21 ms·

While I realize it was likely impractical to meltdown reactors just to develop the technology to clean them up, I find the process here pretty interesting. A lo

While I realize it was likely impractical to meltdown reactors just to develop the technology to clean them up, I find the process here pretty interesting. A lot of good engineering has gone into the effort, and the engineering challenges (and risks) of post runaway reactors has gotten a lot more data. The Chernobyl folks just entombed everything, which is a one approach, even though they can "walk up to"[1] the remains of the nuclear fuel which they call the "elephant foot." I also find it interesting that the "China Syndrome"[2] speculation is pretty much completely debunked. Molten/melted fuel diffuses into the material it is melting into until it loses criticality and then freezes where ever it is. All modern reactors have a borosilicate sand pile underneath the reactor. The boron acts as a neutron absorber (poison) which stops the chain reaction once the fuel has been glassified by the silicate. [1] It is too radioactive for that to be literally true, but it is on a floor with direct access rather than being underwater and only accessible through cracks as the Fukishima fuel is. [2] Speculation that a blob of melted core material would just keep melting into the ground until it "got to china" (which in fact would be interrupted by getting to the earths core). [3] EDIT: Corrected for the effects of Boron on the reaction acting as a neutron poison (absorbs neutrons) rather than a moderator (which just bounces them around)

