417 posts • joined Tuesday 2nd November 2010 18:48 GMT
Gundersen once actually did an SFP-related project, back in his nuclear industry days...
He was responsible for deisgning the storage racks for the SFP at Vermont Yankee. the fact that they were wrongly sized and didn't fit in the ponds was largely repsonsible for why his nuclear career ended quite so quickly.
Re: Sievert calculation assumptions
I can't watch the video (I'm at work), but I do know of a few things wrong with other Starr's claims...Quite a few things...first the claim that Caesium bioaccumulates. It doesn't - it basically mimics potassium in the body, and equilibrium is reached quickly. Which also puts paid to the idea of "biomagnification" (which is a term I've never heard previously). It's worth noting the actual measured levels of 134Cs and 137Cs measured in Fukushima evacuees:
Thosse levels simply aren't consistent with accumulation. What's truly wierd is that the graphs Starr shows in the paper
show exponential decay of body burden following a single ingestion, and the reaching of an equilibrium in the case of chronic ingestion - both of which tell you that metabolic processes are removing Cs (otherwise the level would stay constant from a single ingestion, and continue increasing if there's chronic ingestion).
The interesting thing (which rather puts paid to the "magnification" idea is that the highest internal doses are from people who are eating large quantities of traditional mushrooms, not from anything higher up the food chain...
He then wanders off into the rather wierd territory of a claimed syndrome called "chernobyl heart", where apparently radioactive species of Caesium cause heart arrythmia, but non-radioactive isotopes don't - which is a complete negation of everything known about chemical processes!
We then wander off into conspiracy theories about the researcher's work being suppressed...and worse he starts quoting from the utterly discredited Yablokov studies (the ones that reckon incresaed rates of cirrhosis in the Ukraine is a result of radiation exposure, not because alcohol consumption went up after the fall of the USSR).
Re: Wait, what?
" It turns out the person in charge of the plant at the time of the accident was there because it was his turn to have an upper-level job. Japanese bureaucracy and all. He had a degree in economics or something else just as useless. Did he cause the accident? No. He just didn't know what he was doing "
I realy can't be bothered picking through the farrago of rubbish you've listed in that post, but the slur against the Plant Director can't be let go.
The plant was managed by a gentleman called Masao Yoshida. He was a fully qualified engineer - his degree was in Nuclear Engineering from the Tokyo Institute of Technology, where he also studied at post-graduate level - and spent his entire career in nuclear operations
He's probably the hero of the accident - had Naoto Kan not interefered and let Yoshida run things from the start, there's probably not even have been severe core damage. Yoshida wanted to vent the overpressures in the containments (whtough the filtered stacks) early in the process but was banned from doing so until Kan had held a Press conference. He also took the decision to depressurise the reators, and inject seawater while TEPCO dithered, and Kan tried to ban it.
"They are estimating around 8% of Northern Japan will be completely uninhabitable for the next 30 years"
i've no idea who "they" are, but if that's what they're saying, they're talking drivel
the natural background in cornwall is about 0.9mSv/hour. If you take that as a threshold, the land area contaminated at that level is a few hundred km2 - and the levels are falling as the 134Cs decays (a 2 year half-life).
Re: Not looking at the full picture
"Also, a very big problem with nuclear is the amount of expenditure required on the plant after it reaches the end of its useful life. That isn't something we can rely on the private sector to do."
so, you make them pay a certain amount into a "sinking fund" per kWh sold. And no, it's not that expensive to decommission plant. The ten or so LWRs that have been dismantled and their sites cleared in the US have cost between $700 - $1000 per kW of capacity, falling with experience and less the larger the plant.
And no, it's not "hundreds of years" to clear the site, at least if oyu don't do silly things like build masive gas-graphite plant. "Trojan" - an 1100MW PWR in Oregon took nine years from colure to the site being declared available for other uses.
Re: The Tooth Fairy and Molten Salt Thorium Reactors
"China and India are going ahead with this tech"
No, they're not.
first the Indian programme. That's baed on two technologies - first is a mildly adapted version of their "PHWR" design (based on the old CANDU). It uses conventional solid fuel with additional thorium rods in which 233U is bred. There's no molten salt involved at all - the moderator and coolant are heavy water. In the longer run, they propose to use throium in a sodium-cooled fast reactor.
Second, the Chinese prototype that's under design doesn't use molten fuel either. It's going to use "TRISO" type uranium carbide fuel in a bebble bed design using molten salt only for coolant - which rather precludes it being used as a breeder (the downside of TRISO is it's all but impossible to recycle, and hence any "bred" material isn't accessible". The idea is a small proportion of thorium in the fuel will breed, and extend the life of the fuel in the reactor, much as was done in the trials at Shippingport in the later 70s/early 80s.
By the way, China certainly doesn't intend to have an "operational plant" by 2020. They're saying they intend to have a non-power producing laboratory demonstrator by then. THe earliest they think they might commission a commercial demonstrator would be 2035.
