Send radioactive waste to bottom of the ocean?

[Hercuflea]

Why don't they just place spent fuel rods in canisters and put them on the bottom of the ocean (at a traceable location, of course)? Water is one of the best radiation shields. You wouldn't have to worry about digging out mountain caverns and such.

 

[etudiant]

Afaik, the concern is that there is no known technology that would ensure the waste would not leak unexpectedly.
Sea water is quite corrosive and there are strong currents and large land slides (some from Hawaii have run out as much as 80 miles.
There have been serious proposals to bury the wastes in the ooze at the bottom of some subduction zones, with the thought that any wastes buried there would not reemerge for millions of years, but the reality that most wastes are hot enough to ensure their environment remains chemically and physically active has scotched that.
Imho, we are not going to find a safe place to dump this stuff permanently. We will have to find a way, perhaps through advanced accelerators or similar, to neutralize the waste. Meanwhile, it needs to be stored in reasonably safe containers, casks good for a century or so, but always accessible. That way everything can be kept above board and no slop creeps in, the way it does when people are deluded enough to believe the 'permanent repository' BS.

 

[SteamKing]

Why don't they just place spent fuel rods in canisters and put them on the bottom of the ocean (at a traceable location, of course)? Water is one of the best radiation shields. You wouldn't have to worry about digging out mountain caverns and such.

I guess you don't mind if your fish sticks cook themselves and then glow in the dark.

Yummm!

 

[Hercuflea]

https://en.wikipedia.org/wiki/Radiation_protection#Shielding_design

If placed at the bottom of the ocean, the gamma rays would be practically undetectable (heck, even at the bottom of a lake.). Water's halving thickness is 18cm. Perhaps they could net the area off to keep marine life away, but I don't think it would even be a problem unless wildife got closer than a few feet...

 

[QuantumPion]

Why don't they just place spent fuel rods in canisters and put them on the bottom of the ocean (at a traceable location, of course)? Water is one of the best radiation shields. You wouldn't have to worry about digging out mountain caverns and such.

This is actually a perfectly valid proposal, the opposition to such a solution is political.

 

[SteamKing]

But if the radioisotopes escape containment and enter the food chain, you've got magic food and magic aquatic life which can travel globally. Containment is not so much about radiation shielding as it is about keeping the hot stuff from migrating outside of the storage device and into the air or water.

The Russians have had all sorts of problems trying to keep the containment dome intact over the Chernobyl reactor and it's on dry land. We aren't even 30 years from the accident there and a new containment dome is already being constructed to replace the original.

 

[QuantumPion]

But if the radioisotopes escape containment and enter the food chain, you've got magic food and magic aquatic life which can travel globally. Containment is not so much about radiation shielding as it is about keeping the hot stuff from migrating outside of the storage device and into the air or water.

The Russians have had all sorts of problems trying to keep the containment dome intact over the Chernobyl reactor and it's on dry land. We aren't even 30 years from the accident there and a new containment dome is already being constructed to replace the original.

At the bottom of the ocean that is not really an issue. It's much easier to contain waste under the ocean than in the air. The water is very cold, dense, high pressure, and still. Even if there was a leak, it wouldn't really go anywhere or be hazardous to anything that wasn't in direct contact.

Note that there are at least a couple nuclear reactors sitting at the bottom of the ocean to this day, due to the loss of a few nuclear powered submarines. Theses weren't sealed or designed to be stored in such a condition yet they have still remained contained just fine over decades.

 

[Astronuc]

Why don't they just place spent fuel rods in canisters and put them on the bottom of the ocean (at a traceable location, of course)? Water is one of the best radiation shields. You wouldn't have to worry about digging out mountain caverns and such.

It would be an environment that humans could not control.

Afaik, the concern is that there is no known technology that would ensure the waste would not leak unexpectedly.
Sea water is quite corrosive and there are strong currents and large land slides (some from Hawaii have run out as much as 80 miles.

At the bottom of the ocean under high pressure, in the dark, where it is very cold, corrosion occur very slowly. For example, a lot of the Titanic is preserved.

Nevertheless, it is the lack of engineered barriers (beyond the cannister), lack of control and too much uncertainty that preclude dropping spent fuel cannisters in the ocean depths.

