Nuclear energy
Review: Elements and Isotopes

What are elements defined by?

What are isotopes?

What is the difference between a stable and
a radioactive isotope?
Radioisotopes


experience radioactive decay (the loss of
alpha or beta particles over time)
Result: atoms of one element physically
change into another element.
– Eg Carbon-14 decays to Nitrogen-14 by loss of
negative beta particles

Radioactive half life= the amount of time
it takes for 50% of the radioactive isotope
in a substance to decay.
Practice:
Plutonium-239 has a half-life of 24,000
years. How much of a 4 gram sample will
remain after 96,000 years?
a. 1g
b. 0.5g
c.
0.25g
d. 0.125g
e. 0.625g
Dating with radioactive isotopes

Carbon-14 can be used to
estimate the age of plant and
animal remains
Geological dating with Uranium


Uranium-238 is a very
common radioisotope
that decays to a stable
isotope of lead
It has a half life of 4.5
billion years
The discovery of radioactive atoms




1896 uranium radiation observed
1898 radiation consists of high
energy particles
1919 N nuclei hit with alpha
particles turned into O
1938 First fission reaction
Nuclear rxns vs combustion
Combustion
 Atoms do not change;
are rearranged
 Mass of reactants =
mass of products
 Energy is released as
heat when bonds
break
Nuclear
 Nucleic changes result
in element
transformations
 Small of amount of
matter releases large
amounts of
energy…less mass in
products
Types of nuclear reactions
Fission
Fusion
NUCLEAR ENERGY
 Nuclear
power plants use U-235, a
radioactive isotope of uranium.
– Mining
– Enrichment
 Fuel
assembly
Nuclear power plant
NUCLEAR WASTE
NUCLEAR WASTE
Math Practice
1.
After 100 million years, only 1/32 of the original amount
of a particular radioactive waste will remain. The half-life
of this radioactive waste is how many million years?
a. 10
b. 20
c. 30
d. 40
e. 50
2.
You have 180g of a radioactive substance. It has a halflife of 265 yrs. After 1,325 yrs, what mass remains?
Nuclear waste

Low level
– Radioactive solids, liquids, or gases that give
off small amounts of ionizing radiation
– Sources include power plants, hospitals,
research labs, and industries
– Low Level Radioactive Waste Policy Act 1980 &
1985
 All
states must be responsible for disposal of nondefense related waste produced w/in their borders.

High level
– Radioactive solids, liquids, or gases that
initially give off large amounts of ionizing
radiation
– Sources include anything that was inside the
reactor core (metals, water, gases, spent fuel)
Nuclear Waste Policy Act 1982

Stated that there must be a permanent site for
storing high level waste by 1998
– That was not met; postponed to 2010 at earliest



1987 Congress identified Yucca Mountain in
Nevada as the best potential site
In 2002 it was officially approved by Congress
Rescinded by Obama in 2009
NUCLEAR ENERGY
 Scientists
disagree about the best
methods for long-term storage of highlevel radioactive waste:
– Bury it deep underground.
– Shoot it into space.
– Bury it in the Antarctic ice sheet.
– Bury it in the deep-ocean floor that is
geologically stable.
– Change it into harmless or less harmful
isotopes.
The risks of nuclear energy





Meltdown
Acute radiation syndrome
Daily radiation for workers (carcinogenic over
time)
Radiation into groundwater from stored waste
Small scale persistent radiation to nearby
communities
Radiation and health

We are exposed to natural (background
radiation) and artificial radiation every day
– 300 millirems per year from space/the
atmosphere, the soil (radon), foods we eat
(radioactive potassium)
– 60 millirems from manmade radiation
(radiowaves, hospitals, industries, housing
materials, microwaves, cell phones, tobacco,
television, smoke detectors, etc.)
Figure 16-19