[HermannH]

Henning wrote: And thorium? Well a nice idea, I don’t know much about it. Maybe ten times better than uranium and ten times more abundant (whatever, I don’t really care at the moment). This makes it as much of a problem as uranium before: same amount of waste. But there’s no way of storing that waste safely (exception: the Swedes have a tectonic safe granite vault, but they won’t let anybody else dump their rubbish there).

So same problem with thorium as with uranium: heaps of uncontrollable waste.

Actually, the amount of waste produced by a Thorium reactor is going to be very small compared to the waste from a conventional Uranium reactor. And it is relatively short lived (half time of around 500 years if I remember correctly, compared to 20,000 years for plutonium). Given that many geological formations have lasted for millions of years it should be possible to find one that is ‘almost’ guaranteed to last some 10,000 years.

In general, breeder reactors (Thorium and Uranium as well) not only use their fuel much more efficiently, they also produce less waste.

Of course uranium breeders produce loads of Pu239, which is an excellent weapons material. Thorium breeders produce U233, which is also weapons capable. This is probably one of the reasons why breeder technology hasn’t been pursued much in recent decades.

There are also some other technical challenges associated with molten salt reactors as outlined in this Wikipedia article.

If Focus Fusion (or some other fusion technology) shouldn’t pan out Thorium reactors have a good chance of being our main energy source 40 to 50 years from now. That or solar.

[HermannH]

Brian H wrote:
Typical misrepresentation. The bases are in NO countries that don’t want them, and most howl like banshees when their removal is contemplated for strategic or cost reasons. The justification for the ME wars is something for another locale, but I can refer you to some very grateful Iraqis etc. who say things like …

Really?

About he bases have a look at this.

What did I misrepresent about the ‘Project for the New American Century’?

As for the Iraqis, it appears to me that there have been far more Iraqi losers than winners. Probably well over 100,000 dead, a million who are refugees in other countries and large internal displacements. These losers lost big time and you need a lot of winners to make up for it. Of course the Americans are losers too, they (and other countries) lost thousands of soldiers’ lives, not to mention the tens of thousands wounded and the cost of over a trillion dollars. It isn’t much mentioned, but far more American lives were lost in Iraq than on September 11. And all because of the imperial ambitions of a bunch of neo-cons in the White House.

[HermannH]

Brian H wrote:
P.S. The US is an empire by no definition found in history. That’s “progressive” rhetoric that is nothing more than a ludicrous, egregious, gratuitous, but politically useful insult.

Let’s see:
– 41% of the world’s military budget is spent by the US (5% of population).
– It has military bases in dozens of countries all around the globe.
– It reserves the right to pre-emtively attack countries it feels threatened by (regardless of whether that feeling is actually justified).
– It pressures other countries into joining its wars (‘Coalition of the willing’).

If you look at the CIA world fact book you will find that the US ranks as number 28 in terms of defense spending vs GDP (twice the world average). I did a quick scan of the top 50 countries on that list and I didn’t find many that are shining examples of free and democratic societies.

Also have a good look at the Project for the New American Century. An important part is the last section titled “Associations with Bush administration”.

And of course there is http://en.wikipedia.org/wiki/American_Empire.

In general, the definition of what constitutes an empire is likely a fluid one. There is a good chance that future generations of historians will lump the current US together with previous empires.

That’s not to say that the world would be a better place if the US were crushed to pieces.

[HermannH]

Rematog wrote: But the cost of running it is a very important question.

What if you could make power with only the power of your mind… no fuel, no capital…free power!

If 5 people, without requiring any capital equipmemt, no parts, no fuel, nothing but the power of their minds, could stare at a transmission line and make 5 MW appear…..

It would not be cheap power if they were paid a good union wage.

I love this thought experiment and the surprising conclusion!

A couple of hundred years ago most of our energy needs were provided by humans and some horses and oxen at a rate of far less than 1 kW. Today a rate of 1 MW is barely competitive.

We have come a long way, both in ways of producing cheap energy and also in our rapidly increasing thirst for energy.

[HermannH]

belbear wrote:
Radiator size is not the only issue here, temperature is one too. Radiative cooling becomes more efficiënt with rising temperature (look at the Sun, that’s a very efficient radiator), so all you need to make your radiator panels smaller is to make ’em hotter.

