Concepts for Autonomous Operation of Microreactors

Abstract

Microreactor concepts have seen increasing interest in recent years given their potential use for meeting energy needs in remote and grid-isolated communities. Because of the small power outputs of microreactors and the potential for remote siting, there is a need to significantly reduce operational staffing levels to improve their economic viability. Autonomous control capabilities emerge as a key enabling technology. Autonomous control should not be perceived as a single feature that when added delivers certain functions. On the contrary, autonomous control capability is a highly complex systems engineering process that requires detailed understanding of system dynamic response as a function of operational actions. These advanced capabilities can be achieved at different levels of autonomy, which would then require different levels of human operator involvement in operational decision making. The division of functions and responsibilities between the human operator and the automatic system is the starting point in the system engineering life cycle process. Once this division of functions and responsibilities is established, several options exist for autonomous control ranging from simple automation of some procedures to fully autonomous operational mode with automatic decision-making and execution without the involvement of a human operator. A critical aspect of autonomous decision-making is the ability to have as complete an awareness of the system state as possible. In addition to monitoring the conventional process data, such as temperatures, pressures, flow, and neutron flux, measurements pertaining to the condition of important components become as important as the operational data. This type of information will allow the autonomous control system to adapt its internal configuration to changing conditions of structures, systems and components of importance through the decision-making process. The key capability is to execute these advanced functions with minimal operational disturbance and, of course, without compromising the public health and safety. Several technical and regulatory advances are needed before widespread use of autonomous control in microreactors. These include sensor and instrumentation technologies that are capable of long-term unattended operation in harsh environments, technologies for inferring the state of the microreactor system or subsystems with confidence, algorithms for predictive decision-making that account for the assessed condition of the microreactor subsystems as well as the potential impact on those components of any operational decisions, and actuators and control system hardware that are resilient in harsh environments. In addition, given the need to remotely monitor the operations, cybersecurity requirements will likely need to be imposed to ensure secure operations.

Opportunities and Challenges for Remote Microreactor Operations

“…Another feature of the remote operation system that is essential in determining the I&C system that is necessary would be the level of automation that is desired for the system. Ramuhalli and Cetiner discussed many concepts for autonomous operation [6], such as the various requirements, concepts, and potential approaches for autonomous microreactor operation. A key concept for these operation systems is the degree of automation.…”

“…It is important to find an ideal level of autonomy for the remote operation system when considering the trade-offs involving reduced staffing, system complexity, operational flexibility, etc. [6]. One of the most well-known scales for system automation was defined by Sheridan [7].…”

“…Is it even necessary for the remote operation system to be capable of an emergency shutdown of the reactor? Initial requirements for full autonomous operation have been proposed [6] and fully autonomous control is the most likely end goal for systems such as this. However, since the remote operation of a reactor has not been implemented yet, a remote operation system should initially focus on incorporating a lower level of autonomy for the system.…”

Large-Scale Additive Manufacturing of Silicon Carbide with Process Monitoring

“…• Demonstrating an agile design process to leverage AM and rapidly converge on an optimized, advanced nuclear microreactor design [9][10][11][12][13][14][15] • Advancing new reactor materials such as an yttrium hydride moderator [16][17][18][19][20][21][22], AM 316 stainless steel (316SS) [23], AM silicon carbide (SiC) [24,25], and the novel integration of uranium nitride tristructural-isotropic fuel [26] densely packed in an AM SiC matrix [27] • Developing the digital platform necessary to certify and qualify AM materials for nuclear applications [28][29][30] • Integrating and embedding spatially distributed sensors within AM materials for nuclear applications [31][32][33][34] • Progressing toward semi-autonomous reactor operation [35,36] • Evaluating and understanding radiation effects on AM SiC [37,38], 316SS [39], and integral TCR fuel compacts [27,40] In fiscal year (FY) 2021, the TCR program priorities shifted away from a nuclear reactor demonstration, but the focus on advancing ceramic AM for nuclear applications and qualifying AM components remained. Eventually, the TCR program was merged into the AMMT program and focused on the broader adoption of AM for nuclear applications compliant with American Society of Mechanical Engineers (ASME) Nuclear Quality Assurance (NQA-1) standards.…”