LICENSE RENEWAL FOR NUCLEAR POWER PLANTS
   
   
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   Since the 1973 oil embargo, demand for electricity in the United
   States has increased at a slower rate than historic-demand
   projections would have predicted for the economic growth of the
   past 18 years. Nonetheless, the demand has increased by 60% over
   this time. Commercial nuclear power plants, some of which have been
   operating since the 1960s, have met a significant portion of this
   increased demand. Today nuclear generating capacity in the United
   States totals over 100 gigawatts, representing over 20% of the
   nation's total capacity for generating electricity. In addition to
   their energy contribution, U.S. nuclear plants have offered several
   environmental advantages over plants fired by fossil fuels,
   including the absence of emissions of carbon dioxide (one of the
   greenhouse gases), sulfur dioxide (a possible cause of acid rain),
   and nitrogen oxides (contributors to urban smog and acid rain).   
    
   Although nuclear energy has played an important role over the past
   three decades, it is approaching a crossroads. One decision must be
   made concerning the feasibility of building future nuclear plants,
   and another must be made concerning the need to extend the
   operating life of existing nuclear plants.    
   
   Although the most recent order for a commercial nuclear power plant
   in the United States was placed in 1978, the plants ordered before
   that year have continued to be completed and connected to the
   nation's electrical grid. Today five plants remain to be completed.
   It is recognized that electric utilities probably will not order
   additional nuclear plants unless regulatory requirements are
   restructured to reduce their complexity and the time required for
   license approval and construction. Progress is being made; however,
   DOE, the electric utility industry, the Nuclear Regulatory
   Commission (NRC), and the Congress are taking major steps toward
   establishing designs, regulatory processes, and a legal framework
   for future nuclear plants. For example, in late May 1992 the U.S.
   House of Representatives passed legislation similar to a previously
   passed Senate bill and similar to new NRC procedures that will
   permit one-step licensing of nuclear power plants. Concurrently,
   the industry and DOE are working on designs for passive-water
   reactors and advanced reactor concepts to be certified by the NRC.
   
   Because licenses of the existing plants are for 40 years, they will
   begin to expire at the end of the century, before the advanced
   nuclear plants can be available, even under the license-reform
   rules. Nonetheless, the United States is on the verge of a
   significant increase in nuclear power production capability, an
   increase that will be vital until advanced plants take their place
   in power generation. This increase is to come from the renewal of
   the operating licenses for the existing nuclear plants. Instead of
   permanently shutting down dozens of nuclear plants and removing an
   important source of electricity, the NRC and utilities may extend
   their operating life 20 years. License renewal is the second most
   important decision that must be made at the nuclear energy
   crossroads.      
   
   The figure here shows the rapid loss of nuclear generating capacity
   that will occur after the year 2010 if no additional plants are
   built or licenses extended. However, it is anticipated that up to
   75% of the 112 existing plants, or some 80 plants, will apply for
   license renewal. In addition to helping meet demand for
   electricity, renewal of licenses can lead to major economic
   savings. For example, it has been estimated that if the licenses
   were renewed for 20 years for all of the existing nuclear plants,
   a savings of up to $200 billion could be realized. The principal
   reason is that the utilities have amortized the capital cost of the
   plants over the initial 40-year license period. Increased operating
   and maintenance costs for an aging plant during a renewal period
   will be much less than the capital investment required to build new
   plants, nuclear or fossil. Additionally, the economic
   infrastructure of the utility industry would experience significant
   relief if replacement of these plants were deferred by up to 20
   years.    
   
   Current federal regulations permit license renewal, but they do not
   give guidance on the requirements. Anticipating that nuclear
   utilities would request renewal of plant licenses, the NRC began
   several years ago to establish regulatory policies, technical
   bases, and procedures appropriate to license renewal. The NRC is
   now completing that process, and the regulatory bases to approve
   these renewals and to oversee the plants during the renewal period
   are essentially all in place. For this effort, the NRC has drawn
   heavily on ORNL to conduct supporting research.       
   
   The regulatory requirements for license renewal fall into two
   categories--technical and environmental. The NRC places such
   requirements in the U.S. Code of Federal Regulations. Plants
   seeking license renewal must satisfy review requirements both at
   the time renewal is granted and during the renewal period. As in
   earlier phases of developing nuclear power, ORNL has contributed
   significantly to both areas by supplying data, analysis, and
   technical interpretations to the NRC. The NRC requirements and some
   of ORNL's contributions are presented below.
   
