That paragraph talks about the density of the moderator (water). As I showed in my earlier post, the density of liquid water doesn't change significantly with temperature. So the obvious question is "what does significantly change the density?" That paragraph also talks about "...giving greater 'gaps' between the water molecules..." Those 'gaps' are caused by localized boiling/vaporization of the water. Water expands over 1300x (not 1300% as my earlier post stated) when it boils. In a highly pressurized state, it won't expand as much, but it's still orders of magnitude greater than the expansion due to temperature. The decrease in moderator activity is due to localized boiling/vaporization of the water, NOT due to the increase in temperature of the liquid water. That's what I've stated this entire thread.
The OP then asserted that "Colder water is denser, therefore a better neutron moderator." I pointed out that while that's technically correct, the difference is density due solely to temperature is minimal, that the cause of lower density and therefore lower moderation rates at higher temperatures were primarily due to voids cause by localized boiling of the water, not by the temperature of the liquid water. The voids are dissolved steam in the liquid water, but the voids are not liquid, they're tiny bubbles of steam. In highly pressurized systems (such as a PWR) with a significant heat source (e.g. active fuel rods), there can be significant amount of dissolved steam in the water. In fact, keeping that steam dissolved in the water is the very premise upon which the PWR operates (as opposed to a BWR which is design to allow the steam to escape the water, and is used to directly power the turbine).
To put it very simply, tiny bubbles (of steam) are what decreases the moderator density significantly enough cause a negative coefficient of reactivity. With a sufficient heat source in the water, you can have tiny steam bubbles in any liquid water. When you also factor in pressure, the range of temperatures at which water can remain liquid and contain steam bubbles is very large. So, it's not the temperature of the water that is important, it's the amount of dissolved steam (voids) that affects the moderation rate.
Whether you agree or not, those are the facts, and I'm done trying to explain it to you.
And exactly how much does water expand (without boiling) as the temperature increases from 4c (most dense) to 100c or 250c (pressurized to prevent boiling)? Do the math, the change is insignificant. The decrease in density they're talking about is from the voids caused by boiling.
I'll give you some info to get point you in the right direction. Water expands less than 3% from 4c to 80c, less than 4.2% from 4c to 100c, but it expands over 1300% when it boils (at standard pressure). Less than 4.2% difference in density from a 96c change in temperature vs a change more than 3 orders of magnitude larger, which one is going to be responsible for a significant change in the neutron moderation rate? (Hint, it's the one that causes a big change in density) BTW, those water densities and percentage changes don't change much with pressure.
Better yet, ask them to release all documentation on items they've previously lied about on any FOIA request. Then, get out a really big checkbook for the massive amount of paperwork you may or may not receive.
Yes, yes it does. That's part of how a PWR obtains it's negative reactivity coefficient. (A major part of what makes them safe.) It's why reactor operators fear a cold water accident - the sudden introduction of significantly cooler water into the core.
No, the density change due to temperature of liquid water is not what changed the moderation rate or reactivity coefficient. It is "voids" in the water, aka, water that has converted to a gas, just as I stated in my original reply.
Here is the actual physics: "When the coolant water temperature increases, the boiling increases, which creates voids. Thus there is less water to absorb thermal neutrons that have already been slowed down by the graphite moderator, causing an increase in reactivity.
Voids only occur when: 1. The fuel is very hot relative to the boiling point of water at the current pressure, and 2. The water temperature, pressure, and flow rate are insufficient to remove the heat from the fuel without boiling (thus creating voids).
Lower water temperature DOES NOT significantly increase moderation rate, a lower void coefficient does. Void coefficient is related to temperature, pressure, flow rate, and fuel temperature, but it's not directly related to water temperature, it's directly related to the amount of boiling.
There are two things that can change criticality inside a reactor - a change in fuel geometry and properties or a change in moderator geometry or properties. Fuel alone will not cause such an event - unless a critical mass is present. For that to happen today (months after the accident and thousands of degrees below the fuels melting point) that means you have to have significant chunks of fuel moving about in the core.
