By Rob Smith, Vice President – NDE Solutions, AREVA Inc
The global nuclear energy industry has reached a tipping point. As an important source of safe, low-carbon and reliable base load energy, more than 430 commercial nuclear power reactors around the world support nearly 11.5 percent of global electricity production and play a key role in many countries’ domestic energy portfolios. However, many of the world’s reactors were built between 1950 and 1970, and are reaching the end of their original operational licenses. In the United States, 100 reactors are in operation today, a large majority of which are more than 25 years old, and only five new plants are under construction. As a result, U.S. utilities are faced with the decision of whether to extend the life of their existing nuclear facilities.
The U.S. Nuclear Regulatory Commission (NRC) originally approved plant operating licenses for 40 years, allowing for an optional 20-year renewal after extensive review. Now, with its Subsequent License Renewal (SLR) Program, the NRC is preparing to consider extending operating licenses for an additional 20 years, which means a reactor could run continuously for up to 80 years – twice its original proposed lifespan. According to the NRC, there are no technical limits to plant life:
So long as there are effective inspection and maintenance practices, the plant life is simply limited by economics – the cost of repair or replacement of any components that don’t meet specified accepted criteria.
Right now, the decision to extend plant life is economical. Low energy prices, along with existing generation capacity, call into question the economics of new combined cycle gas turbine (CCGT) plants versus relicensing existing nuclear plants. At $300 million in capital expenditures, a nuclear plant life extension is more economical than a new CCGT plant. Based on a comparative net present value calculation, nuclear energy provides approximately $30 million in annual benefits relative to constructing a new CCGT. In markets where CCGT plants could be considered economical, nuclear plant life extension can be even more cost efficient.
|Areva employees completing a core shroud weld examination using phased-array ultrasonic testing and robotic tooling. Both photos courtesy Areva.|
At the same time, the nuclear industry remains focused on safety and reliable daily operation. Long-term planning and asset management is critical and utilities must be forward-looking to identify risks early and allow for more predictable economic forecasts. Utilities seeking to extend the lives of their plants to 80 years must start building the foundation now.
Working to Extend Plant Life to 80 Years
To extend the lives of nuclear plants to 80 years, the NRC, nuclear utility owners, industry partners and vendors are already planning for license renewal. It takes approximately two years to prepare an SLR application and initial applications will take an estimated four to six years for the NRC to review. Notably, while some efficiency has been gained from previous license renewal activities, the NRC has indicated that new issues may need to be evaluated for license renewal beyond 60 years.
Once the initial regulatory work is complete, plants may require refurbishment or equipment replacement or upgrades in order to finalize the SLR. Additional time will be needed to perform these capital-intensive improvements that are justified only with the certainty of an approved SLR or are driven by SLR commitments.
Challenges facing utilities planning to extend plant life to 80 years include:
- reactor pressure vessel embrittle ment;
- irradiation-assisted stress corrosion cracking of reactor internals;
- concrete structures containment degradation; and
- electrical cable qualification and condition assessment.
According to the Department of Energy’s Light Water Reactor Sustainability Program Expanded Materials Degradation Assessment (EMDA), extending reactor service to beyond 60 years will increase the demands on materials and components. Therefore, an early evaluation of the possible effects of extended lifetime is critical. The EMDA identified nearly the same set of materials and components as the NRC as potentially susceptible to significant degradation during plant operation beyond 60 years (reactor vessel, primary system piping, reactor vessel internals, concrete, and electrical cables).
To extend plant life to 80 years, utility owners need to be forward-looking, and use their currently scheduled outages to complete the inspections and evaluations needed to put the plant on the path toward license extension.
Conducting Non-Destructive Examinations During Outages
Approximately 1,000 highly trained engineers and technicians are on the job for a typical one-reactor outage, usually scheduled for low-demand periods in the spring or autumn. During a typical nuclear plant outage, workers replace about one-third of the reactor’s fuel, conduct required inspections and maintenance, and replace equipment, if necessary.
