The implications and issues behind high-level nuclear waste management

[reptkeu]

Hello,

This topic is an open discussion around the technical, ethical and legal implications and issues behind high-level nuclear waste management.

I am a designer working on a project aimed at exploring the future of nuclear waste, by proposing alternative ways of dealing with the issue. For this project, I need to research and understand certain particularities about nuclear physics, especially the ones behind radioactive waste, but also the legislation, ethics, politics, and economics around the issue. The internet is full of information, but most of it is either too complicated (papers by scientists), or too simplified (papers by journalists). I have started this topic with the hope to get help from the Physics Forum community. And, instead of being specific to my project, keeping the discussion open would potentially benefit a greater number of people.

Let's have an interesting discussion.

 

[reptkeu]

Question 1
I know that high-level radioactive waste still contains a lot of energy (otherwise it wouldn't be radioactive, right), what are the simplest ways to extract this energy?

Question 2
Is it possible to transform radioactivity from waste directly into electricity, like it is done with betavoltaics?

Question 3
Why is it forbidden by law for the average citizen to possesses nuclear waste in (all) most countries?

 

[Hologram0110]

Question 1
I know that high-level radioactive waste still contains a lot of energy (otherwise it wouldn't be radioactive, right), what are the simplest ways to extract this energy?

The simplest way is to simply let it decay. When the radiation gets stopped by material it converts the energy to heat. If you insulated it, the heat would build up and it would get hot.
If you wanted to do something useful with that heat you could use it for virtually any engineering application that needs heat (although it might not be cost effective). Basically the amount of heat it gives off passively is small but significant.

When people talk about how much energy waste contains they usually are not referring to the decay energy. They are usually talking about heavy elements which can be fissioned. The fission product waste is usually a small part of the total waste (less than a few percent by mass). The remaining uranium (and heavy metals) can be recycled and placed in a reactor to produce more power. This is usually what people mean when they say that waste has large amounts of energy left.

Question 2
Is it possible to transform radioactivity from waste directly into electricity, like it is done with betavoltaics?

There are different types of radioactivity. With all types the energy can eventually be converted to electricity but it simply isn't worth it. In most cases you would simply let something get very hot by thermally insulating it till the temperature increase then use the high temperature heat to produce electricity (by running a heat engine or through a solid state device like an RTG or thermionic generator).

Question 3
Why is it forbidden by law for the average citizen to possesses nuclear waste in (all) most countries?

As I understand it anyone is allowed to own it provided they have the proper training and licenses. Without a license it is forbidden simply because it is dangerous material (mostly if it gets lost, neglected or sabotaged). There is no logical reason an average person should want to own high level radioactive waste.

 

[reptkeu]

The simplest way is to simply let it decay. When the radiation gets stopped by material it converts the energy to heat (...) the amount of heat it gives off passively is small but significant.

Approximately how hot is a pellet of spent fuel? Enough to boil a cup of water? (just trying to get a sense here)

When people talk about how much energy waste contains they usually are not referring to the decay energy. They are usually talking about heavy elements which can be fissioned. The fission product waste is usually a small part of the total waste (less than a few percent by mass). The remaining uranium (and heavy metals) can be recycled and placed in a reactor to produce more power. This is usually what people mean when they say that waste has large amounts of energy left.

Ok, so it's only these few percents of the spent fuel that can be used in the so-called fast reactors, and it cannot be used in a normal reactor like 'fresh' uranium, right?
What about the other remaining materials? Can't they be used? Are they the ones that only take a few hundreds years to fully decay? Can they be used to produce energy in any way, like beta-voltaics?

There are different types of radioactivity. With all types the energy can eventually be converted to electricity but it simply isn't worth it. In most cases you would simply let something get very hot by thermally insulating it till the temperature increase then use the high temperature heat to produce electricity (by running a heat engine or through a solid state device like an RTG or thermionic generator).

Producing electricity out of radioactive decay is interesting because, from what I understand, the conversion process is far simpler than turning heat into electricity (those little betavoltaics chips generate electricity thanks to a simple silicon plate that can convert radioactive particles directly into electricity. An RTG is far bigger, more complex and probably a lot more expensive than a betavoltaic chip).

As I understand it anyone is allowed to own it provided they have the proper training and licenses. Without a license it is forbidden simply because it is dangerous material (mostly if it gets lost, neglected or sabotaged). There is no logical reason an average person should want to own high level radioactive waste.

