DOE OSTI2016
Previous papers describe a method for controlling a thermal nuclear reactor by moderator displacement between the reactor core and the reflector. The low neutron loss and high control range of this method enable a design for a molten natural uranium fueled and cooled heavy water moderated reactor. The design is geometrically similar to CANDU (Canadian Deuterium Uranium) reactors but with fewer, larger, vertically oriented fuel tubes. The fuel tubes contain molten natural uranium as both the fuel and the coolant instead of fuel rods and water coolant. The large fuel tubes have a mixed spectrum which is largely thermal at the periphery of the tubes with a very hard spectrum in the large central region of the tube. This configuration provides a fast fission rate of around 15% (mostly of U-238) and an initial conversion ratio of around 1.15. It is a hypothetical reactor because it is unclear what materials could actually be used to fabricate the fuel tubes and other primary coolant plumbing. The molten uranium serves both as the fuel and the primary coolant and as such is continuously circulated through the fuel tubes in the reactor core, the primary heat exchange, and back to the the reactor core. This means that at any point in time all the fuel has the same isotopic configuration no matter where it is in the reactor or heat exchanger. Over time the isotopic configuration changes, but it changes uniformly for all the fuel. Uranium melts at 1135 deg. C, so a proposed temperature range for the circulating molten uranium is 1200 deg. C at the exit of the heat exchanger and entry to the core fuel tubes and 1400 deg. C at the exit from the core fuel tubes and the entry into the heat exchanger. The advantages of this design include: 1. Reduced nuclear proliferation concern because of natural uranium fuel. 2. High conversion ratio and large fuel mass provides 30 to 100 year fuel life. 3. No heavy metal waste because fissile content increases over the fuel life. 4. High output temperatures are suitable for high efficiency turbine generators. This assessment will examine three perspectives: reactor physics, regional grid management, and global resource utilization and impact. This assessment will examine three perspectives: reactor physics, regional grid management, and global resource utilization and impact. The proposed reactor type can generate much of the future CO{sub 2} emission free electric power demand with a low impact on total uranium required to be mined, zero heavy metal waste produced, zero enrichment capability required, and capacity (with thermal storage) to meet fluctuating demand. There are engineering issues to be addressed before such a reactor can be built, but thanks to the demand for high efficiency gas turbines and other high temperature applications, high temperature materials and technology are developing rapidly. An operating temperature of 1400 degrees C does not seem unreasonable in the near future. The implied advantages of this reactor type compared to other existing or proposed reactors suggest that further work on the issues raised would be well worthwhile. (authors)
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