Source: Fierce Energy | Jaclyn Brandt | July 27, 2015
Nuclear energy is hardly new, but there are still plenty of things to learn from it. As some plants are entering the end of their lives, scientists are using the retirements to learn about how to make the energy source better. For instance, a piece of cable from a nuclear reactor could offer significant knowledge for the future.
“That cable was 46 years old when we pulled it out of service,” Jeremy Busby, a senior research staffer at the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL) told the Nuclear Energy Institute (NEI). “Our studies show that that particular type of cable, in that specific environment, probably has a useful life on the order of hundreds of years. And that was through a very systematic analysis. Now, we’d like to reproduce that on other cables from nuclear power plants.”
It is that piece of cabling that the team is looking at to see what happens to components, systems, and structures at nuclear power plants over long periods of time. According to NEI, U.S. nuclear energy facilities are initially licensed to operate for 40 years — but more than 75 reactors have been allowed to extend this for another 20 years.
“To help DOE learn whether nuclear power plants can operate safely and reliably beyond 60 years, samples from decommissioned reactors are key,” NEI said, adding that a research effort funded by DOE and the Electric Power Research Institute (EPRI) is looking at three aspects of a power plant: the reactor vessel, concrete structures, and cabling.
The subject of Subsequent License Renewal came before the Nuclear Regulating Commission (NRC) last year, NRC spokesperson Neil Sheehan toldFierceEnergy.
In August 2014, the commission issued a decision on a staff proposal in the area. However, “the Commission did not support a rulemaking — or the development of new regulations — in this area at this time,” Sheehan explained. “Rather, it instructed the NRC staff to continue to update license renewal guidance, as needed, to provide additional clarity on the implementation of the license renewal regulatory framework. It also told the staff to address emerging technical issues and operating experience through alternative vehicles, such as the issuance of generic communications.”
After the decision, NRC asked to be kept informed on progress in resolving technical issues related to Subsequent License Renewal: reactor pressure vessel neutron embrittlement at high influence; irradiation assisted stress corrosion cracking of reactor internals and primary system components; concrete and containment degradation; and electrical cable qualification and condition assessment.
“The Commission said it wanted to be kept informed regarding the staff’s readiness for accepting an application and any further need for regulatory process changes, rulemaking, or research,” Sheehan explained.
The ruling said the staff should keep in communication with the industry to find resolutions to issues before applications are brought to NRC. The DOE and EPRI research is an attempt to find solutions to the issues by utilizing older plants.
“Our research is focused on components that would essentially be cost-prohibitive to replace,” said Tina Taylor, EPRI’s director of strategic programs. “It is important to develop an understanding of any aging that might be expected beyond 60 years and to initiate aging management plans, monitoring strategies and, if needed, mitigation techniques that can be applied safely and cost-effectively.”
DOE and EPRI have taken samples from the Jose Cabrera plant in Spain — which ran for 38 years — and the decommissioned Zion Station plant in Illinois — which ran for more than 20 years. The two plants are being used because they operated in similar climates.
“Zion has very valuable, relevant material,” Busby said. “We have good archives on what was where. We know what this material was, what its service history was. This allows us some confidence to use it as a reliable benchmark for other things. We know it’s relevant to the U.S. fleet.”
The DOE team has already harvested cabling and insulation from Zion, and is planning to next acquire sections of the reactor pressure vessel and concrete samples.
“With a thing like cable polymer insulation, just placing them in a furnace at a higher temperature will allow you to accelerate that aging and get 60 years equivalent in, say, five years,” Busby said. “You have to be very careful not to cook it at too hot a temperature, or you’ll change the answer. So you also have to bring in modeling to understand what the limits are and if you’re looking at the right mechanism.”
The researchers are doing what they can with the samples they have obtained from the plants, but is also using historic databases to fill any gaps in the records. Busby said, “We didn’t have a lot of data [on concrete]. But we’ve built the database up. Part of that is finding other data from old government programs that wasn’t public that helped us fill the database. We have a lot better feel than we did three years ago.”
Taylor explained that the research has so far indicated that if a plant is maintained correctly, there is no reason it can’t continue operating to 60 years — or beyond. Aging Management Programs (AMPs) at plant sites will be the key to this.
“Much of what nuclear plant owners will need to do to continue safely operating these plants are extensions of existing AMPs,” Taylor said. “These programs are specifically in place to monitor, understand, and mitigate or repair any aging-related degradation.”
In the end, the point is to help regulators decide on industry standards through research. Busby said that their outcomes will help show what is best for plants, and how long they should be in use.
“We want to help inform licensing decisions, and we need to make sure our data is high quality, valuable and useful,” Busby said. “There’s more to learn, but we’ve had some real successes.”