Just for scale, they're proposing to spend about $200 million on that technology by 2020. They're going to spend a couple of $billion on HTGR demonstrators. About $10 billion on LMFBRs (they're buying two BN-800s from the Russians). And at least $200 billion on AP1000 LWRs and derivatives thereof.
Re: Oh dear...
"Lewis may have hit the jackpot this time."
you - and whoever wrote the story you linked to - have about as little idea as each other.
Let's run over the basics....
the fuel rods that are to be removed are in the spent fuel pond of reactor 4. The postponement has been requested by the new Japanese regulator because it wants to observe a rehearsal of the handling procedures for the casks into which the fuel will be placed.
the leakage point that's been identified is in reactor 1.
So, the fact that the story suggests the former is somehow the result of the latter basically shows the ignorance of the author...
as to the "bent" rod. It's a rare, but by no means unknown occurrence in refuelling. The assembly in question was loaded into a perfectly stanadard holding rack within the pond, so hte bend can be no more than a millimetre or two over a metre of length.
Re: Oh dear...
Sorry, you think it's news that water's flowing out of the containment?
Given that the've been injecting a about 5 cubic metres/day invot each reactor since the accident, it's not exactly a surprise to find that it's passing out somewhere - all that this story is telling us is that the flow path (or at least a significant contributor to it) has been located.
If anything, this is a positive development - rather than some sort of gross breach of the containment, this looks relatively easily remedied. Which will make the task of flooding the containment and removing the damaged fuel rather easier.
Re: It's not over yet
"Global Research", eh?
I do love it when people post links from quite such flaky places. If you follow up with something from "Rense", we can then have a think about what you can do to make it a hat-trick...
Re: Humans aren't responsible enough for nuclear power
"I think you'll find that radiation is more harmful to young children than the elderly"
No, it has pretty much the same effect per unit dose...
Re: Well, two thoughts...
"The uranium enrichment processing alone has created some of the worst polluted industrial areas of the planet. "
I used to live about 10 miles from the UK's main enrichment plant at Capenhurst, It's in Cheshire, Close to Ellesmere Port. Here's the Google Maps link
Looks rather green and unpolluted to me.
Here's the French equivalent - "Eurodif" at Tricasitn in South-West France:
A bit browner (well, it is southern France) but still hardly a polluted wasteland.
" Once used, the nuclear fuels become energy sinks from the power grid, requiring continuous cooling for years afterwards during the fuel's initial decay stabilization"
within three years of being removed from a reactor, it's perfectly routine to move fuel into air-cooled natural storage circulation - a PWR or BWR assembly is making well under 100w of decay heat.
" I would LOVE to have someone here prove that the nuclear power plant decommissioning process isn't as onerous as it truly is"
you do know it's now been done at least a dozen times with LWRs in the US; here's a link to the highest profile example:
"Decommissioning is the process of removing the radioactive material from the site and restoring the site for other uses. PGE built Trojan on what was an already an industrial site before PGE bought it. Now that decommissioning is complete, the site is safe for any type of use, including industrial, commercial or even residential....
...The process took about 9 years. Trojan began decommissioning in earnest in spring of 1996. They completed decommissioning December 2004."
I have a sneaking suspicion you've not the faintest idea about what you're talking about.
"All of which ignores the risk that despite the billions spent, fusion may never work economically."
Certainly I'm not seeing much indication that we're withing half a century of commercially viable fusion power - ITER will probably demonstrate some form of sustained burn, but it's a long way from being a demonstrator for an actual generating plant - for a start, it lacks any real means of taking the energy derived from the fusion reaction (which is mostly in the form of high energy neutrons) and turning it into useful heat.
The reality is, even assuming ITER works, it'll take maybe 10-15 years to gain that experience and turn it into a design for a true demonstration generating plant, 1--15 years to build that, then a decade of oeperation - at which point we might JUST be ready to try a commercial demonstation plant.
there 's a difference between "peak" and average, of course....
"Cobblers. Hinkley C is rated at 3.2 GW. Peak demand is 60 GW, so you'd need 19 similar sites to support current peak UK demand, assuming that demand doesn't climb with economic recovery and our rising population."
Average demand's about 45GW - we see a 55GW peak on maybe 2-3 days every other year or so. and minimum demand is about 20-25GW. So, to meet average demand would indeed take about 14 Hinkley C's
Now, enthusiast as I am for nuclear, I've better sense than to suggest using it for exploring the further reaches of the demand curve - it's economics are wrong for that; given that fixed costs are high but marginal cost of generation is negligible, it makes sense to utilise nuclear in a mode where it's kept operating near full capacity continually - just as Sizewell B's been run.
A smart policy would aim to keep nuclear covering baseload (so that miminum 25GW), plus some of the predictable amount of daily variation. 30-35GW (9-11 Hinkleys) would be a sensible sort of number, with CCGT covering the rest.
