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Comment: Re:Is it dead? (Score 4, Insightful) 109

by nojayuk (#46770837) Attached to: Intel Pushes Into Tablet Market, Pushes Away From Microsoft

Intel are reducing power consumption and maintaining performance faster than ARM can improve processing power while keeping power consumption down. The current version of the iPad has a lot more processing power than the first one did but it has a battery three times bigger to give it the same endurance between charges, in large part because the newer ARM chips suck more power than their predecessors did.

Intel-based tablets like the Iconia W series (i3/i5) or Toshiba Encore (Atom quad-core) have the same endurance as ARM-based tablets with similar battery capacities while running a full-fat desktop OS rather than a phone OS with delusions of competency.

Comment: Re: Thorium Sanity Clause (Score 1) 174

by nojayuk (#46745797) Attached to: Cost Skyrockets For United States' Share of ITER Fusion Project

Light-water, heavy-water and carbon moderated power reactors only breed U238 up into Pu239 and Pu240 by "accident", so to speak. They get a few percent of the total energy they produce from fissioning these products in-situ. Breeders meant to produce surplus fuel or "burn" waste require much higher fluxes, usually achieved in a small physical volume hence the higher temperatures involved and the use of sodium, lead/bismuth, helium etc. to conduct away the heat. The LFTR concept requires this high flux density, whether of moderated thermal neutrons or a mixture of fast and thermal neutrons while at the same time having the radiological problem of the high-temperature fuel being less constrained in liquid form.

Comment: Re: Thorium Sanity Clause (Score 1) 174

by nojayuk (#46745525) Attached to: Cost Skyrockets For United States' Share of ITER Fusion Project

Generally we've discovered that very high neutron fluxes (thermal, fast or a mixture of the two) in restricted volumes required for high levels of breeding in reactors and the attendant high temperatures tend to break things, cause leaks and fires and expensive shutdowns. At the same time reactors that work on the basis of moving fuel around (mostly pebble-bed designs) have not had a happy time of it even with lower neutron fluxes and larger working volumes in the core compared to out-and-out breeder designs. LFTR combines both of these iffy concepts.

Steam pipes leak all the time in light-water reactors, usually in the steam generators in the case of PWRs. This isn't a radiological problem as the cooling/moderating water isn't radioactive as it never comes in direct contact with the fuel and its waste isotopes which are ceramic pellets housed in sealed tubes. The steam loop runs at about 400 deg C or thereabouts at high pressure. In the case of LFTR and other breeder designs the coolant loop is at up to 700 deg C at which point most steel alloys have lost half their tensile strength compared to room temperature. Breeders that have broken their cooling loops in the past released molten sodium or helium but this had never came in contact with the fuel or its waste products so it was not particularly a radiological hazard. This is not the case with LFTR, of course.

Comment: Re:Stop Now (Score 3, Informative) 174

by nojayuk (#46732679) Attached to: Cost Skyrockets For United States' Share of ITER Fusion Project

"You could get the experimental platform for a couple of orders of magnitude less money."

No you couldn't, demonstrably. If they could build an ITER-scale reactor for one-hundredth the price they would have. Large-scale sustainable high-Q fusion is difficult. It cost billions to build and operate JET and it was never meant to beat breakeven (Q > 1) but it's come the closest to that of any of the major tokamaks with a couple of seconds of fusion with a Q of about 0.6 back in the 1990s. Heck JET wasn't even built specifically to do fusion, it was mainly supposed to be for plasma research but it got repurposed as plasma control and generation techniques improved. ITER, if it works as planned and the physicists haven't dropped a decimal point here or there, is a fusion reactor which will eventually run with Q >= 10 for several thousand seconds at a time. Maybe.

The "E" in ITER stands for Experimental. It's a testbed platform for trying out stuff and seeing how it breaks, a rig to make mistakes on and gain knowledge. There are nebulous plans to build DEMO and the later PROTO which will be power generating fusion reactors but they'll still be less than fully-commercial designs, just another step closer to the rollout of workable and cost-effective fusion power generation. Nothing is guaranteed though.

Comment: Re: Thorium Sanity Clause (Score 4, Insightful) 174

by nojayuk (#46732487) Attached to: Cost Skyrockets For United States' Share of ITER Fusion Project

Like I said, nobody's ever run a thorium-cycle liquid-salt reactor and there is no Santa Claus. As for a "thorium breeder blanket" add-on to the Oak Ridge reactor, huh? The LFTR concept mixes thorium into the molten-salt stream, breeds it up to U-233 and then fissions it within a moderator to slow down the neutron flux. There is no separate blanket, it's all in one stream, salt, kickstarter fuel (U-233 or U-235/Pu-239), thorium and waste products all at 700 deg C and more, mindbogglingly radioactive, radiochemically very complex and being continuously moved around lots of piping and heat exchangers and chemical processing plant and it has to generate electricity at about 5 cents per kWh to be competitive.

