PRISM (GE-Hitachi, USA) FIG. 12. Schematic View of PRISM Reactor type: Liquid metal cooled fast breeder reactor Electrical capacity: 311 MWe Thermal capacity: 840 MWt Coolant: Sodium Primary Circulation: Forced circulation System Pressure: Low pressure operation Core Outlet Temperature: 485°C Thermodynamic Cycle: Indirect Rankine Cycle Fuel Material: U-Pu-Zr Fuel Enrichment: 26% Pu,10% Zr Fuel Cycle: 18 months Reactivity Control: Rod insertion No. of safety trains: N/A Emergency safety systems: Passive RHRS: Passive reactor vessel auxiliary cooling system Design Life: N/A Design Status: Detailed design Seismic Design: N/A Predicted CDF: 1E-6/reactor year Planned deployment: N/A Distinguishing Features: Underground containment on seismic isolators with a passive air cooling ultimate heat sink; part of the advanced recycling centre for spent nuclear fuel 27 Introduction expansion and reactor vessel expansion. The The PRISM design uses a modular, pool negative feedbacks maintain the reactor in a type, liquid sodium cooled reactor. The safe, stable condition. reactor fuel element design most commonly The passive Reactor Vessel Auxiliary used is a metal alloy comprised of uranium, Cooling System (RVACS) provides primary plutonium and zirconium. The reactor cooling during all design basis accident employs passive shutdown and decay heat conditions and Anticipated Transients removal features. without Scram (ATWS). This passive system Description of the nuclear systems operates effectively without electricity or The PRISM reactor core is designed to meet operator intervention for an unlimited several objectives: amount of time. Heat is transferred from the • To increase fuel burnup; reactor vessel to the containment vessel by • To limit the burnup reactivity swing; and thermal radiation and then to the surrounding • To provide an 18 to 24 month refuelling atmospheric air by natural convection. interval. Redundant decay heat removal is provided The reactor is designed to use a by the Auxiliary Cooling System (ACS), heterogeneous metal alloy core. The core which consists of natural circulation of air consists of 198 fuel assemblies, 114 reflector past the shell side of the steam generator. The assemblies, 66 radial shield assemblies, 10 combination of systems allows for reduced control and 3 shutdown assemblies. The plant outages for inspections and PRISM fuel and core can be tailored to maintenance. specific missions ranging from plutonium Deployment Status and Planned Schedule disposition to the maximization of fuel The PRISM design was commenced in 1981 efficiency. with support from several U.S. Government The primary heat transport system is development programs. The design contained entirely within the reactor vessel. incorporates test data and operating The flow path goes from the hot sodium pool experience from previous U.S. sodium above the reactor core through the reactors such as GE’s Southwest intermediate heat exchangers (IHXs), where Experimental Fast Oxide Reactor, and heat is transferred to the intermediate heat Experimental Breeder Reactor II. PRISM transport system (IHTS); the sodium exits the was reviewed by the U.S.’s Nuclear IHX at its base and enters the cold pool. Four Regulatory Commission from 1987 to 1994 electromagnetic pumps take suction from the as part of a pre-application licensing review. cold pool and discharge into the high GEH envisages PRISM most commonly pressure core inlet plenum. The sodium is deployed with integral used fuel recycling in then heated as it flows upward through the areas interested in improving disposal reactor core and back into the hot pool. strategies for used nuclear fuel. Also, due to Heat from the IHTS is transferred to a steam PRISM’s affinity for use of low-cost, generator where superheated steam is plutonium bearing fuel, GEH is currently produced. This high pressure, high pursuing the use of PRISM to address the temperature steam drives the turbine- UK government’s plans to dispose of generator to produce electricity. plutonium via reuse in power reactors. In Description of the safety concept 2012, the UK’s Nuclear Decommission The passive shutdown characteristics of the Authority contracted GEH to carry out reactor core provide diverse and independent feasibility work in a number of key areas means of shutdown in addition to the control including the proposed commercial structure, rod scram. The passive features comprise the disposability of the fuel, the risk transfer several reactivity feedback properties model, the costs, and the ability to license in including: the Doppler effect, sodium density the UK. and void, axial fuel expansion, radial expansion, bowing, control rod drive line 28 .