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PostPosted: Jul 30, 2016 8:38 pm 
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Well, as you know, I like to think about ways to improve the performance of reactors in an attempt to reach an all nuclear system.
Since I found out about the SUNSTORE projects in Denmark (very interesting work), which amongst other things, have developed very cheap methods of storing vast tonnages of hot water in excavated pits - primarily to support district heating.

They appear to be able to build pit storage for water at 90-95C for roughly ~$26 per cubic metre, based on the stated costs of SUNSTORE 4. In their larger stores they are capable of large scale seasonal storage and assuming a water return temperature to the pit of roughly 40C you can store ~64kWh(t) per cubic metre. Losses are fairly minor in terms of storage capacity, and would be reduced in large stores due to a higher volume:surface area ratio.

Studies on district heating cogeneration performed in Sweden seems to indicate that hot water cogeneration by an ESBWR or EPR would allow 1400MWt to be produced at 95 Celsius at the cost of only 150MWe. So 9.33MWt/MWe. Essentially a virtual heat pump with an effective COP of 9.33.

95 Celsius water in the store can then be held until peak demand and be provided to a organic rankine cycle system using a working fluid like propylene. If we assume a 25C condenser temperature and 95C inlet temperature (which probably requires PCHEs or similar high performance heat exchangers) then we can obtain ~14% gross efficiency.
After derating that to account for auxiliaries we might have ~9% efficiency, which is still ~84% effective 'round trip' efficiency. We traded 1MWh of electricity production in the off peak for 840kWh of production in the peak period, although the former never actually existed.

At ~9% efficiency each cubic meter of water can store ~5.8kWh(e).
Which translates as a storage capital cost of $4.50/kWh
Which is the lowest I have seen without requiring ludicrously high temperatures and molten table salt.

Capital cost of the ORC turbines is much larger, but does not scale with the size of the store, but with the size of demand.
Something on order of ~$1500/kWe seems reasonable.
However $4.50/kWh is so cheap it barely seems to matter - it can be built anywhere you can dig a hole.
And there is room for improvement, if efficiencies could be raised to ~12% instead of my arbitrarily selected
~9% then the cost would fall to ~$3.40/kWh.

Imagine an ESBWR running with 1350MWe and 1400MWt for 16 hours a day, and 1500MWe for the other 8, using the hot water storage for backup. That would be 22.4GWh(t) of stored heat, which would require 350,000 cubic meters of pit storage positioned adjacent to the plant. That is ~2GWh of stored electricity that can be tapped off during those 8 hours. If it was used continuously it would be 250MWe of ORC generation capacity using propylene.
SO for the cost:
350,000 cubic meters of pit storage -> ~ $9.1m
250,000kW of ORC -> $375m
And something like ~$95m for cogeneration modifications to the nuclear power station

Total: ~$480m

We turn a 1500MWe baseload plant into a 1350MWe baseload plant and a 400MWe peaking plant with ~33% capacity factor.
The peaking plant ends up costing roughly $1200/kWe.
Pricier than gas turbines, but its fuel and effective O&M cost is only a couple of cents per kilowatt hour.

Additionally seasonal storage no longer seems so ridiculous, considering the very low cost of pit storage. You could easily have ten time as much storage iwthout seriously boosting the cost of the scheme, and be able to carry heat from warmer parts of the winter into cold snaps, or from autumn into early winter.

So what do you all think?


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PostPosted: Jul 31, 2016 3:53 am 
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Hello!

I like your idea of the off-peak storage capacity. The efficiency gains seem like a very cost-effective way to go. A few thoughts....

1. This plan seems most ideally suited for those power generators that have intermittant or seasonal peaks (wind, solar?) Capture the excess from those windy nights or bright sunny early afternoons with low baseload demand, and return it when most needed at peak demand. Factor in a baseload plant (LFTR, or even with current technology coal, gas, etc.) to smooth out the ripples in demand, and overall efficiency is realized.

2. For the pit storage, how is it designed? Is it an open pit with a cover of some form, or a below-ground excavation, such as an abandoned mine? Either form should have some form of impermeable liner that will withstand 95C temps for years on end. Water quality could become an issue (organics, dirt, leached minerals) requiring on-line treatment to avoid plant piping corrosion and clogs, an added cost.

3. Potential issues for pit construction could include the old 'not in my back yard (NIMBY)' local zoning rules which might interfere, what to do with the excavated tailings if the pit is started from scratch (are there existing pits from mines, for example, which might be suited near enough to the hot water source)?

