Transcript Radioactivity and Spent Nuclear Fuel Fission produces highly radioactive isotopes • All of the highly radioactive materials on earth have been produced by fission.

Radioactivity and
Spent Nuclear Fuel
Fission produces highly radioactive
isotopes
• All of the highly radioactive materials on earth
have been produced by fission.
Cs-137 (Cesium-137)
• Cs-137 is produced by nuclear fission for use in
medical devices and gauges.
• Cs-137 also is one of the byproducts of nuclear
fission processes in nuclear reactors and nuclear
weapons testing.
• Small quantities of Cs-137 can be found in the
environment from nuclear weapons tests that
occurred in the 1950s and 1960s and from
nuclear reactor accidents, such as the Chernobyl
power plant accident in 1986, which distributed
Cs-137 to many countries in Europe.
Cs-137
• External exposure to large amounts of Cs-137 can
cause burns, acute radiation sickness, and even
death.
• Exposure to Cs-137 can increase the risk for
cancer because of exposure to high-energy
gamma radiation. Internal exposure to Cs-137,
through ingestion or inhalation, allows the
radioactive material to be distributed in the soft
tissues, especially muscle tissue, exposing these
tissues to the beta particles and gamma radiation
and increasing cancer risk.
Cs-137
I-131 (Iodine-131)
• I-131 is produced commercially for medical
and industrial uses through nuclear fission. It
also is a byproduct of nuclear fission processes
in nuclear reactors and weapons testing.
I-131
• External exposure to large amounts of I-131 can
cause burns to the eyes and on the skin. Internal
exposure can affect the thyroid gland.
• If I-131 were released into the atmosphere,
people could ingest it in food products or water,
or breathe it in.
• Once inside the body, I-131 will be absorbed by
the thyroid gland exposing it to radiation and
potentially increasing the risk for thyroid cancer
or other thyroid problems.
I-131
• In addition, if dairy animals consume grass
contaminated with I-131, the radioactive
iodine will be incorporated into their milk.
• Consequently, people can receive internal
exposure from drinking the milk or eating
dairy products made from contaminated milk.
I-131
• Potassium Iodide pills will keep the thyroid
from absorbing I-131.
• Frequently Asked Questions About Potassium
Iodide from the Nuclear Regulatory
Commission (NRC)
• http://www.nrc.gov/about-nrc/emergpreparedness/about-emergpreparedness/potassium-iodide/kifaq.html#shelflife
SR-90 (Strontium-90)
• Sr-90 is produced commercially through
nuclear fission for use in medicine and
industry.
• It also is found in the environment from
nuclear testing that occurred in the 1950s and
1960s and in nuclear reactor waste and can
contaminate reactor parts and fluids.
SR-90
• Sr-90 can be inhaled, but ingestion in food and
water is the greatest health concern.
• Once in the body, Sr-90 acts like calcium and is
readily incorporated into bones and teeth,
where it can cause cancers of the bone, bone
marrow, and soft tissues around the bone.
Center for Disease Control (CDC)
https://ippnweupdate.files.wordpress.com/2011/03/cdc-radioisotope-factsheets.pdf
What is radioactivity?
• Radioactivity occurs when an atomic nucleus releases small
energetic particles or waves.
• There are three types of nuclear radiation: alpha, beta, and
gamma.
• Alpha particles are positively charged, beta particles are negatively
charged, and gamma particles have no charge.
• The radiations also have increasing levels of energy, first Alpha,
then Beta, and finally Gamma, which is the most energetic of all
these.
• Alpha and Beta are particles, but Gamma is a wave.
Half-life
• When a radioactive nucleus changes, the remaining
nucleus (and atom) is not the same as it was. It
changes its identity.
• The term half-life describes the time it takes for half of
the atoms in a sample to change, and half to remain
the same.
• Let's say you have 100g of uranium. When 50g remain
(and 50g have become something different because of
radioactive emissions), the amount of time that has
passed is the half-life.
