Our next-generation leaders must begin to think more creatively, using risk-informed solutions to ensure safe, resilient, sustainable, and socially responsible technological advancements to usher in an era void of technological accidents. Probabilistic risk assessment (PRA) research and education provide nuclear engineering students with the scientific expertise and viable skill sets essential for meeting the growing demand for risk analysts in nuclear energy domains.
Since the WASH-1400 Reactor Safety Study in 1975, PRA has played a vital role in policy and decision-making for nuclear power plants; however, there is currently a large gap in the U.S. between the demand for risk-informed analysis of nuclear technologies and PRA research and education in nuclear engineering. This gap is mainly due to (1) the lack of hiring PRA junior faculty for nearly two decades in university nuclear engineering programs and (2) the ever-increasing need for risk-informed analysis to address emergent safety concerns; improve operational efficiencies in existing plants; and promote the design, licensing, and operationalization of advanced reactors.
In 2013, the Department of Nuclear, Plasma, and Radiological Engineering at the University of Illinois–Urbana-Champaign (UIUC) took the lead and established the Socio-Technical Risk Analysis Research Laboratory (SoTeRiA lab) to advance PRA science and applications.
Following the success of the SoTeRiA lab, a few other U.S. university nuclear engineering departments have hired junior PRA faculty. However, to meet short- and long-term goals for nuclear energy, critical PRA educational and research needs and gaps still require urgent attention.
From the educational perspective, only one U.S. nuclear engineering department that has a stand-alone PRA course in its required curriculum, 17 out of 34 nuclear engineering departments/programs1 offer PRA courses as electives, and the rest have no PRA courses. Even though a few departments have included a limited number of lectures on PRA in their required courses, this does not equip nuclear engineering students with enough knowledge about PRA and may not motivate them to take an elective PRA course; thus, a high percentage of nuclear engineering graduates are joining academia, national laboratories, the Nuclear Regulatory Commission, or industry workforces with only a limited PRA background. This fails to satisfy the demand for risk-informed analysis and impedes effective collaboration between PRA experts and those in other areas of nuclear engineering. From the participation of the SoTeRiA lab in the risk-informed resolution of Generic Safety Issue 191, as well as participation in Fire PRA advancement in partnership with the nuclear industry and national laboratories, I have witnessed firsthand how the collaboration among experts from PRA and other areas of nuclear engineering plays a key role in the effectiveness of large-scale nuclear energy projects.
From the research perspective, one of the aspects needing immediate attention is PRA for advanced reactors. It is time-critical to focus on risk-informed analysis of advanced reactors prior to, or in parallel with, technology developments, but the research funding designated for generating technology-inclusive PRA methodologies for advanced reactors is very limited. In recent years, major efforts in PRA development for advanced reactors and its use in risk-informed decision-making include the Licensing Modernization Project, development of 10 CFR Part 53 and other regulatory guidance by the NRC, as well as issuance of Probabilistic Risk Assessment Standard for Advanced Non-Light Water Reactor Nuclear Power Plants (ASME/ANS RA-S-1.4-2021); however, significant research needs for methodology developments still exist. One of the key methodological challenges is that a design-specific experiential database is often limited or not available for advanced reactors, while the applicability and relevancy of the experiential data from the existing fleet to advanced reactors may be questionable due to differences in design principles, physical conditions, and operation and maintenance procedures. A possible path to alleviate this challenge is to incorporate into PRA the simulation of underlying causality, including the interactions of physics of phenomena with human and organizational factors that drive the performance of structures, systems, and components. As an example of this research direction, the SoTeRiA lab, under the International Atomic Energy Agency project that focuses on risk-informed methodology generation for advanced reactors, has created an integrated methodological platform to couple physics of degradation phenomena with models of maintenance work processes (e.g., in-service inspection and repair) and has incorporated this coupling into PRA. Examples of my observations from this project include the following:
- As the modeling and simulation of physical phenomena and human contributing factors become more explicit in PRA, the spatial and temporal resolution of PRA increases; however, to address the trade-off between PRA realism and the resources required for PRA implementation, the spatial and temporal resolution should be gradually refined depending on the phases of analysis (e.g., design, licensing, construction, and operation) and the relative importance of the PRA elements. Under an ongoing Department of Energy project, the SoTeRiA lab is developing a risk-informed decision-making algorithm for the deployment of new technologies in the existing fleet, while future research is required to extend this algorithm for advanced reactors to guide the gradual refinements of the PRA model for advanced reactors.
- For the materials and phenomena that do not exist in operating reactors, no consensus model that has been validated or peer reviewed is available. In addition, the use of artificial intelligence (AI)–based automation has been actively evaluated for advanced reactors to improve the efficiency of operation and maintenance, while validation of AI-based automation technologies remains challenging. The absence of validated models, combined with the lack of relevant experiential data, can significantly increase the uncertainty of the PRA outputs for advanced reactors. This highlights the urgent need for advancing methodologies of uncertainty analysis and management as well as for the automation trustworthiness evaluation in the risk-informed analysis of advanced reactors. In an ongoing NRC project, the SoTeRiA lab is examining how uncertainty analysis in risk-informed regulation should be upgraded to accommodate the need for advanced modeling and simulation. The SoTeRiA lab has also recently been awarded a DOE project to develop a risk-informed methodology for evaluating and improving the trustworthiness and transparency of AI-based automation technologies in the existing fleet. The outcomes from these projects can provide the initial seeds for the expansion of PRA research to address these areas of need for advanced reactors.
- Advanced PRA methodologies are needed for enterprise risk management to facilitate an integration of safety risk with the financial risk associated with the operation and maintenance of advanced reactors. These methodologies should consider severe accident scenarios as well as those that do not generate catastrophic accidents but can lead to financial losses due to plant shutdowns. While several research organizations, including the SoTeRiA lab (under a DOE grant), have focused on extending the scope of PRA for the existing fleet to integrate financial and safety risk, further research is required to establish this integration for advanced reactors.
- Other important areas of research, under PRA for advanced reactors, include the effective use of risk information for determination of the site-specific emergency planning zone, multi-unit/multi-module dependency analysis, common cause failure analysis, and risk-informed security analysis.
Educational and research gaps must be addressed to enable next-generation PRA leaders to meet nuclear energy goals; therefore, immediate action is needed on the following:
- Nuclear engineering departments need to develop strategies to lead PRA education and research by hiring more PRA faculty and by enriching their core curriculums with robust PRA courses, while national laboratories, consulting companies, and the nuclear industry maintain their crucial roles in PRA development and implementation. Academia should advance PRA knowledge sharing with industry and government agencies to help nuclear engineering students conduct PRA research on the real-world problems of nuclear energy. Academia also needs to foster an open scientific environment, enabling next-generation PRA leaders to contribute to international nuclear safety through risk analysis and risk communication.
- Government agencies are asked to allocate adequate research funding for the creation of technology-inclusive PRA methodologies for advanced reactors. These methodologies can support the risk-informed design, licensing, operation, and maintenance of advanced reactors and help evaluate and compare diverse advanced reactor designs with respect to safety, security, and profitability. Results of these risk-informed comparative studies can provide valuable insights for the DOE and other stakeholders as they prioritize investments in advanced reactor technologies.
1. Based on the U.S. Nuclear Science and Engineering Education Sourcebook 2020.