Hazardous Radioactive Materials

[Drakkith]

I've seen a lot of talk recently about radiation and radioactive materials.

I was wondering what the major issues with storing these materials are and what materials are posing the most risks. Which ones are the biggest hazards? Products that are gases instead of solids/liquids? Ones that have a certain type of decay method? Are there certain ones that will react and form compounds that make them more hazardous than others? ETC. Sorry if this is too broad of a question.

 

[Dmytry]

Alpha active materials generally are more dangerous by internal exposure. Those with no gamma decay are difficult to test for. Many elements bio-concentrate. It really is extremely diverse topic.
For example Cs-137 and I-131 get particularly easily released from the fuel - not entirely sure why but I would guess because their compounds are volatile. Cs-137 starts off as Xe-137 with half life of about 4 minutes, I don't know if it finds it's way to diffuse into the pores in the fuel in that time.
For the hazards: Cs-137 is bio-concentrated, most dramatically by mushrooms. Sr-90 stays in bones, and so do transuranics.
Different organs have different susceptibility, bone marrow being most sensitive.
Radioactive noble gasses that decay into stable elements are probably most safe unless inside the building. Them (Kr-85 if i recall correctly) are 100% vented to atmosphere during spent fuel reprocessing.
In the alpha decay, there is also an issue of nucleus recoil
http://en.wikipedia.org/wiki/Alpha_decay#Toxicity
and it matters very much where within the cell the alpha decay takes place.

 

[Astronuc]

I've seen a lot of talk recently about radiation and radioactive materials.

I was wondering what the major issues with storing these materials are and what materials are posing the most risks. Which ones are the biggest hazards? Products that are gases instead of solids/liquids? Ones that have a certain type of decay method? Are there certain ones that will react and form compounds that make them more hazardous than others? ETC. Sorry if this is too broad of a question.

The major risk of a radionuclide is ingestion into a living organism, particularly in humans, in a quantity that would cause injury/illness.

Gases pose an external risk or internal if inhaled.

Volatiles and solids in particulate form would deposit on surfaces and irradiate outside, but they could be ingested if they contaminate food, or come in contact with surfaces where food is prepared or served, or they could be inhaled as dust.

Inhalation of a radionuclide would expose lungs and surrounding tissue to gamma and beta radiation for most radionuclides, or alpha particles if the radionuclide is a U or transuranic isotope. Alphas would damage the lining of the lung, whereas betas and gammas would damage more underlying tissue as well as the lining. Obviously, damage to the lung can cause problems with respiration. But the risk depends on how much damage would occur.

Some isotopes, once absorbed either through ingestion or inhalation would be transported and collected by specific organs. For example, iodine is preferentially taken up by the thyroid gland. Cs and Rb, which are chemically similar to K or Na, would be mostly likely absorbed in cells that use, K or Na. Ba and Sr, which are chemically similar to Ca, would be taken up by the bones that use Ca.

There are other factors to consider.

Most isotopes have short half-lives, in seconds, minutes, hours. Radionuclides with half-lives of days to years are of significant concern. The short half-life isotopes will decay, usually to longer half-life isotopes, or to inert (non-radioactive) isotopes. Eventually, all isotope decay leads to an inert nuclide - but that might take years for certain isotopes.

The bottom line is that no one is supposed to release radioisotopes into the environment - at least not above certain specified limits.

As for ultimate storage, one can either use direct disposition in a respository, in which case the spent fuel is encased in a corrosion resistant container which is placed in a corrosion resistant storage system, which is in a geologically stable (millions of years) repository inside a mountain or deep underground.

An alternative is to process (or reprocess to recover TU and unused U) the fuel into a vitrified or synthetic rock form that immobilize the fuel or fission products in an inert matrix. Then the radioisotopes decay to inert (non-radioactive) form.

 

[Dmytry]

Well i think the best way for long term storage would be to store it in dry casks for at least 100..200 years. Who knows we might well go extinct in that time. Or build a space elevator. Or at least improve our knowledge of geophysics to the point we can be sure about long term storage.
The problem is of course that in 100..200 years we may apply same logic.

IMO the biggest current problem is that instead of storing minimal amount of fuel in pools at top floors of reactor buildings, a maximal amount of fuel is stored there. Dramatically worsening the worst-case accident beyond what public originally agreed to. That may have saved a few bucks short term but look and see how expensive it will be to deal with Fukushima which you can't simply entomb, not with this amount of spent fuel and not with their earthquake risk. And look at how bad it will be for public relations when public realizes that instead of storing minimum amount of spent fuel in open spent fuel floor on top floor, the way public was led to believe it worked, a maximum amount was stored, with re-racking to store more than originally intended. The nuclear energy just fails to live to it's overinflated image as ultra safety conscious and never saving a buck on safety.

