Amid rising global interest in nuclear new build, the American Society of Mechanical Engineers (ASME) is helping to address the critical need to develop new codes and standards, as well as to update the ones that are currently being applied.
Joseph Wendler, ASME, USA
Since the first commercial-scale nuclear reactor opened at Sellafield, England, in 1956, hundreds of nuclear power plants have been brought on line. According to the US Nuclear Energy Institute (NEI), as of August 2010 there were 441 nuclear reactors generating electricity in 29 countries worldwide; the World Nuclear Association (WNA) estimates their total capacity to be 376 GW.
Another 59 new nuclear plants are under construction in 15 countries, according to the WNA. Behind each of these reactors – as well as those planned for future development – lies an intricate framework of technical standards and conformity assessment programmes that not only govern nuclear power plant design, but also ensure their safe, reliable operation.
Drivers of the nuclear resurgence
Much has been written about drivers of a renewed interest in nuclear power, including a projected increase in global energy demand (see Figure 1); the desire for energy security and independence; reduced tolerance for greenhouse gas emissions; environmental preservation; practical limitations of renewable energy sources; improvements in nuclear power technology; competitive production costs; and improved public confidence.
|Figure 1: Projected world marketed nuclear energy use, 1990–2035 Source: US Energy Information Administration, July 2010|
While the industry still has its share of detractors and faces political hurdles, there is at present a window of opportunity for the industry to experience significant growth in various markets (see Figure 2).
Figure 2: Projected world nuclear generating capacity by region Source: US Energy Information Administration, July 2010
Moving from Legacy Landscapes to a Global Framework
In many industries, extending the life of an existing piece of machinery is more economically viable than replacing it with a new one. The same can been said for the nuclear power industry, and in the USA, the Atomic Energy Act provides the Nuclear Regulatory Commission (NRC) with the ability to extend an original 40-year commercial power reactor licence for up to another 20 years.
According to the NRC, the 40-year licence term was selected on the basis of economic and antitrust considerations, not technical limitations. Eighty of the 104 nuclear power plants have already applied to extend their operating licences for 20 years.
While extending the lifetimes of these plants makes sense from a cost/benefit perspective, it also makes the inspection and maintenance aspects of running a power plant even more critical and necessitates the use of standards whose roots are now generations old. Because the underlying standards are in some senses design-specific – and because their highly regulatory nature tends to make them prescriptive – developing a cohesive standards global framework was not at the forefront of the regulators’ strategy.
Hence, differences in standardization approaches persist. In the USA, where the existing fleet comprises both boiling water reactors (BWR) and pressurized water reactors (PWR), many standards were developed by the American Society of Mechanical Engineers (ASME) in conjunction with the local industry, including contractors, regulators, and material and component suppliers.
Section III of ASME’s boiler and pressure vessel code (BPVC), for example, established rules for the construction of nuclear facility components, while Section XI established rules for in-service inspection of nuclear power plant components.
In France, however, it was decided to create a separate mechanism for codifying nuclear practice, and in 1980 AFCEN (French Society for Design and Construction and In-service Inspection Rules for Nuclear Islands) was formed to develop standards independently from ASME’s process. Similar in organization to ASME’s codes, AFCEN’s RCC-M code governs design and conception rules for mechanical components of PWR nuclear islands and its RSE-M code governs the in-service inspection rules for mechanical components of PWR nuclear islands.
Likewise, the Japan Society of Mechanical Engineering (JSME) and the Korea Electric Power Industry Code (KEPIC) develop standards for their respective local markets. With more countries looking to incorporate nuclear power into their energy portfolios – and with suppliers of components looking to compete in multiple markets – understanding the dynamics of the underlying standards are key to enabling cost-effective deployment.
The Multinational Design Evaluation Programme
Recognizing the need for international collaboration, the Organization for Economic Co-operation and Development’s (OECD) Nuclear Energy Agency (NEA) established the Multinational Design Evaluation Programme (MDEP) and convened its first meeting in 2006. Currently, the national nuclear regulatory agencies of ten countries are participating in MDEP: seven NEA members – Canada, Finland, France, Japan, Korea, the UK and the USA – plus China, Russia and South Africa.