 

[SteamKing]

Although the remains of the Titanic are currently recognizable, the very metal of the ship's hull is under constant attack by the microorganisms which live at those depths. In several hundred years, all that may remain of the Titanic is a couple of giant piles of rust at the bottom of the Atlantic. Most, if not all, organic material from the ship disappeared long ago. Oceans are very hungry places to be.

 

[ReDragon]

Why don't they just place spent fuel rods in canisters and put them on the bottom of the ocean (at a traceable location, of course)? Water is one of the best radiation shields. You wouldn't have to worry about digging out mountain caverns and such.

Like other people have said, corrosion, and radiation to the environment are big factors in this. Imagine if even one of the canisters broke how much of an impact it would have on the ocean environment which is already very touchy. The reason they dig out caverns is because there is less environmental impact if there was leakage. But also, they can treat the radioactive waste and instead of having it last thousands of years it only needs several hundred years. Therefore, if it is in a cavern for several hundred years it will lose it's radioactivity, without ever impacting the environment.

 

[Hercuflea]

Why could it not be controlled? We have sonar that has mapped the entire ocean depths of the earth. If we can track sharks and fish with tags, there is no reason why we couldn't track a canister. Water would stop virtually all gamma rays after only about 1.8m (10*halving thickness). So radiation wouldn't be a problem in the ocean. I can maybe see that if the stuff leaked out it could chemically react and be toxic, radiation would not cause trouble underwater. That's why we can take pictures like this

Only water, no other barriers required.

 

[SteamKing]

Your picture was not taken at the bottom of the ocean, though. It was probably taken in a pool located at a nuclear reactor on dry land.

You claim water would stop 'virtually all' gamma rays after 1.8 m. What does 'virtually all' mean? Would you be willing to stand 2 m away from a gamma source with only water between you and the source? What about all that lead shielding that is used? Is that some conspiracy by the lead industry to fool us into thinking that water by itself can't do the job?

So a picture was taken. How do you know that the camera wasn't remotely operated? Do you see anyone swimming in this pool?

You don't seem to understand very much about radiation and its biological effects. Radioactive material is intrinsically toxic; no chemical reaction is required to make it toxic. If a spill does occur underwater, how is it going to be cleaned up? You saw the kind of massive cleanup required for the spill in the Gulf of Mexico, and most of the oil cleaned up floated to the surface. Can you imagine how much more complex a cleanup effort would be made if radioactive material was involved?

Look, doctors now get uneasy if they have a patient who flies a lot or who undergoes too many X-rays or CAT scans in a year's time. Radiation is a serious business, not only due to the effects of immediate exposure, but also due to the lingering effects from radioactive material continuing to persist in the environment after the accident. You may think it is OK to store spent fuel rods in your swimming pool, but not every one is willing to put up with that kind of risk.

 

[nikkkom]

Why don't they just place spent fuel rods in canisters and put them on the bottom of the ocean (at a traceable location, of course)? Water is one of the best radiation shields. You wouldn't have to worry about digging out mountain caverns and such.

I vote for disposal in deep boreholes in subduction zones on land. Under 3+ kilometers of rock and sinking? Sounds safe enough for me!

Spent fuel should be reprocessed.

This recovers unused U and Pu,
reduces waste volume,
allows waste to be converted into insoluble form (glass/synthetic rock),
and most importantly, reduces long-term waste _activity_ (if transuranics are removed too)!

The activity of reprocessing waste is dominated by Cs-137 and Sr-90 and is reduced by 1000 in only 300 years, thus, by a billion times in 900 years. Unprocessed spent fuel is much worse.

I think the confidence level of "this container won't leak for 1000 years" statement is much better than of "this container won't leak for 100000 years" one.

 

[bigaggie]

Although the remains of the Titanic are currently recognizable, the very metal of the ship's hull is under constant attack by the microorganisms which live at those depths. In several hundred years, all that may remain of the Titanic is a couple of giant piles of rust at the bottom of the Atlantic. Most, if not all, organic material from the ship disappeared long ago. Oceans are very hungry places to be.

Totally unrelated, and I agree with your point, but if I remember Ballard's assessment correctly, the biggest issue causing the Titanic's corrosion is that the water it sits in is very stagnant. If it were in an area with a current, chances are the microorganisms wouldn't have attacked quite as badly.