 

[Drakkith]

Please please PLEASE don't bring what Fukushima should or shouldn't have done into this thread. There is WAY more than enough talk about that already in other threads.

Anyways, I've heard about people keeping slightly radioactive things such as a small piece of Uranium or something with a very long half life and doesn't release gamma radiation at there house, at their desk, etc back in the past. Is there really a significant hazard with that or is it blown out of proportion? (I've heard this from my dad and someone else several years ago, so I don't know how true it is.)

As for ultimate storage, one can either use direct disposition in a respository, in which case the spent fuel is encased in a corrosion resistant container which is placed in a corrosion resistant storage system, which is in a geologically stable (millions of years) repository inside a mountain or deep underground.

So something like a big concrete bunker or underground facility?

The major risk of a radionuclide is ingestion into a living organism, particularly in humans, in a quantity that would cause injury/illness.

Gases pose an external risk or internal if inhaled.

So unless these materials are ingested or inhaled, I'm assuming that there won't be a hazard since alpha and beta radiation doesn't penetrate skin and clothing?

Well i think the best way for long term storage would be to store it in dry casks for at least 100..200 years. Who knows we might well go extinct in that time. Or build a space elevator. Or at least improve our knowledge of geophysics to the point we can be sure about long term storage.

I thought we already planned ahead for more than 100-200 years of storage for these things. Are you saying we don't and that we should, or something else?

 

[Astronuc]

Anyways, I've heard about people keeping slightly radioactive things such as a small piece of Uranium or something with a very long half life and doesn't release gamma radiation at there house, at their desk, etc back in the past. Is there really a significant hazard with that or is it blown out of proportion? (I've heard this from my dad and someone else several years ago, so I don't know how true it is.)

Uranium ore taken from nature does emit gamma, alpha and beta radiation. Uranium ore is some complex oxide of uranium - and usually aout 1-3% of the ore is uranium oxide. The ore could by carbonates, or phosphates, or titanium or vanadium compounds, as well as various decay products.

http://en.wikipedia.org/wiki/Uraninite
http://energy.cr.usgs.gov/other/uranium/
http://energy.cr.usgs.gov/other/uranium/pubs_data.html

So something like a big concrete bunker or underground facility?

More or less a big concrete or sythetic rock bunker deep underground. Prefereably a place that has not had volcanic activity in several million years. Granite would be great, but drilling into granite requires a lot of energy.

So unless these materials are ingested or inhaled, I'm assuming that there won't be a hazard since alpha and beta radiation doesn't penetrate skin and clothing?

Well, betas do penetrate the skin, and some alpha emitters also emit betas, or decay into beta emitting radionuclides.
See the decay series here - http://hyperphysics.phy-astr.gsu.edu/Hbase/nuclear/radser.html

I thought we already planned ahead for more than 100-200 years of storage for these things. Are you saying we don't and that we should, or something else?

The current nuclear plants were designed at a time when reprocessing was considered viable. The fuel cycles were annual, and plants would discharge about 1/3 of the core each year (annually). After some cooling time - about 8-10 years, the fuel would be sent to a reprocessor, and the U and Pu extracted. That was also when fast reactors and breeder reactors were considered viable. All that changed when Carter nixed the reprocessing and effectively killed the fast reactor and breeder reactor programs.

In the 1980s, the utilities realized that they were stuck with the fuel they had, except that the US government (DOE) was supposed to start taking the spent fuel - in 1982, then in 1987 - then . . . . The DOE still hasn't taken the fuel. So the utilities decided to increase the fuel cycle length to 18 months, and some for 24 months, and reduce the amount of fuel discharge.

When the DOE didn't take the fuel in the 1990s, utilities started using dry storage in which fuel from the spent fuel pool is moved into storage casks at the NPP site. Utilities may have a common site at one of their NPPs, but they only use it for their own fuel. Until the DOE takes physical possession of the spent fuel, the fuel is the responsibility of the utility which used the fuel.

Now we are looking at dry storage for 60 years, and possibly 80 years. The design lifetime of the current plants is/was 40 years. Some plants have had their lifetimes extended to 60 years. The industry is considering looking at 80 years.

New plants are being designed for 60 years, with the possibility of 80 years.

 

[clancy688]

New plants are being designed for 60 years, with the possibility of 80 years.

Wow. Here in Germany, reactors from 1975 are considered as dangerous "scrap reactors" since at least 10 years...

People have no idea that power plants are only economical if they are used for decades...

 

[Astronuc]

Wow. Here in Germany, reactors from 1975 are considered as dangerous "scrap reactors" since at least 10 years...

