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.

c.

0.5g

0.25g

d.

e.

0.125g

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

1.

Math Practice

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 half life 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 non defense 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 high level 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