I don’t imagine a FF spaceship at full trust using the kind of big, shiny radiators like the ISS has, I imagine them being rather small, sturdy and glowing hot. Using high-temp coolants such as molten metal rather than ammonia. Since energy is not such a scarce commodity on board a FF vessel as it is in a solar-powered one, a two-stage cooling process that steps up the temperature using some sort of refrigerator cycle can be used.

Wouldn’t it be nice if we could just suspend the laws of physics when it suits us!

The laws of thermodynamics dictate that the temperature of the coolant and therefore the radiator must be lower than the maximum operating temperature of the device you need to cool. You cannot ‘step-up’ the temperature.

Well, you could build a device that cools the primary coolant and heats a secondary coolant to a temperature that is even hotter. One such device is a Peltier. However, you need energy to operate that device and you will generate additional heat that needs to be dissipated as well. This additional heat would be of a relatively low temperature and would require even bigger radiators.

In other words, heat voluntarily only flows ‘downhill’ from a hot body to a body that is colder. If you want to reverse that natural flow you need to supply energy and you will generate even more heat in the process. This is the reason why you won’t find a portable air conditioner that you can just put in the middle of your room. Its waste heat needs to be dissipated to the outside; otherwise you end up heating your room not cooling it.

[HermannH]

Tulse wrote:

Radiating waste heat into deep space isn’t so difficult, on condition you shield your radiator from the sun. After all, space shows us a 3 Kelvin black-body and that’s really cold.

Right, but that is purely radiative cooling, which as I understand it isn’t nearly as efficient as conductive or convective cooling — there’s a reason that thermos bottles use vacuum flasks. As “cold” as space may be, you can cool things far more efficiently on earth by, for example, dumping heat into a lower temperature fluid. (I’m sure that some one with way more technical expertise could clarify what sized radiator would be needed to dump 5MW of heat into space.)

I used this calculator to get the blackbody radiation at 300 degrees Celsius. It is a surprising 6 kW / square meter.

The radiation is highly sensitive to the operating temperature; at 200 degrees Celsius it is less than 3 kW / square meter.

[HermannH]

texaslabrat wrote:
As I mentioned before, an F-16 (a small, single-engine, lightweight fighter) in full afterburner consumes the rough equivalent of 300 MW. The top speed of an F-16 in full afterburner is about Mach 2.0 at altitude. Believe me, you’re gonna need power in the GW scale to even think about a hypersonic high-altitude first stage or a hypersonic trans-continental aircraft. As a “fun fact” comparison, each of the 5 Saturn V first-stage engines consumed a heat-content equivalent of over 30GW. It’s hard to wrap your head around the shear power requirements needed for high-performance flight..but they are indeed quite steep.

This is the crux of the story. The F-16 can generate power at a rate of 300 MW, but only for about an hour or two. After that the tank is empty.
A FF reactor will probably never produce enough power to lift itself into low earth orbit. The power to weight ratio is way too small.
Once you are in orbit and want to travel to distant planets or solar systems the story is different: you can let the engine burn for days or months and keep picking up speed. 5 MW for a couple of months beats 300 MW for a couple of hours.

[HermannH]

msmith wrote: Scalability of a reactor?

What about the pulse rate?
If 330 Hz produces 5 MW could the pulse rate be dialed up to 660 Hz with output at 10 MW?
How about 3.2 GHz with output at 48 TW? 😛

Nice try, but the maximum rate is largely determined by the ability to cool the system. Just like computer chips.

[HermannH]

One way for the big companies to stall adoption of FF by smaller entities is through tough regulations.

There is an interesting example of this in the US. The conversion of vehicles to run on natural gas is extremely expensive because of the high cost for a mechanic to obtain a license (apparently $200,000 per engine type per year).

So there is going to be intense lobbying for and against crippling regulations, depending on which side you are on.

On the other hand, it’s a global economy. If FF turns out to deliver cheap energy countries that adopt it without significant restrictions will enjoy an advantage. Governments in countries with severe restriction will face intense pressure from consumers and some industries to reduce regulations to ‘reasonable’ levels.

One possible outcome as Rematog maintained all along is that, at least initially, FF will be installed mostly in large facilities (i.e. retrofitted power plants and large industrial plants that need lots of power). In these places the overhead to comply with regulations is relatively low.