The main objective of the MDEP effort is to enable increased co-operation and establish reference regulatory practices to enhance the safety of new reactor designs. It is envisioned that enhanced co-operation among regulators will improve the effectiveness and efficiency of the regulatory design reviews that are part of each country’s licensing process.
|Standards, such as for refuelling, are key to the safe and efficient operation of nuclear plants Source: ASME|
An overarching concept throughout the work of MDEP is that national regulators retain sovereign authority for all licensing and regulatory decisions. The stated goals of the MDEP programme include enhanced multilateral co-operation within existing regulatory frameworks; multinational convergence of codes, standards and safety goals; and the implementation of MDEP products to facilitate licensing of new reactors, including those being developed by the Generation IV International Forum.
Under the auspices of MDEP a Codes and Standards Working Group (CSWG) is tasked with identifying similarities and differences between codes and standards, and with working with standards development organizations to facilitate convergence of regulatory practices in the area of component design.
MDEP’s 2009 Annual Report, published in June 2010, announced the working group’s significant progress in comparing Class 1 pressure vessel standards, including material, design, fabrication, examination, testing, over-pressure protection and general requirements.
The initial effort focusing on pressure vessel code requirements led to the development in a database that identified the similarities and differences between the ASME code and the Korean, Japanese and French codes.
The project was designed to use the ASME code as the basis for comparison as the codes under review originated from the ASME code. Both Canada and Russia subsequently expressed an interest in contributing to the effort.
The annual report added that a key conclusion of the comparison exercise was that complete international convergence on every aspect of pressure-boundary codes is not currently feasible due to the large differences in the scope of plant designs, as well as the existence of country-specific construction practices, regulatory requirements and adoption processes.
The report suggests future efforts to further expand the scope of work to include Class 2 and 3 vessels, piping, pumps and valves will depend on the success of Phases 1 and 2 and on expanding the codes and standards harmonization effort to areas beyond pressure boundary components. Lastly, the report notes that the CSWG may explore regulatory options to enable the use of foreign codes in the licensing of new reactors.
Nuclear Standards Co-ordination in the United States
In the United States, the Nuclear Regulator Commission is now reviewing design certification applications for several new reactor designs – including GE-Hitachi’s Economic Simplified Boiling Water Reactor; Areva’s Evolutionary Power Reactor; Mitsubishi’s Advanced Pressurized Water Reactor – as well as amendments to Westinghouse’s AP1000 and the South Texas Project Nuclear Operating Company’s advanced BWRs.
Among the technical issues that are presented by a next generation of potential nuclear reactors are passive safety systems; modular construction and design engineering for fewer components, fewer materials, less welding, etc.; improved fuel design for longer refuelling cycles and higher fuel burnup; seismic and aircraft crash resistance; better load-following capability; and the utilization of risk-based management approaches.
In 2009, the American National Standards Institute (ANSI), a non-governmental organization, and the National Institute for Standards and Technology (NIST), a federal agency, established the Nuclear Energy Standards Co-ordination Collaborative (NESCC) in order to identify and respond to the current needs of the nuclear industry.
NESCC’s stated mission is, in part, “to facilitate and co-ordinate the timely identification, development and/or revision of standards that support the design, operation, development, licensing and deployment of new nuclear power plants and other nuclear technologies, including advanced reactor concepts.”
While NESCC is open to all stakeholders – including government legislative and regulatory bodies; industry; standards developing organizations; certification organizations; and other interested parties – its charter also establishes it as “a forum for the NRC to communicate its needs and ensure that priorities for nuclear energy-related standards supporting new licensing and regulatory activities are understood and co-ordinated”.
In addition to including the major US-domiciled standards developing organizations and relevant federal government agencies and national laboratories, the forum includes non-governmental organizations and representatives from nuclear industry.
