Special Purpose Application Reactors: Systems Integration Decision Support

Abstract

Microreactors, also known as very-Small Modular Reactors (vSMRs) or Special Purpose Reactors (SPRs), are being considered for use in unique applications where other methods of megawatt level energy production are uneconomical or unavailable. For the purposes of this report, a microreactor is defined as meeting the following criteria:• Factory manufacturable • Easily transportable by truck, plane, train, and/or ship • Produce no more than 20 megawatt thermal (MWth) energy, in order to qualify as Hazard Category 2 under 10CFR830 • Maintains neutronic simplicity, allowing semi-or fully-autonomous operationIn the United States (U.S.), there are two general types of microreactors under development: high-temperature gas reactors (HTGRs) and heat pipe reactors. These two reactor types may, due to their differences in working fluid temperatures, be more effectively suited to different use cases. Additionally, they will require different interfacing components depending on their intended use.This report identifies a broad range of use cases for micro-reactors. Additionally, multiple reactor technologies are examined with an emphasis on the reactor sub-systems and interconnections. Using this information, a decision support framework is developed to guide future efforts.

Small Reactors in Microgrids: Technology Modeling and Selection (Net-Zero Microgrid Program Project Report)

“…Safety is enhanced due to passive circulation; heat pipes do not need external pumping. Heat-pipe reactors are typically very small and simplified designs significantly reducing the maintenance requirements [30], [31]. Another advantage of heat-pipe reactors is that they can be designed to operate at high temperatures, which increases their efficiency and makes them useful for process-heat applications.…”

“…Heat-pipe reactors typically use metallic fuels in a fast-neutron spectrum. Molten sodium (Na), potassium (K), or NaK are used as working fluids at high temperatures around the boiling point [31]. Potassium heat pipes operate around 760°C; sodium at around 880°C.…”

“…HTGR concepts use accident-tolerant fuel designs. Most of them are based on pebble-bed or prismatic-core designs with multilayer coated TRISO particle fuels or hexagonal assemblies using uranium carbide or UO2 fuels [5], [31]. The enrichment level is typically between 8.5 and 19.75% to ensure higher burnup rates (up to 165 GWd/tHM).…”

“…TRISO fuels are also being considered for molten-salt reactor concepts. TRISO fuel has some limitations in terms of packing fraction [31]. The current limit for TRISO packing fraction is approximately 40% before the particles begin to experience damage during compacting.…”

Small Reactors in Microgrids: Technical Studies Guidance

“…Military bases with secure boundaries and 24/7 mission-critical loads are prime locations for the initial installation of SRs [30]. The physical-and cybersecurity risks are mitigated by a controllable operating environment.…”