An apparatus, comprising: a first energy transfer system configured to divert a first selected portion of energy from a portion of a first nuclear reactor system of a plurality of nuclear reactor systems to at least one heat storage material of at least one thermal reservoir, wherein the first nuclear reactor system includes a first nuclear reactor and a first energy conversion system; a second energy transfer system configured to divert a second selected portion of energy from a portion of a second nuclear reactor system of the plurality of nuclear reactor systems to said at least one heat storage material of said at least one thermal reservoir, wherein the second nuclear reactor system includes a second nuclear reactor and a second energy conversion system; a first heat supply system configured to supply at least a portion of thermal energy from said at least one heat storage material of said at least one thermal reservoir to the first energy conversion system of the first nuclear reactor system of the plurality of nuclear reactor systems; and a second heat supply system configured to supply at least a portion of thermal energy from said at least one heat storage material of said at least one thermal reservoir to said second energy conversion system of the second nuclear reactor system of the plurality of nuclear reactor systems; characterised in that: one or more of the first and second energy transfer systems comprises at least one energy transfer system configured to divert a first selected portion of electrical energy from a portion of the first or second nuclear reactor system of the plurality of nuclear reactor systems to said at least one thermal reservoir, said at least one energy transfer system preferably comprising at least one electrical-to-thermal conversion system configured to divert a first selected portion of electrical energy from a portion of the first or second nuclear reactor system of the plurality of nuclear reactor systems to said at least one thermal reservoir; said at least one electrical-to-thermal conversion system preferably comprising at least one resistive heating device. a first energy transfer system configured to divert a first selected portion of energy from a portion of a first nuclear reactor system of a plurality of nuclear reactor systems to at least one heat storage material of at least one thermal reservoir, wherein the first nuclear reactor system includes a first nuclear reactor and a first energy conversion system; a second energy transfer system configured to divert a second selected portion of energy from a portion of a second nuclear reactor system of the plurality of nuclear reactor systems to said at least one heat storage material of said at least one thermal reservoir, wherein the second nuclear reactor system includes a second nuclear reactor and a second energy conversion system; a first heat supply system configured to supply at least a portion of thermal energy from said at least one heat storage material of said at least one thermal reservoir to the first energy conversion system of the first nuclear reactor system of the plurality of nuclear reactor systems; and a second heat supply system configured to supply at least a portion of thermal energy from said at least one heat storage material of said at least one thermal reservoir to said second energy conversion system of the second nuclear reactor system of the plurality of nuclear reactor systems; characterised in that: one or more of the first and second energy transfer systems comprises at least one energy transfer system configured to divert a first selected portion of electrical energy from a portion of the first or second nuclear reactor system of the plurality of nuclear reactor systems to said at least one thermal reservoir, said at least one energy transfer system preferably comprising at least one electrical-to-thermal conversion system configured to divert a first selected portion of electrical energy from a portion of the first or second nuclear reactor system of the plurality of nuclear reactor systems to said at least one thermal reservoir; said at least one electrical-to-thermal conversion system preferably comprising at least one resistive heating device.