The Gas Turbine Modular High-temperature Reactor (GT-MHR) has a long history and got its start in the mid-1980s during the push in the USA to develop smaller reactor designs with assured safety. Since that time, variants of the GT-MHR have been considered for the New Production Reactor program, the Weapons Material Disposition program, and most recently the Next Generation Nuclear Plant program. As such, information sources for the GT-MHR tend to be quite varied with respect to specific parameters of the design, which reflect the different program priorities and constraints. Fundamentally, the design uses TRISO-coated uranium-oxicarbide particle fuel that is dispersed into cylindrical pellets and stacked into vertical fuel channels within hexagonal graphite moderator blocks that are 0.36 m wide (across flats) by 0.79 m tall. The moderator blocks are stacked 10 rows high in 66 columns forming an annular ring. Additional non-fueled moderator blocks fill the center of the annulus and surround the core as an outer reflector. The uranium contained in the uraniun oxycarbide (UCO) fuel kernels is enriched to 15.5% 235U. The heated helium flows to the vertically mounted gas turbine via a concentric cross-duct.

Although the GT-MHR design is relatively mature and has been considered for multiple programs, there is no current commitment to construct a demonstration or

Compressors

Figure 2.18 GT-MHR (United States) — General Atomics (GA).

commercial unit. The most promising project is a joint program between the United States and the Russian Federation to build a demonstration GT-MHR for disposition of weapons-grade material. Key parameters and a representative graphic for the GT-MHR design are given in Figure 2.18. [16]