Half-life
• Every element has its own unique half-life.
• The half-life of uranium-235 is 713,000,000 years.
• The half-life of uranium-238 is 4,500,000,000 years,
• These uranium isotopes are not changing rapidly and
consequently are not very radioactive.
• However many of the things that the original atoms
change into are very radioactive and dangerous!
Half-life and radioactivity
• U-238 with a half-life of 4.5 billion years is not
emitting much radioactivity and not changing
rapidly .
• The shorter the half-life, the more radioactive
the isotope is.
Radioactivity can be bad
• Radioactivity is generally not good for living organisms.
There are times that radiation passes right through
organisms with no effect, but there are other times that it
hits DNA or affects replicating cells.
• Bad things can happen when DNA is exposed to radiation.
• One result of moderate levels of radioactive particles can
be cancer. Cells reproduce in ways that are not normal.
• High doses of radioactivity can kill a human within 24
hours.
Radioactivity can be useful
• Medicine has learned how to use radioactivity
to stop some cancers.
• Since excess levels of radioactivity can kill
cells, doctors target areas of cancer with
radioactivity to stop the cancer cells from
dividing.
Radiation Therapy for Lung Cancer
Fission always produces highly
radioactive isotopes
• The fission of U-235 in a nuclear reactor produces
some highly radioactive isotopes.
• Small reactors intentionally produce highly
radioactive isotopes for medical uses, such as
radiation treatment for cancer.
• These small reactors are called research reactors
and do not produce electricity.
Big reactors also produce highly
radioactive isotopes
• Big reactors use the heat from fission to make
steam to turn a turbine and produce
electricity.
• The fission of U-235 in these big reactors also
produces a lot of highly radioactive isotopes.
• When the fuel no longer fissions efficiently, it
is removed.
Spent Nuclear Fuel (SNF) is highly
radioactive
• The fresh fuel put into the reactor was not
highly radioactive.
• 95% U-238 (half-life 4.5 billion years)
• 5% U-235 (half-life 713 million years)
• The removed Spent
Nuclear Fuel (SNF) has
become highly radioactive.
How is radioactivity measured?
• Lots of ways!! Is it a conspiracy?
• MilliSieverts, mSv, is the current most popular
measure of the effect of radiation on humans.
• Humans receive about 3 mSv per year of
natural background radiation.
Some set 2.4 mSv as average
background radiation for humans
Radiation from medicine will increase
exposure
Spent Fuel is Highly Radioactive
• It is well known that Spent Nuclear Fuel (SNF) is
deadly radioactive, but numbers measuring that
radioactivity are hard to come by on the Internet.
• The information in the following slides came from
this document from Posiva, a nuclear waste disposal
company in Finland. We don’t need to go to this link
unless we want to verify the information.
• http://www.tvo.fi/uploads/File/2012/Kaytetyn_ydinpolttoaineen_loppusij
oitus_Olkiluodossa_lowres_EN.pdf
Posiva
• “Posiva Oy is an expert organisation responsible for the
final disposal of spent nuclear fuel of the owners. Posiva
has been established in 1995.”http://www.posiva.fi/en
• “Posiva works in cooperation with several expert
organizations, both Finnish and foreign, and assigns
universities, research institutes, and consulting companies
to undertake research into nuclear waste management.”
• Here is a short video from Posiva Oy about its plans to store
spent fuel in bedrock in Finland.https://youtu.be/Jqsc3vZ8wU
“Geologic disposal of spent nuclear
fuel in Olkiluoto”
• “In Finland, each producer of nuclear power
generated electricity is fully responsible for its
own nuclear waste management. Teollisuuden
Voima Oyj (TVO) and Fortum Power and Heat
Oy have been managing their own nuclear
waste since the start of their nuclear power
plants.”
