Naked Science Forum
Life Sciences => The Environment => Topic started by: alice00141 on 28/06/2011 20:06:43
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Nuclear energy is the American’s largest source of clean electricity, which is affordable and reliable. Nuclear power plants produce nearly 20% of U. S. electricity. No other source of electricity can provide the combined benefits of nuclear energy: Large amounts of reliable and affordable electricity, long-term stability and green house gas emissions.
In my point of view, we shouldn't get rid of the Nuclear Power plants. Because it's already become a very important part of our energy life.
Here are what I learn from my research of this topic:
1.Nuclear Power plants produce tremendous energy supply with clean-air benefit better than the new tech like solar energy, etc.
2.Nuclear Power plants is the lowest-cost producer of busload electricity.
3.Nuclear Power plants have low-level waste.
What do you guys think of these nuclear power plants? Thank you.
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Nuclear energy is the American’s largest source of clean electricity, which is affordable and reliable. Nuclear power plants produce nearly 20% of U. S. electricity. No other source of electricity can provide the combined benefits of nuclear energy: Large amounts of reliable and affordable electricity, long-term stability and green house gas emissions.
In my point of view, we shouldn’t get rid of the Nuclear Power plants. Because it's already become a very important part of our energy life.
Here are what I learnt from my research of this topic:
1.Nuclear Power plants produce tremendous energy supply with clean-air benefit better than the new tech like solar energy, etc.
2.Nuclear Power plants is the lowest-cost producer of busload electricity.
3.Nuclear Power plants have low-level waste.
What do you guys think of these nuclear power plants? Thank you.
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Nuclear Power is an important source of electricity in the USA, and around the world, and should not be ignored. We do, however, have to make sure it is a safe energy source.
As far as renewable resources, we currently generate about half as much energy with hydroelectric as nuclear power. So far it has proven to be a long-term safe and effective power source with no waste, although it does change fish migratory patterns, and potentially can warm the water in the rivers. However, I don't see a lot of future growth in continental hydroelectric. Wind & Geothermal energy supplies certainly should be considered for the potential of future energy sources, as well as exploring energy based on ocean waves, tides, currents, and temperature gradients. Much more can be done with residential solar hot water and solar electricity generation.
As far as Nuclear Power, we must:- Double and Triple check safety plans and backup control and cooling systems.
- Make sure our plants are well sited. Earthquake tolerance, floods, cooling water supply, risk to communities and ecosystems
- We need to start recycling spent fuel in the USA, and to start using MOX fuel in our reactors. Currently in the USA, 3% or 4% of the fuel is used, and 96% is put into very very long term storage. That is just unacceptable.
- Like our cars, Nuclear power plants shouldn't be considered to last forever. After a finite amount of time, they should be decommissioned or completely rebuilt.
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3.Nuclear Power plants have low-level waste.
and high level waste (http://en.wikipedia.org/wiki/High_level_waste) too.
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I have merged the two topics (good spot Clifford).
There are nations around the world that, after Fukashima, are reconsidering their committment to Nuclear Energy.
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Nuclear Power Stations are much more marginal as energy providers than their promoters would have you believe. If you do a "dawn to dust" analysis of the cost of a nuclear power station in energy terms, and compare it with the total energy output during its working life, you will find that the net overall energy advantage in running a nuclear power station is surprisingly small.
To set up the power station in the first place, you must have a lot of concrete shielding, a lot of electronic devices for monitoring, and failsafe circuitry and switching. You also need a huge water supply.
Energy must be spent to enrich the U-235 content of the uranium in the nuclear fuel, and a "use" or a safe disposal method must be found for the large quantity of depleted U-238 that will be the inevitable by-product of this enrichment process.
Anything by way of pipes or tubes or structural material that is intended for use inside the "hot" part of the reactor needs to be prepared to much higher engineering specifications than normal because of radiation damage that will be done to all of this material during the working life of the reactor.
Safe disposal of nuclear waste is a difficult problem, and there is major controversy about whether or not, and how well it has been solved.
And finally there is the problem of how to decommission the facility after a working life that probably cannot safely be extended beyond half a century, and how to dispose of all of the low level waste that this will entail.
Every one of these aspects of the operation has an energy cost, which needs to be offset against the total energy production.
How to reduce the "dawn to dust" energy cost of a power station project is an engineering problem, and it may well be that there are large improvements on the horizon. But at present if you have a station producing 500 MW it may well be that a proper analysis of capital energy cost on a total lifetime basis would produce a 400 MW energy costing for constructing, operating, and decommissioning the facility, and you could only really count it as a net energy contribution of 100 MW (arbitrary figures off the top of my head).
Unfortunately, another way to reduce the energy cost is to cut down on safety margins by relaxing engineering standards, exposing risks to safety or to smoothly continuing operation. Attempting to extend a working life may also have similar effects. And on the face of it, there is a huge commercial incentive to go down this path.
