What Fire and Leakage At WIPP Means For Nuclear Waste Disposal

Lasrick (2629253) writes "An underground fire and a separate plutonium leak at the Waste Isolation Pilot Plant (WIPP) has left the US with no repository for transuranic (TRU) waste--that is, radioactive elements heavier than uranium on the periodic chart, such as plutonium, americium, curium and neptunium. WIPP is a bedded salt formation in New Mexico, chosen because of its presumed long-term stability and self-sealing properties, and it currently holds, among other things, 4.9 metric tons of plutonium. Despite assurances from the DOE that the plant would soon reopen, New Mexico has cancelled WIPP's disposal permit indefinitely. Robert Alvarez, who has served as senior policy adviser to the Energy Department's secretary and as deputy assistant secretary for national security, explores what happened at WIPP, and what it means for defense nuclear waste storage."

Comments

Oopsie!

[Peter Simpson]

[sigh] Yet another contractor who seems to have been doing the minimum required to get paid. Fire suppression turned off, flammable materieals stored after repeated inspections required that they be removed. Outsource responsibility and this seems to be the result. Words cannot express how disappointed I am that "business" seems to be going on "as usual" even when managing something as hazardous as nuclear waste.

Re:Oopsie!

[fnj]

Half-life is half-life; there isn't a process we can use to change that

OK, to begin, the following is simplified to skip some points of extreme nuisance, and to be suitable for non nuclear engineers (like me).

Radioactive decay isn't as simple as one might be forgiven for thinking given the simplistic concept "half-life". You might ideally start off with a pure form of a single isotope of a single element. In practice, you never do. Reactor fuel as it goes into the reactor is about 5% U235, 95% U238, with traces of other elements and isotopes. When it comes out of the reactor, it is a lesser percentage of U235, still a bunch of U238 left, plus a bunch of plutonium and a witch's brew of other isotopes of elements resulting from the nuclear "cooking" in the reactor involving neutron bombardment.

But for simplicity, let's take an imaginary bunch of U235.

The U235 decays to Th231 in a decay process with a half-life of 704 million years
The Th231 decays to Pa231 in a decay process with a half-life of 25.5 hours
The Pa231 decays to Ac227 in a decay process with a half-life of 32,500 years
The Ac227 decays to 98.6% Th227 and 1.4% Fr223 in a decay process with a half-life of 21.6 years
The Th227 decays to Ra223 in a decay process with a half-life of 18.2 days
The Ra223 decays to Rn219 in a decay process with a half-life of 11.4 days
The Rn219 decays to Po215 in a decay process with a half-life of 4.00 seconds
The Po215 decays to Pb211 in a decay process with a half-life of 1.78 milliseconds
The Pb211 decays to Bi211 in a decay process with a half-life of 36.1 minutes
The Bi211 decays to 99.7% Tl207 and 0.3% Po211 in a decay process with a half-life of 2.15 minutes
The Tl207 decays to Pb207 in a decay process with a half-life of 4.79 minutes
The Pb207 is stable and hangs around for the balance of eternity

The first thing to realize is that an instant after the imaginary start with pure Uranium235, and continuing for many billions of years, we have a constantly changing mix of various isotopes of elements, shading from pure U235, and asymptotically approaching (but never mathematically quite reaching) pure Lead207.

The constituents of that mix are busy decaying all at their own rates.

But the individual decay rates are mathematical models. A tiny little bit of that U235 has already changed all the way to Pb207 within the first hour, and a tiny little bit is still stuck at U235 after some billions of years. The rate of each individual decay process averages out to the half-life given by the particular model for that process.

So to get all the way to the point: yes, you actually can effectively change the rate of transmutation of the stuff that comes out of the reactor. You can re-enrich it back to a sufficiently rich mixture of uranium and plutonium oxides (and do some other reprocessing chores, such as cleaning out the fission poisons so it's usable again) and put it back in a reactor. Or you can separate out the plutonium and put it in a nuclear bomb and that will transmute really fast if you set it off. After you take out the plutonium it is at least theoretiucally possible to re-enrich the remainder back to 5% U235 and put THAT back in a reactor.

Note that the process during reactor operation is not the same as the decay process. In the reactor, you can "use up" a substantial percentage of the starting U235 in just a few years, in the process "creating" a bunch of plutonium (more than one isotope!) where there was none.