Incidentally, unless regulations have changed remarkably since my ime in the power industry, larg thermal plant (i.e anything using HP steam) has to come down for extended inspections every 2 years; vcertainly having worked on Eggborough, the maintenance of the station was pretty much planed around those outages - it was the only chance to do remedial work on things like the ball-mills, a turbine overhaul and so on.
Re: Quite right too....
The strike price deal for Hinkley C - £93/MWh - drops to £88.50 if Sizewell C's built. Which implies a unit price of £84/MWh expected for Sizewell C.
Which in it's turn implies a 15% or so unit cost reduction if you assume the cost of nuclear ouput is 80:20 capital versus operations.
"This is considering that about 800-900 square miles of Japan is now uninhabitable for at least a generation"
800-900 square miles uninhabitable?
you must be looking at different maps to me. Taking that as a semicircular area centred on the plant, that'd suggest a radius of getting on for 20 miles is "uninhabitable" - which is utter tripe.
Taking the most recent report I can find (from March), the area that has more than the sorts of background radiation you see in Cornwall is a corridor about 2Km wide and about 10km in length running North-East from the plant. Or, about 1% of the area you suggest.....
" Plus the waters off Fukushima and northeast Honshu are now irradiated to the point that local sea life is functionally inedible"
so far as I know, the only sealife that's now over even EU thresholds is stuff like sandeels caught within the station harbour.
Even more tripe -
Re: In other news... first new UK nuclear power station approved
"and with the idiotic decommissionings of LCPD you can be sure no good will come of it"
that I part company with you on - the LCPD adresses SOx, NOx and particulates emissions. The fact that we've screwed up on timing is one thing - retiring plant that can't be economically retrofitted with control kit for those can't be a bad thing at least in principle.
Re: In other news... first new UK nuclear power station approved
"But in general it is always windy somewhere, so as long as you spread turbines across the UK, you are OK. The same is true for tides, when it is low tide in one place, other places would be at 100% capacity."
The UK certainly isn't big enough to get significant dispersion as far as wind is concerned - in fact, even across North-West europe, there's still significant coupling (all our weather systems are driven by the same Atlantic systems).
And with tide, although there's some staggering, it's not that great - after all, it's the same moon that's pullling for all of us.
The bigger issue with tide, tbh, is sheer cost. It's bad enough on the Severn, which is about the best site in europe - where £20-30Bn for an average output is bad enough. But that's cheap compare to other sites, resulting in probable costs in the area of £300/MWh.
Tidal output is broadly proportionate to the tidal range - up to 7 metres on the Severn. Costs are mostly driven by civil engineering costs in building the barrage.
Think about doing the same on something like the Mersey or the Wash, and you're doubling the size of the civil works to move similar volumes of water, and half the tidal range. Tidal is VERY site conditions dependent.
Re: In other news... first new UK nuclear power station approved
"Actually wind power is as predictable as tides, you know what weather is coming days ahead and take appropriate action"
Not according to National Grid, based on experience to date:
"In our previous consultation, it was explained that we had experienced changes in
wind output of 50% over 2 hours against our current relatively low levels of wind
penetration. Similar changes in output have been seen in continental Europe where
there is a higher level of penetration with greater dispersion. It is necessary to ensure
in the event of a loss of wind output, sufficient reserve is available in appropriate
timescales to cover such an eventuality. .....
..... the forecast aligns with actual generation for a majority of the
week. However, within each week there is one day where the error is significant.
It is apparent from Figure 2, that in this instance the forecast profile for 26-February
was consistent with the actual output, but the magnitude or level of output was over
forecast by between approximately 30% and 80% over the 26th February 2010....
...An additional operational challenge that will increasingly present itself in the future is
that which can be termed wind cut-out. This occurs when wind speeds are sufficiently
high that wind turbines automatically shut down to maintain structural integrity.
6.19 The speed at which this happens will vary depending on the location and size of wind
turbine, although on-shore turbines tend to cut out at wind speeds of ~25m/s.
6.20 National Grid has recently witnessed such an event, when wind speeds in Scotland
were sufficiently high to create this phenomenon. National Grid does not currently
have the wind speed data for all wind farm locations; however, Figure 5 illustrates the
effect witnessed on 3-February 2011.
6.21 The effect of cut out can have a significant impact, not only due to the resultant loss
in expected generation but also the speed and additional uncertainty that can arise
when production starts again as wind speed drops. In the example shown above, a
significant decrease in generation occurred when wind speed exceeded 25m/s, which
resulted in a reduction of ~50% of the wind production over the course of an hour. As
wind speed dropped below 20m/s, output was restored before a further loss a short
not THAT predictable, then.......
Re: In other news... first new UK nuclear power station approved
Offshore turbines are located on shallow water banks for exactly the reason that they can then have proper foundations.
there are proposals to build floating systems, but so far they're just that or an ocassional prototype. All the actual commercial developments to date, and that are currently in the application process use grouted foundations of one sort or another.
Re: Pity no-one did the maths......