I do not think that an advantage for nuclear power generation over exploitation of wind, water, and direct solar energy is nearly as great as it is usually painted. Moreover I think (in terms of fuel reserves) that it can never be considered more than a very temporary stop-gap in our planning for future energy needs. Of course if a safe way could be found to exploit U-238 as well as U-235 in breeder reactor type technology, that would make a major difference. At present 99% of uranium is just a very dangerous by-product.
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I think yo are right that one must consider the "Cradle to Grave" costs, and very very long-term waste handling costs. And this is also likely the reason we will use up every drop of accessible petroleum before converting to another alternative energy source.
You also need a huge water supply.
This is likely why many nuclear plants are situated near major rivers. 3-mile-island in the middle of a river. Trojan near the Columbia (below a dozen major dams). The Fort Calhoun nuclear plant is now being flooded by the Missouri river.
One could put all the nuke plants in Utah, but there would be problems with water supply, and power transmission loss to New York would be excessively high.
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Nuclear energy is not cheap, nor is it clean. You must look beyond the actual power generation. Building the plants is very expensive, handling and very long term safe storage of the waste is very expensive. Decommissioning the plant is also very expensive and the reactor also requires long term safe storage. Some nuclear waste has a half life running into thousands of years
Apart from the threat of terrorism, there is the threat from malfunction and human error in addition to natural disasters as at Fukushima.
Germany has the right idea. We must find genuinely clean sources of energy.
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Because money drives our world (much as I dislike this fact), and there is a energy demand that will not decrease, we currently have two choices: keep and build more nuclear power plants, or start using more fossil fuels.
Renewable energy sources do not produce enough energy to satisfy the inevitable rise in demand for more energy.
I disagree with Don_1, Germany is closing the power plants and is increasing the energy output from natural gas. Wind power simply will not generate enough energy for that country.
In the end we have to choose the lesser of two evils until we are able to harness fusion: http://science.discovery.com/stories/week/chinese-technology-wikileaks.html
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I don't know, it's okay until something happens, when it happens it will not be okay anymore. I liked the discussion of costs relative output but it's still comparatively cheap energy as I understands, but as Damocles points out, that's partially because we still haven't found what it really will cost to store it all after its use, including the whole reactor building here. If we could bury it deep enough I would naively expect earth to take care of it, but that would mean a very deep hole for (somewhere around ? 35 km maybe?) each deposit, that we then have to close up. And that is assuming us to have a way to stop groundwater too :) Not very realistic, is it? We will need energy though, and we will need to solve it someway.
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I don't believe there is any freshwater at 35km depth. But, there may be brackish water which there are plans to potentially mine in the future... but perhaps not so deep.
If one goes too deep... is there a risk of disturbing the mantel with potentially disastrous consequences?
If one reprocesses the nuclear waste to separate out the fissionable material from the Neutron Poisons. Would it be possible to put the neutron poisons back into the reactor as some sort of shielding? Would it help stabilize them, or just create more waste?
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I don't believe there is any freshwater at 35km depth. But, there may be brackish water which there are plans to potentially mine in the future... but perhaps not so deep.
If one goes too deep... is there a risk of disturbing the mantel with potentially disastrous consequences?
If one reprocesses the nuclear waste to separate out the fissionable material from the Neutron Poisons. Would it be possible to put the neutron poisons back into the reactor as some sort of shielding? Would it help stabilize them, or just create more waste?
On the one hand, the energy required and the possible problems introduced by trying to dig to 35 km depth are enormous. I do not even think the technology is in place to let us drill so deep. On the other hand, a kilometre or two is more than enough to make sure that the surface environment is not affected by radioactive emissions, PROVIDED that the material remains immobile. Leaching out of waste products by groundwater is problematic.
One of the more promising approaches to dealing permanently with medium and low level waste has been the suggestion of locking the material in a glassy matrix that is quite impervious to groundwater. It would then be buried in pre-existing, disused underground mines (I hope that readers of this forum will be able to use search engines to save me the trouble of finding on-line references here).
Talk about "fissionable material" and "neutron poisons" refers mainly, if not entirely to recovery and recycling of fission fuel form "spent" fuel rods. It does not have much to do with the waste problem from decommissioned plants. The process of recovering fission fuel from "spent" fuel rods is likely to be at least as money-costly and energy-costly as preparing the fuel rods from freshly mined uranium. It does have the advantage, though, of helping deal with medium level waste that is already on your hands. Whether it would be a useful approach would depend on the fine detail of the engineering and economics.
Now, about "neutron poisons". When a neutron encounters another atomic nucleus (that is not a fissionable one) there are basically three other things that can happen.
--The first is that the neutron might be "absorbed" by the other nucleus, and removed from the system. This is what is meant by neutron "poisoning", and is a generally undesirable thing to have happening within the fuel rods of a working reactor. Lighter isotopes of each particular element are more likely to d this than heavier ones. This is one of the main reasons why a heavy water (H-2)2O reactor requires less fuel enrichment than a light water (H-1)2O reactor. Fission products are usually the heavier isotopes of each of their elements, and thus not particularly good "neutron poisons".