cpeterso 8y ago
> melted core material would just keep melting into the ground until it "got to china" aka "China Syndrome", just like the 1979 film: https://en.wikipedia.org/wiki/Nuclear_meltdown#China_syndrome https://en.wikipedia.org/wiki/Nuclear_meltdown#China_syndrom...
- __m 8y ago
  Now that convincingly debunks the China syndrome, China is obviously not the antipode to Fukushima
petschge 8y ago
Boron actually mostly acts as a neutron poison, i.e. it absorbs neutrons. That way further (stimulated) decay of other nucleii that were hit by a neutron is eliminated and the chain reaction stops, reducing the production of thermal energy. A moderator on the other hand inelastically scatters neutrons, converting some of the kinetic energy of the neutrons to heat and leaving a slower neutron. Moderators are used in reactors to bring neutrons down from their initial velocity to velocities where they are more likely to stimulate fission in another nucleus.
- ChuckMcM 8y ago
  Correction noted! Thanks!
- pfdietz 8y ago
  > A moderator on the other hand inelastically scatters neutrons, Most moderators elastically scatter neutrons. What other kind of collision could there be with a hydrogen nucleus?
  - petschge 8y ago
    You are of course right. The scattering conserved total energy, but not the energy of the neutron.
  - hexane360 8y ago
    When discussing scattering of particles, "elastic" usually refers to electrostatic slingshots where almost the entire kinetic energy of the particle is conserved. Inelastic, however, refers to a direct collision where there is a significant energy loss of the particle. Obviously the former doesn't happen with neutrons, but I believe it's still a typical convention in particle physics.
    - pfdietz 8y ago
      No, elastic means an encounter where kinetic energy is conserved, rather than being converted to some other form of energy. THe neutron/nucleus collisions in a moderator are largely elastic. The total kinetic energy of the neutron and the nucleus is conserved, although kinetic energy is transfered from the neutron to the nucleus. An inelastic collision would involve (for example) nuclear excitation of the target nucleus, or ejection of particles from the target nucleus. The neutrons from fission are usually too low in energy for this to be very likely, though.
pvaldes 8y ago
> the "China Syndrome" speculation is pretty much completely debunked You would be dissapointed. Cou-cou! surprise! The ocean strikes back!. Unexpected source of Fukushima-derived radiocesium to the coastal ocean of Japan. 2017. Sanial, Buessler, Charette, and Nagao. PNAS. DOI:10.1073/pnas.1708659114 "Sanial, Buessler, Charette and Nagao, scientists from Massachusetts and Japan found a new source of Caesium-137 to the environment after the Fukushima accident. From 2013 – 2016 they visited 8 different beaches within 100 km of the accident site, took sand and water samples and measured its radioactivity. They found that at the bottom of their sand samples, up to 2 m deep into the beach, the 137Cs concentrations were incredibly high, up to 480,000 Bq per square meter in their deepest samples. The soil in the restricted zone of the Fukushima site, up to 100 km away, measured ~100,000 Bq per square meter. This means even tens of kilometers away, the radiation can actually be higher than near the disaster. (Because, huh?, 137Cs sticks to the sand grains). https://oceanbites.org/going-nuclear-radioisotopes-from-fukushimi-power-plant-stay-in-sand-for-years/ https://oceanbites.org/going-nuclear-radioisotopes-from-fuku...
- ChuckMcM 8y ago
  That is a great paper[1], thanks for the reference I've added it to my nuclear effects library. It doesn't involve the China Syndrome speculation though, what it does find is much much more interesting. The paper reports that beach sand is capable of 99% adsorption of Cs137. And then goes on to discuss how it gets de-adsorbed (up to 11%) when Cs137 free sea water is mixed with it. What this says to me is that you can use really cheap beach sand to filter the discharge water from a nuclear reactor and collect 99% of the Cs137 in the water which will stick to the sand. The sand in your filter can be replaced and the cesium rich sand can be sequestered for the Cs137 to decay over time. This is an excellent finding that suggests reactors have a reservoir of sand for pumping cooling water through especially during reactor compromise. Knowing this a future even would release significantly less Cs into the ocean, collecting it instead in the sand filter. [1] The experiments showed that beach sands have an adequate ion exchange capacity for this level of 137Cs, with an average adsorption fraction of 99% regardless of the salinity, sediment grain size, or mineralogy (Table S3). ---https://www.pnas.org/content/early/2017/09/26/1708659114 https://www.pnas.org/content/early/2017/09/26/1708659114
m_mueller 8y ago
Obviously it couldn’t melt through to China but AFAIK the way Czernobyl played out was that they had to somehow stop it from melting down to a flooded basement due to the fear of a long lasting series of hydrogen explosions that could have been truly disastrous for the region, if not Europe. Thus I think that the true worst case has so far never happened: A reactor without any of the modern safeguards (such as boronic sand pits) melting down to groundwater. Though, I guess subcritical core melts would not lead to hydrogen explosions, rather the creation of a lot of steam - it would be interesting to know how likely such a worst case would be and whether any of the world‘s reactors are configured to make this possible. Incredibly, 10 Chernobyl-type RBMK reactors are still in service.
- petschge 8y ago
  Part of that problem is that water is actually a decent moderator and neutron reflector, so it helps a lot in keeping a chain reaction with lots of energy output going. Some of the energy also goes into splitting water into hydrogen and oxygen. The hydrogen can then collect in some corner of the building until it reaches an concentration where it explodes rather easily. The explosion can then damage the building, ruining containment and scatter radioactive material around. Moral of the story? Keep your box of boronic sand nice and dry.
  - logifail 8y ago
    > Moral of the story? Keep your box of boronic sand nice and dry. See also: "For every three units of energy produced by the reactor core of a U.S. nuclear power plants, two units are discharged to the environment as waste heat. Nuclear plants are built on the shores of lakes, rivers, and oceans because these bodies provide the large quantities of cooling water needed to handle the waste heat discharge."[0] [0] https://www.ucsusa.org/nuclear_power/nuclear_power_technology/got-water-nuclear-power.html https://www.ucsusa.org/nuclear_power/nuclear_power_technolog...
