Abstract: Disclosed is a passively cooled nuclear reactor, comprising a heat exchanger and a nuclear reactor core disposed proximal to the heat exchanger. The nuclear reactor core comprising a fuel rod, a heat pipe located proximate to the fuel rod and extending from the nuclear reactor core into the heat exchanger, a moderator monolith configured to house and space the fuel rod and the heat pipe, and a thermal bond material disposed internally throughout the moderator monolith to surround the fuel rod and the heat pipe with the thermal bond material and to facilitate heat transfer from the nuclear reactor core to the heat exchanger.