Risk-informed, performance-based design in INL’s MARVEL reactor
The American Nuclear Society’s Risk-informed, Performance-based Principles and Policy Committee (RP3C) has held another presentation in its monthly Community of Practice (CoP) series. Former RP3C chair N. Prasad Kadambi opened the meeting with brief introductory remarks about the RP3C and the need for new approaches to nuclear design that go beyond conventional and deterministic methods. He then welcomed this month’s speaker: Doug Gerstner, a nuclear safety engineer at Idaho National Laboratory, who presented “Application of a Qualitative RIPB Approach for the MARVEL Microreactor at INL.”
Some background: RP3C is a special committee created by the ANS Standards Board and chaired by Steven Krahn that provides guidance to ANS standards committees on the use of risk-informed, performance-based (RIPB) methods. The CoP is part of RP3C’s charter, which includes training and knowledge-sharing of RIPB principles to exchange ideas outside of the normal management and project processes. Over the past five years, CoPs have frequently been used by organizations to help break down barriers that impede the flow of information.
MARVEL overview: Gerstner launched his presentation by giving a high-level refresher on the MARVEL reactor’s design, explaining it as a 20-kWe demonstration reactor using NaK coolant and TRIGA fuel. The reactor’s basic design was originally modeled after the early-1960s SNAP-8, one of the reactor projects from the Atomic Energy Commission’s Systems for Nuclear Auxiliary Power program, which ran from 1955 to 1973.
Basic aspects of the MARVEL reactor's design. (Source: Doug Gerstner/INL)
MARVEL was originally dubbed P-53, so named because it was intended to be the 53rd reactor built at INL with an original timeline to be operational within 53 weeks. According to Gerstner, Yasir Arafat was “the original driver” for P-53. Today, Arafat is the chief technical officer of Aalo Atomics, a private reactor start-up that recently broke ground at INL for its 10-MWe Aalo-X pilot reactor.
Now, five years after P-53’s initial envisioning, the MARVEL project has evolved into a significantly more complicated concept and machine that is still in the process of being redesigned and fabricated. The team plans to site the reactor in INL’s Transient Reactor Test Facility.
RIPB approach: After discussion of which standards and regulatory guides the MARVEL project operates under, Gerstner dove into the project’s approach to safety design. A significant difference between establishing MARVEL’s safety case and that of a typical power reactor is the MARVEL team’s decision to not perform a probabilistic risk assessment (PRA). The PRA is a quantitative approach to determining the possibilities, likelihood, and consequences involved in nuclear plant accidents.
Because of the simplicity of P-53’s design and the time limit of the project, the team determined a PRA would not be needed. Instead, they opted for a qualitative approach for MARVEL’s hazard evaluation.
The decision to progress without a PRA presented issues in following the safety evaluation approach laid out in NEI-18-04. That framework provides risk-informed guidance for non–light water reactor licensing basis development by relying in part on a PRA. Without one, the MARVEL team had to devise a new approach that avoided this issue.
The team’s new framework was partially based on a white paper from Brookhaven National Laboratory, “Regulatory Review of Micro-Reactors—Initial Considerations.” That white paper recommended a qualitative approach to safety for microreactors.
According to Gerstner, MARVEL’s evaluation methodology, despite its significant differences from NEI-18-04, still meets the intent of the DOE’s 10 CFR Part 830 for a hazard evaluation and for the protection of the public, workers, and the environment.
Go deeper: To learn much more about the performance-based side of MARVEL’s hazard evaluation process, the intricacies of its methodology, and the specifics of the standards it is operating under, along with more of the project’s history, the full presentation is available at the above link.