   
   TECHNICAL REQUIREMENTS    
   
   The technical requirements for license renewal are based on two key
   principles: (1) the existing current licensing basis (CLB) for each
   operating reactor provides an acceptable level of safety for
   operation during the renewal term, and (2) each plant's licensing
   basis must be maintained during the renewal period, using existing
   or new programs that focus on the management of age-related
   degradation of plant systems, structures, and components (SSCs).
   Evaluators of a renewal application will determine if the applicant
   has taken the required steps toĽ document the CLB for that
   plant--that is, state all the codes, standards, and regulatory
   guides that apply to that specific plant; 
   
        - identify the SSCs--safety equipment plus those components
          that may affect the performance of safety equipment;
   
        - complete an assessment of the plant to verify that it
          complies with the CLB at the beginning of the renewal
          period;
   
        - establish a program that can identify and monitor
          age-related degradation of SSCs throughout the renewal
          period; and
   
        - establish a program to demonstrate that the plant is in
          compliance with the CLB throughout the renewal period.    
   
   The CLB is composed of the original licensing requirements (e.g.,
   codes, standards, regulatory guides) plus requirements that have
   been added for the plant during its current license period.
   Compliance with the CLB ensures that at least the current margins
   of safety are maintained throughout the renewal period. One major
   emphasis for the NRC has been to identify exactly which parts of
   the plant should be required in the SSCs to avoid or mitigate the
   consequences of hypothetical accidents.     
   
   ORNL has been a major participant in conducting research on the
   age-related degradation of many of these structures and components.
   This work has included identifying degradation mechanisms,
   developing methods for monitoring degradation, evaluating
   approaches (rules, criteria, and limits) for mitigating the effects
   of degradation, and establishing technical bases for rules limiting
   the effects of aging. In particular, ORNL researchers have
   addressed concrete structures, pressure vessels, and engineered
   safety systems components.
   
   
   CONCRETE STRUCTURES STUDIED AT ORNL    
   
   The containment building and the basemat, on which the reactor
   sits, are the two most important concrete structures in a nuclear
   power plant in terms of safety. Material and structural degradation
   resulting from aging and environmental influences must be
   understood and managed to ensure the integrity of these components
   and the associated defense against release of radiation to the
   environment.     
   
   ORNL addresses concrete structures in the NRC-sponsored Structural
   Aging Program, led by Dan Naus and Barry Oland, both of the
   Engineering Technology Division. The program's chief goal is to
   establish technical bases for regulatory criteria, which will
   identify for license reviewers and licensees potential structural
   safety issues and provide acceptance criteria.     
   
   ORNL researchers are studying the aging and environmental
   influences on the properties of both concrete and steel-reinforcing
   materials, potential degradation mechanisms, structural inspection
   and monitoring techniques, repair methods, and procedures for
   structural evaluations, especially of the containment building and
   basemat.     
   
   The ORNL group has compiled extensive information from domestic and
   international sources for nuclear and non-nuclear civil structures
   and research activities. The information is being compiled into
   comprehensive data bases on long-term material properties, concrete
   aging mechanisms, inspection, repair, and structural integrity
   experience. One important part of this effort is ORNL's development
   of a Structural Materials Information Center, which makes these
   data bases available in handbook and electronic formats. It will be
   an important resource for assessing concrete structures during
   license renewal evaluation.     
   
   Other developments include (1) an aging assessment methodology,
   which can be used to rank concrete structures in terms of safety
   significance and resistance to environmental damage, and (2) a
   methodology to assess the current condition and predict the
   lifetime reliability of concrete structures. Other guidelines on
   inspection and repair will be issued by ORNL.
   
   
   REACTOR PRESSURE VESSEL RESEARCH AT ORNL    
   
   Reactor pressure vessel (RPV) research continues to receive high
   priority from the NRC because of its importance to safe plant
   operation and other factors. ORNL, through the Heavy-Section Steel
   Technology (HSST) Program, has been the lead laboratory for this
   research for more than 25 years. The principal factors of concern
   are that vessels are subjected to active aging mechanisms, such as
   increasing embrittlement caused by neutron radiation; can be
   potentially exposed to stresses, such as sudden decreases in
   temperatures and pressures, under accident conditions; contain
   fabrication flaws; and cannot be easily replaced to extend the
   plant's life.     
   
   Before the creation of the NRC, the Atomic Energy Commission (AEC)
   initiated research to obtain data and develop methods to ensure
   that adequate margins of safety existed for the thick-wall pressure
   vessels in commercial nuclear power plants. In 1966 ORNL was chosen
   to be the lead laboratory for that research and has provided
   continuous support to the AEC and NRC. The work has produced many
   of the methods that are incorporated in codes and standards used by
   the nuclear industry and the NRC, such as the reference fracture
   toughness procedures in the American Society of Mechanical
   Engineers (ASME) code and the NRC Regulatory Guide 1.154, which
   gives guidelines for evaluating RPV integrity under pressurized
   thermal-shock (PTS) scenarios in which a hot, pressurized,
   irradiated vessel is suddenly chilled by the introduction of
   cooling water.     
   