Any such reactor is going to require a neutron flux way higher than the ORNL reactor ever experienced, a mix of fast neutrons to do the breeding and slower neutrons to fission the resulting U-233. This isn't a problem for existing well-tested light-water and heavy-water reactors delivering about 15% of the world's electricity demand right now, of course. In their case the ceramic fuel sits in zirconium tubes and water circulates around them to transfer heat and in some cases moderate the neutron flux, no fast neutrons specifically required for breeding purposes (although some breeding does happen anyway). Much simpler and more reliable, no explosives required.

I agree that uranium will not be scarce for decades, at least one conventional and proven light-water/heavy-water reactor operation cycle of about 60 years. It's possible it would never be scarce at all if the process to extract from seawater can be operated commercially -- it's been tested, its cost is estimated at about three or four times the price of conventionally mined uranium today. Some countries don't have much uranium within their boundaries so ongoing supply is not guaranteed. India is one such country hence their interest in developing a fuel cycle involving thorium for their heavy-water reactors. They're still building and operating conventionally-fueled reactors too though.

Comment: Re:Stop Now (Score 4, Informative) 174

by nojayuk (#46732471) Attached to: Cost Skyrockets For United States' Share of ITER Fusion Project

The ITER is designed to do more than "break even", it's expected to return 10 times the energy input for heating and controlling the plasma -- a return of 500MW for an input of 50MW and to sustain this for periods of thousands of seconds. This is just heat, not electricity, there's no plans to try and extract energy from the system yet. It's an experimental platform, not a prototype power generating system.

Whether ITER succeeds in this aim we won't know until it actually runs. One school of thought is that bigger tokamaks make it easier to control the plasma generated. Pessimists think more problems will crop up as the engineering scale increases. That's why they're building it, to find out.

Comment: Re:Should have gone with thorium (Score 5, Informative) 174

by nojayuk (#46730151) Attached to: Cost Skyrockets For United States' Share of ITER Fusion Project

No "they" didn't have a LFTR reactor working in the 70s. Nobody's EVER had an LFTR working. There is no liquid-fluorine thorium Santa Claus, just a lot of grad student Powerpoint presentations.

There was a molten-salt reactor, a laboratory-scale device fuelled with U-233 and later U-235 in intermittent operation at Oak Ridge National Laboratories for a few years in the 1960s. It never used thorium and wouldn't have been any good if it had because it couldn't breed thorium up into U-233 to fission for energy. It took a long time to decommission this small reactor in part as several bad things had happened to the piping inside it. Folks reckon the corrosion could have been fixed with a little tweak but you don't get to "tweak" sizeable reactors. Chernobyl 4 is a worked example of "tweaking" a large reactor.

China might sell you their CAP1400 light-water reactor design (an upgrade of the Westinghouse AP1000) or maybe their HTR-PM modular reactors; they're actually building one at the moment to test the concept and they have a small testbed gas-cooled pebble-bed reactor running at the moment. India is working on using thorium in regular heavy-water reactors as part of the fuel mix, not in molten-salt systems and nobody else is really interested in buying into what they're doing. Other folks are looking into pebble-bed reactors which can burn thorium as part of the fuel mix but the previous history of attempting this is not a success, mostly -- the Germans are still trying to figure out how to decommission their thorium-mix pebble-bed reactors. They've been filled with concrete for the moment to stop the leaks of radioactivity.

There are also experiments going on to see how thorium works in regular light-water reactors. The physics says it will work, it's not as energetic as regular uranium fuels though. Baby steps baby steps.

Comment: Re:Incom.... (Score 1) 630

by nojayuk (#46723449) Attached to: Navy Debuts New Railgun That Launches Shells at Mach 7

Ballistic coefficient varies with shape too but generally it's dependent on mass and size. A .223 bullet and a .50BMG bullet are similar in shape and muzzle velocity but the .50MBG goes a lot further because it loses speed less quickly than the smaller round. It still can't fly as far as a battleship gun round though even if it's a better shape.

