This glowing keychain is an ampoule filled with Trithium, radioactive Hydrogen. It has nothing to do with the main reactor. But it is funny to know, that Trithium is one of the main component in hydrogen-bombs. Regular Hydrogen (H) nuclear, consists only of a proton, then there are heavy Hydrogen, Deuterium (D), that consists of a proton and a neutron, and there is Trithium (T), which consists of one proton and two neutrons.
It emitts β-radiation and have a T½ of 12,32 years. In fusion-bombs (hydrogen-bombs), Trithium is fusioned with Deuterium, and releases a high amount of energy. Also there is a big research to develope fusion-reactors.