FHR designs combine the advantageous characteristics of prior reactor classes and thermal power plants. Russian scientists claim to have originated the idea of an FHR during the 1970s. However, the idea was never pursued or widely published. In 2002 staff members from ORNL, the University of California at Berkeley, and Sandia National Laboratories independently reconceived the idea of FHRs. ORNL initially pursued the idea with Laboratory-directed funding. Since 2004 the DOE Office of Nuclear Energy (DOE-NE) has been supporting FHR development on a small scale through its laboratories and university research programs. In 2010 ORNL hosted the first DOE workshop on FHRs, at which the Assistant Secretary of Energy for Nuclear Energy endorsed FHRs as a potential means for achieving the administration’s R&D goals for nuclear energy.
FHRs rely upon technologies not available during the earlier MSR era. However, since the 1970s, when the MSR program was cancelled, substantial technical progress has been made on other reactor classes and technologies that support FHRs. In 1986 the Experimental Breeder Reactor II demonstrated that decay heat from low-pressure, liquid-cooled reactors could be passively rejected to the local air without fuel damage. Similarly, the ongoing advanced gas reactor fuel-testing program is demonstrating that coated-particle fuel is mechanically robust and can be manufactured at an acceptable price. Industry standards necessary for FHRs have also advanced significantly. The new Division 5 of Section III of the ASME Boiler and Pressure Vessel Code provides construction rules for high temperature reactors, including rules for graphite core components. ASTM (committee C28.07) is pursuing code development activities that support the use of silicon carbide fiber/silicon carbide matrix (SiC-SiC) composite structures as channel boxes at boiling water reactors. In addition, the NRC is participating in an initiative that has an intended outcome of developing advanced reactor general design criteria, a central requirement for effectively licensing FHRs in the United States.