Reactor Cool is a Blue Magic spell in Final Fantasy XI learned from Zdei. It enhances defense and covers the user with magical Ice Spikes for a duration of 120 seconds. It costs 5 Blue Magic points to set. When set, it grants INT +3 and MND +3. It takes 3 seconds to cast and can be recast every 60 seconds.

Reactor Cool is also an enemy ability used by the Zdei family.