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dougal
Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
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 Posted: Tue Jul 12, 05 6:48 pm Post subject: |
 
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JB, I think you're wide of the mark in a few aspects.
The radiation that leaks from a nuclear power station while it is operating correctly is simply not the problem.
This is called a "straw man" argument, setting up a case (nuclear generators emitting radiation) purely in order to dismiss it (more radiation from a pile of coal).
Whether or not your facts are even correct doesn't matter - that's not the problem!
The problems I see are:
- the risk of an unplanned, uncontrolled release of radioactive material (whether by accidental failure of systems, personnel or equipment, or external agency - such as terrorism)
- safe, really long term storage of "waste", specifically but not solely spent fuel residues
- the long term contamination of the site. When the plant can no longer operate safely - because of radiation accelerating normal processes such as metal fatigue and corrosion, it has to be taken out of operation. But there are *thousands* of tonnes of contaminated material - and radioactive contamination is so difficult to concentrate that the best proposals are not even to try to do much dismantling for a long time after shutting the plant down.
- the great reduction in net energy generated when due allowance is made for the energy invested in construction, and that needed for decommissioning and waste management - even before considering the energy needed to make glass...
Glass. You avoided saying that the "amorphous" structure of glass is actually that of a liquid which has been chilled quickly to below its "melting point", retaining its liquid structure even though in a solid phase.
However that solid has characteristic physical properties. Notably low "creep strength". Over a long period of time, glass flows. It is a commonplace that window glass in ancient buildings is seen to have dramatically thickened at the bottom - flowing under its own weight. The hotter it is, the more 'runny' it is. Any glassified radioactive waste is still going to be radioactive - metaphorically and literally "hot". And so is not going to hold its shape over 200,000 years or so.
These are long timescales. Considering that humans are thought to have learnt to talk about 50,000 years ago, 4x that into the future is a *very* long time for humanity to have to guard our mess.
But, I don't have any information at all on the physical properties of any specific glasses made with radioactive waste. Do you?
When I was shown round Windscale/Sellafield, (more than 20 years ago) I was told that glassification was something they hoped might be a practical possibility in future.
Do you have references to this being a practical technology, in use today in the civil nuclear power industry?
I understand that there is a plant at the US's Savannah River "Defense Waste Processing Facility" which is due to take another 25 years to glassify the waste already on site from nuclear weapons manufacture. And that a plant under construction at Hanford, again for dealing with weapons waste and costing now nearer $7billion than the budgeted $4billion, was due to start operation in 2007.
It seems it is late, over budget and only a fortnight ago there were calls in Congress for an audit of the project - the largest single federal construction project...
https://seattletimes.nwsource.com/html/politics/2002351617_hanford29m.html
One clear implication is that this technology is so expensive, in capital and operating costs, that it is uneconomic in the civil industry, both in financial and energy terms.
I think it would be good for those unfamiliar with nuclear waste management issues to have a look at https://www.hanfordwatch.org/
Especially before comparing such issues to the disposal of coal ash, as that would be so inappropriate as to make one look very foolish. |
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Jb
Joined: 08 Jun 2005
Posts: 7761
Location: 91� N
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| Posted: Wed Jul 13, 05 10:19 am Post subject: |
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Well there are so many points there its hard to know where to start. So this answers your points in pretty much the same order in which you raised them.
First a trivial point - I didn't raise the point about the amount of radiation that leaks from an operational nuclear plant being less than that from fossil fuel, that was raised by Northern_Lad, so accusing me of creating a straw man argument is not only wrong but aiming at the wrong target completely!
Just as you think I am wide of the mark I think you are wide of the mark; a clear sign that we are not even debating on the same ground. I argue that the total emission and damage caused by nuclear power is less than that from fossil fuel when one considers the volume and impact of both their radioactive and 'normal' waste products and byproducts from mining, construction, transport etc. From your post I get the impression that you focus on the radioactive waste products and accident risks, clearly important but only part of the problem.
You express concern about the "risk of an unplanned, uncontrolled release of radioactive material" but omit to mention the planned deliberate dumping of millions of tonnes of waste from fossil fuel on a regular basis. Somewhat similar to the public reaction to rail disasters at which point the public demands billions be spent on any spurious safety feature and cheerfully ignores that fact that more people die every day on the road than die in a year on rail - most people are very bad at assessing risk and concentrate on the big consequence rather than the frequent small incidents.
The net energy argument that the energy cost of construction, decomissioning and waste management count against the energy production has some value but the same argument is also true for fossil fuels with higher values for fuel production and lower for decommissioning.