Always amusing to see downvotes, but no comment arguing the point made.
I can only assume it's done by people who don't like the message, but lack the firepower to make an argument against what was said!
Well, I used to live three miles form Heysham, and I now live about 7-8 miles from Aldermaston and 10 or so from Burghfield - not power plants, but sites with rather a lot of enriched uranium, plutonium and tritium around. I can't say any of them causes me the slightest worry.
I also spent a few years living within five miles of Drax - which both from particulates and from the regular deposits of wind-blown fly-ash probably did far more damage to my long-term health.
Pity no-one did the maths......
One thing that was notable in the Press coverage, (and, to be fair, the TEPCO intial press release) is that no-one bothered doing the numbers on how hot the pools were likely to get (not least since they'd have to be boiled to call cause a problem).
all of the following, btw, is the sort of stuff you'd be taught in the first term of the heat transfer course of an engineering degree (or cold work out from A level physics), so we certainly aren't talking rocket science....
First off, how much heat is being produced. The Unit 4 SFP is the "hottest" so we'll wok around that.
At the time of the accident there were 784 older assemblies in there, making about 400KW of heat in total, and 584 "new" assemblies which had been out of the core for about 2 months, making about 1.87MW.
For the newer fuel, taking an initial average production of (1870/584) = 3.2 KW/assembly. but that was at the time of the accident. The standard decay curve for spent fuel is shown in the slide headed "Decay heat in Light Water Reactor Fuel) from
60 days is about 6*10^6 seconds. We're now at about 800 days from the fuel being removed from the reactor, so about 7*10^7 seconds. Using the ratio between 10^6 seconds after shutdown and 10^7 seconds (which will be near enough for a rough calculation), that says the newer fuel assemblies will be making about 1/3rd the amount of heat they were at the time of the accident. So about (3.2/3=~ 1000 watts each).
The older ones will also have decayed, but not by much - so we'll ignore that.
total heat production will therefore be about 1MW. (584KW from the newer fuel, 400KW form the older)
OK, what's the heat balance...
The pond contains about 1240 cubic metres/tonnes of water - there's also racking etc. in there, but we'll ignore that for the sake of simplicity.
If it's heating that mass of water through 1C takes 1.24*10^6*4.2*10^3 joules = 5.2*10^9 joules. 5.5C in 15 hours is 1*10^-4 C/second.
So, 5.2*10^5 joules/second (or 520KW) was going into heating the water on average over the time that the active cooling was off. The rest is being lost to ambient (in the absence of forced cooling) - so about 480KW, or about 50% of the total for this rough calculation
Heat loss from a fluid surface (in the absence of boiling), and by convection/conduction through the walls of the tank is proportional to the temperature differential to ambient.
If ambient is about 12C, then the average delta so far has been about (30-12) = 18C. 2 times that is 36C, which suggests the whole system would be in equilibrium with the water at around 48 - 50C so, no mass boiling.
You'd nee to periodically dribble some water in to make up for evaporation - but that's about it. Any boiling seems highly unlikely.
Re: Failure modes to be considered...
"I can't say how exactly BN-800 is designed, but I'm pretty certain it's nothing like VVER-1000"
It's certainly not anything like VVER-1000. It's a sodium cooled fast design, VVER is the Russian for Vodo-Vodyanoi Energetichesky Reactor, which translates as Water (cooled), Water (moderated) Power Producing Reactor.
there was no explosion at TMI.
There was some panic at the time (including Jimmy Carter), because there was hydrogen generation inside the RPV, from the reaction between hot zirconium and steam. It's not catalytic, though, it's a prefectly ordinary oxidation of the zirconium and H20, as below
Zn + H2O -> ZnO +H2
Which should give you a clue as to why there was no possibility of an explosion inside the RPV - there was no free oxygen with which the H2 could combust.
At Fukushima, the H2 was vented into the reactor buildings (instead of what should have been done, which was to vent it through the filtered exhaust staccks to atmosphere - mostly becuase Naoto Kan, the Japanese PM over-ruled the site engineers who'd wished to start venting early in the process - Kan banned it until he'd been able to hold a press conference!).
Obviously, O2 was available in the reactor buildings. BWRs run with an inerted atmosphere inside the primary containment, but not the secondary containment/reactor building. PWRs are built differently - the primary containment is much larger (pretty much equivalent to the BWR reactor building), and it's now usual practice to run with an inerted atmosphere except when personnel access is needed.
And no, water's not "sprayed" into BWRs in normal operation. Primary circuit water comes back to the RPV from the turbine condensor, enters as a flow on the outside of the "shroud", flows down outside the auunulus formed between the shroud and RPV wall to the bottom head, where it turns and flows up (as bulk liquid) through the core. The rate of flow, and the resultant height of the water column is used as a means of controlling reactivity. As it flows up through the core it boils in a perfectly normal nucleate boiling process, such that there's an increasing void component as you move up through the core.
