Nuclear reactor shutdown system and method of nuclear reactor shutdown

A method of nuclear reactor shutdown for a system that includes:

• a shielded path that passes through a reactor core fuel housed in a nuclear reactor vessel in a hermetically sealed manner, one end of the shielded path having an opening and another end of the shielded path being closed;
• a neutron absorber that is allowed to enter from the opening of the shielded path;
• an elastic member that is configured to urge the neutron absorber in a direction entering inside from the opening of the shielded path by being released from a compressed state;
• and
• a braking part that is disposed so as to maintain the compressed state of the elastic member and is configured to release the elastic member from the compressed state when the braking part reaches or exceeds a threshold temperature, the method comprising
• causing the neutron absorber urged by the elastic member to enter inside from the opening of the shielded path by releasing the elastic member from the compressed state when the braking part reaches or exceeds the threshold temperature.