[HermannH]

annodomini2 wrote: From what I understand the plan is to use some mechanism to convert the x-rays into usable energy? So the mechanism used here could be the shielding here could it not?

So is the biggest concern the neutron emissions?

That’s right.
The proposed setup is one meter of water to slow down the neutrons followed by ten centimeters of boron to absorb them.

[HermannH]

annodomini2 wrote:
Which type of radiation, neutons or x-ray? (again have I missed something?)

Both are generated. In fact x-rays make up about half of all the energy that is generated. The design of the system is meant to capture the x-rays and convert them to electricity like a solar cell.
However, a small amount of neutrons is also generated in a side reaction to the main p11B reaction. For details see Aneutronic fusion.

[HermannH]

KeithPickering wrote:
Thanks for that link, and the very interesting technical paper.

You are welcome! There is a link to a second technical paper and a lot of other interesting stuff on the home page.

A couple of final results then: at a ratio of 1.57 (energy recovered to energy input), the salable output of a reactor using 5 kg of borax per year (see my previous post for computations) would be 1111 kW. To convert ALL electric production worldwide (2.5 million megawatts) to pB11 fuel would require 12,500 tonnes or borax per year, or about 8% of current worldwide production.

So, no matter what the efficiency, the supply of boron is not going to be an issue.

[HermannH]

Brian H wrote:
I disagree, of course. The fundamental design of FF is to generate electricity; the heat is either icing on the cake or urine in the punch. ;-P
In general, ANYTHING above unity would do, I think. The Tokamak and similar designs project numbers in the low single digits, IIRC. They’re just heat engines, of course. Once FF attains/exceeds unity, it will attract more than money; there will be brainpower and ingenuity applied en masse to refine and maximize its output.

That’s mostly correct, the point of FF is to generate electricity directly. In order for the technology to be even theoretically viable the reaction needs to generate more electrical energy than you put in. To be economically viable you need to be quite a bit above unity as explained earlier.

Of course, once you demonstrate that you can achieve even close to unity you can attract a lot of money to develop the technology further. But this development effort may take huge amounts of money and many years before we have a system that economically produces electricity. Economically, in this case, could initially mean about the same cost as coal or regular fission not necessarily ‘too cheap to meter’.

I do hope that we get well above unity quickly and this discussion is just academic.

[HermannH]

Tulse wrote: All the above points are indeed true, but I’m still not clear how far over unity one needs to be for economic viability, nor where other fusion approaches would sit on that curve. (For that matter, I’m not sure what the relative “mine to outlet” energy gain is for coal-fired or nuclear powerplants — does anyone have estimates on that?)

As far as I know FF is closer to unity (or above) than any of the other approaches. The big question is: can it get high enough above unity? Many of the other systems need to be physically scaled up (very expensive) to achieve unity or above. Even then there is no guarantee that they will be economical.

[HermannH]

Tulse wrote:

Also, if you have low overall gain the waste heat that is generated is going to be very large compared to the net electrical output.

Of course, the “waste” heat itself can be used either to generate further electricity, or for heating and industrial applications, making the system more economical than figures for just direct electricity generation might suggest.

That is theoretically true, but the coolant temperature must be significantly lower than the maximum operating temperature of the part that needs to be cooled. Therefore the waste heat is probably at a relatively low temperature unlike in a coal power plant where the boiler temperature is pushed as high as possible. The higher the ‘steam’ temperature the more useful things you can do with it. It’s like a car, the waste heat from the engine is good for heating the car in the winter, but otherwise it is just a problem.

My expectation is that the steam temperature is going to be barely high enough to make it worthwhile to generate electricity from it. Also, keep in mind that having to attach a conventional steam based power plant to a FF reactor negates many of the cost advantages.

Imagine a reactor where you have only 10% gain over unity. That means if you feed 1 Mega Joule of energy from the capacitors into the device the electrical energy harvested is 1.1 Mega Joule. 1 Mega Joule of that is needed to charge the capacitors for the next shot, so you are left with a net output of 100 kilo Joules. But you also just generated close to 1 Mega Joule of heat that needs to be disposed. Your ratio of waste heat to useful electrical power is 10 to 1. If your gain is 5% over unity that ratio goes up to 20 to 1 and you will use up all the generated electricity just to power the cooling pumps.

So it is critically important that the gain is significantly higher than unity.

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