"Flash Boiling" is a bit of a myth. Provided the water's able to wet the fuel surface, there's usually good heat transffer and there's no excessive pressure generation. What is a problem is a phenomenon called "film boiling", when a layer of steam gets form on the outside of the fuel, preventing wetting, and reducing heat transfer. It's a very transient issue - any roughness at all on the fuel can surface, or turbulence in the rising stream and the film collapses in milliseconds.
Re: Thorium Cycle
The obvious comment would be - how would you transmit the power back to where it's needed, i.e. here?
You do raise some interesting points, though. But first, once small correction. The in core time for every Pebble bed design I've seen is in weeks or months (you'd need significant dwell time to get useful levels of transmutation). What you wouldn't want is the sort of dwell time for fuel needed for LWRs - 18 months to 2 years.
As to the dwell time outside the reactor for 233Pa to decay to 233U, 45 days would be insufficient. Taking the old "ten half lives for 99.9% decay" rule, from memory the 233Pa half life is about 30 days - so, something in the order of 200-300 days to get reasonably pure 233U.
There's an additional aspect to this, which is to do with the nature of the fuel for pebble bed reators and its associated economics. The outer layers of PBR fuel is an extremely tough carbide ceramic (and the fuel inside is granules of uranium carbide in a carbon matrix). It's basically reprocessing-proof.
Which means if you don't have some fertile material in there, and sufficient enrichment that the fuel can carry a large burden of accumulated poisons, you can only use it on a once-through cycle and a burn-up to perhaps 50-60MWd/tonne.. That's probably acceptable at the moment, when uranium prices are low, but were they to rise significantly, or other technologies to establish better economy (IFR can easily run to an equivalent of 3000MWd/tonne).
So, if we're going to see commercial deployment of pebble bed designs, they'd almost certainly have to have soemthing of what you suggest - "seeding" with thorium alongside high uranium enrichment, and also loading the fuel with burnable poisons to supress reactivity in the earlier parts of the cycle.
BTW, there's another challenge on operating any reasonably conventional power source on the moon - any guesses what it might be?
Re: Failure modes to be considered...
One other oddment. There's now been a pretty comprehensive survey of the suppression torus of R2, - the one that was supposed have been damaged by a hydrogen explosion.
gives you the inspection summary.
It's been focussed on the vent pipes that connect the torus to the drywell. These have a large steel bellows arrangement to accomodate thermal movement, and are the weakest part of the overall system. They also have carious rubber and metal seals.
The striking thing is, five out of six have been inspected (by robotic camera), and so far, none has shown evidence of leakage.
This is the radiation survey I mentioned above:
And this is the water sampling exercise.
Note how different it is to the water in the turbine building - LOWER levels of radioactivity, and lower salinity. It suggests that even in the early stages of the accident, when seawater was being used to col the reactor, water wasn't tending to flow from the RPV to the PCV.
That suggests a number of things - one of which is that the flow path for the water that's now being used to ccool the fuel is bypassing the PCV, and going into the reactor basement directly - probably through failed seals on something like the recirculation system, parts of which sit outside the PCV.
And that's NOT compatible with the idea that the bottom end of the RPV is grossly damaged. Or that PCV integrity is particularly bad - both of which should make fuel removal much easier.
Re: Failure modes to be considered...
Actually, there was water in the the lower parts of the Fukushima containments ("PCVS"s) if/when fuel exited the RPVs.
Before I go into that, just one point. There's a general assumption that fuel "melted through" the RPV bottom heads - however, what's emerging as instrumentation's introduced into the PCV's doesn't actually support that, or the idea that the PCVs are damaged to anything like the degree assumed.
On the first point, the most striking part is that in October last year, TEPCO introduced a radiation detector into the R1 PCV (R1 is generally assumed to be the worst damaged). They plotted radiation levels at various heights above the water level in the bottom of the PCV.
If the fuel had exited the RPV, the radiation levels should rise as you get closer to the base of the PCV - obviously, since the fuel would be the main source, and if the fuel was in large measure at the bottom of the PCV (even if part penetrating it) it'd be hottest nearest to the fuel.
In fact, that wasn't the case. Radiation levels were highest roughly on a level with the bottom of the RPV. Levels fell as the detector was moved lower into the PCV. It was LOWEST at the surface of the water pool in the bottom of the PCV.
The only sensible interpretation of that is that at very least the overwhelming majority of the fuel is in the RPV bottom head. But that's to be confirmed....
It was also interesting that the isotopic composition of the water in the bottom of the PCV was markedly different from that in the reactor basements - suggesting that the flow-path isn't RPV -> PCV -> basement.
Back to the water.....it's true the drywell wouldn't normally have water in it - but there was serious overpressurisation during the accident which would have buggered lots of seals, and have water flowing anyhow. There was also an issue that the suppression torus became overfilled, probably to a degree there'd have been back-flow into the drywell
Re: Such a shame...