    - londons_explore 8y ago
      Pretty much every energy source has a lot of waste heat produced. Solar panels get hot, gas turbines have hot exhausts, coal plants have cooling towers etc. They all approximate a heat engine, and they must theoretically give off heat to the cold reservoir
srcmap 8y ago
About the engineering challenges : I love to know the camera, sensors, electronic that let them take that picture in such high radioactive environment.
transistor-man 8y ago
@ Melting down fuel to determine its properties, the US just restarted a facility that does exactly that! The TREAT reactor purposely melts fuel to determine its failure points and to study new cladding materials. https://en.wikipedia.org/wiki/Transient_Reactor_Test_Facility_(TREAT) https://en.wikipedia.org/wiki/Transient_Reactor_Test_Facilit...
- ChuckMcM 8y ago
  Very cool with a link to a video https://www.youtube.com/watch?v=h0o4P_F4s9s https://www.youtube.com/watch?v=h0o4P_F4s9s where you can watch a fuel rod actually melt. Glad to hear they restarted it last year for additional research into these topics.
  - nate_meurer 8y ago
    Holy shit, wikipedia says it handles transients of up to 19 GW. They don't say for how long, but the transient control rod actuators take a quarter second to cover their full range, so I'm guessing that means 19 GW for up to a quarter second. That's about 4.5 gigajoules. As it happens, that's roughly the explosive energy of 1 ton of TNT. From a reactor core the size of a small closet. Makes me wonder, in fascinated terror, what power output we're seeing in that video. Wikipedia says it can simulate six different reactor loop types. This is a seriously impressive facility.
darkpuma 8y ago
Could crushed borosilicate glass be used as concrete aggregate when constructing containment buildings? Edit: apparently yes: https://www.ncbi.nlm.nih.gov/pubmed/28189090 https://www.ncbi.nlm.nih.gov/pubmed/28189090
anigbrowl 8y ago
I also find it interesting that the "China Syndrome"[2] speculation is pretty much completely debunked. That term was never meant to be taken literally, in the movie where it originates it is presented as a fanciful exaggeration meant to emphasize the seriousness of the risk. The actual plot concerns the risk of groundwater contamination following a nuclear accident, not a planet-piercing tunnel.
- jobigoud 8y ago
  But is there a material that humans could build that would sink into Earth like that, for a few kilometers say, either due to melting its way down or gravity or density?
  - anigbrowl 8y ago
    I really don't know. I've never thought of it as anything other than a colorful metaphor and don't know enough physics or chemistry to speculate.
- GordonS 8y ago
  > That term was never meant to be taken literally As a kid growing up in the 80's, I remember people, even school teachers, did take that term literally! It was one of those things I kind of forgot about for years and took for granted as being "truth", until I actually read about nuclear power!
k4l3 8y ago
I agree with your assessment that it's impractical to meltdown reactors just to learn how to clean them up, but apparently the US government didn't: https://en.wikipedia.org/wiki/BORAX_experiments https://en.wikipedia.org/wiki/BORAX_experiments
randomsearch 8y ago
> realize it was likely impractical to meltdown reactors just to develop the technology to clean them up That's a great insight. Maybe if some technologist approaches you and says "this is a great tech but we can't possibly recreate the worst case scenario, even in an expensive simulation" then that tells you that this is a straight "no". Fukushima is evidence that the worst case cannot be sufficiently modelled and mitigated, at least in a commercial market. Not saying "don't build nuclear", just that pro-nuclear lobbies should have been able to predict this situation (with a small chance of occurrence) and model it. If not, don't build. If you can predict it, but govt doesn't care about the risks, publicly document it, and that's OK. OT, but at this point the nuclear debate looks irrelevant - direction of travel is that renewables win. [ further OT ...moment of wild speculation: the idea that energy will be scarce will, within the 21st century, become as crazy as the idea that food could be scarce in rich nations right now. The race to renewables will look irrelevant as solar costs hit rock bottom, and no-one will remember why coal/nuclear plants were ever a thing. Within our lifetimes. I genuinely think that scenario is more likely than not. ]
- AngryData 8y ago
  I don't entirely agree with you, based mainly on when these reactors were originally designed. They started building in '67, but the actual construction designs were based on even earlier plans and tests that were conceived of in the 50s. So the original designs of the plant were born only around 15-20 years after we even invented nuclear technology. I find it similar to discussing automobile safety based on a Model-T. Sure they have upgraded some things over the years, but there are only so much you can do when your modifications are done after it was already built or even in the middle of being built. I just don't see how we can really compare nuclear technology of the 60s, with nuclear technology of the 2019.
- dralley 8y ago
  The Chernobyl reactors were built after Fukushima. It was a really, really old plant, that had already gone 10 years past it's intended lifespan, but they kept it open despite that because they didn't have a viable replacement source of energy.
- 8y ago
ww520 8y ago
> [2] Speculation that a blob of melted core material would just keep melting into the ground until it "got to china" Are people seriously considered that's a possibility? Even if the melted core went through the earth unstopped, a little bit of physic would conclude that Earth's gravity would pull the melted core toward the Earth's Core, and passing that, it would just be pulled back in the opposite direction, oscillating back and forth until stopping at the Core.
robotresearcher 8y ago
> [1] It is too radioactive for that to be literally true They walked up to it anyway https://rarehistoricalphotos.com/the-elephant-foot-of-the-chernobyl-disaster-1986/ https://rarehistoricalphotos.com/the-elephant-foot-of-the-ch...
Aeolun 8y ago
I think a few years ago, when all their robots kept dying, I suggested just using a big stick, possibly with mirrors, to look inside. Funny to see that after years they finally reach the fuel with a big stick :P
cladari 8y ago
In a pressurized water reactor the water is the moderator (bounces and slows the neutrons) and dissolved boron is the poison used to control the reaction.