There must have been a moderator for any notable amount of fission to occur, but a single of water seeping into a crack in the cooling fuel is sufficient to have produced the amount of Xenon measured. The water would act as a moderator first, increasing the fission rate, then it would heat up and create voids, decreasing the fission rate, in the process, producing slightly more fission product than spontaneous fission in the absence of a moderator.
The takeaway here is that anyone can follow the link I provided and determine which posts are correct.
1. It wasn't past it's design lifetime. The reactors were each 35-40 years into a 40 year initial license (but only 25-30 years since first criticality). With a design lifetime of at least 50 years.
2. It was designed for a maximum of a magnitude 8 quake. A magnitude 8+ earthquake did not have "a relatively high probability" in it's lifetime when it was built. There is an average of 1 per year worldwide, 81% of those along the 40,000km "ring of fire". That does not translate into a "relatively high probability" for one in a 60 year span even in Japan. If you look at the history of large earthquakes in Japan, you'll find that M8+ quakes were very infrequent prior to it's construction, and that it has survived a number of magnitude M6.5-M8.3 quakes in it's lifetime. I would say it performed extremely well.
3. It wasn't predictable: "It was the most powerful known earthquake ever to have hit Japan."
4. While the actual ground movement from the earthquake at the plant was only 1/2 what it was designed to withstand, the tsunami was nearly 3x what it was designed to withstand. "The design basis accident for an earthquake was between 0.42 g (4.15 m/s2) and 0.52 g (5.12 m/s2) and for a tsunami was 5.2 m" Actual ground movement was 0.21g-0.28g and the tsunami was 14m-15m.
The density change in liquid water does not significantly alter it's ability to moderate neutron flux. It's only when the water is hot enough that some of it vaporizes that it's ability to moderate neutron flux changes significantly. Therefore, that part of your statement is materially incorrect, even though it is technically correct.
The shape, and current status of the fuel is unknown, and that alone is the likely source of this event.
Nothing wrong with being liberal. Nothing the OP said fits the definition of liberal, so please stop misusing the word.
Liberal - adjective 1. favorable to progress or reform, as in political or religious affairs. 2. (often initial capital letter) noting or pertaining to a political party advocating measures of progressive political reform. 3. of, pertaining to, based on, or advocating liberalism. 4. favorable to or in accord with concepts of maximum individual freedom possible, especially as guaranteed by law and secured by governmental protection of civil liberties. 5. favoring or permitting freedom of action, especially with respect to matters of personal belief or expression. 6. of or pertaining to representational forms of government rather than aristocracies and monarchies. 7. free from prejudice or bigotry; tolerant. 8. open-minded or tolerant, especially free of or not bound by traditional or conventional ideas, values, etc. 9. characterized by generosity and willingness to give in large amounts. 10. given freely or abundantly; generous. 11. not strict or rigorous; free; not literal. 12. of, pertaining to, or based on the liberal arts. 13. of, pertaining to, or befitting a freeman.
True, but they still produce plutonium, and the energy and cost to extract sufficient heavy water for the reactor is significant, and you have the ongoing problem of removing tritium from the heavy water. Because of these factors, HWR are probably not a good long term solution.
Judging nuclear power's safety by a first generation reactor design that was built nearly 40 years ago, and that despite a M9 earthquake and 15m tsunami has not killed anyone, and is predicted to eventually cause up to 100 deaths from cancer is foolish. It's like judging hydro power by the dams that have burst and flooded and killed thousands, or by natural gas pipeline explosions that have killed hundreds, yet you're not protesting those types of power.
Nuclear power has caused fewer deaths per TWh generated than any major power source, including wind, solar, geothermal, hydro, or fossil fuels. Nuclear power is the safest power source yet tried, and that's even with the older reactor designs and the Russian RBMK design (e.g Chernobyl) that is inherently unstable and should never have been built.
Gen III reactors have passive safety designs that allow full cold shutdown with no external power. And thorium fueled reactors don't produce usable quantities of plutonium so they're not a proliferation concern, and doesn't require uranium enrichment (which is itself expensive and dangerous). And using fuel reprocessing dramatically lowers the nuclear waste (by a factor to 10 to 100).
