It is often incorrectly assumed that the combustion behavior of graphite is similar to that of charcoal and coal. Numerous tests and calculations have shown that it is virtually impossible to burn high-purity, nuclear-grade graphites. Graphite has been heated to white-hot temperatures (~1650C) without incurring ignition or self-sustained combustion. After removing the heat source, the graphite cooled to room temperature. Unlike nuclear-grade graphite, charcoal and coal burn at rapid rates because: * They contain high levels of impurities that catalyze the reaction. * They are very porous, which provides a large internal surface area, resulting in more homogeneous oxidation. * They generate volatile gases (e.g. methane), which react exothermically to increase temperatures. * They form a porous ash, which allows oxygen to pass through, but reduces heat losses by conduction and radiation. * They have lower thermal conductivity and specific heat than graphite. In fact, because graphite is so resistant to oxidation, it has been identified as a fire extinguishing material for highly reactive metals.
The oxidation resistance and heat capacity of graphite serves to mitigate, not exacerbate, the radiological consequences of a hypothetical severe accident that allowed air into the reactor vessel. Similar conclusions were reached after detailed assessments of the Chernobyl event; graphite played little or no role in the progression or consequences of the accident. The red glow observed during the Chernobyl accident was the expected color of luminescence for graphite at 700C and not a large-scale graphite fire, as some have incorrectly assumed. The New Scientist published a discussion of the General Atomic claim in its November 4. 1989 edition. The New Scientist investigation pointed out that the graphite in the Windscale fire was inpure, while the relatively pure graphite at Chernobyl contributed little to the that fire's heat. General Atomics in the past offered a demonstration to skeptics who wanted further convincing of their "Graphite does not burn," claim. A block of graphite would be brought out and heated to a red hot temperature. Then oxygen would be blown over the red hot graphite which would not catch fire. The New Scientist did not entirely support the General Atomics Graphite does not burn claim, but the analysis came down on the side of a graphite does burn reluctantly, and is not very dangerous conclusion, pointing to Peter Kroeger's research for support.
Peter Kroeger of Brookhaven National Laboratory (http://www.osti.gov/bridge/product.biblio.jsp?query_id=0&page=0&osti_id=6131128&Row=1)used a compluter simulation to check on General Atomic's claim. He found that if openings developed at two opposite ends of a graphite reactor containment structure, air could flow through the core, and graphite structures would burn some, but not very much, and certainly not enough to release radioactive materials embedded in the graphite. Air ingress into the primary loop requires prior depressurizatlon with significant subsequent air inflow. Scenarios that have been considered are, for Instance, a primary vessel leak such that during decay heat removal via a main loop or an auxiliary loop, significant amounts of gas can be exchanged between the primary loop and the RB, while the operating loop forces the re- sulting gas mixture through the core [34]. (It may be hard to conceive significant air ingress and combustible gas discharge from a single break; but only with such a large break or with several separate breaks and with simultaneous forced flow conditions can significant amounts of air be forced through the core.) Order of magnitude computations indicate that natural circulation can only result In about.1 to.3 kg/s of gas circulation through the core of a typical modular pebble bed reactor. The initial RB air Inventory of about 80 kg mol (even if none were lost during the Initial blowdown) can only cause the burn
insubordination or repeated violation of rules such as showing up on time.
Either the journalist is a product of the LA school system or the LA school system mandates that teachers show up late.
Looks more like YOU are a product of the LA school system. The reporters usage is correct. He is talking about a rule, i.e., the rule to show up on time.
How about a dedsign requirement that the core cannot go critical with even the most reactive single control rod totally removed from the reactor under any circumstances?
This is what we have now and is a direct result of that 1960 accident.
One thing you do not mention is the nasty waste stream that results from the manufacture of all that solar collection surface area. And I agree with the previous poster, the suraface area would be huge. Impractical to REPLACE other forms of energy supply. But maybe possible to supplement them, assuming you can deal with the toxic waste created from manufacture.
Your reply about killing the power before shorts occur doesn't fully comprehend the magnitude of the complexity of operating a large grid electrical distribution system. Only as a last resort do you drop circuits. Things get too hard to control, balance load etc when you start leaving the normal load practices. No power company is going to advocate dumping circuits in case of a short. Such a strategy will be worse than the cure. And would likely result in the whole grid possibly going down, just when you need to keep as much load up as possible. It is complicated and time consuming to restore a large grid if it goes down, not a trivial thing. I hear your comment about the fire prevention, but there are actually more important considerations system wide militating against a pre-emptive dumping of load on an earthquake warning.
