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. 1gb. 0.5gc. 0.25gd. 0.125ge. 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 reactionsFission

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 Practice1. 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 16-19Figure 16-19