4. Could above-ground storage using insulated large tank farms be an option? Modern insulation, such as aluminized mylar wraps like those used in the lunar landers, and more freely available today seem to be quite efficient and could prove cost-effective to enclose large above ground tanks and pipes. For example, the largely above ground Alaskan oil pipeline is insulated quite well using methods and materials which are probably now obsolete. As LFTRs become a standard, and we use less petroleum (we surely hope!), existing oil tanks may come available. Tank farms can be modular, and built to size to accommodate local sources and conditions. True, the same 'NIMBY' problem may occur, but there would be virtually no tailings to deal with. Tank storage could minimize water treatment issues as well.

5. On the recovery side, extraction of heat from 95C to 25C will probably involve a cooling system of some form to accommodate the heat flow unless the recovery is direct use, such as piping to communities for home heating (Iceland, Sweden, Denmark) or to industrial use. Is this cost taken into account with the ORC generation schema?

6. For those areas of the U.S.A. that are nominally 'too warm' for efficient direct home use (Florida, Southern California, Hawaii) would you foresee additional uses for the hot water supply in addition to peak electricity supplement?

7. I think your efficiency calculations may actually be a bit on the low side, as additional efficiency may be gained in the direct home use aspect for the hot water, reducing the local electricity demand during cold snaps and long
northern U.S. winters (U.P. Michigan, Minnesota, upstate N.Y., New England) If that is the case, add a plus-sign to the cost effective arguments for proceeding! Cooling (#5 above) is also less of an issue up north, as nominal winter temps of -20C give cooling schemes a seasonal natural boost, although summers still get pretty hot.

8. The ability to run a baseload plant (LFTR, hopefully) at a more constant load with 'excess' capacity stored in hot water on demand should reduce stress on the plant as it can run at a relatively steady state increasing overall efficiency. Also, with smaller, localized LFTR sources, combined with intermittant existing local wind and solar, tailored hot water demands are more easily realized and accommodated by the locale, allowing smaller more cost effective local infrastructure for storage, piping, etc.

Just a few thoughts off the top of my head. I like the concept!

Mike


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PostPosted: Jul 31, 2016 7:39 am 
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Mikeaustria wrote:
1. This plan seems most ideally suited for those power generators that have intermittant or seasonal peaks (wind, solar?) Capture the excess from those windy nights or bright sunny early afternoons with low baseload demand, and return it when most needed at peak demand. Factor in a baseload plant (LFTR, or even with current technology coal, gas, etc.) to smooth out the ripples in demand, and overall efficiency is realized.

The idea here is to allow nuclear to fill the role traditionally assigned to a gas turbine plant.
It can only function using a steam turbine "primary" plant, otherwise the round trip efficiency is badly affected by the energy consumption of the heat pumps required to generate the heat in the first place. Additionally it might be possible to use solar hot water panels to provide some seasonal shifting if required.
Mikeaustria wrote:
2. For the pit storage, how is it designed? Is it an open pit with a cover of some form, or a below-ground excavation, such as an abandoned mine? Either form should have some form of impermeable liner that will withstand 95C temps for years on end. Water quality could become an issue (organics, dirt, leached minerals) requiring on-line treatment to avoid plant piping corrosion and clogs, an added cost.

The current concept used in Denmark at the 'SUNSTORE' facility and at the world's largest seasonal heat storage at Vojens is a simple pit lined with aluminium foil and a HDPE liner, the former being to provide a diffusion barrier proof against very hot water which can diffuse through HDPE slowly. The pit is then filled and a top cover with insulation floated out over it, it is a very cheap and efficient method of working.
Mikeaustria wrote:
3. Potential issues for pit construction could include the old 'not in my back yard (NIMBY)' local zoning rules which might interfere, what to do with the excavated tailings if the pit is started from scratch (are there existing pits from mines, for example, which might be suited near enough to the hot water source)?

Disposal of spoil is indeed a major issue, but it seems to me that with proper design it might be possible to engineer a berm around the outside of the tank using the spoil that would shield the tank surface from view and potentially allow the surface of the tank to be above the ruling ground level - although that has major safety problems in making sure that a dam burst does not release a torrent of potentially hundreds of thousands of tonnes of scalding hot water.
Mikeaustria wrote:
4. Could above-ground storage using insulated large tank farms be an option? Modern insulation, such as aluminized mylar wraps like those used in the lunar landers, and more freely available today seem to be quite efficient and could prove cost-effective to enclose large above ground tanks and pipes. For example, the largely above ground Alaskan oil pipeline is insulated quite well using methods and materials which are probably now obsolete. As LFTRs become a standard, and we use less petroleum (we surely hope!), existing oil tanks may come available. Tank farms can be modular, and built to size to accommodate local sources and conditions. True, the same 'NIMBY' problem may occur, but there would be virtually no tailings to deal with. Tank storage could minimize water treatment issues as well.