ASME’s Response to a Potential Nuclear Renaissance
ASME has recently established new committees to address the issues of ageing plants as well as anticipated new builds.One such group is the Special Working Group on Nuclear Plant Aging Management, which is responsible for monitoring, evaluating and recommending actions to the Section XI Committee on In-service Inspection governing all aspects of ageing management and long-term operation of nuclear plants.
Among its specific task assignments is to understand the technical, economic and regulatory aspects of ageing management and long-term operation of plants and to review, recommend or draft rules and requirements for modification of the Section XI code.
Another recently established committee is the Subgroup on Industry Experience for New Plants, which was formed to consider new reactor designs and to identify technical areas/issues or changes that are needed based on design, materials, inspection, accessibility or documentation requirements.
As industry increases its experience with new plants, the joint subgroup will use that knowledge to incorporate appropriate revisions into the Section III (Construction) and Section XI (Inspection) codes.
Technology-specific committees have also been set up, such as working groups on advanced light water reactors, liquid metal reactors, and high-temperature gas-cooled reactors.
In 2008 ASME published a standard jointly with the American Nuclear Society (ANS) titled, ‘Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications’. This standard sets forth the requirements for probabilistic risk assessments used to support risk-informed decisions for commercial nuclear power plants, and also prescribes a method for applying these requirements for specific applications.
Other risk-based works in progress include standards for the probabilistic risk assessment of radiological release and risk-informed in-service inspection.
Further collaborative efforts are currently ongoing between ASME and the American Concrete Institute (ACI) in the areas of composite concrete and steel reactor vessels, containments, storage tanks and components supports, including graphite core supports. Independently from NESCC, ASME has established a task group in order to support the NRC’s process for endorsement of revision of ASME’s nuclear related standards.
According to Kevin Ennis, director of ASME’s nuclear standards and certification activities, “ASME has a long track record of actively engaging all materially affected stakeholders and ensuring consistently rigorous levels of technical review; consequently, we feel the nuclear power industry will continue to look to ASME as a global leader in standards development.”
Redoubling efforts at standards development is not limited to ASME. ANS has issued a number of new and revised standards reflecting renewed interest in the nuclear power industry, such as ANS-3.5-2009, ‘Nuclear Power Plant Simulators for Use in Operator Training and Examination’; ANS-15.11-2009, ‘Radiation Protection at Research Reactor Facilities’; and ANS-8.27-2008, ‘Burnup Credit for LWR Fuel’.
Several new standards are also in the pipeline, ranging from ANS-2.17, ‘Evaluation of Subsurface Radionuclide Transport at Commercial Nuclear Power Plants’ to various standards addressing emergency planning and response.
Conformity Assessment and Workforce Development
While standardization is vital to ensuring the safety and reliability of power plants (and underlying components), conformity assessment – that is, the process by which components or processes are verified to comply with a given standard – is equally important. One means of doing this is by having a third party perform a survey that examines all aspects of a supplier’s operation.
Assuming the survey is successful, a certification is issued that indicates the supplier’s capability to provide products that are suitable for use in nuclear power applications. In some regulatory frameworks, such certifications are required; in others, they provide a recognized assurance of quality as part of a contractual agreement between a purchaser and a supplier.
To a large extent, standards are the language of technical commerce, and becoming fluent in their application is an important part of the design, construction and operation of power plants. With the nuclear industry poised for growth, many standards developing organizations recognize the importance of developing skills in the proper application of standards and provide training as part of their ongoing operations. Improvements in and global spread of information technology make it easier for organizations to conduct this training via the Internet, which improves the overall availability while substantially driving down costs.
A Look to the Future
It is difficult to determine to what extent convergence in standards and regulatory systems, such as those envisioned by MDEP, will be achievable. In a global economy, much depends on the political actions and financial conditions of countries having – or seeking to establish – nuclear power programmes.
Given the perspective of previous setbacks caused by real and perceived quality and performance issues, it is understandable if the industry seizes this opportunity to co-operate to its fullest extent to reach its maximum potential.
About the author
Joseph Wendler, P.E., is a project engineering manager of ASME Standards & Certification who is based in New York City, USA. The views expressed in this article are those of the author and do not necessarily represent those of ASME.
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