Glass does not flow in the manner you describe, it's one of those urban myths that old windows illustrate the 'flow' of glass by being heavier at the bottom, if it did then the examples of roman, greek and even egyptian glass tht we have would be puddles and not antiques. Old windows could not be made perfectly flat and it was more stable to install them with the heavy end at the bottom. Glass does 'flow' but then again so do many other materials which people have no problems regarding as solid, gold and lead for example also flow and have viscosities considerably lower than that of glass. Having said that it does not matter if the glass does deform as long as it remains solid which short of trying to store it in a volcano will be the case. Whether it retains a specific exact shape over 200 000 years seems a rather arbitrary figure to pick. I know 'guest' raised that value but it has no particular significance for nuclear processes (a rather crude guide would be that if the waste is highly radioactive then it won't be for long and if its going to be radioactive for that long then it will be low level waste) and it is dwarfed but the timescales over which glass remains stable.
I don't have any current references to vitrification in the nuclear industry, although a quick google turns up https://www.geomelt.com who run a commercial service doing exactly this. This is a technology I haven't had to consider since 1990 when I was working on a DoE contract for Nyrex investigating long term storage options and sites, even then vitrification wasn't my speciality which was groundwater flow simulations and decay chain modelling for 'conventional' containment structures.
On two points I agree with you. Site contamination does create problems, while we can process the contents of the containment vessel there is a basic problem in how to deal with the containment vessel itself (a bit like how does a cat clean its tongue). Secondly I would definitely agree with you that I think it would be a good idea for those unfamiliar with nuclear waste management issues to study the issues first to avoid, as you say, looking foolish. |
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nathanbriggs
Joined: 23 Mar 2005
Posts: 35
Location: Chester
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tahir
Joined: 28 Oct 2004
Posts: 45674
Location: Essex
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Jb
Joined: 08 Jun 2005
Posts: 7761
Location: 91� N
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Blue Peter
Joined: 21 Mar 2005
Posts: 2400
Location: Milton Keynes
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dougal
Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
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| Posted: Mon Jul 18, 05 6:36 pm Post subject: |
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Fusion is a "reality" in the sense that we can make the reaction happen.
BUT it isn't a practical, let alone commercial, means of generating power - at least not yet awhile.
We *can* make an H-bomb (a Hydrogen fusion weapon). However, human technology does not (yet) extend to containing that reaction while extracting more energy than is used to contain it... (well, AFAIK, not for longer than a tiny fraction of a second.)
I believe JET holds the record for fusion power output, 16megawatts for two minutes - unfortunately that was only 70% of the energy *input*...
While fusion is what powers the sun, there's an awful lot that is unknown about just how the sun 'works' - for example, the cause of the 11 year sunspot cycle.
There has been a certain amount of political manoevering as to where the joint international research group's next fusion reactor project should be sited. Britain, through the EU, is contributing to the project costs, and the research efforts, but its France that is hosting this construction.
This project, ITER, should be capable of a 500megawatts output - but it is still thought that "Although that is on the scale needed for a power station, there will still be technological issues to address to produce steady, reliable electricity, so it is anticipated that a prototype power station will be needed after ITER. Electricity generation is expected in 30 to 40 years, depending on how focussed the research and funding decisions remain."
source https://www.fusion.org.uk/faq/answers.html
And the design life of a fission power station is about 25 years... hmm.
My perception is that all the major projects over the last 50 years have been heralded as being 'hopefully the last one before a prototype production reactor can be designed. From ZETA to JET, it was the same story.
It would be wonderful if it were true this time.
But my expectation is not great. The deeper the knowledge of the problems, the harder they seem, and the bigger a research machine must be.
I am not holding out great hopes for the technology proving 100% Green, either.
The question is as to what other reactions and processes would occur in whatever the final machine might be. The question arises as to the extent to which the production of free neutrons, which when captured in the materials of the plant would then produce unstable isotopes - radioactive waste.
The official line is " The radiotoxicity of a fusion power station's waste materials decays rapidly, and they present no accumulating or long-term burden on future generations. They would not need guaranteed isolation from the environment for very long timespans."
ie, not *entirely* clean, but nothing like the problems of fission. And its not clear that the plant decommissioning is being considered.
Source: https://www.fusion.org.uk/focus/index.htm
And the more effective experimental fusion reactors (TFTR at Princeton and JET at Culham) have used a mixture of Deuterium and *radioactive* (12.5 years halflife) Tritium (the even heavier form of Hydrogen) which is *not* extracted from water, but produced by irradiating Lithium (metal) in a nuclear reactor...