Problem with that is I can't help but imagine that the construction costs of above ground tank farms are going to be collosal - the whole idea here is to get the minimum cost of storage possible to enable less reuse of storage and hence move towards the holy grail of seasonal storage.
Mikeaustria wrote:
5. On the recovery side, extraction of heat from 95C to 25C will probably involve a cooling system of some form to accommodate the heat flow unless the recovery is direct use, such as piping to communities for home heating (Iceland, Sweden, Denmark) or to industrial use. Is this cost taken into account with the ORC generation schema?

I thought about district heating, but the networks tend to cost something like £8000/house, which woudl require something like £180bn to fit the entire UK, it would partially solve my winter time heating problem but it is an awful lot of capital investment to achieve that goal. I am attempting to provide storage to enable heat pumps to take up the slack, but the peak UK heat demand is something like 300GWt, and heat pumps with on site thermal storage are still in their infancy.
Mikeaustria wrote:
7. I think your efficiency calculations may actually be a bit on the low side, as additional efficiency may be gained in the direct home use aspect for the hot water, reducing the local electricity demand during cold snaps and long
northern U.S. winters (U.P. Michigan, Minnesota, upstate N.Y., New England) If that is the case, add a plus-sign to the cost effective arguments for proceeding! Cooling (#5 above) is also less of an issue up north, as nominal winter temps of -20C give cooling schemes a seasonal natural boost, although summers still get pretty hot.

The best cold source available in the UK in winter is actually the North Sea, which has a surface temperature as low as 6C in the depths of winter. But I was using some pre available data and after all a warmer condenser reduces cooling water pumping costs which could easily overwhelm any gains in efficiency.

One thing that might be possible, if they can be made light enough and cheap enough, is to cover the tank roof with vacuum-insulated solar collectors to provide seasonal recharge, which would at least reuse what would otherwise be acres of empty space.
Digging deeper would partially resolve that issue however.


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PostPosted: Aug 02, 2016 9:54 am 
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E Ireland wrote:
Mikeaustria wrote:
3. Potential issues for pit construction . . . what to do with the excavated tailings if the pit is started from scratch . . . ?
Disposal of spoil is indeed a major issue, but it seems to me that with proper design it might be possible to engineer a berm around the outside of the tank . . .
E.

May I relate that later after reading your interesting discussion with Mike on "the holy grail of seasonal storage" and wondering "What is a berm?" I just happened to come across the film:

Published on YouTube February 17, 2016 by Oak Ridge National Laboratory

Alvin Weinberg - This biographical documentary explores the life of the internationally renowned nuclear scientist and former ORNL Director. Copyright © 2015 Secret City Films.

At 16:58 (of 59:10), Pat Postma, wife of ORNL Director Herman Postma, tells this charming anecdote about Alvin Weinberg at a meeting:
Quote:
Alvin was sitting on the front row . . . and I mentioned that this tract started after the "berm" . . . . When I first encountered that word--berm--I didn't know what it was but I looked it up and it means a man-made hill.

And I mentioned that at the speech and Alvin raised his hand and he said . . .

"What is a "berm"?"

And I thought, "Oh, thank God I wasn't the . . . [laughs]"
And we assume what Pat meant before they segued was that even a brilliant scientist and citizen, who with Dr. Wigner essentially created domestic nuclear power, did not "know it all"--a testament to the great virtue of humility. The more I learn about Dr. Weinberg, the more I realize that his own belief in the necessity of the LWR and the uranium fuel cycle and his firing from ORNL distracted him from the MSBR thorium cycle program. He lived through Three Mile Island and Chernobyl all through the 1990s and into the aughts. He regretted being so dedicated to reactors that he didn't give nuclear waste its due number one priority status. That is odd because his own thorium MSBR and molten fluoride salts fluid-fueled designs were an avenue to higher burn-up of fertile/fissile and integral processing of reactor FPs and DPs with the goal of getting the waste output utterly minimized to only the 300-year residue while directing refined FP/DP output to strategic supply chains.

It's very odd to me that my own first encounter with "berm" here on the ETF would coincide with my finding and viewing this wonderful film about the founder of the very technology that has led Kirk Sorensen to starting this forum ten years ago in November 2006, the year Alvin passed on the 18th of October, and happened to have this anecdote about Alvin likewise being unfamiliar with the earthworks term.