The efficiency of a Stirling engine is still limited by the good old issue of peak temp relative to the temperature at which heat is rejected to ambient. THats fundamental/inherent.
IMO, stirling engines do have their place - but in those applications where the available heat source is comparatively low temperature. However, they don't as a rule look economically attractive when higher temperatures are available - or at larger scales.
I'd not sure you'd be about to convince me that we're about to see gigawatt-rated stirling units - afer all, reciprocating units really don't look good in any form in the megwatt and higher range.
Re: And how do we get at the existing stuff that's buried in various sealed sites?
There aren't any "sealed sites".
The world's first geological repository is under construction in Sweden, but that's some years away from completion. Pretty much all the waste produced to date remains "above ground". In the UK, France and a few other places, a proportion of the waste is at reprocessing sites (Cap de la Hague in France, Sellafield UK). Even in those cases, only a minority of the waste has been reprocessed, and the fission products/non-fuel actinides separated out.
Outside that, almost all fuel remains at the reactor sites, in cooling ponds (in a couple of cases, it's in air cooled storage facilities - the largest is at the Wylfa magnox plant). In the Us, a lot of fuel has been moved out of ponds into air-cooled storage flasks, also held at individual reactor sites - since the US has failed to move ahead with a repository.
In that latter case, if they'd any sense, they'd simply move those flasks to somewhere like New Mexico, on a seismically stable site with dry weather,
Re: salt plug
But, as I've pointed out before, all the drain-down gains you is that it ensures there's no continuing reaction. You have exactly the same problem of decay heat removal. Which is probably harder with a discrete mass, than if fuel is divided into individual pins (think of the surface area:volume ratio.
Let's just be clear - there was no continuing chain reaction at Fukushima. There was none at TMI.
In both of those cases, the issue was of decay heat removal.
And I'd really not try to "absorb" all the heat from decay. Assuming the average production over the first day of an accident is about 10MW (which is probably optimistic),and that's 860 Gigajoules - enough to raise about 1000 tonnes of steel from room temperature from it's melting point, and then to melt it.
You can't "absorb" the heat - you have to get rid of it to the atmosphere, or to water.
Re: salt plug
It's slightly more complex than that Ru - let's recall we're discussing a mass of heavily radioactive material, that's only pump-amble when heated to something over 400-500C.
And no, I don't think you can make easy assumptions about drain-downs clearing pipework. Recall that this stuff starts cooling as soon as the nuclear reaction is closed down - and you've not a massive temperature range between operating range and solidification (since the meltable plug wouldn't work otherwise).
All of this has to be done technologies that basically involve no moving parts in contact with the actual salt
The thermal stressing implicit in (say) having one end of a heat exchanger at 500C, with the other end isolated from flow, maybe C cooler don't bear thinking about. Once, about 30 years ago I spent an amusing month modelling thermal stresses in the boiler skirt of the proposed commercial fast reactor, during a shutdown transient. it'd shear mild steel, easily. That didn't involve anything so severe as this.
And let's also recall, any pipework failure here doesn't just involve a loss of cooling function - it's spilling actual fuel, in a highly corrosive salt matrix,
"But in a hundred years when the satellites and the models are telling us that the sea levels have risen by a metre"
Actually, about 15cm.
Re: Not going to happen@tony72
Small point of information....
"WInd farms under construction now expect to get wholesale prices of around £45/MWh, ROCs worth around £43/MWh and LECs worth around £5/MWh. "
A ROC is worth rather more than that. They pay out two ways. One is the baseline price, which is what you've got there. The second is the payment from the "buy-out" fund.
Basically, any supplier who can't source enough ROCs pays a "fine" to DECC, equivalent to what the shortfall of ROCs should have cost. This is then divided up by those who have produced ROCs as a credit.
It's usually been worth £5-10 per ROC. Last year was the lowest ever, being worth an extra £3.58.
So the real worth of an ROC is about £46.60.
Re: What about plastics...
It's even more subtle than that....
I once got stuck next to the Tech Director of the UK's biggest plastic bag maker on a flight back from India (oh, the glamour of international business.....).
Most of the material that goes into plastics is used simply because there's not much other use for it. It's not readily crackable for petroleum products, and it's a bit more valuable than it would be just leaving it as part of the Asphalt residue. If the plastics industry didn't buy it, it'd mostly just end up in road tar - as the money is getting the petroleum bits out.
Re: As a few have said, there's nothing much new here....
There's a variation on
"2/. If it was feasible, would it be worth doing? Here its less clear, If it were massively expensive with no hope of getting cheaper, probably not."
that you need to add in - are there alternative technologies that do the same job better/cheaper.
Re: Recycling of ideas
" I'd be more interested in their work if they can substantiate their claims of utility and safety."
How about running the plant at full power then turning off the coolant pumps as a demonstration?
Re: Thorium Breeder reactor
However, 233U is also fissile. Look up the bizarrely named "Teapot" bomb test.
