Neutronic design of the first core of the replacement research reactor

Full text: This paper describes the general neutronic characteristics of the first core of the Replacement Research Reactor (RRR) for the Australian Nuclear Science and Technology Organisation (ANSTO). A compact core with 16 FA has been designed to fulfill all the very demanding neutronic requirements of the RRR facility. The contractual performance parameters must be verified for the equilibrium core, anyway a very important design effort was carried out in the initial fresh core to have a similar performance. The RRR Facility is a multi-purpose open-pool type reactor. The nominal fission power of the reactor is 20 MW. The core is located inside a chimney, surrounded by heavy water contained in the Reflector Vessel. The whole assembly is at the bottom of the Reactor Pool, which is full of demineralized light water acting as coolant and moderator and biological shielding. The description covers different aspects of the neutronic design: fuel assembly (FA) characteristics, irradiation facilities, operational requirements, etc. Reactor shut down can be achieved by two independent means, which are the insertion of five control rods into the core, or the partial drainage of the heavy water from the Reflector Vessel. Several irradiation facilities are located around the reactor core. Three types of neutron sources: a cold neutron source with two tangential beams and several neutron guides, a thermal neutron source with two beams and several neutron guides, and a room reserved for a future hot neutron source with a beam. The reactor has also 17 vertical irradiation tubes for bulk radioisotope production (for example: Ir, Mo and I), 19 pneumatic rigs with 57 target positions for different purposes: such as, for example radioisotope production, neutron activation analysis (NAA). Finally it has 6 neutron transmutation doping (NTD) facilities. A general description and main characteristics of the present core design is also given. The whole paper includes the detailed nuclear designs of U3Si2 first core and the design calculation tools, together with a comparison of the core performance against the core design criteria and the equilibrium core performance. In the present abstract we show the design goals of the first core and a figure with the three types of U3Si2 fuel assemblies (different U235 mass) Additional to the nuclear safety design criteria, the following design goals were deemed: The reactor must operate at maximum power; All irradiation facilities must be available with a high performance; The operating cycle should meet the requirements of the equilibrium core; Fresh FA's are used; Minimize the number of different FA; The differences between these fuels are only Uranium load and the BP distribution. Three types of fuel assemblies are used: 212 Gr U235/FA without burnable poison; 383 Gr U235/FA with burnable poison; 484 Gr U235/FA with burnable poison. (author)