Calculate signed reaction energy from mass defect or a channel Q-value, or estimate total nuclear energy from fuel mass. Fuel mode also reports an energy-equivalent TNT conversion and average power over one day.

Find signed reaction energy from the difference between two mass totals.

Use consistent atomic or nuclear masses for a balanced reaction. Fuel estimates are nuclear energy, not electrical output; Q-values exclude later radioactive decay.

Fission Reaction Energy Release Formula

For mass-defect and Q-value modes, use complete initial and final mass totals for a balanced reaction, including free neutrons. Use a consistent atomic or nuclear mass convention.

Ef = (Mi - Mf) × c²
  • Where Ef is the energy released from fission (J)
  • Mi is the initial mass of the reactants (kg)
  • Mf is the final mass of the products after the reaction (kg)
  • c is the speed of light in vacuum (299,792,458 m/s)

Multiply initial minus final mass by c². A positive answer is energy released; a negative answer is energy required. Fuel mode uses E = (fuel mass in g ÷ molar mass in g/mol) × Nₐ × fission fraction × energy per fission. Its defaults approximate pure U-235 at 235.0439 g/mol, 200 MeV per fission and 100% fission; change these assumptions as needed. This is nuclear energy, not electrical output. The three illustrative reaction presets use AME2020 ground-state atomic masses and exclude subsequent decay energy; mass uncertainties are not propagated.

What is Fission?

Definition:

Fission is a nuclear process in which the nucleus of a heavy atom splits into two (or occasionally more) lighter nuclei, typically releasing free neutrons and gamma rays (photons). This is accompanied by the release of large amounts of energy because the products have a higher total binding energy than the original nucleus.

In reactors, fission is usually induced when a nucleus absorbs a neutron and becomes unstable; it does not require extremely high temperatures (unlike fusion). The process involves a balance between the attractive strong nuclear force (which binds nucleons together) and the repulsive Coulomb force between protons.

Fission chain reactions are used to generate power in nuclear reactors and in fission weapons; in thermonuclear weapons, a fission “primary” provides energy and neutrons to initiate fusion. Most fissions are binary (two main fragments), but about 0.2% are ternary fissions in which a light charged particle (often an alpha particle) is emitted in addition to the two main fragments.

How to Calculate Fission Reaction Energy Release?

Example Problem:

The following example outlines the steps and information needed to calculate Fission Reaction Energy Release.

First, determine the initial mass of the reactants. In this example, the initial mass is found to be 10.00345 kg.

Next, determine the final mass of the products after the reaction. For this problem, the final mass is 10.00211 kg.

Finally, calculate the energy release using the formula above:

Ef = (Mi-Mf)*c^2

Ef = (10.00345-10.00211)*299,792,458^2

Ef = 1.20433194e14 Joules