cpeterso 8y ago

> melted core material would just keep melting into the ground until it "got to china" aka "China Syndrome", just like the 1979 film: https://en.wikipedia.org/wiki/Nuclear_meltdown#China_syndrome https://en.wikipedia.org/wiki/Nuclear_meltdown#China_syndrom...

__m 8y ago
Now that convincingly debunks the China syndrome, China is obviously not the antipode to Fukushima

petschge 8y ago

Boron actually mostly acts as a neutron poison, i.e. it absorbs neutrons. That way further (stimulated) decay of other nucleii that were hit by a neutron is eliminated and the chain reaction stops, reducing the production of thermal energy. A moderator on the other hand inelastically scatters neutrons, converting some of the kinetic energy of the neutrons to heat and leaving a slower neutron. Moderators are used in reactors to bring neutrons down from their initial velocity to velocities where they are more likely to stimulate fission in another nucleus.

ChuckMcM 8y ago
Correction noted! Thanks!
pfdietz 8y ago
> A moderator on the other hand inelastically scatters neutrons, Most moderators elastically scatter neutrons. What other kind of collision could there be with a hydrogen nucleus?
- petschge 8y ago
  You are of course right. The scattering conserved total energy, but not the energy of the neutron.
- hexane360 8y ago
  When discussing scattering of particles, "elastic" usually refers to electrostatic slingshots where almost the entire kinetic energy of the particle is conserved. Inelastic, however, refers to a direct collision where there is a significant energy loss of the particle. Obviously the former doesn't happen with neutrons, but I believe it's still a typical convention in particle physics.
  - pfdietz 8y ago
    No, elastic means an encounter where kinetic energy is conserved, rather than being converted to some other form of energy. THe neutron/nucleus collisions in a moderator are largely elastic. The total kinetic energy of the neutron and the nucleus is conserved, although kinetic energy is transfered from the neutron to the nucleus. An inelastic collision would involve (for example) nuclear excitation of the target nucleus, or ejection of particles from the target nucleus. The neutrons from fission are usually too low in energy for this to be very likely, though.

pvaldes 8y ago

> the "China Syndrome" speculation is pretty much completely debunked You would be dissapointed. Cou-cou! surprise! The ocean strikes back!. Unexpected source of Fukushima-derived radiocesium to the coastal ocean of Japan. 2017. Sanial, Buessler, Charette, and Nagao. PNAS. DOI:10.1073/pnas.1708659114 "Sanial, Buessler, Charette and Nagao, scientists from Massachusetts and Japan found a new source of Caesium-137 to the environment after the Fukushima accident. From 2013 – 2016 they visited 8 different beaches within 100 km of the accident site, took sand and water samples and measured its radioactivity. They found that at the bottom of their sand samples, up to 2 m deep into the beach, the 137Cs concentrations were incredibly high, up to 480,000 Bq per square meter in their deepest samples. The soil in the restricted zone of the Fukushima site, up to 100 km away, measured ~100,000 Bq per square meter. This means even tens of kilometers away, the radiation can actually be higher than near the disaster. (Because, huh?, 137Cs sticks to the sand grains). https://oceanbites.org/going-nuclear-radioisotopes-from-fukushimi-power-plant-stay-in-sand-for-years/ https://oceanbites.org/going-nuclear-radioisotopes-from-fuku...