Quite strange. Does this coincidence have any meaning? Ten years. Too bad our DOE and NRC and our government do not value Alvin Weinberg's great vision. It's not too late. Time for the lawmakers to respect the brilliance of our great citizen.

On point, E, and sorry for the anecdotes, I'm also puzzled about the need for thermal battery. Is it that reactors have to adjust to loss of load? Apologize.

Related is pumped storage. I saw a recent film on Madiera Island, Portugal, pumped storage that captures and manages rain water, hydro power generation, and leverages using wind turbines with the evening winds for returning the daily generator volume uphill again. Wow, what a hybrid! I think it's a 15 MW(e) system? But I bet the Madeira power/water engineers might like the kind of make-up power a 250 MW(e) FE LFTR could offer?

I find the conclusion to the Madeira paper fascinating:
Quote:
In the last decades, the managers of water distribution systems have been concerned with the reduction of energy consumption, and the strong influence of climate changes on water patterns. The subsequent increase in oil prices has increased the search for alternatives to generate energy using renewable sources and creating hybrid energy solutions, in particular associated to the water consumption. Renewable energy includes hydro, wind, solar and many others resources. To avoid problems caused by weather and environment uncertainties that hinder the reliability of a continuous production of energy from renewable sources, when only one source production system model is considered, the possibility of integrating various sources, creating hybrid energy solutions, can greatly reduce the intermittences [sic] and uncertainties of energy production bringing a new perspective for the future. These hybrid solutions are feasible applications for water distribution systems that need to decrease their costs with the electrical component. These solutions, when installed in water systems, take the advantage of power production based on its own available flow energy, as well as on local available renewable sources, saving on the purchase of energy produced by fossil sources and contributing for the reduction of the greenhouse effect.

An optimization model for determining the best pump and turbine hourly operation for one day was developed. The model was applied to the “Multi-purposes Socorridos” system located in Madeira Island, Portugal, which is a pumped storage system with water consumption and hydropower production.

The model is very flexible in terms of input data: wind speed, water consumption, reservoirs volume, maximum flow and electricity tariff, and the numerical computations take less than a minute. The results can immediately be introduced in EPANET hydraulic simulator in order to verify the system behavior.

With non linear programming, the results showed that a saving of nearly 100 €/day can be achieved when compared to the normal operation mode, maintaining the hydraulic restrictions and water delivery to the population. When a wind park is added to the system, the profits are much higher, approximately 5200 €/day, for winter and summer wind conditions.

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Last edited by Tim Meyer on Aug 02, 2016 10:37 am, edited 1 time in total.

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PostPosted: Aug 02, 2016 10:35 am 
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Unfortunately pumped storage only works when you have lots of hilly terrain that people don't mind being covered in lakes.
This is difficult to obtain in the UK - whereas out in East Anglia and Lincolnshire you could dig numerous pits and noone would even notice - flat as a pancake and sparsely populated.

The objective here is to provide some seasonal load shifting to help meet the enormous winter demand peak without having 50+GWe of reactors idling all summer, although I have ways to use up some of that capacity - desalination and salt/chemical production being obvious choices.

If you wanted to reduce the amount of spoil these pits could potentially be created at sea by the construction and lining of dykes in a box near the reactor facility. But that would likely be significantly more expensive until you reached truly enormous scales.


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PostPosted: Aug 02, 2016 10:39 am 
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Excellent points, E.

Are you retired or currently in energy? --If I may. Thanks.

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PostPosted: Aug 02, 2016 11:28 am 
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No - currently going into a masters degree year in Physics at University - attempting to line up a place on a Nuclear Power Engineering PhD.
But I have always been interested in energy policy and industrial technology, my degree background is in Chemistry.
I wish to bring about what I refer to as the "Atomic Future".


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PostPosted: Aug 02, 2016 12:01 pm 
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Excellent, E! That means you're young. Compare that to my masters in chemistry from ASU in 1987 a generation ago! I put my age in my profile here on the EFT, my location, and the only decent science professional photo I have on hand. I have nothing to hide. It's nice to know people, I feel.

Thank you for sharing a little of your background and goals. I applaud you and wish you great success. I'm glad you don't have to experience my debacle. I'm too old to retrain in the hands-on but the policy efforts are still open. I join your Atomic Future.

