While still lacking a deep geological repository for the permanent disposal of its commercial used nuclear fuel and high-level radioactive waste, the United States does have regulatory standards for geological nuclear waste disposal.

Having been written nearly 40 years ago, however, those standards are outmoded and lack transparency, according to a special committee of the American Nuclear Society, which has released draft recommendations on revising public health and safety standards for future geological repository projects in the United States.

The new standard ANSI/ANS-30.3-2022, Light Water Reactor Risk-Informed, Performance-Based Design, has just been issued by the American Nuclear Society. Approved by the American National Standards Institute (ANSI) on July 21, 2022, the standard provides requirements for the incorporation of risk-informed, performance-based (RIPB) principles and methods into the nuclear safety design of commercial light water reactors. The process described in this standard establishes a minimum set of process requirements the designer must follow in order to meet the intent of this standard and appropriately combine deterministic, probabilistic, and performance-based methods during design development.

Matthew Denman

Probabilistic risk assessment is a systematic methodology for evaluating risks associated with a complex engineered technology such as nuclear energy. PRA risk is defined in terms of possible detrimental outcomes of an activity or action, and as such, risk is characterized by three quantities: what can go wrong, the likelihood of the problem, and the resulting consequences of the problem.

Matthew Denman is principal engineer for reliability engineering at Kairos Power and the chair of the American Nuclear Society and American Society of Mechanical Engineers Joint Committee on Nuclear Risk Management’s Subcommittee of Standards Development. As a college student at the University of Florida, Denman took a course on PRA but didn’t enjoy it, because he did not see its connection to the nuclear power industry. Later, during his Ph.D. study at the Massachusetts Institute of Technology, his advisor was Neil Todreas, a well-known thermal hydraulics expert. Todreas was working on a project with George Apostolakis, who would leave MIT to become a commissioner of the Nuclear Regulatory Commission. The project, “Risk Informing the Design of the Sodium-Cooled Fast Reactor,” was a multi-university effort funded through a Department of Energy Nuclear Energy Research Initiative (NERI) grant. Todreas and Apostolakis were joined in this project by a who’s who of nuclear academia, including Andy Kadak (MIT, ANS past president [1999–2000]), Mike Driscoll (MIT), Mike Golay (MIT), Mike Lineberry (Idaho State University, former ANS treasurer), Rich Denning (Ohio State University), and Tunc Aldemir (Ohio State University).

The ASME/ANS Joint Committee on Nuclear Risk Management (JCNRM) has achieved a significant milestone in the advancement of probabilistic risk assessment (PRA) technology. ANSI/ASME/ANS RA-­S-­1.4–2021 [1], Probabilistic Risk Assessment Standard for Advanced Non-­Light Water Reactor Nuclear Power Plants, has been approved by the JCNRM, the ANS Standards Board, the ASME Board of Nuclear Codes and Standards, and the American Nuclear Standards Institute.

March 11 will mark the 10-­year anniversary of the Fukushima Daiichi event, when a 45-­foot tsunami, caused by the 9.0-­magnitude Great Tohoku Earthquake, significantly damaged the reactors at Japan’s Fukushima Daiichi nuclear power plant. In response to this event, the U.S. Nuclear Regulatory Commission took actions to evaluate and mitigate beyond-­design-­basis events, including a new requirement for the staging of so-­called Flex equipment, as well as changes to containment venting and improvements to emergency preparedness. The U.S. Department of Energy also addressed beyond-­design-­basis events in its documented safety analyses.

As industry steps up its efforts to design, develop, and deploy advanced reactors, codes and standards must be developed to support these technologies. Toward that end, ANS and the Nuclear Energy Institute collaborated to host a virtual workshop on June 23 for industry partners to discuss the development of advanced reactor codes and standards.

NEI’s senior director of new reactors, Marc Nichol, welcomed more than 400 attendees to the online meeting, and ANS’s director of government relations, John Starkey, outlined the meeting logistics.

Since the 1980s, the nuclear power industry in the United States has worked to enhance the regulatory framework for nuclear facilities by making it more risk-informed and performance-based (RIPB). This has had some success in improving safety and reducing regulatory burden by focusing resources on the most risk--significant areas and allowing greater flexibility in choosing ways to achieve desired safety outcomes. However, there are further opportunities for the use of RIPB approaches in addressing current regulations and applying implementation tools, and in developing new RIPB regulations and advanced tools to further sharpen the focus on risk and performance outcomes.

The American Nuclear Society and the Nuclear Energy Institute have organized a workshop for industry partners to discuss standards needs to support advanced reactors. The workshop will be conducted virtually through the Zoom platform

The workshop will be held on Tuesday, June 23, from 10:00 a.m. to 4:30 p.m. (EDT).

The Risk-informed, Performance-based Principles and Policy Committee (RP3C), a special committee of the ANS Standards Board, has launched a Community of Practice (CoP) to support risk-informed, performance-based (RIBP) methods in ANS standards. The CoP consists of interested professionals who can contribute to standards development priorities identified in the Standards Committee Strategic Plan and in ANS Position Statement #46, “Risk-Informed and Performance-Based Regulations for Nuclear Power Plants.”

The ANS Standards Committee has just published ANSI/ANS-19.6.1-2019, “Reload Startup Physics Tests for Pressurized Water Reactors” (revision of ANS-19.6.1-2011). The standard, approved December 19, 2019, provides guidance for verifying the nuclear characteristics of a commercial pressurized water reactor core following a refueling or other alteration of the reactor core for which nuclear design calculations are required. The standard provides the minimum acceptable startup physics test program, while recognizing that additional tests may be required by special design features of a particular core.