 

[QuantumPion]

Your picture was not taken at the bottom of the ocean, though. It was probably taken in a pool located at a nuclear reactor on dry land.

You claim water would stop 'virtually all' gamma rays after 1.8 m. What does 'virtually all' mean? Would you be willing to stand 2 m away from a gamma source with only water between you and the source? What about all that lead shielding that is used? Is that some conspiracy by the lead industry to fool us into thinking that water by itself can't do the job?

Radiation shielding is an exponential function. Every 18 cm of water reduces the radiation by half. So 180cm of water would reduce the radiation by 1-0.5^10=99.9%. That would be sufficient for the level of radiation emitted by spent nuclear fuel.

You don't seem to understand very much about radiation and its biological effects. Radioactive material is intrinsically toxic; no chemical reaction is required to make it toxic. If a spill does occur underwater, how is it going to be cleaned up? You saw the kind of massive cleanup required for the spill in the Gulf of Mexico, and most of the oil cleaned up floated to the surface. Can you imagine how much more complex a cleanup effort would be made if radioactive material was involved?

Radioactive waste processed for long-term disposal would be vitrified into a solid, chemical inert material such as glass. Even if small amounts of radioactive waste were dispersed, they would be confined to the extreme depths of the ocean and eventually diluted. You wouldn't have to clean it up.

The neat thing about nuclear power is that the waste is so concentrated and compact. The gulf oil spill was a hundred billion gallons of oil. The total world spent fuel inventory is something like 250,000 tons, of which 90% is uranium which could be reprocessed first. So you're looking at 25,000 tons of high level waste. That's a pretty small volume in the grand scheme of things.

Look, doctors now get uneasy if they have a patient who flies a lot or who undergoes too many X-rays or CAT scans in a year's time. Radiation is a serious business, not only due to the effects of immediate exposure, but also due to the lingering effects from radioactive material continuing to persist in the environment after the accident. You may think it is OK to store spent fuel rods in your swimming pool, but not every one is willing to put up with that kind of risk.

Yet doctors have no qualms about their patients driving to the clinic, which is about a hundred trillion times more dangerous than getting an x-ray or flying on a transatlantic flight.

 

[nikkkom]

Radiation shielding is an exponential function. Every 18 cm of water reduces the radiation by half. So 180cm of water would reduce the radiation by 1-0.5^10=99.9%. That would be sufficient for the level of radiation emitted by spent nuclear fuel.

Not really.
For example, freshly poured stainless steel containers with vitrified waste at La Hague emit in excess of one million rems per hour.

 

[QuantumPion]

Not really.
For example, freshly poured stainless steel containers with vitrified waste at La Hague emit in excess of one million rems per hour.

That would be a dose rate of 16 R/minute. I wouldn't want to stay too long at that distance but it wouldn't be immediately harmful. But at 2.5 m the dose rate would be 10x lower and would be safe for an extended period of time.

 

[nikkkom]

That would be a dose rate of 16 R/minute.

?

It's 277 rem per *second*.

 

[QuantumPion]

?

It's 277 rem per *second*.

Not through 180 cm of water, which reduces the intensity by roughly 99.9%.

 

[nikkkom]

That would be a dose rate of 16 R/minute. I wouldn't want to stay too long at that distance but it wouldn't be immediately harmful. But at 2.5 m the dose rate would be 10x lower and would be safe for an extended period of time.

Screw poor fish which doesn't know not to swim closer than 3 meters to those glowing blue cylinders, who cares about it?

By this logic, dropping nuclear waste in shallow holes in the most inaccessible part of the Sahara should be relatively safe.
No humans would approach it nearer than a few tens of kilometers, and desert foxes, well, they had it coming.

 

[Astronuc]

For spent fuel, transportation cannisters provide shielding. At the bottom of the ocean, the waste cannisters would sink into the ooze and sediment that accumulats at the bottom. Ideally, the waste containers would end up in a subduction zone and slowly move under the local continental shelf. Over thousands and millions of years, most of the waste would decay into stable (non-radioactive) isotopes, which is the point of long term storage/disposal in any geological repository.