And the new ITER project to be built in France also uses (radioactive) Tritium as fuel...
So fusion, if it can be harnessed, is for the future, and it is misleading to present it as being perfectly clean, emitting nothing but a whiff of harmless Helium.
For the present, and immediate future plans, we seem to face the practical choice between more fossil carbon burning and more nuclear fission. Global warming or nuclear waste. The Devil or the Deep Blue Sea. (I really don't see power station ash as having any sort of comparability to those major strategic problems.)
To my mind, the only justification for saying that nuclear might be the "least worst" is that the problems can be contained by active human management. Unfortunately, the problems *require* active human management to be contained... and that costs money. Hence the frightful question of how clean one can afford to be. And the resulting ultra-long-term pollution seen in discharges from Sellafield.
Fission waste material is vile stuff.
And the most that you can hope to do with it is to contain it.
A nightmare both of conventional chemistry and radiochemistry - which is alchemy made real, transmutation of elements. It is **not** just chunks of dense metal that might glow a bit but aren't going anywhere. Metals turn into gases. Which can turn back into different metals. The products react with each other. The radiation damages the containment, and accelerates processes such as corrosion and weld embrittlement. And it still generates heat.
There's no practical means of dealing with it other than to put somewhere safe and leave it well alone (other than replacing its containers before they leak). Glassification is one possibility for future containment. (BTW Geomelt's business seems to be dealing with contaminated soil, potentially with some radioactive contamination, not high level fission power station wastes.)
The French thought they could transmute the stuff into stable isotopes, but have now shut down the Phenix and Superphenix reactors built for that purpose...
Although fission is basically the decay of Uranium into elements of *smaller* Atomic Mass, that's not a simple process. Elements with *higher* Atomic Mass are also being formed by decay fragments merging with whatever they happen to bump into. That's how Plutonium is formed, it has a higher Atomic Mass than the original Uranium.
Side note: the likelihood of capture (the "capture cross section") is measured in wonderfully named units - Barns - as in "hitting a Barn door" - really!
Its not terribly hard to chemically separate out the Plutonium - awkward because of radiation, not chemically difficult. But what you get ain't much use for a fission bomb, because its contaminated with the 'wrong' isotopes of Plutonium. And it is hard to separate the isotopes, just ask Saddam. However, if you wait a *very* long time, those "wrong' ones will have decayed away, and you'll be left with only the right sort of Plutonium to make a bomb out of. This is the risk that is referred to as nuclear waste dumps becoming the Plutonium mines of the far future.
Its arguable as to whether or not Plutonium really is the most toxic material known to man, Botulinum toxin takes about the same number of microgrammes to kill you. But there's Tonnes of Plutonium needing to be put out of harms way. And as little as 10kg in one lump makes a critical mass, emitting lethal quantities of neutrons even if it doesn't explode...
Fission waste is really horrible stuff, don't believe otherwise.
My personal hope would be that the need for new generating capacity could be minimised by more agressive efficiency and conservation measures, expanded use of biofuels, and an appreciation of the benefit of diversity in harvesting renewables.
Personally, I'm not worried by the proximity of a British nuclear power station, (not quite so sure about the French ones lining the other side of the Channel), but I certainly wouldn't want to live anywhere around Sellafield.
And, if it came to a choice, I'd be prepared to sacrifice quite a few estuaries and lochs, as well as fine moorland and marine views, to obviate the need for Sellafield at all. |
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Jb
Joined: 08 Jun 2005
Posts: 7761
Location: 91� N
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dougal
Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
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| Posted: Tue Jul 19, 05 10:46 am Post subject: |
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| JB wrote: |
| dougal wrote: |
| Personally, I'm not worried by the proximity of a British nuclear power station, (not quite so sure about the French ones lining the other side of the Channel) ... |
What do the French do with their reactors that the British don't? |
I am proximate to a pair of AGR reactors at Dungeness 'B', and the shut down pair of Magnox reactors at Dungeness 'A'.
They don't worry me at all really. They are pretty safe designs, my understanding being that, in extremis, convective cooling alone, even with air rather than CO2, should keep temperatures below the level at which the fuel pins might leak. And Magnox was actually derived from the first air-cooled designs anyway. Safe, unexciting generating performance, albeit quite efficient at producing plutonium...
There's a bunch of elderly PWRs at Gravelines. |
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jema
Downsizer Moderator
Joined: 28 Oct 2004
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Jb
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Blue Peter
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