Transcript Nuclear Waste - University of South Carolina

Nucular Waste
A Technical Analysis
Ian Baird
5/12/08
Nuclear Waste…Why?
•Recently nuclear power has entered many discussions as world
energy needs rise and oil reserves diminish.
•Most opponents of nuclear power point to two main arguments:
meltdowns and nuclear waste.
•Nuclear waste is any form of byproduct or end product that
releases radioactivity.
•How to safely dispose of nuclear waste is pivotal for the
continued operation of nuclear power plants, safety of people
living around dump sites, and prevention of proliferation of
nuclear materials to non-nuclear states.
Nuclear Fuel Cycle
Most nuclear waste comes from the byproducts of the nuclear
fuel cycle. The cycle typically is split into three sections:
front end, service period, and back end. There can be
intermediate stages that include the reprocessing of nuclear
waste elements.
Nuclear Fuel Cycle (Cont.)
Classifications
• Nuclear waste is segregated into several
classifications.
• Low level waste is not dangerous but sometimes
requires shielding during handling.
• Intermediate level waste typically is chemical
sludge and other products from reactors.
• High level waste consists of fissionable elements
from reactor cores and transuranic wastes.
• Transuranic waste is any waste with transuranic
alpha emitting radionuclides that have half-lives
longer than 20 years.
Low Level Waste
LLW
• Low level waste is any waste that could be
from a high activity area.
• 90% volume of waste
• It does not necessarily carry any
radioactivity.
• Split into four catagories: A, B, C, and
GTCC.
Intermediate Level Waste
ILW
• Intermediate level waste requires shielding
when being handled.
• 7% volume of waste
• Dependent on the amount of activity it can
be buried in shallow repositories.
• Not recognized in the United States.
High Level Waste
HLW
• High level waste has a large amount of
radioactive activity and is thermally hot.
• 3% volume of waste
• 95% of radioactivity
• Current levels of HLW are increasing about
12,000 metric tons per year.
• Most HLW consists of Pu-238, 239, 240,
241, 242, Np-237, U-236
Transuranic Waste
TRUW
• Transuranic waste consists of all waste that
has radionuclides above uranium.
• TRUWs typically have longer half-lives
than other forms of waste.
• Typically a byproduct of weapons
manufacturing.
• Only recognized in the United States.
Creation of Nuclear Waste
•Nuclear waste is generated at all points of
the fuel cycle.
•Front end waste consists primarily of low
level alpha emission waste.
•Service period waste typically includes
LLW and ILW such as contaminated reactor
housings and waste from daily operation.
•Back end waste normally is the most
radioactive and includes spent fuel rods and
reactor cores.
Front End Waste
• Front end waste consists mostly of LLW
and ILW.
• The primary front end waste is depleted
uranium and radium.
– DU has several uses due to its high density
(19,050 kg/m3).
– Mix with uranium to form reactor fuel
Service Period Waste
• Consists of mostly ILW.
• Mostly waste produced at the plant during
normal operation.
• Spent fuel rods are the most dangerous
waste produced during the service period.
Back End Waste
• Nuclear waste developed
during the back end of the
fuel cycle is the most
dangerous and includes
most of the HLW
produced.
• Most back end waste emits
both gamma and beta
particles.
• Also uranium-234,
neptunium-237,
plutonium-238 and
americium-241are found in
back end waste.
Spent nuclear fuel in a cooling pond in North
Korea.
Waste Management (LLW)
• There are several
options available for
the disposal of LLW
due to its lack of
radioactivity.
• Waste Isolation Pilot
Plant
• On-site disposal
Map of WIPP Facility
Treatment (LLW)
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•
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Filtration
Ion Exchange
Evaporation
Incineration
Compaction
Solidification
Typical LLW treatment facility.
Waste Management (HLW)
• Most common utilized
option are reactor pools
and dry cask storage.
• Other Options for waste
management include:
– Deep Geologoical
Storage
– Transmutation
– Reuse
– Launching it into space
Locations of storage sites for nuclear
waste in the U.S.
Treatment
• Most common initial treatment of waste is
vitrification.
– Waste is first mixed with sugar and then passed
through a heated tube to de-nitrite the material.
– This material is then fed into a furnace and
mixed with glass.
– The molten glass mixture is poured into steel
cylinders and welded shut.
Treatment (Cont.)
• Mid level active waste is commonly treated
with ion exchange
• Process reduces the bulk volume of
radioactive material.
• Typically, mixed with concrete for a solid
storage form.
Treatment (Cont.)
• Synroc is a new method for storing nuclear
waste developed in 1978 by Ted Ringwood.
• Attempts to hold radioactive material in a
crystalline matrix.
• Currently in use for military waste
management at Savannah River Site.
• Can hold 50%-70% volume of waste.
Deep Geological Repository
• Most common method
for handling nuclear
waste.
• Typically kept separate
from actual plants and
buried far below ground.
• First used in 1999 in the
US.
• Current research is
focusing on Yucca
Mountain.
Yucca Mountain Site
Transmutation of Nuclear Waste
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Reduces transuranic waste.
Integral Fast Reactor
Banned 1977-1981 (U.S.)
MOX Fuel
– Behaves as low-enriched uranium
• Research now in subcritical reactors.
• Fusion also being researched.
Reuse of Nuclear Waste
• Research is being performed to find uses for
nuclear waste.
• Caesium-137 and strontium-90 already used
in industrial applications.
• Some waste can be used for radioisotope
thermoelectric generators (RTGs).
• Overall can reduce total HLW but not
eliminate it.
Launch it into Space
• Near infinite storage
space
• Completely removes
waste from biosphere
• Technical risks and
problems
• Political
entanglements
Conclusions
• HLW is most dangerous
byproduct of nuclear
power.
• Borosilicate glass most
common storage.
• Several venues being
researched for the safe
disposal of HLW.