 

[etudiant]

If past experience is any guide, the 'out of sight, out of mind' process has not served us very well.
So I'm deeply skeptical of any efforts to dispose of spent fuel into inaccessible places such as the ocean deeps,
even though it seems plausible.
A repository that ensures continued access to this highly refined and valuable material seems much preferable.
It makes it impossible for anyone to try to duck their responsibility to take care of this stuff while also maintaining economic and social pressure to come up with a way to use this stuff.

 

[Hercuflea]

If the waste were to be placed at a subduction zone in the ocean, it could eventually be pushed under the crust and into the Earth's mantle, where there are already a plethora of radioactive elements, whose radiation already dwarf that of the contents of the human produced waste canisters. The waste would be dissipated into the mantle. Sure, the containers would break and spill it out, but there is 2 miles of water and rock above it to stop all of the radiation. This process is already happening naturally.

 

[etudiant]

Indeed it could be eventually pushed under.
However, there is no guarantee of that and the waste could equally well be distributed through the ecosystem by a break in the container long before any subduction takes place.
Out of sight out of mind is not a good approach, imho.

 

[nikkkom]

At the bottom of the ocean, the waste cannisters would sink into the ooze and sediment that accumulats at the bottom. Ideally, the waste containers would end up in a subduction zone and slowly move under the local continental shelf.

I prefer putting the same containers into the same subduction zones, but through boreholes drilled from land.

This way, we do not "hope" that they will end up in subducting rocks. We *ensure* it.

 

[nikkkom]

For spent fuel, transportation cannisters provide shielding.

We are not talking about transportation, but about burial. Transportation casks can be reused, burial canisters can't be.

Steel half-attenuation thickness is about 2.5 cm.
You would need 50 cm thick steel case to shield French vitrified waste canister enough to sit next to it for one hour without significant health hazard. It seems excessive to me (the canister itself is less than a meter wide).

However, it's somewhat of a moot point, because fresh canisters are too hot (thermally) for burial: they may overheat if they are immediately buried in rocks. They need to be temporarily (on the order of 10-30 years) stored in controlled facilities.

 

[SteamKing]

And a subduction zone is not like a black hole or a conveyor belt to the center of the earth. It takes geological time for the crust to dive under an adjoining plate. These zones also tend to occur in the deepest parts of the ocean, making monitoring quite difficult. What happens to the canisters in the meantime? Can the canisters withstand being subducted without rupture? Would we just be creating radioactively hot zones in these areas?

 

[Steve Brown]

The high-pressure water-cooled, solid fuel uranium/plutonium reactor is very inefficient in the utilization of fuel, as it fissions only 2% to 3% of the fissile material before the fuel rods have become so degraded by heat and radiation that they have to be replaced. These spent fuel rods contain long-lived transuranic waste, yet they also contain valuable fissile material which should be extracted by processing the fuel rods. I do not say that the fissile material should be recycled into new fuel rods, because there is a much better reactor technology that fissions 100% of its fuel, creating very little waste, which contains short-lived fission products and practically no long-lived transuranic isotopes. That technology is the molten salt reactor which fissions U-233 bred from thorium-232 in a blanket surrounding the core. The core consists of molten salt in which fissile material is dissolved, and the blanket consists of molten salt in which the fertile thorium is dissolved. Although U-233 is the natural fissile material of the MSR, the reactor and breeding cycle can be started by loading the core salt with fissile material such as uranium or plutonium derived from spent fuel rods. It would be terribly wasteful to dispose of spent fuel rods in such a way that they can never be recovered and processed, because the uranium in the fuel rods was mined and refined at great expense and considerable environmental impact. More information about molten salt reactor technology is available at the following web sites.
www.energyfromthorium.org
www.thoriumenergyalliance.org

 

[nikkkom]

That technology is the molten salt reactor which fissions U-233 bred from thorium-232 in a blanket surrounding the core.

Please, no off-topic posts.
This same section of the forum has a "Liquid Fluoride Thorium Reactor" thread: https://www.physicsforums.com/showthread.php?t=520161&page=13

 

[Steve Brown]

My previous post is not really off topic, as it addresses the proposed method of disposing of spent fuel rods in such a way that they cannot be recovered. My point is that such disposal is not a good idea, because spent fuel rods contain recoverable fissile material which can be used in a type of reactor that does not create spent fuel assemblies to dispose of.