The "prolifeferation-proof" claims for MSR leave me a little cold. It's usually claimed that the 233U produced is laced with a small but significant 232U content, and that this makes the resulting material hard to handle. But, looking at the decay chains, the 232U wouldn't be that problematic - it's it's decay daughters that are more of an issue.
So, first, assuming that there's an efficient Pa extraction process, it's hard to see why there'd be a parallel extraction of 232U - or that the two couldn't be separated chemically subsequently. Second, even if that weren't the case, chemical removal of the highly active daughters should be relatively simple (no harder than conventional extraction of Pu from spent fuel).
Re: @ Andydaws
"Is the energy density of the salt sufficiently high that decay heat is only a limited meltdown/containment failure risk? So passive cooling arrangements and heat sinks are sufficient."
I've not considered density per se - I don't think it's a major driver in this. What I'm working on is a simple assumption that the decay heat removal requirements in toto are roughly similar between thermal designs - which has to be agood assumption. For a 500MWe unit, even assuming a 40-50% thermal efficiency, you're still producing 1-1.2GW at full power. And decay curves give us 7% or so of full power heat production on shutdown ((70MW or so) decaying over the first day to 20MW or so, and down to 10MW in another couple of days.
That's a lot of heat to lose - and without making the drain down tank huge, or of a geometry that'd be hideous to shield, I really can't see passive air cooling doing the job.
There's also a bit of a misunderstanding about the Oak Ridge reactors. They were extremely small - 5MWTh at full power, if I recall rightly. It's also worth understanding that yes, they were drained down - but also that they operated only intermittently. They also lacked any breeder blanket/salt arrangements, and (I think) had nothing like the full fission product extraction functions that would be needed in a commercial design. And, let's recall - radiological standards in the fifties were by current standards hideously lax!
I agree re the advanced fast concepts - and in all honest, see concepts like IFR as far more developed and ultimately viable that MSR. For the longer term, I suspect that the lead-cooled designs will emerge as leaders - concepts like BREST-1200 using online electrochemical processing of nitrate fuel, and operating at 700--800C have to be attractive. Yes, there are coolant chemistry issues (to do with the behaviour of oxygen in lead), but they look minor compared to the chemical challenges of MSR!
Re: Blimey - Sounds Too Good To Be True - Help Please.
how long have you got....?
basically, it's the same as any other reactor - neutrons arise from fission events, then get absorbed into other fissionable nuclei, which fission and produce more neutrons than they absorb - the idea being you balance the production of neutrons, their absorbtion into fissionable nuclei and other parasitic materials, and losses by leakage out of the core.
The graphite is there because uranium nuclei are more prone to absorbing neutrons moving at around 2200m/s (thermal energies) than they are ones that have just been produced from fission at much higher speeds ("fast" energies). The neutrons bounce around hitting carbon atoms in the graphite (which doesn't absorb them) losing a bit of speed with each collision until they've slowed to thermal levels f energy, and will then tend to be absorbed and cause fission.
Re: Looks like an update to me, not new
I think you're misunderstanding where Wigner energy comes from. It's not heat storage per se - at least the input energy isn't heat, albeit it manifests itself as heat on release.
It's actually energy that's arisen from neutron collisions with the carbon atoms of the graphite crystalline matrix - basically, atoms that have been "knocked out of place" and have re-bonded in distorted patterns. That being the "annealing" point - it's when temperatures rise high enough that those distorted bonds are broken, and the matrix "snaps back" into it's lowest energy alignment state.
SO, unless, you happen to have an intense neutron source to hand, and a material that allows various forms of cross-bonding, wigner ain't going to happen.....
Re: As a few have said, there's nothing much new here....
I've been seeing stuff like that for a good few years, John Smith, and as I said, it's more than a touch naive - and given that we're talking of at least three or four entirely separate physical processes (a spay/sparge for volatiles, vaccum distillation for medium-weight semi volatives, pyrolitics or similar for actinides, and a protactinium extraction process), I think someone's indulging in wishful thinking, if they think a single compact plant will do it.
We've then got minor issues like high-integrity, actively cooled shielded storage for the first two (and probably the space where the protactinium will have to dwell for a couple of years while it undergoes decay to 233U).
And no, simple redundancy won't do it - we're talking highly integrated plant that will be working in direct contact with a medium that's not only laced with fission products, but is in intimate contact with neutron emitters. It'll therefore be subject to significant activation. That's going to mean maintenance access will be essentially zero, unless you allow significant periods to allow activity to decay, before attempting access; which in it's turn means you're not talking about simple duplicate or triplicate redundancy, but manifold. If yuo've ever seen the maintenance access problems on plants like those at Sellafield - which only handle fuel, recall, after a decade or two of decay time, where as this is needing to cycle through the entire fuel load every month or so - you'd not dismiss this quite so casually.
"The design of equipment using molten salt is specialized but not uncommon. ",
However, not at nuclear standards or integrity/reliability. And not dealing with activated products in real time.