People have no idea that power plants are only economical if they are used for decades...

The pre-Konvoi and Konvoi plants are some of the best designs in the world. I've done projects for most of the German utilities.

 

[Dmytry]

Uranium ore taken from nature does emit gamma, alpha and beta radiation. Uranium ore is some complex oxide of uranium - and usually aout 1-3% of the ore is uranium oxide. The ore could by carbonates, or phosphates, or titanium or vanadium compounds, as well as various decay products.

one extra safety thing to know, uranium ore constantly releases radon, which is a gas and decays into polonium-210 which sticks to the lungs.

http://en.wikipedia.org/wiki/Uraninite
http://energy.cr.usgs.gov/other/uranium/
http://energy.cr.usgs.gov/other/uranium/pubs_data.html

More or less a big concrete or sythetic rock bunker deep underground. Prefereably a place that has not had volcanic activity in several million years. Granite would be great, but drilling into granite requires a lot of energy.

Well, betas do penetrate the skin, and some alpha emitters also emit betas, or decay into beta emitting radionuclides.
See the decay series here - http://hyperphysics.phy-astr.gsu.edu/Hbase/nuclear/radser.html

The current nuclear plants were designed at a time when reprocessing was considered viable. The fuel cycles were annual, and plants would discharge about 1/3 of the core each year (annually). After some cooling time - about 8-10 years, the fuel would be sent to a reprocessor, and the U and Pu extracted. That was also when fast reactors and breeder reactors were considered viable. All that changed when Carter nixed the reprocessing and effectively killed the fast reactor and breeder reactor programs.

In the 1980s, the utilities realized that they were stuck with the fuel they had, except that the US government (DOE) was supposed to start taking the spent fuel - in 1982, then in 1987 - then . . . . The DOE still hasn't taken the fuel. So the utilities decided to increase the fuel cycle length to 18 months, and some for 24 months, and reduce the amount of fuel discharge.

Most importantly, utilities opted to store as much spent fuel in what was originally a cooling pond as possible, using either boral (aluminium powder, in water, wtf), or boraflex (plastic?!) to keep it subcritical. Neither of those materials behaved as expected, those materials degrade in unexpected ways but the studies were done and the http://www.ralentz.com/old/space/feynman-report.html" , sorry, the sheets were empirically found to still maintain subcritical margin in the few cases that were checked. Nevermind the variation in temperature, chemical composition of the water, etc, if the worst they seen was something not supposed to be eroded get eroded 3rd of the way, there must be a safety factor of 3.
One thing about storage of fuel in particular is that it has to be kept subcritical.

 

[Astronuc]

one extra safety thing to know, uranium ore constantly releases radon, which is a gas and decays into polonium-210 which sticks to the lungs.

Most importantly, utilities opted to store as much spent fuel in what was originally a cooling pond as possible, using either boral (aluminium powder, in water, wtf), or boraflex (plastic?!) to keep it subcritical. Neither of those materials behaved as expected, those materials degrade in unexpected ways but the studies were done and the http://www.ralentz.com/old/space/feynman-report.html" , sorry, the sheets were empirically found to still maintain subcritical margin in the few cases that were checked. Nevermind the variation in temperature, chemical composition of the water, etc, if the worst they seen was something not supposed to be eroded get eroded 3rd of the way, there must be a safety factor of 3.
One thing about storage of fuel in particular is that it has to be kept subcritical.

Boraflex is a composite material (similar to rubber) made by dispersing boron carbide B4C in a silicone elastomer matrix (Silica and Polydimethyl siloxane).

Issues of boraflex degradation have been well-known for nearly two decades.

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1996/gl96004.html

5-percent subcriticality requirement.

Several corrective actions have been used to account for any reactivity
increase due to Boraflex loss. Many licensees have taken credit for the
reactivity decrease associated with fuel depletion or have restricted storage
patterns to a checkerboard-type configuration. Others have inserted neutron
absorber rods into stored assemblies with protective features to prevent
inadvertent removal. The NRC is also presently evaluating a proposed
methodology by which credit could be taken for the soluble boron in PWR pool
water. Although some of these schemes cannot be used for BWR fuel storage
facilities, there have been discussions and demonstrations of specially
designed neutron absorbing inserts as a replacement for deteriorating Boraflex
which would be applicable to both PWR and BWR storage racks.

. . .

See the discussion here for how utilities address the issue.
http://pbadupws.nrc.gov/docs/ML0928/ML092810279.pdf

 

[Bob S]

I have been using 1/4" thick Boral plate (B4C clad between two thin sheets of aluminum) since about 1960, primarily for neutron shielding of sensitive radiation detection equipment. The biggest problem with Boral plate seems to be corrosion of the aluminum when it is in direct contact with H2O. In my experience, if the pH of the H2O is maintained very close to 7.0, or very slightly lower, the corrosion problem is minimized.