   Current work on RPVs at ORNL consists of three programs: the HSST
   Program, managed by Bill Pennell of the Engineering Technology
   Division; the Heavy-Section Steel Irradiation (HSSI) Program,
   managed by Bill Corwin of the Metals and Ceramics Division; and the
   Surveillance Data Bases, Analysis, and Standardization Program,
   managed by Frank Kam of the Computing and Telecommunications
   Division. ORNL's leadership in these areas is recognized worldwide,
   and the ORNL staff maintain strong relationships with their
   counterparts in many countries and at the International Atomic
   Energy Agency.     
   
   The first sidebar to this article addresses the HSST Program and
   some of the issues it examines. The HSST goal is to provide the NRC
   with the best available technology to ensure margins of safety
   against fracture of the RPV under hypothetical scenarios. The PTS
   scenario has gained the most attention because it combines the
   elements of fracture-prevention analysis, material properties,
   fabrication factors, and aging effects resulting from irradiation.
   
   Mechanisms responsible for age-related degradation of pressure
   vessels include prolonged radiation exposure, sustained pressure
   and thermal loadings, and transient pressure and thermal loadings.
   Understanding these mechanisms and the materials making up vessels
   is the key to ensuring that a vessel will not rupture under
   prescribed conditions. In this area, ORNL has developed a series of
   advanced data bases and computer codes for use in making fracture
   predictions.     
   
   ORNL researchers are continuing to conduct advanced studies of the
   fracture characteristics of the materials, fracture behavior of
   structures, and analytical methods applicable to complex
   structures. Careful performance of many large-scale fracture
   experiments and their supporting analyses have defined the validity
   of and margins for the current RPV assessment methods. These
   efforts now include a focus on conditions that would exist beyond
   the initial license period.     
   
   RPV life is based not exclusively on time, but rather mostly on the
   embrittlement of the RPV steels, which depends on the amount, rate,
   and temperature of neutron radiation. In other words, the
   life-limiting conditions for a vessel depend on the neutron
   exposure and the conditions under which it is accumulated. Of
   course, during the approved period of extended operation, the
   accumulated radiation exposure will be greater than for the plant's
   initial 40 years. Current limits on allowable embrittlement are
   expected to apply in principle during renewal periods, and the
   current research is aimed at verifying that these limits will not
   be exceeded during a 20-year extension. With respect to monitoring
   RPV aging, one key need is in-reactor surveillance programs that
   give accurate data on the neutron exposure and vessel embrittlement
   during operation. Frank Kam and his project team are working
   closely with the NRC to improve surveillance programs by combining
   the best available dosimetry techniques with the periodic testing
   of tensile and fracture specimens made of the RPV steel and weld
   materials that are exposed to actual reactor operation. They also
   maintain for the NRC a carefully documented national surveillance
   data base on which regulatory guidance for embrittlement
   assessments is based.     
   
   If the calculated embrittlement for the vessel in a specific plant
   reaches the allowable limit, regulations permit the owner to
   thermally anneal the vessel to remove a portion of the accumulated
   embrittlement. In work for the HSSI program, Bill Corwin and Randy
   Nanstad are verifying the correct times and temperatures for
   annealing to achieve acceptable levels of recovery for vessel steel
   and welds that may be more than 20 cm (8 in.) thick. Their
   experiments on welds removed from the vessel of the cancelled
   Midland Nuclear Plant Unit No. 2 will determine the degree of
   recovery from annealing and reembrittlement rates during subsequent
   radiations for prototypically thick welds. The HSSI Program staff
   are carefully combining these results with those from earlier and
   smaller specimen studies to provide the NRC with the best available
   basis for establishing annealing standards. The NRC is completing
   development of a regulatory guide to permit utilities to anneal
   their RPVs and to continue operation after annealing even under
   license renewal.    
   
   Radiation-induced embrittlement is not the only age-related
   degradation mechanism affecting RPVs. Material damage caused by
   thermal and mechanical stress cycles over time results in
   degradation that must be factored into the allowable life
   assessments. By knowing the plant's operating history, the owner
   can compute accumulated damage resulting from thermal aging,
   fatigue, and other factors to determine the remaining allowable
   life for the vessel, as defined by the code criteria in the CLB.
   Thus, accurate records of a plant's operating and maintenance
   histories are recognized by utilities as important for license
   renewal. Nanstad's group also continues to study the aging of these
   steels under long-term thermal exposure conditions. 
   
