Passive inherent reactivity coefficient control in nuclear reactors

A method of controlling a nuclear reactor comprising:

• providing nuclear fuel comprising Pu-239;
• providing a neutron moderator which behaves as an Einstein oscillator and as the temperature of the reactor increases said neutron moderator increases the energy of thermal neutrons into a neutron absorption resonance of said Pu-239;
• and
• adding a neutron absorbing element with strong neutron absorption around 0.3 eV to one or more components of a reactor core of said nuclear reactor, wherein said neutron absorbing element is provided in an amount calculated to suppress, at any time during the life of said nuclear fuel, a reactivity gain with temperature due to said neutron moderator increasing the energy of thermal neutrons into said neutron absorption resonance of said Pu-239.

A method of controlling a nuclear reactor comprising:

• providing nuclear fuel comprising atomic elements that breed Pu-239;
• providing a neutron moderator which behaves as an Einstein oscillator and as the temperature of said nuclear reactor increases said neutron moderator increases the energy of thermal neutrons into a neutron absorption resonance of said Pu-239;
• and
• adding a neutron absorbing element with strong neutron absorption around 0.3 eV to one or more components of a reactor core of said nuclear reactor, wherein said neutron absorbing element is provided in an amount calculated to suppress, at any time during the life of the fuel, a reactivity gain with temperature due to said neutron moderator increasing the energy of thermal neutrons into said neutron absorption resonance of said Pu-239.