See http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0933/sec3/196.html

Bob S

 

[pdObq]

Anyways, I've heard about people keeping slightly radioactive things such as a small piece of Uranium or something with a very long half life and doesn't release gamma radiation at there house, at their desk, etc back in the past.

I have a related, maybe stupid question. So, suppose you have two radioactive elements with all things equal except for their half-lifes, that directly decay into some stable element (I know, I know, just hypothetically). So, say one has a half-life of 3 days, the other of 30000 years.

In some sense, the media make it sound like the second one clearly is much worse and generations will have problems with it, while the first one is not so bad. But on the other hand, doesn't the much longer half-life mean that the element is much less active than the first? I.e. there are much fewer dacys per unit time, such that the dose rate from the second one might effectively be less than from natural background radiation?

The first one, however, should lead to a very high dose rate during the first say month until most of it has decayed away? Total dose (infinite time integral) should be exactly the same if starting from the same amount for both cases.

The next question would then be, what real properties make e.g. Pu so bad, apart from that it is toxic/cancerogen even if it wasn't radioactive. Other radioactive isotopes in the decay chains? Neutrons? Excited states of the nucleus decaying via emitting gamma photons?

 

[Drakkith]

I have a related, maybe stupid question. So, suppose you have two radioactive elements with all things equal except for their half-lifes, that directly decay into some stable element (I know, I know, just hypothetically). So, say one has a half-life of 3 days, the other of 30000 years.

In some sense, the media make it sound like the second one clearly is much worse and generations will have problems with it, while the first one is not so bad. But on the other hand, doesn't the much longer half-life mean that the element is much less active than the first? I.e. there are much fewer dacys per unit time, such that the dose rate from the second one might effectively be less than from natural background radiation?

The first one, however, should lead to a very high dose rate during the first say month until most of it has decayed away? Total dose (infinite time integral) should be exactly the same if starting from the same amount for both cases.

The next question would then be, what real properties make e.g. Pu so bad, apart from that it is toxic/cancerogen even if it wasn't radioactive. Other radioactive isotopes in the decay chains? Neutrons? Excited states of the nucleus decaying via emitting gamma photons?

I believe this is correct. I know that certain features of the elements to consider are how much will stay in the body if inhaled or ingested, type of radiation released, products of decay, ease at which the element is ingested/inhaled, ETC. If you have a long lived radioisotope that is easily ingested and concentrates in one particular organ, it will much worse for you than an equally long lived isotope that doesn't collect in the body or in one organ.

 

[pdObq]

I believe this is correct. I know that certain features of the elements to consider are how much will stay in the body if inhaled or ingested, type of radiation released, products of decay, ease at which the element is ingested/inhaled, ETC. If you have a long lived radioisotope that is easily ingested and concentrates in one particular organ, it will much worse for you than an equally long lived isotope that doesn't collect in the body or in one organ.

I found some kind of answer or confirmation of my half-life question while browsing through another thread. Basically starting from https://www.physicsforums.com/showthread.php?p=3266565#post3266565" onwards.

So, in short, the really bad nuclides for humans are the ones with a half-life on the order of a human "half-life", since for those the integral over the number of decays over the time of a human life is maximal. I guess from that one should conclude that the 30 year half life cesium isotope is much more harmful than plutonium, neglecting the other factors you mention.

But that brings me back to my second question, why exactly is Pu always portrayed as the really bad stuff requiring very-long-term safe storage (tying into the discussion linked to above), if other isotopes are way more dangerous to human health on a human time scale?

EDIT: Ok, so after taking a look at actual half-lifes, I suppose Pu-238 is the bad guy with its 88-yr half-life, and another one is Pu-241 with 14 years. My question now basically reduces to why there is the need to safely store the really-long-lived isotopes? Is it because of the decay products or because of activation of other elements around or because of something completely different?

 

[Drakkith]

Portrayed where? In public EVERYTHING is bad. Here in the forums most people have been pointing to other isotopes I think.

 

[clancy688]

But that brings me back to my second question, why exactly is Pu always portrayed as the really bad stuff requiring very-long-term safe storage (tying into the discussion linked to above), if other isotopes are way more dangerous to human health on a human time scale?

I think it's very very poisonous. And it's always the bad guy, because the public logic goes the following way.

Long half time -> stuff will be around longer -> stuff will be dangerous longer -> PU halftime 24.000 years -> ZOMFG WTF hundreds of thousands of years danger by PU -> we're doomed