Nuclear, O&M, Reactors

The Design Certification Process for U.S. SMRs

Issue 10 and Volume 119.

By Sharryn Dotson, Associate Editor

NuScale completed the full-scale upper module mockup of its small modular reactor in March. Photo courtesy: NuScale

Small modular reactors (SMRs) are a new and advanced technology in the U.S., yet manufacturers must meet design certification requirements similar to those used for large-scale nuclear reactors, with some differences.

SMRs are generally 300 MW or less of generating capacity. They are designed for modular construction, meaning the parts can be put together offsite, then moved into place in the power plant. Conversely, large-scale reactors are built on site from the ground up, which usually calls for a large amount of land, materials, workers and equipment. SMRs are also designed with passive safety equipment so that, in the case of an emergency or if no power is available, the reactors can operate safely for several days before manual intervention is needed.

These unique characteristics are some of the reasons that SMR design certifications must be handled differently than a typical large-scale reactor. However, the U.S. Nuclear Regulatory Commission (NRC)’s Office of New Reactors (NRO) said that if certification applications for non-light-water reactors were to come across the staff’s desks in a five-year timeframe, the department would not be ready. The NRC also needs to consider other designs that may apply for certification and plan accordingly.

NRC Readiness for Licensing SMRs

In August 2012, the NRC provided a report requested by Congress that addressed advanced reactor licensing. The report spelled out the NRC’s strategy for, and approach to, preparing for licensing of advanced non-light water reactors (LWRs). The report addressed the number of expected licensing applications over the next twenty years for light water and non-LWRs, and any potential licensing activity beyond then. The report also illustrates regulatory challenges that may occur if various advanced reactor initiatives evolve into licensing applications. The “Report to Congress” also examined NRC’s readiness to license non-LWR designs in the longer term of 10 years or more. The report found the agency would be challenged only if there is an application within five years or less. However, the report did find that agency efforts and the readiness status have not changed since the 2012 report was released.

It was recommended that NRO work with international nuclear regulators that have experience operating non-LWR plants in order to leverage that experience for potential domestic designs. Additional research may be necessary to develop independent analytical tools and methods for designs that significantly differ from the LWR design so that the analysis methods and supporting experimental data can support an independent safety finding by the NRC, the report said.

NRO said in an August 2014 report to the NRC that it is ready to conduct safety and environmental reviews of new SMR applications, including light water and non-light-water SMR designs. The design certification process for SMRs generally takes 39 months, according to Scott Burnell, Public Affairs Officer with NRC. The NRC said it expects SMR manufacturers to seek design certifications under the 10 CFR Part 52 Combined Operating License (COL) process. Utilities that plan to site the reactors, such as the Tennessee Valley Authority (TVA) at its Clinch River Site in Tennessee, will seek Part 52 early site permits and combined licenses.

NRC staff expects differences between SMR licenses and those for large light-water reactors, including emergency preparedness, licensing fees and security, according to Burnell.

NRO is currently working to identify and manage the review factors that are within the agency’s control, such as open policy issues, guidance development, and SMR-related technical questions. NRO is also interacting with potential applicants and other stakeholders to identify external factors that could cause extended review schedules, such as the need for early design finality and the need for timely, complete responses to requests for additional information (RAIs) during the application review. The goal of these interactions is to develop a common understanding of the information exchange necessary to conduct efficient and effective SMR application reviews.

Additional research may be required to develop independent analytical tools and methods for designs that differ significantly from LWR technology, so that the analysis methods and supporting experimental data can support an independent safety finding by the NRC.

Where the SMR Designs Stand

Westinghouse, NuScale, Holtec International and Generation mPower have all started the design certification process for their SMR technologies. More on each company’s progress follows:

NuScale Power LLC

NuScale Power LLC is furthest along in the design certification process for the 50-MWe NuScale Power Module (NPM) that can be scaled to 600 MWe (gross) in a single facility. Areva agreed to complete the testing and design for the certification application.

The completed design certification application is expected in the second half of 2016, according to the NRC website. Utah Area Municipal Power System selected NuScale and partner Energy Northwest to supply its system for the nuclear power project to be sited in Idaho.

NuScale completed fabrication and assembly of a full-scale, upper module mockup of the NPM in March. The upper module mockup consists of the top assembly of the reactor, the reactor vessel head, control rod mechanisms, the module access platform and major valves.

The full-scale mockup gives NuScale’s engineers insights into the inspection and maintenance activities essential for plant operation. It provides a life-sized replica of the reactor, supports the planning of maintenance, inspection, radiation protection and fabrication, and provides the ability to plan for worker safety and safety requirements.

“The fabrication of this full-scale, upper module mockup is an important step in the continued support of our reactor design,” stated Dale Atkinson, NuScale’s Chief Operating Officer and Chief Nuclear Officer.

The NRC said it is ready to certify NuScale’s reactor design. “The NRC worked with NuScale for more than a year to develop a design-specific review standard for the company’s proposed SMR,” NRC’s Burnell said. “In the same way, other vendors can continue pre-application discussions with the NRC to support review standards for their SMR approaches.”


The NRC staff is engaged in pre-application activities with Westinghouse on the company’s 225-MW reactor that uses passive safety systems similar to what is in the AP1000 reactor, “a key benefit” of the Westinghouse SMR, said Jeff Benjamin, Westinghouse senior vice president for new plants and major projects.

The reactor has a design life of 60 years and features a compact integral design and a 24-month time between refueling outages.

The NRC approved Westinghouse’s testing approach for its SMR design in March 2015. Approval is a significant step toward design certification and will reduce the time ultimately needed to license the Westinghouse SMR, the company said yesterday.

“The development program has involved many years of testing and analysis, which can be successfully applied to advance our SMR program as the market for the technology matures in the future,” Benjamin said.

In a letter dated Feb. 27, 2015, the NRC told Westinghouse that the staff granted a Safety Evaluation Report for the licensing topical report the company submitted in April 2012 for agency review and approval. The report identified what would occur in the unlikely event of accident due to a small break in the water circuit that cools the reactor. The report also defined the test program that Westinghouse will conduct to prove that its safety systems would safely shut down the reactor in response to such an accident.

Westinghouse said the potential for intermediate and large breaks in the reactor coolant loop – and the more serious accident conditions – is eliminated in the SMR design because there are no large primary penetrations of the reactor vessel or large loop piping. The design is an integral pressurized water reactor with all primary components located inside of the reactor vessel. As a power unit, it would produce 225 MWe in operation.

Clinch River Site

Clinch River initially planned to site up to six 180-MW BWXT mPower reactors from Generation mPower, a company made up of BWX Technologies Inc., formerly known as Babcock & Wilcox, and Bechtel. TVA said in its operating license application that it still expected Generation mPower to submit a Part 52 design certification for the mPower reactor, but work slowed when the company decided to restructure its SMR program and decrease funding in development to focus more on technology development.

Generation mPower notified DOE in 2014 that funding from an up to $226 million cost-sharing program with the DOE’s Small Modular Reactor Licensing Technical Support Program, but work would continue toward development milestones. TVA planned to submit the application for up to four mPower SMRs in the second quarter of 2015 before the announcement.

The NRC is ready to review design certification applications from Westinghouse, Generation mPower and NuScale Power, but not for non-light-water reactor developers that apply for certification in the next five years. The commission staff continues to work on a set of regulations specific for SMRs and their unique designs and safety benefits.