Drillhole nuclear reactor

A nuclear reactor system, comprising:

• a first drillhole extending from a terranean surface through one or more subterranean formations;
• a reactor core positioned in the first drillhole, the reactor core comprising at least one nuclear fuel element;
• a second drillhole extending from the terranean surface through the one or more subterranean formations and separated from the first drillhole by a portion of a rock formation of the one or more subterranean formations;
• a heat exchanger positioned in the second drillhole in thermal communication with the reactor core through the portion of the rock formation;
• and
• a coolant system thermally coupled to the heat exchanger and configured to transport a fluid coolant between the heat exchanger and the terranean surface.

A method of constructing a nuclear reactor system, comprising:

• forming a first drillhole from a terranean surface through one or more subterranean formation;
• forming a second drillhole from the terranean surface through the one or more subterranean formation and separated from the first drillhole by a portion of a rock formation of the one or more subterranean formations;
• moving at least one nuclear fuel element into the first drillhole;
• positioning the at least one nuclear fuel element at a first depth of the first drillhole;
• moving a heat exchanger into the second drillhole;
• positioning the heat exchanger in thermal communication with the reactor core through the portion of the rock formation;
• and
• installing a coolant system in thermal communication with the heat exchanger and configured to transport a fluid coolant between the heat exchanger and the terranean surface.

A method, comprising:

• identifying a nuclear reactor system that comprises:
• a first drillhole that extends from a terranean surface through one or more subterranean formations;
• a reactor core positioned in the first drillhole, the reactor core comprising at least one nuclear fuel element;
• a second drillhole that extends from the terranean surface through the one or more subterranean formations and is separated from the first drillhole by a portion of a rock formation of the one or more subterranean formations;
• a primary coolant system;
• and
• a secondary coolant system thermally coupled to the primary coolant system with a heat exchanger positioned in the second drillhole and in thermal communication with the reactor core through the portion of the rock formation, the secondary coolant system configured to transport a secondary fluid coolant between the heat exchanger and the terranean surface;
• transporting a primary fluid coolant in the primary coolant system through the reactor core;
• transporting a secondary fluid coolant heated in the heat exchanger by the primary fluid coolant, through the portion of the rock formation, in the secondary coolant system between the heat exchanger and the terranean surface;
• and
• generating power with the heated secondary fluid coolant.