Environmental Engineering FOURTH EDITION

Radioactive Waste 33 1

and so on, until a stable element (usually a lead isotope) is reached. Table 16-9 shows

the U-238 decay series. The plutonium isotopes also decay in a series of radionuclides.

Spent nuclear fuel (HLW) thus contains fission products, tritium, neutron activa-

tion products, plutonium, and plutonium and uranium daughter elements in a very

radioactive, very long-lived mixture that is chemically difficult to segregate.

Reprocessing Waste and Other Reactor Waste

In the United States, plutonium is used only for nuclear warheads, which were manufac-
tured from the end of World War I1 until 1989. Plutonium was produced by irradiating
U-238 with neutrons (in the reaction given above) in military breeder reactors. The
irradiated fuel was then completely dissolved in nitric acid, and plutonium along with
fissile uranium and neptunium were extracted with tributyl phosphate. Further parti-
tion and selective precipitation resulted in recovery of plutonium, uranium, neptunium,
strontium, and cesium.
The fissile isotopes of plutonium and uranium are categorized as special nuclear
material; the other nuclides are considered by-product material. The term reprocessing
refers to the entire process of extracting fissile material from irradiated fuel. Although
the production and extraction of special nuclear material have ceased, the very large
quantities of neutralized acid solvent sludge and the organic extraction solvents used
contain high concentrations of radionuclides and are classified as HLW. The process
also yielded TRU waste and LLW.'
Commercial fuel is not currently reprocessed in the United States. In France,
plutonium for nuclear power generation is produced from fertile material in the Super-
phenix breeder reactor. Plutonium for nuclear weapons has not been produced in the
United States since 1993, and surplus plutonium from the U.S. weapons program
is now being fabricated into mixed uranidplutonium oxide (MOX) fuel. Great
Britain and France also produce MOX fuel. Although no MOX fuel is presently
burned in U.S. commercial nuclear power plants, it is being used in Europe and
Canada.
The primary and secondary coolants in a nuclear generating plant pick up consid-
erable radioactive contamination through controlled leaks. Contaminants are removed
from the cooling water by ion exchange and the loaded ion-exchange columns are
Class C or GTCC waste. Class A and Class B wastes are also produced in routine
cleanup activities in nuclear reactors.
After 30 to 40 years of operation, the reactor core and the structures immediately
surrounding it will have become very radioactive, primarily by neutron activation,
and the reactor must be shut down and decommissioned. At present, 10 commercial
reactors in the United States have either been decommissioned or are undergoing
decommissioning.

81nformation about the exact quantities of particular constituents of reprocessing waste is not made
available to the public for reasons of national security.