-- the second is that the neutron might become "thermalized". That is, it will bounce around, encountering several other nuclei, losing a little energy in each collision, until it is effectively moving not much faster than other particles in its environment. A U-235 fission reaction is triggered most effectively by low-energy neutrons, and slowing them down is the function of the "moderator" in the reactor (usually water or graphite). Atoms of light elements -- H, C, O -- are by far the best at thermalizing stray neutrons.
-- the third is that the neutron might be reflected back towards the fission reaction. It will undergo a single collision, or perhaps a handful, without losing much energy. Heavy atoms are best at producing this effect (think of a marble bouncing off a cannon ball). It has been exploited in the design of nuclear weapons (where depleted U-238 has been used to reflect stray fast neutrons back to the fission zone). It could also be part of any breeder reactor technology, because unlike U-235, Pu-239 fission works best with fast neutrons.
The bottom line for CliffordK's comment is
-- after the removal of any fissionable component for recycling into fuel rods, the remaining waste will be fairly useless as a neutron absorber or thermalizer, but might find application as the inner part of radiation shielding in some future plutonium reactor technology.
I have a good general knowledge of nuclear reactors, but I am not expert in this area. If these comments interest you, please cross check and research them with sources from nuclear experts.
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I think that idea was tried in USA. They used diluted radioactive waste sealed in glass and some other material that I don't remember for the moment, but they found that the hard radiation and heat weakened the material creating cracks, if I remember right. And I know that we haven't found any perfect container in Sweden, what they seem to lean to is a blend of iron at the core and copper at the outside of the capsules, to give it both tensile strength and protection from corrosion and then fill the chamber with mud.
But I would prefer a deep enough hole myself :) . If the holes are just some kilometers deep there is a lot of uncertainty about what can happen, the rock change from layer to layer for example, so even though we have some of the oldest rock (most stable) in the world we will have to look at from hole to hole, and groundwater will leak in it as you bore. We have one hole in Dalarna that is 6 km deep where there is water, not leaked but very saline water at that depth. So I think we need to get to such a depth that you pass the rock, and that should be around 35 km(?) myself. But nobody has gone that deep, and the costs, and engineering difficulties, in doing so should be astronomical, as a guess :)
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One of the issues with deep wells is casing. One method used is to start with very large casing, then at each successive depth putting in a smaller casing... until the well becomes quite small, and thus limits the depth of the drilling. I suppose one could potentially do the well without casing, with plans to immediately fill it with a concrete plug. But, one of the benefits of using a casing is that it will prevent contamination between successive layers.
Radioactive Glass?
They used to sell it for plates and serving ware here in the USA. [???]
http://en.wikipedia.org/wiki/Uranium_glass
I had thought that some nuclear waste was currently being vitrified... but perhaps it is still at an experimental phase.
http://en.wikipedia.org/wiki/Radioactive_waste#Vitrification
It may be more expensive to reprocess spent fuels, but in theory it should give about a 96% waste reduction. I would think that that alone would be a reason to do it.
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As to the waste being hard to contain. just look at natural reactors, that ran for millions of years, in rock fractured by faults, and with flowing ground water as both moderator and coolant. These are now mines, where the ore is mined to make reactor fuel, it not having moved much in the millions of years it has been there, and with most of the by products still being there, enabling study of these natural reactors in Gabon at a site called Oklo.
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And what do you mean by that Sean?
That Fukushima and Chernobyl is the way to go? I'm not sure I follow how you reason there? Those 'natural reactors' has to be very weakly radioactive, or else they will have forced a lot of genetic mutations in the area as it seems to me?
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"Geologists found that it had been in a reactor before—two billion years ago. At that time the natural uranium had a concentration of about 3% 235U, and could have gone critical with natural water as neutron moderator." Is it this you was thinking of?
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When it comes to borated glass I know that USA found it to crack from the heat and chemical processes. Can't seem to find the article any longer though? It seems buried under research trying to support it as a 'safe procedure' for storing nuclear waste? Don't like that, it's not the correct way to treat such a subject. If someone have the article still, link it :)
Here is a recent link discussing it, although a 'pay per view'. Neptunium Diverges Sharply from Uranium and Plutonium in Crystalline Borate Matrixes: Insights into the Complex Behavior of the Early Actinides Relevant to Nuclear Waste Storage. (http://onlinelibrary.wiley.com/doi/10.1002/ange.200906127/abstract)One of the scientists think that the radioactive glass rods might crack upon contact with water according to an article in Angewandte Chemie (Germany) but on the other hand "The take home message from the article is that the chemistry of neptunium can not be predicted based on studies with uranium or plutonium." according to Thomas Albrecht-Schmitt which is one of the authors.
But I find it problematic and curious that the article on real tests done can't be found? Hopefully I have saved it somewhere, not on this cmpta though.