The present invention relates to a prevention device for loss of coolant accident (LOCA) and a nuclear reactor having the same. The prevention device for LOCA includes a nozzle portion integrally formed in a reactor vessel and having a communication hole communicating with the inside of the reactor vessel, a nozzle finishing portion assembled to the nozzle portion and an injection line for injecting a fluid to the inside of the reactor vessel respectively on both sides thereof in a communicating manner, and a check valve mounting portion installed to be embedded inside the nozzle portion and having at least one check valve opened by flow such that the fluid is injected into the reactor vessel, wherein the check valve blocks outflow of a reactor coolant from the reactor vessel in case of failure of the injection line.