Very high temperature reactor design features

This appendix provides a brief description of the Fast Flux Test Facility (FFTF) fuel handling system and its operation as described by Cabell (1980) and in the Fast Flux Test Facility System Design Description (FFTF, 1983). The description is limited to those system features that are potentially relevant to the refueling of a liquid-salt very high-temperature reactor (LS-VHTR). Because the FFTF was designed as a reactor to test fuel, it has additional capabilities and equipment compared with a sodium-cooled fast reactor designed only to produce electricity. 

As the AHTR concept includes a very high temperature reactor option (with the core outlet temperature of 1000°C), the additional design features to prevent the consequences of severe accidents are provided. The reactor has a second guard vessel and is located in an underground silo. The effectiveness of heat conduction to earth through the walls of the silo (an ultimate heat rejection in BDBA) is being examined. 

These reactors operate near equilibrium, and therefore the first reactor must be heated to high temperatures because this reaction is endothermic, and the second must be cooled to fairly low temperatures. The kinetics of these reactions are very important if one is designing a reactor in detail, but the major features of the process are governed by equilibrium limitations and heat effects. 

A major goal in wall cooling is to spread out the hot zone and prevent very high peak temperatures. High peak temperatures cause poor reaction selectivity, cause carbon formation, deactivate catalysts, and cause corrosion problems in the reactor walls. CocuJTent flows spread out the hot zone and cause lower peak temperatures, but many additional design features must be considered in designing jacketed reactors. 

---