Can Radioactive Material Be Recycled?

[Astronuc]

Spent fuel is mostly U238 in the form of UO2. In modern fuel cycles, the content of U235 varies between 4-5%, so 95-96% of U is U238.

During operation in a LWR core, two things happen with the U, 1) the U-235 fissions producing two fission products, and 2) U-238 absorbs neutrons to eventually produce Pu-239 (and other isotopes of Pu, Am, Cm, with the latter two being in low levels).

At discharge, modern fuel with have a burnup (energy produced/unit mass of U) of 50-60 GWd/tU. This is roughly equivalent to 5-6% of initial U consumed, which is now in the form of highly radioactive fission products. Also, part of the fissioning occurs in the Pu-239 that is produced by conversion of U-238, as Morbius pointed out elsewhere, and in high burnup fuel, as much as half the fissions are in Pu-239.

Mine tailings have 'natural' amounts of radioactive elements (related to the decay of U-235 and U-238), which are left after the U ore has been extracted.

Every mining operation (for copper, gold, silver, iron, lead, zinc, molybdenum, etc) leaves tailings which release heavy metals into the environment - so it is not just U mining that causes hazards, although due to their nature, U mine tailings would have higher level of radioactivity.

"According to the National Council on Radiation Protection and Measurements, sedimentary rocks such as shale and sandstone (quarts) contain about one (1) to four (4) micrograms of uranium per gram of rock. Beach sands contain about three (3) micrograms of uranium per gram of sand. And soil contains, on average, one (1) to three (3) micrograms of uranium per gram.

Igneous rocks, such as basalt, salic and granite, can contain from 0.5 to four (4) micrograms of uranium per gram of rock. However, there can be wide variations in this range in certain regions of the world. Because of the way these rocks were formed during the cooling of magma, light-colored igneous rocks tend to have the highest concentrations of radioactivity." from http://www.iem-inc.com/askq32r.html

So radioactivity is not unique to U-mine tailings, although there is somewhat higher levels than the examples just stated.

 

[Morbius]

Maybe because U-238 in nature is not as concentrated as in radioactive waste.

tumor,

As astronuc correctly points out - the concentration of U-238 in nuclear
waste is about 96% or so.

The concentration of U-238 in natural uranium is 99.3%

So the concentration of U-238 in natural uranium EXCEEDS the percentage
in spent fuel.

So much for your argument.

Dr. Gregory Greenman
Physicist

 

[CharlesP]

The US uses depleted uranium in some munitions because of its density. There has been quite a controversy about it.

Houses were built on ground contaminated with mine tailings in Colorado and I suspect those developments were abandoned.

There was a criticality accident in Japan a few years back in which at least one person was exposed or killed. The result has been resignation of at least one corporate officer and a public relations disaster for the Japanese nuclear industry.

The continued use of fuel rod cooling pools in the US has been a very undesirable development.

I was told by an ex Navy reactor man that there is no way to safely contain nuclear waste.

 

[hitssquad]

there is no way to safely

This is a philosophy question and it belongs in the philosophy section of Physics Forums.

 

[Morbius]

I was told by an ex Navy reactor man that there is no way to safely contain nuclear waste.

Charles,

Then your ex Navy reactor man doesn't know what the hell he's talking
about.

The National Academies of Science and Engineering say that nuclear
waste can be safely contained. [ In fact it was the National Academy of
Science that first suggested a "Yucca Mountain" type repository back
in the late '50s.]


Scientists from our National Laboratories say nuclear waste can be
safely contained:

http://www.llnl.gov/str/Glassley.html

Nuclear waste storage has been very thoroughly studied.

Additionally, it's not like we have any option - nuclear waste exists!
We can't "unmake" it - it HAS to be stored somewhere!

Dr. Gregory Greenman
Physicist

 

[russ_watters]

I was told by an ex Navy reactor man that there is no way to safely contain nuclear waste.

This is obviously false at face value: nuclear waste has been safely contained for 50 years.

 

[Nereid]

Wouldn't it be nice to have some natural reactors, with buried spent fuel and decay products, to study? Maybe then we could see how many harmful effects there are, through a perfectly natural experiment We could also calibrate ... you know, near this natural reactor, there seem to have been no increases in harmful effects due to radiation, over those of similar natural sites of enhanced radiation (e.g. certain basalts and granites), and way below such unnatural activities as flying thousands of hours in jets at 35k feet (or higher ... do the calculations on the increased exposure due to cosmic rays - or don't, if you don't want to get a big shock).

Ah, but there aren't any natural reactors, are there. Too bad.

But wait! Did I hear someone say http://www.curtin.edu.au/curtin/centre/waisrc/OKLO/index.shtml ?

 

[Morbius]

Wouldn't it be nice to have some natural reactors, with buried spent fuel and decay products, to study?

Nereid,

EXACTLY.

The natural reactors at Oklo and Gabon have been extensively studied.

It's been shown that soil is such a good ion exchange medium, that the
fission products get trapped and don't migrate very far in millions of years -
even though there were absolutely no measures taken to inhibit that
migration.

Contrast that with the Yucca Mountain repository - where the waste is
encapsulated in something like borosilicate glass, which is then encased
in steel containers...

The scientific consensus, as opined by the National Academies of
Science and Engineering, from our best Ph.D. level scientists state that
nuclear waste CAN be successfully contained, the opinions of unidentified
Navy reactor operators, nothwithstanding.

Dr. Gregory Greenman
Physicist

 

[nikkkom]

Carnot's law. The hotter the core temperature of a heat engine, absolutely relative to the coolant temperature, the more efficient it is. A heat engine (such as a turbine, which would be a poor choice for a low-temperature heat source) running off of the decay heat of spent reactor fuel would be too inefficient to produce electricity economically.

Well, nuclear fuel's temperature can be high - it all depends on how much energy you take away from it. IOW: if you have lots of spent fuel sitting in relatively well-insulated water tank and use a *small* amount of steam from it to drive a *small* turbine, then the temperature of that tank can be kept high enough to have a decent efficiency.

I guess it is just not economical.

 

[nikkkom]

How about all the other radioactive isotopes in a fuel rod. Doees each get a bunch of steps too? Which is first?
If uranium is not dangerous how come there is all this fuss about Uranium mine tailings?

Uranium mine tailings contain not so much uranium but its decay products - which are about 8 times more radioactive than uranium per se, and have varying chemical and biological properties - some are gaseous (radon), some are absorbed into the bones when ingested (radium).

 

[jim hardy]

i'd like to see mankind do a better job of isolating the "bad" components

tha actual mass of them isn't so great

i've wondered for years whether the really nasty stuff could be shot into the sun, where the extreme conditions would likely dissociate it down the curve of B.E. ?

 

[etudiant]

i'd like to see mankind do a better job of isolating the "bad" components

tha actual mass of them isn't so great

i've wondered for years whether the really nasty stuff could be shot into the sun, where the extreme conditions would likely dissociate it down the curve of B.E. ?

Given that no current space launch system has even 99% reliability, that possibility is unfortunately excluded. The failure is too messy.