"Because the fuel is a liquid the moderator elements are much simpler (essentially rectangular pillars in the referenced report outline)."
To put it delicately - balls. The AGR moderator "bricks" were not notably complex in shape (basically octagonal section blocks with keyways for jointing.. And no, they weren't subject to direct loading from high velocity gas - each fuel channel had an inner liner, and the fuel stringers sit in their own sleeve. Geometry wasn't especially the issue - the reason they tended to distort was that partly there is obviously a neutron flux gradient across the brick. Now, if you think of the scale of an AGR core, and the scale of an MSR core - the latter being very much smaller - I'd reasonably expect gradients to be steeper in a smaller core.
And, I don't see concepts of in-situ replacement being even mildly credible - not after direct contact with fission-product bearing fuel salt. There were some thoughts given to trying that on AGRs in a depressurised state (and they don't have anything like the direct contamination issues) but it was quickly kyboshed as infeasible.
No, you need the chemical plant to remove the poisons even if the plant IS run without fuel breeding, or if you run separate fuel/breeder loops.
It should be obvious, really - if you're going to breed 233U from 232Th, it has to involve a neutron absorbtion, then a decay period (the actual process transmutes 232 Th to 233Pa by neutron capture, which then undergoes beta decay to become 233U). The necessary neutron flux is only available in the core, where active fission is going on. Therefore, you're pumping the breeder salt through the core, therefore it's absorbing neutrons, and if you allow the Pa burden to become too high, it closes the reaction down - and you need it to undergo two more captures to become useful fuel, ie 235U). It doesn't matter if it's mixed in with the fuel salt, or a separate circuit, its still absorbing neutrons.
MSRs also depend on active and continual removal of fission products from the fuel loop. Some of that's easy (letting Xe and I come out of solution) and some's hard (CS, Sr and similar via tricks like vacuum distillation, which is a sod, and would be a horror to maintain in a highly active environment). And if there's any production at all of higher transuranics (which there would be in there were any 238U in the fuel salt - and that's inevitably until and if you get to a completely closed 233U based cycle), there's no removal mechanism at all, short of pyrolitics or something like purex.
Re: Even if it does generate Pu
"This is important, when you realise that the high level radioactivity associated with spent rods in current technology is Cobalt and Caesium, with a dangerous lifepsan of about 200-500 years. After that, your waste repository becomes a low-emission, extremely high quality plutonium mine (98% U238) - and before that the Pu is easily separated from the nasties via chemical processes (in a thorium reactor you leave them in solution to burn up. It's only U234 whic h needs to be removed as it will poison the process if levels get too high. It's all pretty elegant, enriching isn't needed and because 100% of the fuel is used, a lump of thorium goes 30-40 times further than the same size lump of reactor-grade uranium (the process can be used to convert u238 to reactor fuel, eliminating 99% of the current volume of "high-level nuclear waste")"
Mostly correct (certainly in the fission products argument), but you miss a few of the "hard to handle" products - mostly the "heavier than plutonium" transuranics like Amerecium. They're the biggest contributor to spent fuel activity after the 200-300 year mark, and will keep fuel a lot hotter than the original ore (the baseline target for disposal) for some thousands of years. And no, an MSR cycle doesn't make significantly smaller proportions of those than a uranium one (after all, it's still ultimately fissioning uranium, with a 238 content in there).
They're fissionable - but not very much so at thermal energies. They can be burned, but only in fast reactors.
That's in large measure the elegance of design like IFR, that use a mixed actinide metal fuel. Using a pyroprocessing method that's basically electroplating in a molten salt medium, you don't ever need to separate the U/Pu/Am etc. from each other. The real virtue, though, is it doesn't have to happen in real time - the fuel can have a couple of years of cooling/decay, to get rid of the really hot stuff, then processed. With an MSR, you have to do it "real time", otherwise the reactor shuts down.
And looking at the reliability challenges of operating plant in a "hot" enviroment, real-timne scares me sh*tless.
Re: connected to a drain plug of salt that has been frozen solid
I think you slightly underestimate the heat removal issue - we're talking in the order of 10-20MW in the immediate aftermath of a fuel drain-down. Expecting to do that simply through convection into air would require a pretty immense large area, nless you assume either pumped flow, or two-phase of some sort - and that implies a secondary coolant supply (probably water)
In reality, it probably two-phase cooling to get the decay heat away - which puts you back in the same sort of place that you've got on the 72-hour passive cooling arrangements on an AP1000 or EU-BWR. That is, a tank above the decay heat source, allowing boiling off the walls of the fuel draw down tank, with water supply by gravity.
Oh, and by the way - that drain-down tank is going to be a pretty huge source of "gamma shine" - which means it'd have to be behind several meters of concrete, and but still have to have good air/water low. And it also means that any equipment associated with it would have to be entirely remote-operation, and maintenance. Once that tank had been used, you'd not be re-entering it's immediate area for a few decades, to fix anything - like the pumps required to move the fuel back into the reactor.
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