Supercritical CO2 Direct Cycle Gas Fast Reactor (SC-GFR) Concept

by Edward J. Parma1, Steven A. Wright1, Milton E. Vernon1, Darryn D. Fleming1, Gary E. Rochau1, Ahti J. Suo-Anttila2, Ahmad Al Rashdan3, & Pavel V.Tsvetkov3
1Sandia National Laboratories
2Computational Engineering Analysis
3Texas A&M University

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The current trend in advanced power reactor concepts is to develop right size reactors (RSRs), grid appropriate reactors, and small modular reactors (SMRs) as alternatives to the current status quo, which are large (3000 MWth) light water reactors (LWRs) that will cost several billion dollars and many years to construct and license. Included in these advanced reactor concepts are small LWRs, liquid metal cooled reactors, high temperature gas cooled reactors, molten salt cooled reactors, and others. These advanced reactor concepts will use either a water Rankine cycle or an advanced Brayton cycle for power conversion.

This work presents a relatively new transformational reactor concept that uses supercritical carbon dioxide (S-CO2) as the coolant in a direct cycle gas fast reactor (SC-GFR). The concept is a combination of the CO2-cooled Advanced Gas Reactor developed and operated in the United Kingdom and the direct cycle Gas-Cooled Fast Reactor concept. The SC-GFR concept is a relatively small (200 MWth) fast reactor that is cooled with CO2 at a pressure of 20 MPa. The CO2 flows out of the reactor vessel at ~650°C directly into a turbine-generator unit to produce electrical power. The thermodynamic cycle that is used for the power conversion is a supercritical gas Brayton cycle with CO2 as the working fluid. With the CO2 gas near the critical point after the heat rejection portion of the cycle, it can be compressed with less power as compared to a standard gas Brayton cycle, thereby allowing for a higher thermal efficiency at the same turbine inlet temperature. A cycle efficiency of 45-50% is theoretically achievable for an optimized configuration. This type of reactor concept maintains some potentially significant advantages over ideal gas-cooled systems and liquid metal-cooled systems. The major advantages of the concept include the following:
  • High thermal efficiency at relatively low reactor outlet temperatures;
  • Compact, cost-effective, power conversion system;
  • Non-flammable, stable, inert, non-toxic, inexpensive, and well-characterized coolant;
  • Potential long-life core and closed fuel cycle;
  • Small void reactivity worth from loss of coolant;
  • Natural convection decay heat removal;
  • Feasible design using today’s technologies.
Scoping analyses show that for a 200 MWth reactor using a S-CO2 Brayton cycle, a relatively small long-life reactor core could be developed that maintains decay heat removal by natural circulation of the CO2 coolant through the power conversion heat rejection system.