Most useful I would think would be to give firemen the time to move their highly useful emergency apparatus out of a building that might fall down, or at least open big heavy doors that might get jammed. Several fire stations in San Fran had their outer doors get jammed in the last sizeable quake, rendering that euipment useless just when it is most needed.
"Electrical systems could prepare for shutdown to prevent fires and other damage from short circuits (kill the circuit breakers at the first heavy shaking), and hospitals and the like could automatically start their emergency generators to prepare for cutover."
Since I work in the power generation industry (in CA actually) I believe the first part of your comment above is not really applicable. Most of the damage to the grid in the past has come from the ground shaking uprooting and breaking stuff such as foundation bolts hold heavy stuff in place, or ceramic insulators on transformers or large power circuit breakers and transmission towers. Then this damage can cause an electrical short, which is then almost instantaneously isolated. The systems that are already in place can isolate shorts, grounds and opens in fractions of a second, on the order of a few cycles of a waveform of ac. I.e., the existing fault isolation systems and relays are already so fast a thirty second warning would be superfluous.
The second part of the above comment is useful however, because most blackstart emergency diesel or combustion turbine generators can take anywhere from 10 seconds to 2 minutes to get up to to speed and voltage and assume load. With a thirty second headstart you could get them up to speed and have a near seamless transfer of load when and if the shaking knocks out your circuit on the main grid.
It was the original CPU chosen for the Amiga 1000 and several of the Atari machines. It was the first consumer 32 bit device (16/24 bit address bus, 32 bit for everything else).
It had a clock speed of 7.14 MHz, or 0.000714 GHz.
Slashdot Mirror
You are an FUD-idiot.
It is often incorrectly assumed that the combustion behavior of graphite is similar to that of charcoal and coal.
Numerous tests and calculations have shown that it is virtually impossible to burn high-purity, nuclear-grade graphites. Graphite has been heated to white-hot temperatures (~1650C) without incurring ignition or self-sustained combustion. After removing the heat source, the graphite cooled to room temperature. Unlike nuclear-grade graphite, charcoal and coal burn at rapid rates because:
* They contain high levels of impurities that catalyze the reaction.
* They are very porous, which provides a large internal surface area, resulting in more homogeneous oxidation.
* They generate volatile gases (e.g. methane), which react exothermically to increase temperatures.
* They form a porous ash, which allows oxygen to pass through, but reduces heat losses by conduction and radiation.
* They have lower thermal conductivity and specific heat than graphite.
In fact, because graphite is so resistant to oxidation, it has been identified as a fire extinguishing material for highly reactive metals.
The oxidation resistance and heat capacity of graphite serves to mitigate, not exacerbate, the radiological consequences of a hypothetical severe accident that allowed air into the reactor vessel. Similar conclusions were reached after detailed assessments of the Chernobyl event; graphite played little or no role in the progression or consequences of the accident. The red glow observed during the Chernobyl accident was the expected color of luminescence for graphite at 700C and not a large-scale graphite fire, as some have incorrectly assumed. The New Scientist published a discussion of the General Atomic claim in its November 4. 1989 edition. The New Scientist investigation pointed out that the graphite in the Windscale fire was inpure, while the relatively pure graphite at Chernobyl contributed little to the that fire's heat. General Atomics in the past offered a demonstration to skeptics who wanted further convincing of their "Graphite does not burn," claim. A block of graphite would be brought out and heated to a red hot temperature. Then oxygen would be blown over the red hot graphite which would not catch fire. The New Scientist did not entirely support the General Atomics Graphite does not burn claim, but the analysis came down on the side of a graphite does burn reluctantly, and is not very dangerous conclusion, pointing to Peter Kroeger's research for support.
Peter Kroeger of Brookhaven National Laboratory (http://www.osti.gov/bridge/product.biblio.jsp?query_id=0&page=0&osti_id=6131128&Row=1)used a compluter simulation to check on General Atomic's claim. He found that if openings developed at two opposite ends of a graphite reactor containment structure, air could flow through the core, and graphite structures would burn some, but not very much, and certainly not enough to release radioactive materials embedded in the graphite. .1 to .3 kg/s of gas circulation through the core of a typical modular pebble bed reactor. The initial RB air Inventory of about 80 kg mol (even if none were lost during the Initial blowdown) can only cause the burn
Air ingress into the primary loop requires prior depressurizatlon with significant subsequent air inflow. Scenarios that have been considered are, for Instance, a primary vessel leak such that during decay heat removal via a main loop or an auxiliary loop, significant amounts of gas can be exchanged between the primary loop and the RB, while the operating loop forces the re- sulting gas mixture through the core [34]. (It may be hard to conceive significant air ingress and combustible gas discharge from a single break; but only with such a large break or with several separate breaks and with simultaneous forced flow conditions can significant amounts of air be forced through the core.) Order of magnitude computations indicate that natural circulation can only result In about
Don't confuse Radiotoxicity with Radioactivity. They are not the same thing.
