Fuels in Nuclear Reactors (Oxford AQA IGCSE Physics)

The table shows some information about different nuclei involved in a nuclear fission reaction within a nuclear reactor.

 A nucleus of uranium undergoes fission when bombarded with a slow-moving neutron (n) causing it to split into the daughter nuclei barium and krypton plus the release of further neutrons.

Write a balanced nuclear equation for this fission reaction.

Answer:

Step 1: Write a word equation using the information in the question

• Underline or highlight the keywords in the question which give information about the nuclei on the left-hand side (LHS):

"A nucleus of uranium undergoes fission when bombarded with a slow-moving neutron"

• Underline or highlight the keywords in the question which give information about the nuclei on the right-hand side (RHS):

"causing it to split into the daughter nuclei barium and krypton plus the release of further neutrons"

• Write a word equation for the reaction:

uranium + neutron → barium + krypton + neutrons

Step 2: Determine the correct symbols for each nucleus or particle

• We need to write each nucleus or particle in  notation

• It can be useful to draw an extra row and column onto the table to do this (green indicates the changes made to the table):

 Step 3: Write the nuclear equation using the symbols

Step 4: Check the total number of protons on each side

• Total number of protons (given by the atomic number):

  • On the LHS: 92 + 0 = 92

  • On the RHS: 56 + 36 + 0 = 92

• The total number of protons is the same on both sides

Step 5: Check the total number of nucleons on each side and balance the equation

• Total number of nucleons (given by the mass number):

  • On the LHS: 235 + 1 = 236

  • On the RHS: 144 + 89 + 1 = 234

• There is a difference of 2, and the question states there is a "release of further neutrons"

• This means there must be 2 extra neutrons released i.e. 3 neutrons in total

• To represent this, we put a 3 in front of the neutron symbol on the RHS, so, the fully balanced equation is:

You do not need to know the specific details of how a nuclear reactor generates electricity but you are expected to know the specific isotopes (uranium-235 and plutonium-239) that are used as fuels in nuclear reactors.