Special Purpose Nuclear Reactor (5 MW) for Reliable Power at Remote Sites Assessment Report

Abstract

The Phenomena Identification and Ranking Table (PIRT) technique was conducted on the Special Purpose Reactor nuclear plant design. The PIRT is a structured process to identify safety-relevant/safety-significant phenomena and assess the importance and knowledge base by ranking the phenomena. The Special Purpose Reactor is currently in the conceptual design phase. The candidate reactor has a solid monolithic stainless steel core with an array of heat pipes and fuel pellets embedded in the monolith. The heat pipes are used to remove heat from the core using simple, reliable, and well-characterized physics (capillarity, boiling, and condensation). In the initial design, one heat exchanger is used for the working fluid that produces energy, and a second heat exchanger is used to remove decay heat in emergency or shutdown conditions. In addition, a power conversion cycle such as an open-air Brayton system is available as an option for power conversion and process heat. This report summarizes and documents the process and scope of the four PIRT reviews, noting the major activities and conclusions. The identified phenomena, analyses, rationales, and associated ratings are presented along with a summary of the findings from the four individual PIRTs, namely (1) Reactor Accident and Normal Operations, (2) Heat Pipes, (3) Materials, and (4) Power Conversion. The PIRT reports for these four major system areas evaluated are attached as appendixes to this report and provide considerably more detail about each assessment as well as a more complete listing of the phenomena that were evaluated.

Status Update on the Development of Transducers and Bonding Techniques for Enabling Acoustic Measurements of Damage in Microreactor Components

“…Publicly available data for the expected neutron flux or fluence to which microreactor components would be exposed are more limited. Sterbentz et al reports a fast flux at the core midplane of 5.5 × 10 13 n/cm 2 /s for a heat pipe-cooled microreactor [14]. For constant operation times of 1, 5, and 20 years, this would correspond to fast neutron fluences of 1.73 × 10 21 , 8.67 × 10 21 , and 3.47 × 10 22 n/cm 2 , respectively.…”

“…Sterbentz et al analyzed three different 5 MWth heat pipe-cooled designs and reported maximum heat-pipe wall temperatures of 712.5, 677, and 712.5 • C for each of these designs [14,15]. Therefore, for heat pipe-based microreactors that integrate heat pipes within monolithic metal structures, acoustic sensors would be required to survive temperatures up to 800-900 • C to provide data regarding the structural health of the monolithic core block.…”

Special Purpose Application Reactors: Systems Integration Decision Support

“…• Manufacturing of the monolith core: The LANL MegaPower design calls for a stainless steel monolith to house the heat pipes and fuel. In a 2017 Phenomena Identification and Ranking Table (PIRT) analysis of the MegaPower concept by INL, the manufacturability of the steel monolith was identified as a significant issue [37]. Hot isostatic press (HIP), 3D printing or other advanced manufacturing processes may yield a path forward on monolith manufacturability.…”

“…The INL PIRT analysis conducted for the LANL MegaPower reactor examined the power conversion system in some detail [37]. The report examined an air Brayton cycle due to its wide use in power conversion systems, and therefore the wide availability of components.…”

Coupled Multiphysics Simulations of Heat Pipe Microreactors Using DireWolf

“…8, 9, and 10), culminating in a successful test of a kilowatt-scale space reactor 2,3 and a conceptual design of a megawattscale design. 11 These early successes have led to an interest in the commercial sector for terrestrial and offworld applications.…”