Nuclear Waste and Half Life

Nuclear Waste and Half Life

Name: ______Class: ______Date: ______

Nuclear Waste and Half Life

One of the biggest issues with nuclear energy is the dangerous and toxic waste that is leftover as the fuel rods are depleted. Fortunately, this material will naturally decay into less-dangerous elements over time. Unfortunately, this process can take an extremely long time.

The half-life of a radioactive material is the time needed for half of the radioactive atoms in a sample to decay. In this lab we will be looking at half-life in a different manner. Since we can’t actually watch a radioactive sample decay, we will represent the process with colored water instead. The colored water will represent strontium-90, which has a half-life of 29 years.


  • Test tube rack
  • 8 test tubes
  • Beaker of colored water
  • 10 mL graduated cylinder
  • Wash bottle


  1. Measure 10mL of colored water and pour into the first test tube. Label this as nuclear waste.
  1. Measure 5mL of the water from the nuclear waste test tube and add it to the next test tube. Add an additional 5mL of regular water. Label this as one half-life.
  1. Measure 5mL of the water from the one half-life test tube into the next test tube. Add an additional 5mL of regular water. Label this as two half-lives.
  1. Continue this process until you have 8 total test tubes. Pour out 5mL from the last test tube to make them all even.
  1. Shade in the test tubes below to show the amount of food coloring still present in each. Place a blank piece of paper behind each test tube to see the food coloring more easily.

  1. Calculate the percent of original nuclear waste remaining on the table below, as well as the time needed for decay based on the half-life of strontium-90 (29 years).

Test Tube / Percent of Original Nuclear Waste Remaining / Time Needed For Decay (years)
1 / 100% / n/a
2 / 50% / 29
  1. Graph the decay of your sample of Strontium-90. The number of years passed will be the independent variable, while the percent of strontium-90 remaining will be the dependent variable.

  1. Assume that strontium-90 is considered safe once its levels drop below 1% in a sample. Draw a horizontal line on your graph to show where the 1% mark would be.

Post-Lab Questions:

  1. If your test tubes actually contained strontium-90, which one (or ones) would have been safe using the 1% guideline?
  1. About how many half-lives would it take for a pure sample of strontium-90 to decay to about 1% of its original concentration?
  1. How long would this take, in years?
  1. The original standard for nuclear waste storage was that the facility could safely contain the material for 10,000 years. Would this be enough time to safely allow the strontium-90 to decay?
  1. Plutonium-239, another component of nuclear waste, has a half-life of 24,000 years. How long would it take this material to decay down to a 1% concentration?