ChuckMcM 8y ago
That is a great paper[1], thanks for the reference I've added it to my nuclear effects library. It doesn't involve the China Syndrome speculation though, what it does find is much much more interesting. The paper reports that beach sand is capable of 99% adsorption of Cs137. And then goes on to discuss how it gets de-adsorbed (up to 11%) when Cs137 free sea water is mixed with it. What this says to me is that you can use really cheap beach sand to filter the discharge water from a nuclear reactor and collect 99% of the Cs137 in the water which will stick to the sand. The sand in your filter can be replaced and the cesium rich sand can be sequestered for the Cs137 to decay over time. This is an excellent finding that suggests reactors have a reservoir of sand for pumping cooling water through especially during reactor compromise. Knowing this a future even would release significantly less Cs into the ocean, collecting it instead in the sand filter. [1] The experiments showed that beach sands have an adequate ion exchange capacity for this level of 137Cs, with an average adsorption fraction of 99% regardless of the salinity, sediment grain size, or mineralogy (Table S3). ---https://www.pnas.org/content/early/2017/09/26/1708659114 https://www.pnas.org/content/early/2017/09/26/1708659114

m_mueller 8y ago

Obviously it couldn’t melt through to China but AFAIK the way Czernobyl played out was that they had to somehow stop it from melting down to a flooded basement due to the fear of a long lasting series of hydrogen explosions that could have been truly disastrous for the region, if not Europe. Thus I think that the true worst case has so far never happened: A reactor without any of the modern safeguards (such as boronic sand pits) melting down to groundwater. Though, I guess subcritical core melts would not lead to hydrogen explosions, rather the creation of a lot of steam - it would be interesting to know how likely such a worst case would be and whether any of the world‘s reactors are configured to make this possible. Incredibly, 10 Chernobyl-type RBMK reactors are still in service.

petschge 8y ago
Part of that problem is that water is actually a decent moderator and neutron reflector, so it helps a lot in keeping a chain reaction with lots of energy output going. Some of the energy also goes into splitting water into hydrogen and oxygen. The hydrogen can then collect in some corner of the building until it reaches an concentration where it explodes rather easily. The explosion can then damage the building, ruining containment and scatter radioactive material around. Moral of the story? Keep your box of boronic sand nice and dry.
- logifail 8y ago
  > Moral of the story? Keep your box of boronic sand nice and dry. See also: "For every three units of energy produced by the reactor core of a U.S. nuclear power plants, two units are discharged to the environment as waste heat. Nuclear plants are built on the shores of lakes, rivers, and oceans because these bodies provide the large quantities of cooling water needed to handle the waste heat discharge."[0] [0] https://www.ucsusa.org/nuclear_power/nuclear_power_technology/got-water-nuclear-power.html https://www.ucsusa.org/nuclear_power/nuclear_power_technolog...
  - londons_explore 8y ago
    Pretty much every energy source has a lot of waste heat produced. Solar panels get hot, gas turbines have hot exhausts, coal plants have cooling towers etc. They all approximate a heat engine, and they must theoretically give off heat to the cold reservoir

srcmap 8y ago

About the engineering challenges : I love to know the camera, sensors, electronic that let them take that picture in such high radioactive environment.

transistor-man 8y ago

@ Melting down fuel to determine its properties, the US just restarted a facility that does exactly that! The TREAT reactor purposely melts fuel to determine its failure points and to study new cladding materials. https://en.wikipedia.org/wiki/Transient_Reactor_Test_Facility_(TREAT) https://en.wikipedia.org/wiki/Transient_Reactor_Test_Facilit...

ChuckMcM 8y ago
Very cool with a link to a video https://www.youtube.com/watch?v=h0o4P_F4s9s https://www.youtube.com/watch?v=h0o4P_F4s9s where you can watch a fuel rod actually melt. Glad to hear they restarted it last year for additional research into these topics.
- nate_meurer 8y ago
  Holy shit, wikipedia says it handles transients of up to 19 GW. They don't say for how long, but the transient control rod actuators take a quarter second to cover their full range, so I'm guessing that means 19 GW for up to a quarter second. That's about 4.5 gigajoules. As it happens, that's roughly the explosive energy of 1 ton of TNT. From a reactor core the size of a small closet. Makes me wonder, in fascinated terror, what power output we're seeing in that video. Wikipedia says it can simulate six different reactor loop types. This is a seriously impressive facility.

