Scene Context: The crew hides in the central compartment, surrounded by water and fuel tanks, to survive the main particle stream.
Essence of the Phenomenon: Hydrogen-rich materials like water, polyethylene, and similar substances work best for shielding against solar energetic particles. They reduce the proton dose much more effectively than a simple thin metal shell. That is why the concept of a "storm shelter" inside the ship, surrounded by water, supplies, and other mass, is physically justified.
Scientific Basis: NASA has seriously considered storm shelter concepts for Solar Particle Events, where existing onboard mass—primarily water, polyethylene, and logistics modules—is used for additional shielding instead of wrapping the entire spacecraft in an equally thick armor layer. Large SPEs are short-lived but intense events, making a compact shelter inside the vehicle a highly practical solution.
Current Limitations: Such a shelter reduces the dose but does not make the crew invulnerable. It works better against solar protons than against galactic cosmic rays, which require much thicker shielding. Thus, "The Citadel" in the scene is not absolute protection, but the best available solution during an acute event.