Since you're chemistry, perhaps you can clarify my arrested development. I think one of the greatest features of the molten salt reactor is that the salt can be continuously "cleaned" with a "kidney" or "liver" as one of the original ORNL contributing scientist-engineers remarked early in the MSBR program. But they were not supported then in funding and personnel long enough to refine the techniques, test, and establish the codes. The chemical processing and even better online integral partitioning techniques seem would kill multiple birds at once: optimized reactor performance for energy and breeding, generation of strategic materials from FPs and DPs, and highest reduction of 300-year waste.

I hope when you decide on your dissertation goals, you kickass.

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PostPosted: Aug 02, 2016 6:02 pm 
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The cost of pit storage is attractive, but the form of the storage is not.

The working temperatures are higher, but close to an OTEC system. (Ocean Thermal Energy System). OTEC usually works off the temperature differential of deep water, and tropical surface water, which is similar.

Arguing by analogy (always risky) I'd guess there would be issues with developing turbines for nonstandard working-fluids (propylene), the cost of the low-temperature final turbine stages, and the cost of the low temperature heat exchanger.

Turbines using non-standard fluids, especially large turbines, are very expensive to develop. E.g. OTECs, the South African pebble-bed reactor, and General Atomic's high-temperature gas-cooled reactor have all foundered on this problem. Low temperature turbines are especially problematic because they tend to be very large. This means that any mistake at all is deadly to the development budget, and is likely to kill the project.

The exit heat exchanger often has to be very large. Possibly the entrance HX, also. I.e. expensive.

This all militates against the $1.5/W for the turbomachinery and heat exchangers. That cost BTW, is very reasonable only for a steam plant.

I suggest that you estimate sizes for these items, and then weight, and apply typical materials and manufacturing costs, i.e. cost of the steel, then ~US$ 22/Kilo for fabrication.


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PostPosted: Aug 03, 2016 9:43 am 
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Indeed this could be an issue, I will endeavour to do the calculations.


There is another alternative - use resistive heating to melt molten sodium chloride and then feed it to an Ultra Super Critical steam turbine plant, and just accept the ~48% round trip efficiency.
Low cost storage at the cost of terrible efficiency.


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PostPosted: Aug 05, 2016 2:53 pm 
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Having water as a storage medium for nuclearpower is kind of silly. If you repace the steam generator in a typical PWR with a L2L HEX and transfer that high temp heat to a phase-change heat storage unit, you can then extract the heat at higher power to generate extra power when needed. You can convert a 1x24/7 NPP to a 2x12/7 NPP or any varient where the YxZ equals 24.

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PostPosted: Aug 05, 2016 4:44 pm 
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Finding a suitable salt that isn't enormously expensive is hard.
See my previous work on this forum on that topic.

Water is enormously cheap.


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PostPosted: Aug 08, 2016 4:14 pm 
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E Ireland wrote:
I thought about district heating, but the networks tend to cost something like £8000/house, which woudl require something like £180bn to fit the entire UK, it would partially solve my winter time heating problem but it is an awful lot of capital investment to achieve that goal. I am attempting to provide storage to enable heat pumps to take up the slack, but the peak UK heat demand is something like 300GWt, and heat pumps with on site thermal storage are still in their infancy.


Interesting, is that cost per single apartment or building (for example, a big building containing 10 or more different apartments, as typically happens in urban contexts where DH networks have more sense) ?


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PostPosted: Aug 08, 2016 4:19 pm 
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Apartments cost a bit less - but that is considered to be the average price per dwelling.
Heat Interface Units apparently cost ~£1600 alone, although that can be reduced using direct connection between the house's heating plumbing and the district heating system. Hot water cylinder and radiators fed directly.


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PostPosted: Aug 08, 2016 11:50 pm 
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I'd like to point out that pumped (hydro) storage technically isn't limited to appropriate geography. There is a company called Gravity Power that would like to use vertical tunnel boring machines (TBM) to construct shafts for a closed loop pumped hydro scheme. 8 vertical storage shafts have a concrete piston each, feeding a center return shaft. Center shaft feeds water turbines at the top of the storage shaft, dumping water on top of the free piston. They appear to be preparing a demo in germany at the moment.

I wonder if some sort of hybrid setups might be appropriate. A japanese group recently did a split hybrid steam solar CSP system, where primary water evaporators were long trough fresnel lens systems, feeding a heliostat heated tower steam super heater receiver. The idea being using the cheaper troughs for the bulk of the work, and the more expensive heliostats for the finishing work for steam generation.

Cycle-wise, where are those low hanging fruit that might be achievable via changing or mixing storage system types? Using underground concrete shafts with syntactic foam inserts might enable the storage of high pressure steam/water that is continuously pressurized by the piston in the shaft.


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