You sir are ignorant and opinionated about something you clearly know little about.
You fit in on /. perfectly.
Norman Borlaug beat him to death with his dwarf wheat.
> ... there is no independant research to show if they are even practical.
Except that there is:
http://www.energyfromthorium.com/pdf/
TWR is the Traveling Wave Reactor. A theoretical design. None have been built. http://en.wikipedia.org/wiki/Traveling_wave_reactor
Yes a different sort of high level waste.
The sort that is down to background radiation in 300-500 years as compared to 10,000 years.
I work at a real life central station baseloaded power plant that puts out 2250+ MW.
You sir, are an idiot.
You recall incorrectly. Only very high energy beta particles can penetrate the skin.
Yep. The Thorium is bred to U-233, then the U-233 is fissioned.
Thorium Reactors ARE breeder reactors.
Looks more like YOU are a product of the LA school system. The reporters usage is correct. He is talking about a rule, i.e., the rule to show up on time.
How about a dedsign requirement that the core cannot go critical with even the most reactive single control rod totally removed from the reactor under any circumstances?
This is what we have now and is a direct result of that 1960 accident.
One thing you do not mention is the nasty waste stream that results from the manufacture of all that solar collection surface area. And I agree with the previous poster, the suraface area would be huge. Impractical to REPLACE other forms of energy supply. But maybe possible to supplement them, assuming you can deal with the toxic waste created from manufacture.
Just count the number of derivatives of "I" in his message. Says it all right there.....
Your reply about killing the power before shorts occur doesn't fully comprehend the magnitude of the complexity of operating a large grid electrical distribution system. Only as a last resort do you drop circuits. Things get too hard to control, balance load etc when you start leaving the normal load practices. No power company is going to advocate dumping circuits in case of a short. Such a strategy will be worse than the cure. And would likely result in the whole grid possibly going down, just when you need to keep as much load up as possible. It is complicated and time consuming to restore a large grid if it goes down, not a trivial thing. I hear your comment about the fire prevention, but there are actually more important considerations system wide militating against a pre-emptive dumping of load on an earthquake warning.
Most useful I would think would be to give firemen the time to move their highly useful emergency apparatus out of a building that might fall down, or at least open big heavy doors that might get jammed. Several fire stations in San Fran had their outer doors get jammed in the last sizeable quake, rendering that euipment useless just when it is most needed.
"Electrical systems could prepare for shutdown to prevent fires and other damage from short circuits (kill the circuit breakers at the first heavy shaking), and hospitals and the like could automatically start their emergency generators to prepare for cutover."
Since I work in the power generation industry (in CA actually) I believe the first part of your comment above is not really applicable. Most of the damage to the grid in the past has come from the ground shaking uprooting and breaking stuff such as foundation bolts hold heavy stuff in place, or ceramic insulators on transformers or large power circuit breakers and transmission towers. Then this damage can cause an electrical short, which is then almost instantaneously isolated. The systems that are already in place can isolate shorts, grounds and opens in fractions of a second, on the order of a few cycles of a waveform of ac. I.e., the existing fault isolation systems and relays are already so fast a thirty second warning would be superfluous.
The second part of the above comment is useful however, because most blackstart emergency diesel or combustion turbine generators can take anywhere from 10 seconds to 2 minutes to get up to to speed and voltage and assume load. With a thirty second headstart you could get them up to speed and have a near seamless transfer of load when and if the shaking knocks out your circuit on the main grid.
Of course. After their grocery billl went down they were able to afford it... ;)
This just in....
The US Govt will require all recreational computer users to rtestrict their computer use to the hours of 6:00 A.M to 2:00 P.M. in each time zone.
No more late night gaming and sleeping in till noon.....
I left out the Apple line as an experiment to see how long before someone posted about the fact.
Took longer than I thought it would actually.
I forgot about Palm. I have a IIIc so I should know better.
Wrong.
6800 (Aug '74) was an 8-bit chip.
68000 (Sep 79) was a 16/24/32 bit chip (16 data 24 address 32 everything else. It was the first consumer available chip capable of 32 bit math.
Ooops. Stuttered on the "0".....
Hardly.
It was the original CPU chosen for the Amiga 1000 and several of the Atari machines. It was the first consumer 32 bit device (16/24 bit address bus, 32 bit for everything else).
It had a clock speed of 7.14 MHz, or 0.000714 GHz.