I think you are right, anyone can own a license, as long as you manage to get one. And I think there has only been one single individual owning one to date: James Acord, an artist who worked with and about radioactive materials (he even had it tattooed on his neck). Other license owners, I guess, must be companies, hospitals, governmental institutions, etc.
Are there certain parts of the spent fuel that are less dangerous? I am asking this because apparently certain particles (beta) aren't as harmful as alpha. Is there any beta-particles emitting materials in spent fuel?


Thanks for your answers. A lot of what I am saying/asking might sound naive, sorry about this.

 

[nikkkom]

Approximately how hot is a pellet of spent fuel? Enough to boil a cup of water? (just trying to get a sense here)

Meaningless question. The temperature of the pellet depends on how well insulated it is. Ability to boil a cup of water depends on how long you are planning to heat it up, how much of the heat is lost [and how big is the cup, how low is the pressure, etc :) ]

What you want to ask is something along the lines of "how many watts one kilogram of 10 year old spent fuel with 50 megawatt-days/kg burnup generates?".

I found a table at http://www.nrc.gov/reading-rm/doc-collections/reg-guides/fuels-materials/rg/03-054/

According to that table, the answer to my questions is "about 1.9 watt".

 

[nikkkom]

Ok, so it's only these few percents of the spent fuel that can be used in the so-called fast reactors,

You mean "can't be used". ~95% of the spent fuel is Uranium (mostly U-238) and ~1% is Plutonuim. They can be used in fast reactors. (The problem is that there are very few fast power reactors in use today). Plutonium can be chemically separated and used in MOX fuel in today's LWR reactors, which is being done today.

and it cannot be used in a normal reactor like 'fresh' uranium, right?

Generally yes, it (spent fuel's uranium) either can't be used outright (in BWRs and PWRs), or it can be marginally useful in heavy water reactors like CANDU, and after it is being burned in CANDU, it will become even more depleted but will still have >90% unburned Uranium-238.

What about the other remaining materials? Can't they be used? Are they the ones that only take a few hundreds years to fully decay?

http://en.wikipedia.org/wiki/Nuclear_fission_product
http://en.wikipedia.org/wiki/Spent_nuclear_fuel

Can they be used to produce energy in any way, like beta-voltaics?

For specialized applications like RTGs, yes, it can be used (and was used by Russians).
It's most likely not economical to do on the large scale.

 

[nikkkom]

Are there certain parts of the spent fuel that are less dangerous? I am asking this because apparently certain particles (beta) aren't as harmful as alpha. Is there any beta-particles emitting materials in spent fuel?

*Energetic* betas are producing secondary gammas. That's why RTGs on Sr-90 are not as attractive as RTGs on Pu-238 (an alpha emitter), despite of far greated availability of Sr-90 from the spent fuel.

Low-level betas are much safer. Tritium is an example, however, spent fuel from LWRs doesn't contain that much of it (heavy water reactors are hundreds of times more efficient producers of tritium).

 

[reptkeu]

The temperature of the pellet depends on how well insulated it is. Ability to boil a cup of water depends on how long you are planning to heat it up, how much of the heat is lost [and how big is the cup, how low is the pressure, etc :) ]

Yes, I know my questions are all asked in a rather unscientific manner. I am definitely more an adept of cookbook recipes, where the size of a cup or a tea spoon doesn't matter too much, and where cooking is often done at room temperature/pressure ;-)

The list is great, it's going to be useful.

 

[reptkeu]

I just came across one of these websites that sell radioactive isotopes, like this one.
Why are they allowed to sell (and we are allowed to buy) radioactive material without license?

I am guessing the answer could be that they have so little uranium in them that they are harmless?

 

[russ_watters]

None of those were uranium.

 

[Astronuc]

I just came across one of these websites that sell radioactive isotopes, like this one.
Why are they allowed to sell (and we are allowed to buy) radioactive material without license?

I am guessing the answer could be that they have so little uranium in them that they are harmless?

As Russ mentioned, they do not contain uranium (above impurity levels). They are sealed calibration sources, and they will make a record of the purchase. The purchaser is legally responsible for the sources.

 

[nikkkom]

I just came across one of these websites that sell radioactive isotopes, like this one.
Why are they allowed to sell (and we are allowed to buy) radioactive material without license?

I am guessing the answer could be that they have so little uranium in them that they are harmless?

These samples contain one microcurie (37 kBq) each. Average human body contains 5kBq of natural radioactivity (K-40 and C-14). IOW: one sample contains about as much radioactivity as 7 human bodies.