In addition to the required inspections, supplemental inspections to detect the effects of aging degradation are key elements in both the license renewal process to safely extend plant life to 80 years and day-to-day plant operations. Each plant, as part of its license agreement, is required to perform routine inspections during every outage, known as non-destructive examinations (NDE). In addition to routine inspections during outages, utilities perform certain inspections every 10 years as part of their In-Service Inspection (ISI) program. NDE ensures the integrity of the plants’ pressure retaining systems and equipment to safeguard the public, employees and environment from the possibility of a radioactive release. Thousands of these examinations are conducted at each plant every year on everything from welds to reactor vessel nozzles to steam generator tubes.
To put this into perspective, AREVA’s 26-person NDE team completed 21,000 examinations over the past 24 months at one, three-unit site alone. That’s 7,000 examinations per unit completed within a six-day outage window that will help keep the units running safely and reliably.
NDE is unique in that an individual plant can control its inspection schedule. With a 10-year interval to complete the required license examinations, a plant can spread the examinations across any number of outages. However, proper planning for these examinations is critical because some components are available for inspection only in certain plant configurations. For example, reactor core barrels are typically removed and available for examination only every 10 years. Meanwhile, the inside of the core barrel can be inspected during a routine refueling outage. It can take several outages over a number of years for plants to complete all required examinations. Forward-looking planning becomes even more crucial when the plant is planning for license renewal because flawed inspection results could lead to additional engineering and equipment refurbishment or replacement.
In the license renewal process, the NRC has developed a required set of inspections outlined in the Electric Power Research Institute’s (EPRI) Materials Reliability Program (MRP)-227 document, which must be completed prior to granting life extension. In fact, those 21,000 inspections that AREVA’s NDE group performed in the past 24 months were all part of the MRP program. All the examinations in EPRI’s MRP-227 document are NDE inspections, the majority of which are above and beyond what is typically required in a plant’s ISI program. Among these “non-routine” NDE inspections for life extension are instances where NDE examiners are looking at items that have not been inspected since the component was built, such as core barrel welds and baffle bolts.
In older plants, NDE is critical to the license renewal process. Ensuring the plant is running safely, while keeping costs down, is important for the economics of plant license renewal. The total NDE inspections required over a 10-year period could cost utilities anywhere from $20 million to $50 million per unit.
New inspection techniques and innovative tools can help keep costs and personnel exposure down while improving plant safety and performance during planned outages. These new technologies can support full 10-year, intermediate, and follow-up surveillance inspections with minimal disruption of outage activity. In the last three years, AREVA has developed eight innovative tools and robots to help support NDE for sustained operation and license renewal – several of which have won industry recognition such as “Best of the Best” at the Nuclear Energy Institute’s annual Top Industry Practice Awards. Some of these newly developed tools for NDE inspections include the SUSI submarine, the Lower-Girth Weld Inspection Tool (LGWIT) and NEMO.
- The SUSI robot, a submarine built to support a large number of ultra sonic and visual underwater ex aminations, is being used for volu metric examination of bolting com ponents and visual examination of welded components.
- The LGWIT is a cutting-edge tool used to remotely inspect reactor vessel internals with unique plant configurations. The automated tool replaces the need for human in tervention, reducing costs and low ering personnel exposure. The in spection of reactor vessel internals is essential for maintaining the long-term functions of pressurized water reactor internals safely and economically to ensure the long- term operation of nuclear power plants, and is a key requirement in the license renewal process.
- NEMO is a tool specifically built to AREVA is developing these ad vanced robotic systems and tools, which can be used across a variety of plant configurations in anticipaq tion of the industry’s need to dem onstrate plant safety in support of license renewal. In addition to newly developed tools, improved inspection techniques can also re duce costs and improve outage per formance for utilities.
