During the operation of a heavy-water moderated nuclear reactor, high-energy neutrons undergo interactions with deuterium nuclei. Explain, in terms of momentum and kinetic energy transfer, how this moderation process reduces the speed of these neutrons.

Control rods containing silver-indium-cadmium alloys are lowered into the reactor core to regulate the neutron flux. State the specific nuclear process that occurs when a thermal neutron collides with a nucleus in these control rods.

In a pressurized water reactor, a thermal neutron is captured by a uranium-235 nucleus, triggering a fission event. Detail the three main steps of this process, starting from the initial capture to the release of subsequent products.

The decommissioning of fuel assemblies yields high-level radioactive waste (HLW) which must be managed with extreme care.

Discuss the management of this high-level waste.

In your response, you should:

• State what constitutes the primary source of HLW within the spent fuel assemblies.
• Describe the sequential stages of treatment and storage of this waste before final disposal.
• Explain the physical and geological hazards associated with its long-term storage and how engineering solutions mitigate these risks.