Radioactive Waste

[Jstas]

So I know some people here have a vastly superior to me understanding of nuclear physics and nuke plants in general.

What I do know is that nuke plants operate similarly to coal fired or natural gas fired plants where the radioactive fuel generates heat which in turn heats a boiler system that then uses the steam to power turbines or other electrical generation devices and thereby generate electricity to power really big monoblocks for the Amazings.

So I keep seeing news stories about towns in Sweden and Finland saying that they want the nuke waste because they think they can store it safely in bedrock.

Well, I'm wondering what the properties of this nuke waste are. I know that there is a method that is being worked on for using thorium as a fuel and using spent uranium or plutonium-238 (both of which are the majority of radioactive waste we have sitting around) as seed material to start the reaction in thorium that would generate the power. The benefit there is that the thorium ends up with less waste overall and actually reduces the levels of waste we currently have by expending the the plutonium seeds as well.

But satellites are powered by nuke reactors in some cases. These nuke reactors use small amounts of decaying radioactive waste such as a Plutonium-238 oxide to generate power. Now, such pellets will actually start to glow from the heat of radioactive decay if under insulated cover. If they can glow like that then they can make steam, typically. 'Cause I know of no exothermic reaction that can glow and not release enough heat energy to increase the temperature of water past the boiling point.

So my question is, if this radioactive waste can generate heat from the decay process then why can't we use that in a different kind of reactor to generate heat and boil water? Or maybe even another "coolant" that has a lower boiling point? It would certainly reduce the waste problem we have and since the decay process has a 100,000 year life span, an efficient heat exchanging system could sap many decades worth of heat out of the decaying waste.

Or am I way off base here? 'Cause I know these ideas are doable because the space program uses them daily to power complex electronic equipment in space where there is no oxygen available for exothermic reactions of oxidizing fuel to generate the heat that creates steam. So if we can use it there, why not here?

[JustinHEMI]

For the space program, you are talking about electrical requirements on the millivolt level. For power generation, you are talking about kilivolts (22000 volts).

Radioactive waste does not produce anywhere close to the heat required to generate that kind of power.

You need high temperature, pressurized water in order to turn turbines and generators big enough to generate that power.

After a reactor shutdown, decay heat is <1% of 100% max power within an hour. Enough to damage the fuel if left unchecked, but not near enough to spin a turbine.

Hope that helps.

Justin

PS I am a senior reactor operator at a nuclear power plant in the US.

[Keiko]

So my question is, if this radioactive waste can generate heat from the decay process then why can't we use that in a different kind of reactor to generate heat and boil water?

Do you really want to end up looking like this, John?



:tongue:

[nooshinjohn]

Do you really want to end up looking like this, John?



:tongue:

Too Late!:tongue:

[Jstas]

For the space program, you are talking about electrical requirements on the millivolt level. For power generation, you are talking about kilivolts (22000 volts).

Radioactive waste does not produce anywhere close to the heat required to generate that kind of power.

You need high temperature, pressurized water in order to turn turbines and generators big enough to generate that power.

After a reactor shutdown, decay heat is <1% of 100% max power within an hour. Enough to damage the fuel if left unchecked, but not near enough to spin a turbine.

Hope that helps.

Justin

PS I am a senior reactor operator at a nuclear power plant in the US.

That pretty much answers my questions!

Does the spent fuel radiate enough radiation? Could it be used like, say a microwave, to heat up another substance to create the steam? Or could that radiation be harnessed with cell like the kind used in solar panels?

[renowilliams]

There are a lot of technologies going into dealing with radioactive waste. I work for a company involved in this. They are also taking weapons grade radioactive material and converting it so it can be used in the generation of power.

[JustinHEMI]

That pretty much answers my questions!

Does the spent fuel radiate enough radiation? Could it be used like, say a microwave, to heat up another substance to create the steam? Or could that radiation be harnessed with cell like the kind used in solar panels?

What the poster said above. Only time will tell. In the past, it was thought that spent fuel was useless and required burying forever. However, with new technology comes new possibilities. I am afraid I cannot speak intelligently about what is on the horizon as far as spent fuel processing/reuse is concerned, but I can tell you that it is highly radioactive and instantly deadly. What they can do with that, I don't know. I spend most of my time keeping my units online and studying more near future technologies such as the new generation nuke plants that are being built throughout the world (except in the USA, save one site).

Also, I don't see it being used to generate steam, because like I mentioned above, the steam has to have enough energy to turn a turbine, which is a massive piece of steel. That is why we use high temp/pressures to accomplish that goal, and spent fuel doesn't have it in it to do it, alone.

Justin

[mrbigbluelight]

Very nice thread.

Jstas mentiong using waste materials to generate heat for steam. I didn't bookmark it but there's a video on YouTube (?) that shows waste material in a cylindrical shape that theoretically could be used to generate high temp/psr steam
SUPPOSEDLY this cigarette-shaped cylinder "burns" the radioactive waste, leaving behind less radioactive "ash". This "ash" is then either recycled in some fashion or can be stored in a safer manner.

I'll try to dig that video back up. Sounds "too good to be true", but it did get my attention.

Kind of off-topic, but have you any knowledge Justin of the extent of radioactive contamination in Japan ? Don't care about radiation levels, curious as the degree of contamination surrounding the reactors and in the ocean.

[JustinHEMI]

Not anymore knowledge than you have. I have stopped keeping track about a week and a half ago.

Justin

[Jstas]

Here we are talking about radioactive waste and I saw this on Slate.com



It's a photo essay type deal from this guy Paul Fusco who documented the children born within the radiation zone of Chernobyl from 1997 to 2000. Pretty riveting footage.

[mrbigbluelight]

Very potent video, Jstas. Very potent.

Justin's descriptions of U.S. commerical reactor operations gives one more hope that something like Chernobyl won't occur in the U.S.

[JustinHEMI]

There was a lengthy thread about the Japanese disaster which I put more detail about US nuke plants.

Justin

[Joe08867]

Jstas, Thanks for posting that video. I never saw that before and all I can say is wow, how moving, how scary, how sad.

JustinHEMI, thanks for your posts on this stuff. It is nice to get the perspective of someone in the know. And also someone that can explain it to a dummy like me...

[JustinHEMI]

Anytime! :)

Justin

[cheddar]

Kind of off-topic, but have you any knowledge Justin of the extent of radioactive contamination in Japan ? Don't care about radiation levels, curious as the degree of contamination surrounding the reactors and in the ocean.

The contamination is serious enough that they are now setting up security around the 12mi(IIRC) exclusion zone around the plant to keep people from going back to their homes to check on things and maintain their farms and livestock (which is the major industry in this area). And the plant was releasing contaminated water directly into the ocean. Both by mistake (cracked trench walls) and on purpose (to make room in tanks for even more highly contaminated water that needed to be pumped from flooded basements. Officials released a statement saying the ocean contamination was of no concern outside the local area.