Depending on the results of NDE inspections, plants sometimes need to replace and repair aging and obsolescent components. In addition to offering NDE Solutions, the AREVA Solutions Complex is a full-service campus of eight facilities that helps U.S. electric utilities and equipment manufacturers meet ever-increasing safety requirements for nuclear electricity production, with the unique ability to package engineering and services to extend plant life and improve plant operations. This complex houses commercial grade dedication and component testing and qualification all under one roof, making AREVA the only NSSS-designed company that is doing equipment CGD, testing and qualification. AREVA plays an ongoing role in the daily nuclear energy renewal, delivering to utility’s NDE excellence, project management expertise and technology innovations to meet the challenge of life to 80.
|Areva employees train with a NUMAN under-head manipulator to complete a mock PWR head examination and repair.|
Looking to the Future for Nuclear Power Plants
While plants have focused historically on primary systems and components associated with those systems, the work to extend plant life to 80 years is broadening the scope of necessary inspections. The future of NDE applications is positioned for concrete, cables, and manual encoded ultrasonic testing of piping. While the U.S. nuclear energy industry has not yet started to focus on concrete and cable, in the coming years, plants and suppliers will need to include these components as part of inspections to ensure the safety of aging plants. In addition, NDE inspections are increasingly more automated. Years of experience operating nuclear plants is driving the development of encoded ultrasonic testing, which provides an electronic record of examinations. These technological advances are driving the development of NDE inspection tools and techniques that will help keep nuclear plants running safely and reliably to 80 years.
And while technical advances are important, extending the safe operating plant life of America’s nuclear fleet is made possible through the innovations from field technicians and engineering experts. It is this skilled workforce that will bring the plants to a healthy and robust 80 years, yet a growing number of nuclear energy professionals are nearing retirement and there are not enough qualified individuals to fill these job openings. While the technology is changing and adapting, it is equally important to develop and invest in people. NDE examiners are categorized as level I, II and III. The level III individuals are the experts in the field with years of experience, which takes time and significant financial resources to develop. With a limited number of NDE level III examiners, shortages are possible during peak outage periods. The industry must address this issue, particularly as utilities are working to extend their plants’ operating licenses to 80 years, because examiners cannot become industry-recognized level III examiners overnight.
The industry is working to meet both the technical and personnel challenges in the face of license renewal. Partnerships with local universities and community colleges, the promotion of science, technology, engineering and math (STEM) careers and education, as well as recruitment of military veterans are all key avenues the industry must follow to develop the next generation of nuclear energy professionals and NDE inspectors, specifically. For example, AREVA works extensively with the Center for Advanced Engineering and Research in Virginia, providing advanced nuclear plant control room equipment and expertise to support its mission to foster knowledge creation, facilitate technology transfer, and improve and grow the scientific and engineering workforce. In response to STEM education promotions, AREVA Inc. and its employees contributed almost $80,000 and over 900 volunteer hours in 2012 to support the growth of STEM interest at the middle and high school, and university levels to bridge the gap between demand and availability of STEM talent, and cultivate tomorrow’s STEM-skilled workforce. In addition, the U.S. Department of Energy (DOE) recently selected Mike Rencheck, AREVA Inc. president and CEO, to serve as one of the department’s ambassadors for the Minorities in Energy Initiative. As an ambassador, Rencheck will serve as an advocate for expanding the role of minorities in the energy sector, including raising awareness of STEM education; creating better partnerships between students and industry professionals; and improving energy literacy. AREVA has also been very successful in efforts to recruit military veterans, who comprise nearly 10 percent of AREVA’s U.S. workforce. To encourage and continue this trend, AREVA supports the Troops to Energy program, as well as many other military recruiting events, and even launched a webpage in 2012 specifically dedicated to opportunities for veterans.
Completed during regularly scheduled outages, NDE inspections are a key part of the license renewal process. With three U.S. nuclear energy plants already working to receive approval for 80 years of operation, now is the time for other utilities to prepare and plan for the future of their nuclear plants. To be successful, it is essential that utilities and suppliers collaborate to meet the stringent requirements for safe operation of the plants. NDE excellence during outages and qualified, talented personnel both play critical roles in plant life to 80 years.
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