layers of carbon or ceramics materials to stabilize the eventual waste products. These particles are formed into stable cylindrical pellets or billiard-ball-sized spheres called "pebbles." It is more resistant to neutrons, corrosion, oxidation, and high temperatures than conventional fuels. These pebbles do not melt in the reactor, which can run at higher temperatures. The fuel gradually proceeds through the reactor,. Spent pebbles exit the bottom of the reactor while fresh pebbles replace them at the top. In 2012, as part of its next generation nuclear plant competition, Idaho National Laboratory approved a design similar to Areva's prismatic block Antares reactor to be deployed as a prototype by 2021. The Chinese government began construction of a demonstration HTR-PM 200-MW high temperature pebble bed reactor in 2012 as a successor to its HTR-10. Very-high-temperature reactor (VHTR) The very-high-temperature reactor (VHTR) uses a graphite-moderated core with a once-through uranium fuel cycle, using helium or molten salt. This reactor design envisions an outlet temperature of 1,000°C. The reactor core can be either a prismatic-block or a pebble bed reactor design. The high temperatures enable applications such as process heat or hydrogen production via the thermochemical sulfur-iodine cycle process. In January 2016, X-energy was provided a five-year grant of up to $40 million by the United States Department of Energy to advance their reactor development. The Xe-100 is a PBMR that would generate 80 MWe, or 320 MWe in a 'four-pack'. Molten-salt reactor (MSR) A molten salt reactor (MSR) is a type of reactor where the primary coolant or the fuel itself is a molten salt mixture. It operates at high temperature and low pressure. Molten salt can be used for thermal, epithermal and fast reactors. Since 2005 the focus has been on fast spectrum MSRs (MSFR). Other designs include integral molten salt reactors (e.g. IMSR) and molten chloride salt fast reactors (MCSFR). Early thermal spectrum concepts and many current ones rely on uranium tetrafluoride (UF4) or thorium tetrafluoride (ThF4), dissolved in molten fluoride salt. The fluid reaches criticality by flowing into a core with a graphite moderator. The fuel may be dispersed in a graphite matrix. These designs are more accurately termed an epithermal reactor than a thermal reactor due to the higher average speed of the neutrons that cause the fission events. MCSFR does away with the graphite moderator. They achieve criticality using a sufficient volume of salt and fissile material. They can