Tokyo Electric Power Co. said Thursday the detection of radioactive xenon at its stricken Fukushima Daiichi power plant, indicating recent nuclear fission, was not the result of a sustained nuclear chain reaction known as a criticality, as feared, but a case of "spontaneous" fission.
Not all of us can be mathematicians. Some of us can make a contribution by paying attention to the news as it happens and not sucking on the party line.
So, you're "contribution" is an uninformed opinion regurgitated from some anti-nuclear site/blog that you don't have the facts or knowledge to back up? How generous of you to contribute in such a fashion.
The test results that came out of UC Berkeley during the event are relevant. Some great results were coming out of Seattle for a while, too. Then they shut down the testing. Now it's hard to even find any of this stuff.
And none of those results showed dangerous levels. The reason the stopped publishing (but not performing) the tests is that the levels weren't dangerous, but there were news sites reporting on the results and misinterpreting them in ways that were causing a panic.
You spreading misinformation is part of the problem, not a "contribution". Either go learn something about the topic, or keep your misinformation to the anti-nuclear sites. When you have actually learned about nuclear energy, then form an opinion about it.
There's enough thorium in the US to supply energy for a lot more than 1000 years, especially if we use fuel reprocessing, which also dramatically reduces the amount of waste.
No, the old designs never incorporated passive safety systems, they were all active safety systems. They were fault tolerant, not fail-safe. Anyone who claimed otherwise was lying or misinformed because it was known at the time that they weren't fail-safe. However, they did believe the active safety systems were sufficient to prevent a major problem, and until Fukushima (which a greater than design basis earthquake, a much greater than design basis tsunami, and a full station blackout), history backed that position.
I excluded Chernobyl because the RBMK design is inherently unstable, those reactors should not have been built. Under normal operation, they can be operated without incident by using a lot of active safety systems, but if those safety systems are bypassed or disabled, they can experience a runaway reaction that blows up the reactor, which is what happened at Chernobyl.
Fail-safe for nuclear power doesn't mean the reactor itself will necessarily be undamaged (although that's certainly the goal), but that it can achieve full "cold-shutdown" using no external power (nor backup generators) and that it can't experience a runaway reaction. That is achieved with a combination of reactor design, passive shutdown and cooling systems, and some redundant self powered active systems (intended to shut it down faster and lower the risk of damage to the reactor). With those in place, even a disaster the scale of the one in Japan would release little or no radiation, and probably would not damage the reactors enough to decommission them.
Yes, but it does continue to set precedence which is what we direly need lots of. Once enough precedence is set, the courts will have more of a foundation to stand on when throwing these bum's cases out the window.
The term is precedent, the plural is precedents. Precedence is a completely different thing. Sound almost the same, but the meanings are totally different.
Don't use helium. Helium's primary advantages are that it's radioisotopes are so short lived that any escaping helium would be stable by the time it made it through the container wall, and it decays back to helium. Instead, use the larger nitrogen (N2) or neon (Ne). Both are much cheaper and easier to contain and have good thermal properties, and when they absorb neutrons, they rapidly decay to stable isotopes. They will produce stable isotopes of other elements (notably 15N->16O, and 22Ne->23Na), so filtering and replenishment is necessary, but since they're cheap gases that are easily contained, they're much less problematic than helium.
The point is that the whole premise of "it's a casino" or that the developers program cost "make it extremely hard for anyone to be able to make a profit" is complete BS. If your $0.99 app sells 12 copies a month, you cover the developer program fee. If your app doesn't sell 144 copies in a year, maybe you should rethink being a developer.
That's not to say that a developers time isn't worth money, but that's a risk you take when developing a new product/business. If you don't develop a product/service people want/need at a price they're able/willing to pay, or can't sell enough volume to cover your development, marketing, production, and distribution costs, you shouldn't be in that business. Intro to capitalism 101.
Slashdot Mirror
Perhaps to continue to develop and test subject matter and methodologies?
There is no randomness, it is you who must be random.
That explains why my packets disappear when they have too many neighbors.
Shotgun blast to the head, right? But what kind of shotgun do you use for a corporation?
