the United Kingdom and the United States. The non-active members are Argentina and Brazil. The 36th GIF meeting in Brussels was held in November 2013. A brief overview of the reactor designs and activities by each forum member has been made available. An update of the technology roadmap which details R&D objectives for the next decade was published in January 2014. Timelines The GIF Forum introduced timelines for each of the six systems. Research and development divide into three phases: Viability: test basic concepts under relevant conditions; identify and resolve all "potential technical show-stoppers"; Performance: verify and optimise "engineering-scale processes, phenomena and materials capabilities" under prototypical conditions; Demonstration: complete and license the detailed design and carry out construction and operation of prototype or demonstration systems. In 2000, GIF stated, "After the performance phase is complete for each system, at least six years and several US$ billion will be required for detailed design and construction of a demonstration system." In the Roadmap update of 2013, the performance and demonstration phases were considerably shifted to later dates, while no targets for the commercialisation phases are set. According to the GIF, "It will take at least two or three decades before the deployment of commercial Gen IV systems." Reactor types Many reactor types were considered initially; the list was then refined to focus on the most promising technologies. Three systems are nominally thermal reactors and four are fast reactors. The Very High Temperature Reactor (VHTR) potentially can provide high quality process heat. Fast reactors offer the possibility of burning actinides to further reduce waste and can breed more fuel than they consume. These systems offer significant advances in sustainability, safety and reliability, economics, proliferation resistance (depending on perspective) and physical protection. Thermal reactors A thermal reactor is a nuclear reactor that uses slow or thermal neutrons. A neutron moderator is used to slow the neutrons emitted by fission to make them more likely to be captured by the fuel. High-temperature gas-cooled reactor (HTGR) A high temperature gas-cooled reactor (HTGR) typically operates at temperatures two or three times those of conventional reactors. It is graphite-moderated and typically uses helium cooling. It offers lower power density. The concept originated in the 1940s and has only begun to mature. HTGR runs on TRi-structural ISOtropic (TRISO) particle fuel. It is made of individual particles Instead of rods. TRISO consists of uranium, carbon, and oxygen sealed in three