As for drag, well we have worked examples of clean shapes flying at high speeds. The SR-71 flying at Mach 3 glowed a dull red from skin friction and that was at 80,000 feet where the air pressure is something like 0.5 lbs/square inch or 3% that at sea level. Drag and skin heating effect goes up as the square of the speed so the railgun dart at sea level and Mach 7 would experience something like 4 x 30 or more than a hundred times the amount of drag the SR-71 experienced, and the railgun dart doesn't have engines pushing it along and sustaining its velocity in flight.

BTW I was wrong about the late-model US battleship guns, the perils of working from memory rather than checking the numbers. Their muzzle velocity was similar to most rifles, about 2700 fps and they were of course 16" bore.

Comment: Re:Incom.... (Score 1) 630

by nojayuk (#46710409) Attached to: Navy Debuts New Railgun That Launches Shells at Mach 7

Modern large-calibre artillery shells usually have base-bleed which coverts them effectively into a full boat-tail configuration in flight by filling in the space at the base of the shell with hot gas. They're actually more efficient than the best rifle bullets in this regard.

I can't find this information on the web but has anyone actually fired a railgun projectile over the sorts of distances described in the goshwow articles and promotional bumpf designed to get more funding out of Congress? Has there actually been a 100-mile ballistic test of this system yet? 50-mile? 10?

The movies I've seen of railgun test firings have all been straight-line non-ballistic shots over a few dozen metres demonstrating the sort of armour penetration capabilities DU spears fired by 120mm smoothbores have been able to achieve for decades. I recall reading about folks experimenting with high-velocity wildcat rifles (.30 cal bullets in necked-down .50BMG cases and the like) who ran into problems with solid projectiles melting from air friction at muzzle velocities of only 4000fps (less than Mach 4) over a range of a few hundred metres. It's entirely possible a railgun round would vapourise if fired several kilometres through sea-level air at Mach 7. Not something, of course, a slower seaskimming Tomahawk missile has problems with even though it can fly seven times farther than this railgun can fire, can alter course, is terminally guided and can even carry EW jamming kit.

Comment: Re:Incom.... (Score 1) 630

by nojayuk (#46709673) Attached to: Navy Debuts New Railgun That Launches Shells at Mach 7

Ballistic coefficient is dependent on the surface area of the projectile and its mass and a big heavy projectile with the same muzzle velocity as a small light projectile will retain more velocity all the way to the target. A .223 bullet will lose about 200 m/s of its original muzzle velocity over a distance of 300 metres. A similarly-shaped but larger and heavier .50BMG bullet with a similar muzzle velocity will lose about 80 m/s over the same distance, according to Hornady ballistics tables. If you've done any large-calibre shooting you'll know something like a .50BMG will carry a lot further than a .223.

Comment: Re:Incom.... (Score 5, Interesting) 630

by nojayuk (#46707605) Attached to: Navy Debuts New Railgun That Launches Shells at Mach 7

Smaller diameter projectiles have more drag per unit mass and slow down faster due to air resistance. It's called their ballistic coefficient.

The practice for howitzer-like weapons like railguns is to fire their projectiles in a high arc to get them out of thick atmosphere as fast as possible to reduce air friction. They still won't hit their target at anything like their muzzle velocity even after they recover some kinetic energy on the way back down to target from the top of their parabolic arc.

The ballistically efficient shells from the late-model 15" US Naval rifles had a muzzle velocity of about 3500 feet/second and a flight time to target at maximum range (25 miles or so) of a couple of minutes. Their velocity at impact was half that of their muzzle velocity. I don't see these railgun projectiles achieving anything like that performance as drag increases roughly as the square of velocity and their ballistic coefficient will be a lot less.

Comment: Re:Phones yeah (Score 1) 227

by nojayuk (#46696723) Attached to: Nanodot-Based Smartphone Battery Recharges In 30 Seconds

Flats in this block and neighbouring sell for US $500,000 plus when they come on the market which is rarely. Round the corner from us are million-buck town houses and if you're really got the moolah or work for Google there's a place for sale about 200 metres to the west, offers to exceed US $40 million.âZ

Bad area, I don't think so. Overcrowded by the standards of an American gated McMansion gulag, definitely. After all we have a main-line railway station across the street, bus and express coach stops outside our door and a (useless) new tram stop across the street at the railway station entrance. We have many pubs, restaurants and shops a few minutes walk from the front door, supermarkets ten minutes walk away, cinemas (including a couple of award-winning arthouse places) fifteen minutes walk from here. What we don't have is a lot of parking spaces and garages suitable for electric vehicles and without the ability to charge them where they're parked they're not much use compared to the many conventionally-fuelled cars and hybrids littering the surrounding streets.

You are in a maze of little twisting passages, all alike.