User:David MacQuigg/Sandbox/Nuclear waste
A more realistic view of nuclear waste hazards
Figure 1 in the article exaggerates the long term danger of spent nuclear fuel.
Long term radioactivity is mostly alpha particles and electrons harmlessly trapped in the spent fuel. The more dangerous gamma rays die out in a few hundred years. See Figure 3.
To understand the nuclear waste problem, we must understand the difference between the three
forms of radiation emitted by the used fuel: alpha particles, electrons, and photons (often called
gamma rays). Alpha particles have no penetrating power. They are stopped by a piece of
paper or a few centimeters of air. Electrons (confusingly called beta rays in this context) have
very little penetrating power. Most are stopped by the outer layer of our skin. Alpha particles
and electrons must be swallowed to be a health hazard. Photons on the other hand can have
enormous penetrating power. High energy photons can pass all the way through a human being.
Fresh used fuel puts out a lot of high energy photons and needs lots of shielding.
Dose is the amount of radiation energy absorbed by our tissue. Dose is measured in joules
per kg of tissue. Gray is a shorthand name for joules per kg. Figure 3 is in milligrays per day
(mGy/d). The key feature of Figure 3 is that photon decay is relatively rapid. By year 600,
almost all the photon emitters are gone. In fact, the photon dose rate is so low that, according
to DOE rules, the used fuel elements can be contact handled, without any shielding at
all. After year 600, the spent nuclear fuel must be swallowed in order to do any damage.