darkpuma 8y ago

Could crushed borosilicate glass be used as concrete aggregate when constructing containment buildings? Edit: apparently yes: https://www.ncbi.nlm.nih.gov/pubmed/28189090 https://www.ncbi.nlm.nih.gov/pubmed/28189090

anigbrowl 8y ago

I also find it interesting that the "China Syndrome"[2] speculation is pretty much completely debunked. That term was never meant to be taken literally, in the movie where it originates it is presented as a fanciful exaggeration meant to emphasize the seriousness of the risk. The actual plot concerns the risk of groundwater contamination following a nuclear accident, not a planet-piercing tunnel.

jobigoud 8y ago
But is there a material that humans could build that would sink into Earth like that, for a few kilometers say, either due to melting its way down or gravity or density?
- anigbrowl 8y ago
  I really don't know. I've never thought of it as anything other than a colorful metaphor and don't know enough physics or chemistry to speculate.
GordonS 8y ago
> That term was never meant to be taken literally As a kid growing up in the 80's, I remember people, even school teachers, did take that term literally! It was one of those things I kind of forgot about for years and took for granted as being "truth", until I actually read about nuclear power!

k4l3 8y ago

I agree with your assessment that it's impractical to meltdown reactors just to learn how to clean them up, but apparently the US government didn't: https://en.wikipedia.org/wiki/BORAX_experiments https://en.wikipedia.org/wiki/BORAX_experiments

randomsearch 8y ago

> realize it was likely impractical to meltdown reactors just to develop the technology to clean them up That's a great insight. Maybe if some technologist approaches you and says "this is a great tech but we can't possibly recreate the worst case scenario, even in an expensive simulation" then that tells you that this is a straight "no". Fukushima is evidence that the worst case cannot be sufficiently modelled and mitigated, at least in a commercial market. Not saying "don't build nuclear", just that pro-nuclear lobbies should have been able to predict this situation (with a small chance of occurrence) and model it. If not, don't build. If you can predict it, but govt doesn't care about the risks, publicly document it, and that's OK. OT, but at this point the nuclear debate looks irrelevant - direction of travel is that renewables win. [ further OT ...moment of wild speculation: the idea that energy will be scarce will, within the 21st century, become as crazy as the idea that food could be scarce in rich nations right now. The race to renewables will look irrelevant as solar costs hit rock bottom, and no-one will remember why coal/nuclear plants were ever a thing. Within our lifetimes. I genuinely think that scenario is more likely than not. ]

AngryData 8y ago
I don't entirely agree with you, based mainly on when these reactors were originally designed. They started building in '67, but the actual construction designs were based on even earlier plans and tests that were conceived of in the 50s. So the original designs of the plant were born only around 15-20 years after we even invented nuclear technology. I find it similar to discussing automobile safety based on a Model-T. Sure they have upgraded some things over the years, but there are only so much you can do when your modifications are done after it was already built or even in the middle of being built. I just don't see how we can really compare nuclear technology of the 60s, with nuclear technology of the 2019.
dralley 8y ago
The Chernobyl reactors were built after Fukushima. It was a really, really old plant, that had already gone 10 years past it's intended lifespan, but they kept it open despite that because they didn't have a viable replacement source of energy.
8y ago

ww520 8y ago

> [2] Speculation that a blob of melted core material would just keep melting into the ground until it "got to china" Are people seriously considered that's a possibility? Even if the melted core went through the earth unstopped, a little bit of physic would conclude that Earth's gravity would pull the melted core toward the Earth's Core, and passing that, it would just be pulled back in the opposite direction, oscillating back and forth until stopping at the Core.

robotresearcher 8y ago

> [1] It is too radioactive for that to be literally true They walked up to it anyway https://rarehistoricalphotos.com/the-elephant-foot-of-the-chernobyl-disaster-1986/ https://rarehistoricalphotos.com/the-elephant-foot-of-the-ch...

Aeolun 8y ago

I think a few years ago, when all their robots kept dying, I suggested just using a big stick, possibly with mirrors, to look inside. Funny to see that after years they finally reach the fuel with a big stick :P

cladari 8y ago

In a pressurized water reactor the water is the moderator (bounces and slows the neutrons) and dissolved boron is the poison used to control the reaction.