   
   ENGINEERED SAFETY SYSTEMS COMPONENTS STUDIED AT ORNL    
   
   ORNL researchers are studying aging of nuclear reactor plant
   components, such as valves, pumps, steam generators, and vessel
   internals. Because the condition of these aging SSCs must be
   considered throughout license renewal periods, the research is
   focused on (1) developing guidelines for assessing the condition of
   components at the end of the current license period, (2) devising
   methods for monitoring age-related degradation during the license
   renewal period, and (3) where possible, identifying approaches to
   mitigate age-related degradation effects.     
   
   For the past eight years, ORNL has been a lead laboratory for the
   NRC in this area and has made some major breakthroughs, especially
   in developing techniques for nonintrusive monitoring of valves.
   This work has led to patented techniques and substantial technology
   transfer to industry. Don Casada, the manager of this research,
   describes these developments in the second sidebar to this article
   on p. 95. The research at ORNL is part of the NRC's overall Nuclear
   Plant Aging Research Program.
   
   
   ENVIRONMENTAL EFFECTS    
   
   A proposed NRC rule will cover environmental effects that should be
   addressed during the process of license renewal. Over the past few
   years, a multidisciplinary team led by Rich McLean, Lance McCold,
   and Johnnie Cannon, all of the Energy Division, has intensively
   studied the potential environmental impacts of extended nuclear
   plant operation (see the interview on p. 114). The study identified
   more than 100 issues, made detailed assessments of potential
   environmental impacts, and examined the relationships of the issues
   to the National Environmental Policy Act (NEPA). The final goal was
   to identify the many issues that can be treated on a generic basis
   and the remaining few that must be handled on a plant-by-plant
   basis.     
   
   The results of the study were published for public comment in late
   1991. The public-comment period recently ended, and ORNL is helping
   the NRC formulate responses. After the NRC makes its final
   responses, this part of the license extension rule will be
   complete. The NRC will document the final rule as a modification to
   Part 51 of Element 10 of the U.S. Code of Federal Regulations (10
   CFR 51).
   
   
   IMPLEMENTING THE LICENSE RENEWAL PROCESS    
   
   Upon completion of the generic environmental impact statement for
   extending nuclear plant operation, all the regulatory instruments
   will be in place to allow applications for license renewal. The
   first license renewal application was expected to be for the
   pressurized-water reactor of the Yankee Atomic Electric Company's
   (YAEC) Yankee Nuclear Power Station in Rowe, Massachusetts (see
   photo on p. 88). Commonly called Yankee Rowe, it was the oldest
   operating nuclear power plant in the United States, and its license
   was scheduled to expire in 2000. However, YAEC recently decided to
   retire this plant because of economic considerations, including the
   cost of the extensive efforts that would have been required to
   qualify its embrittled reactor vessel for continued service.     
   
   The first application to renew a license for a boiling-water
   reactor is expected to come from the Northern States Power Company
   (NSPC) for its Monticello Nuclear Power Plant, whose license is
   scheduled to expire in 2010. Both of these plants have in recent
   years been the focus of advanced studies by DOE and the Electric
   Power Research Institute to assess the issues of aging and
   potential procedures for license renewal. The NSPC is expected to
   submit its application for license renewal in early 1993.    
   
   The lead time between submittal of a renewal application and
   expiration of the initial license period is expected to be about 15
   years. About 5 years will be required to obtain approval for all
   aspects of the application, and the other 10 years are allowed for
   the plant owner to provide an alternative source of electricity
   should the application be denied or if the owner decides not to
   extend the plant's operation. The license renewal is to become
   active when the approval is granted and to extend through the
   renewal period. For example, if the renewal is approved 10 years
   before expiration of the initial 40-year license, the renewal will
   cover the remaining 10 years plus the approved renewal period.    
   
   In conclusion, meeting the growth in demand for electricity in the
   next several decades in the United States can be easier and less
   costly if the operating licenses of existing nuclear power plants
   are renewed for another 20 years. ORNL has played an important role
   by providing the NRC with technical expertise, data, and analyses
   on which to base regulatory criteria and guidelines for license
   renewal. The development of the regulatory procedures is now
   essentially complete. It is expected that ORNL will continue to
   contribute to the development of nuclear power technologies,
   including the advanced reactors that will be certified by the NRC
   for the next generation of nuclear power plants. 
   
   
   Claude E. Pugh
   
   (keywords: nuclear power, nuclear power plants)
   
   
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   Date Posted:  2/7/94  (ktb)