't actually all that radioactive as they are being fabricated and placed into the reactor.
There's a finite amount of Pu-239 around today - waste from existing thermal reactors and from weapons programme so even if the technology worked, there would be a limit to how many could be built and fuelled with the plutonium we have today. I haven't be able to work out how fast the reaction could potentially be - ie how long does it take a single Pu-239 fast reactor to bread enough plutonium to refuel itself and start up another. I suspect it takes a long time, limiting the rate of growth.
skeptik wrote:
Probably theres quite a bit of Uranium out there that hasnt yet been found yet. Its geological occurence is not as restricted as oil. We stopped looking seriously quite a while ago. Uranium prospecting has ony recently picked up again.
Yeah ? and probably there?s quite a bit more oil that hasn?t yet been found? I don?t expect there?s much more uranium to find since the usefully high concentration ores are rather good at giving themselves away!
skeptik wrote:
Even if the price of Uranium goes up significantly it wont have a big impact on the price of nuclear electricity, as theres an enormous ammount of energy in a pound of Uranium compared with a pound of coal, and most of the cost is in build , operation and decommisioning.
The price of uranium might not affect the price of the electricity but other than that costs are extremely unpredictable. When the Magnox fleet was built did anyone factor in ?70bn on decommissioning? I realise the future build won?t be like the past ? but we still don?t know what do about the waste so how can we know how much it will cost?
skeptik wrote:
er...
waste hot water can be used for shrimp farming?
( no really...honest!)
Same could be said for any thermal generator.
skeptik wrote:
thats it
As I expected ? I remain unconvinced.