Nuclear waste comes in many types
• “The types of nuclear waste generated in a
nuclear power plant are: waste exempted from
control, low and intermediate level reactor waste,
high level spent fuel, and decommissioning
waste. The low and intermediate level waste
generated during the operation and outages of
the Olkiluoto and Loviisa power plants is stored in
the final repository for reactor waste, located at
the plant site.”
Spent fuel is High Level Waste (HLW)
• “The spent fuel, regarded as high level waste,
is currently kept in water pool storage at the
plant sites. Later, it will be disposed of in the
Olkiluoto bedrock. TVO and Fortum have
established Posiva Oy to manage the disposal
of spent nuclear fuel produced in their power
plants in Finland and associated research and
development work. The disposal activities are
scheduled to begin in about 2020.”
Radioactivity of Spent Fuel decreases
over time
• The following slides give radiation measures
for spent fuel after the passage of various
lengths of time. Quotes from the text are in
red.
• Each measure is the radiation level of spent
nuclear fuel without shield canister, measured
one meter away from the fuel assembly
surface.
After 1 year
• 1 year / 50 000 mSv/h:
• The radioactivity of a removed fuel assembly
decreases to approximately one hundredth in
one year
• Apparently the radiation initially measured
5,000,000 mSv/h.
• Is 5 million mSv/hour a little or a lot?
Natural radiation exposure
• 3 mSv/year is an
ordinary radiation
exposure from natural
sources such as radon
gas and cosmic rays.
5 million mSv per hour!
• 3 mSv/year is the ordinary.
• 5 million mSv/hour is an unimaginably huge
amount of radiation.
How long to die?
• The pro-nuclear Posiva document will soon
inform us that exposure to 8000 mSv will kill you.
• At 5 million mSv/hour, it would take
8000/5 million = 0.0016 hours to get a lethal dose.
= 0.0016 (60 minutes)
= 0.096 minutes
= 0.096 (60 seconds)
= 5.76 seconds for a lethal dose.
6 seconds to death
• No wonder spent nuclear fuel (SNF) is only
handled robotically.
• If you are standing 1 meter from fresh spent
fuel, it will take 6 seconds for you to acquire a
lethal dose of radiation.
40 years after removal
• 40 years / 3000 mSv/h:
• An acute exposure to 1 000 mSv will cause
radiation sickness; acute exposure to 8 000
mSv will cause death
• So after 40 years it would take < 3 hours of
exposure to a SNF rod to kill you.
100 years after removal
• 100 yrs / 70mSv/h
• In radiation work, a worker’s five-year dose
limit is 100 mSv
• So after 100 years, a worker would get the
five-year dose limit in 100/70 = 1.4 hours
working within a yard of a spent fuel
assembly.
500 years after removal
• 500 years / 4 mSv/h:
• The average radiation dose incurred by a Finn
in one year is approximately 4 mSv
• So 500 years after removal, the spent fuel
would still deliver an annual radiation dose in
1 hour and a radiation worker’s five year limit
of 100 mSv in a little over four days.
10,000 years after removal
• 10 000 years / 0,3 mSv/h:
• The radiation dose caused by a mammography xray examination is approximately 0.3 mSv
• By now, it actually would take 4/0.3 = 13 hours to
get an average annual radiation dose.
• This stuff remains dangerous a very long time.
Plutonium is also produced by fission
• In addition to highly radioactive elements, the fission
of U-235 produces plutonium.
• When U-238 absorbs a neutron and becomes U-239,
two beta-minus decays result in Pu-239.
Plutonium can explode with a nuclear
fission explosion
• Pu is not a natural
element.
• Pu is produced
reactors.
• Pu is named for Pluto,
God of the Underworld
.
in
Nagasaki after the Pu bombing
Spent Nuclear Fuel
is 1% Pu
• Production reactors
fission U-235 to
produce Pu
for bombs.
• Pu for Nagasaki was
produced at the
Hanford Site in
Washington
Reprocessing
• Extracting the Plutonium from the Spent Fuel
is called “reprocessing.”
• People can’t work with spent fuel due to its
intense radioactivity. Machines reprocess.