That paragraph talks about the density of the moderator (water). As I showed in my earlier post, the density of liquid water doesn't change significantly with temperature. So the obvious question is "what does significantly change the density?" That paragraph also talks about "...giving greater 'gaps' between the water molecules..." Those 'gaps' are caused by localized boiling/vaporization of the water. Water expands over 1300x (not 1300% as my earlier post stated) when it boils. In a highly pressurized state, it won't expand as much, but it's still orders of magnitude greater than the expansion due to temperature. The decrease in moderator activity is due to localized boiling/vaporization of the water, NOT due to the increase in temperature of the liquid water. That's what I've stated this entire thread.
The OP then asserted that "Colder water is denser, therefore a better neutron moderator." I pointed out that while that's technically correct, the difference is density due solely to temperature is minimal, that the cause of lower density and therefore lower moderation rates at higher temperatures were primarily due to voids cause by localized boiling of the water, not by the temperature of the liquid water. The voids are dissolved steam in the liquid water, but the voids are not liquid, they're tiny bubbles of steam. In highly pressurized systems (such as a PWR) with a significant heat source (e.g. active fuel rods), there can be significant amount of dissolved steam in the water. In fact, keeping that steam dissolved in the water is the very premise upon which the PWR operates (as opposed to a BWR which is design to allow the steam to escape the water, and is used to directly power the turbine).
To put it very simply, tiny bubbles (of steam) are what decreases the moderator density significantly enough cause a negative coefficient of reactivity. With a sufficient heat source in the water, you can have tiny steam bubbles in any liquid water. When you also factor in pressure, the range of temperatures at which water can remain liquid and contain steam bubbles is very large. So, it's not the temperature of the water that is important, it's the amount of dissolved steam (voids) that affects the moderation rate.
Whether you agree or not, those are the facts, and I'm done trying to explain it to you.
No, it doesn't say what you think it says. It says specifically that it's caused by changed in the void coefficient. QED, case closed.
And exactly how much does water expand (without boiling) as the temperature increases from 4c (most dense) to 100c or 250c (pressurized to prevent boiling)? Do the math, the change is insignificant. The decrease in density they're talking about is from the voids caused by boiling.
I'll give you some info to get point you in the right direction. Water expands less than 3% from 4c to 80c, less than 4.2% from 4c to 100c, but it expands over 1300% when it boils (at standard pressure). Less than 4.2% difference in density from a 96c change in temperature vs a change more than 3 orders of magnitude larger, which one is going to be responsible for a significant change in the neutron moderation rate? (Hint, it's the one that causes a big change in density) BTW, those water densities and percentage changes don't change much with pressure.
The "Gaps" between molecules are the "voids" caused by boiling.
Pretending you know what you're talking about is no substitute for actually being correct.
Better yet, ask them to release all documentation on items they've previously lied about on any FOIA request. Then, get out a really big checkbook for the massive amount of paperwork you may or may not receive.
Had to post to undo my accidental mod down. Meant to mod you up.
Yes, yes it does. That's part of how a PWR obtains it's negative reactivity coefficient. (A major part of what makes them safe.) It's why reactor operators fear a cold water accident - the sudden introduction of significantly cooler water into the core.
No, the density change due to temperature of liquid water is not what changed the moderation rate or reactivity coefficient. It is "voids" in the water, aka, water that has converted to a gas, just as I stated in my original reply.
Here is the actual physics: "When the coolant water temperature increases, the boiling increases, which creates voids. Thus there is less water to absorb thermal neutrons that have already been slowed down by the graphite moderator, causing an increase in reactivity.
Voids only occur when:
1. The fuel is very hot relative to the boiling point of water at the current pressure, and
2. The water temperature, pressure, and flow rate are insufficient to remove the heat from the fuel without boiling (thus creating voids).
Lower water temperature DOES NOT significantly increase moderation rate, a lower void coefficient does. Void coefficient is related to temperature, pressure, flow rate, and fuel temperature, but it's not directly related to water temperature, it's directly related to the amount of boiling.
There are two things that can change criticality inside a reactor - a change in fuel geometry and properties or a change in moderator geometry or properties. Fuel alone will not cause such an event - unless a critical mass is present. For that to happen today (months after the accident and thousands of degrees below the fuels melting point) that means you have to have significant chunks of fuel moving about in the core.
