By Paul Menser for INL Communications and Outreach 

A study that began in 2009 by the U.S. Department of Energy (DOE) and the Electric Power Research Institute (EPRI) has finished its third and final phase. The study provides important insight that will not only extend the life of the United States’ fleet of nuclear power plants but also provides an example of a joint government-industry testing program. 

Before the study, there was limited data on how materials behave in the tough reactor environment – specifically the cracking behavior and fracture-toughness in two materials that are commonly used reactors – alloy X-750 and XM-19. For reactor licenses to be extended 40, 60, and even 80 years, more information on the long-term impacts to these materials was needed. As envisioned by EPRI and the Nuclear Science User Facilities (NSUF), the X-750/XM-19 Pilot Project offered a chance to gather this data.  

An independent, nonprofit organization for public interest energy and environmental research, EPRI focuses on electricity generation, delivery, and use. Collaborative research with DOE involving Idaho National Laboratory’s Advanced Test Reactor (ATR) became possible after DOE founded the NSUF in 2007. This made the reactor’s unique capabilities available to universities and the commercial nuclear industry. ATR’s one-of-a-kind design makes it possible to conduct multiple experiments simultaneously at different irradiation levels. Previously, ATR had been dedicated to experiments for the U.S. Navy and DOE, so making access to this unique facility available is a game-changer in nuclear research. 

“It’s the only available reactor in the U.S. that can perform these kinds of experiments,” said Bob Carter, a technical executive with EPRI and the primary project point of contact. “In general, the irradiation program resulted in an outcome that closely met our original objectives. We now have a better understanding of how these materials react when exposed to neutron irradiation.” 

As one of the very first experiments through NSUF, this was a pioneering effort that led to the current “NSUF Access” class of awards available to industry through DOE’s yearly Consolidated Innovative Nuclear Research funding opportunity announcements. This project helped pave the way for important administrative tools to be developed such as the “nonproprietary user agreement,” shipments between facilities, and experiment cataloging and storage.  

Perhaps most importantly, the pilot project gave INL and NSUF staff experience and confidence in irradiating full-size specimens in the controlled water chemistry loop in ATR’s center flux trap, a first for NSUF. The pilot project also brought new capabilities to INL and NSUF, the Irradiation-Assisted Stress Corrosion Cracking (IASCC) hot cells installed at INL’s Materials and Fuels Complex that can be used for testing mechanical property changes in irradiated full-size specimens. 

Caption 1: (Left) IASCC hot cell under construction; (Right) Completed IASCC hot cell. 

Three EPRI tests were run in ATR between 2013 and 2016, to damage levels comparable to previous studies, damage levels currently experienced in boiling water reactors, and expected future damage levels. Several types of testing were then conducted on the samples, such as transmission electron microscopy to see microstructural changes and mechanical testing to see how durable the materials still were. A May 2020 final report on Phase III offered the following conclusion: 

Although there clearly are opportunities for additional research on the remaining materials from this project, the project is considered a success overall. It has shown that both materials retain a high level of integrity even at the highest fluence, synonymous with beyond end-of-life for (boiling water reactor) components that utilize these materials. Valuable experience was gained in testing protocol and processes, and the path was paved for future NSUF experiments on structural materials involving IASCC. 

“It was not all roses,” said John Jackson, distinguished staff scientist at INL who is the NSUF primary point of contact. “In our first irradiation, we were sort of shooting in the dark in terms of water chemistry because it was the first time we had used the water loop in ATR. There were definitely some lessons learned but by the time of the last irradiation capsule, we had the issues solved.” 

“There were unknowns in the boiling water reactor environment,” said Carter. “But we proved the feasibility of using ATR to address these unknowns.” 

Costs of the project were shared between DOE and EPRI. In addition to gathering data, the program was designed to: 

• Develop a path forward for cooperative research, such as cooperative agreements and funding. 

• Develop research capabilities and staffing required to address future R&D needs. 

• Develop a level of confidence in generating relevant data. 

NSUF has expanded to include one international affiliate and 19 partner organizations including INL, making more testing capabilities available to national laboratories, universities, and industry partners. 

“With those capabilities established, the way is open to future collaborations,” Carter said. “There is a strong push to adopt some of that workload,” he said. “In my view, NSUF is a great opportunity for civilian nuclear research. The groundwork has been laid here.”