10 Fusion and fission are nuclear reactions in which large amounts of energy are released - Edexcel - GCSE Physics - Question 10 - 2018 - Paper 1

To find the decrease in mass, we use the equation that relates energy and mass:

$E = mc^2$

Substituting the given energy value:

$4.5 × 10^{-12} ext{ J} = m (3.0 × 10^8 ext{ m/s})^2$

Rearranging the equation to solve for mass, we have:

$m = \frac{4.5 × 10^{-12}}{(3.0 × 10^8)^2}$

Calculating this:

$m = \frac{4.5 × 10^{-12}}{9.0 × 10^{16}} = 5.0 × 10^{-29} ext{ kg}$

The graphite core in a nuclear reactor serves as a moderator, slowing down the neutrons produced during fission reactions. This moderation increases the likelihood of these slower neutrons being absorbed by fissile material, which keeps the chain reaction going at a controlled rate.

Movable control rods, made of materials that absorb neutrons, can be inserted or removed from the reactor core to manage the rate of the fission reaction. When the control rods are inserted deep into the core, they absorb more neutrons, reducing their availability to sustain the reaction, thus lowering the reactor's power output. Conversely, withdrawing these rods allows more neutrons to cause further fission, increasing the reactor's output. This dynamic adjustment allows operators to maintain a stable and safe chain reaction.