There must have been a moderator for any notable amount of fission to occur, but a single of water seeping into a crack in the cooling fuel is sufficient to have produced the amount of Xenon measured. The water would act as a moderator first, increasing the fission rate, then it would heat up and create voids, decreasing the fission rate, in the process, producing slightly more fission product than spontaneous fission in the absence of a moderator.
The takeaway here is that anyone can follow the link I provided and determine which posts are correct.
1. It wasn't past it's design lifetime. The reactors were each 35-40 years into a 40 year initial license (but only 25-30 years since first criticality). With a design lifetime of at least 50 years.
2. It was designed for a maximum of a magnitude 8 quake. A magnitude 8+ earthquake did not have "a relatively high probability" in it's lifetime when it was built. There is an average of 1 per year worldwide, 81% of those along the 40,000km "ring of fire". That does not translate into a "relatively high probability" for one in a 60 year span even in Japan. If you look at the history of large earthquakes in Japan, you'll find that M8+ quakes were very infrequent prior to it's construction, and that it has survived a number of magnitude M6.5-M8.3 quakes in it's lifetime. I would say it performed extremely well.
3. It wasn't predictable: "It was the most powerful known earthquake ever to have hit Japan."
4. While the actual ground movement from the earthquake at the plant was only 1/2 what it was designed to withstand, the tsunami was nearly 3x what it was designed to withstand. "The design basis accident for an earthquake was between 0.42 g (4.15 m/s2) and 0.52 g (5.12 m/s2) and for a tsunami was 5.2 m" Actual ground movement was 0.21g-0.28g and the tsunami was 14m-15m.
In short, everything you claimed is false.
The density change in liquid water does not significantly alter it's ability to moderate neutron flux. It's only when the water is hot enough that some of it vaporizes that it's ability to moderate neutron flux changes significantly. Therefore, that part of your statement is materially incorrect, even though it is technically correct.
The shape, and current status of the fuel is unknown, and that alone is the likely source of this event.
Nothing wrong with being liberal. Nothing the OP said fits the definition of liberal, so please stop misusing the word.
Liberal - adjective
1. favorable to progress or reform, as in political or religious affairs.
2. (often initial capital letter) noting or pertaining to a political party advocating measures of progressive political reform.
3. of, pertaining to, based on, or advocating liberalism.
4. favorable to or in accord with concepts of maximum individual freedom possible, especially as guaranteed by law and secured by governmental protection of civil liberties.
5. favoring or permitting freedom of action, especially with respect to matters of personal belief or expression.
6. of or pertaining to representational forms of government rather than aristocracies and monarchies.
7. free from prejudice or bigotry; tolerant.
8. open-minded or tolerant, especially free of or not bound by traditional or conventional ideas, values, etc.
9. characterized by generosity and willingness to give in large amounts.
10. given freely or abundantly; generous.
11. not strict or rigorous; free; not literal.
12. of, pertaining to, or based on the liberal arts.
13. of, pertaining to, or befitting a freeman.
True, but they still produce plutonium, and the energy and cost to extract sufficient heavy water for the reactor is significant, and you have the ongoing problem of removing tritium from the heavy water. Because of these factors, HWR are probably not a good long term solution.
Judging nuclear power's safety by a first generation reactor design that was built nearly 40 years ago, and that despite a M9 earthquake and 15m tsunami has not killed anyone, and is predicted to eventually cause up to 100 deaths from cancer is foolish. It's like judging hydro power by the dams that have burst and flooded and killed thousands, or by natural gas pipeline explosions that have killed hundreds, yet you're not protesting those types of power.
Nuclear power has caused fewer deaths per TWh generated than any major power source, including wind, solar, geothermal, hydro, or fossil fuels. Nuclear power is the safest power source yet tried, and that's even with the older reactor designs and the Russian RBMK design (e.g Chernobyl) that is inherently unstable and should never have been built.
Gen III reactors have passive safety designs that allow full cold shutdown with no external power. And thorium fueled reactors don't produce usable quantities of plutonium so they're not a proliferation concern, and doesn't require uranium enrichment (which is itself expensive and dangerous). And using fuel reprocessing dramatically lowers the nuclear waste (by a factor to 10 to 100).
From Mainichi Daily News
Tokyo Electric Power Co. said Thursday the detection of radioactive xenon at its stricken Fukushima Daiichi power plant, indicating recent nuclear fission, was not the result of a sustained nuclear chain reaction known as a criticality, as feared, but a case of "spontaneous" fission.
Not all of us can be mathematicians. Some of us can make a contribution by paying attention to the news as it happens and not sucking on the party line.
So, you're "contribution" is an uninformed opinion regurgitated from some anti-nuclear site/blog that you don't have the facts or knowledge to back up? How generous of you to contribute in such a fashion.
The test results that came out of UC Berkeley during the event are relevant. Some great results were coming out of Seattle for a while, too. Then they shut down the testing. Now it's hard to even find any of this stuff.
And none of those results showed dangerous levels. The reason the stopped publishing (but not performing) the tests is that the levels weren't dangerous, but there were news sites reporting on the results and misinterpreting them in ways that were causing a panic.
You spreading misinformation is part of the problem, not a "contribution". Either go learn something about the topic, or keep your misinformation to the anti-nuclear sites. When you have actually learned about nuclear energy, then form an opinion about it.
Good answer. :)
There's enough thorium in the US to supply energy for a lot more than 1000 years, especially if we use fuel reprocessing, which also dramatically reduces the amount of waste.
Which has nothing to do with the comparison of the cost of solar to nuclear.
No, the old designs never incorporated passive safety systems, they were all active safety systems. They were fault tolerant, not fail-safe. Anyone who claimed otherwise was lying or misinformed because it was known at the time that they weren't fail-safe. However, they did believe the active safety systems were sufficient to prevent a major problem, and until Fukushima (which a greater than design basis earthquake, a much greater than design basis tsunami, and a full station blackout), history backed that position.
I excluded Chernobyl because the RBMK design is inherently unstable, those reactors should not have been built. Under normal operation, they can be operated without incident by using a lot of active safety systems, but if those safety systems are bypassed or disabled, they can experience a runaway reaction that blows up the reactor, which is what happened at Chernobyl.
Fail-safe for nuclear power doesn't mean the reactor itself will necessarily be undamaged (although that's certainly the goal), but that it can achieve full "cold-shutdown" using no external power (nor backup generators) and that it can't experience a runaway reaction. That is achieved with a combination of reactor design, passive shutdown and cooling systems, and some redundant self powered active systems (intended to shut it down faster and lower the risk of damage to the reactor). With those in place, even a disaster the scale of the one in Japan would release little or no radiation, and probably would not damage the reactors enough to decommission them.
Yes, but it does continue to set precedence which is what we direly need lots of. Once enough precedence is set, the courts will have more of a foundation to stand on when throwing these bum's cases out the window.
The term is precedent, the plural is precedents. Precedence is a completely different thing. Sound almost the same, but the meanings are totally different.
Don't use helium. Helium's primary advantages are that it's radioisotopes are so short lived that any escaping helium would be stable by the time it made it through the container wall, and it decays back to helium. Instead, use the larger nitrogen (N2) or neon (Ne). Both are much cheaper and easier to contain and have good thermal properties, and when they absorb neutrons, they rapidly decay to stable isotopes. They will produce stable isotopes of other elements (notably 15N->16O, and 22Ne->23Na), so filtering and replenishment is necessary, but since they're cheap gases that are easily contained, they're much less problematic than helium.
Already accounted for. $0.99 * 144 = $142.56 * .7 (100%-30%) = $99.79.
The point is that the whole premise of "it's a casino" or that the developers program cost "make it extremely hard for anyone to be able to make a profit" is complete BS. If your $0.99 app sells 12 copies a month, you cover the developer program fee. If your app doesn't sell 144 copies in a year, maybe you should rethink being a developer.
That's not to say that a developers time isn't worth money, but that's a risk you take when developing a new product/business. If you don't develop a product/service people want/need at a price they're able/willing to pay, or can't sell enough volume to cover your development, marketing, production, and distribution costs, you shouldn't be in that business. Intro to capitalism 101.