Coming of age2 September 2004
The seventh meeting on plant life management and plant licence extension (PLIM + PLEX) took place in New Orleans, Louisiana on 13-14 October 2003. It was the first PLIM + PLEX meeting held in the USA and over two-thirds of the 30 papers that were presented were from North America. By Garry Young and Tim Abney
Dan Keuter, vice president of business development for Entergy Nuclear, welcomed the participants to New Orleans, which is the corporate headquarters for Entergy. New Orleans “likes to celebrate,” he said, unlike the nuclear industry in recent years.
Now, however, “we do have something to celebrate. Performance of the nuclear industry has been nothing short of outstanding in the last ten years.” He continued: “Ten years ago if you would have told me that the average capacity factor of all nuclear plants in the USA would be 92%, I would say that you’re crazy. But it’s averaging greater than 92%.”
Today – nearly 50 years after president Eisenhower’s famous ‘Atoms for Peace’ presentation at the United Nations on 8 December 1953, which marked the beginning of the US nuclear industry – “our performance is going up; our costs are going down.” The US nuclear industry is currently enjoying a renaissance due to heightened public awareness resulting from recent events such as power shortages and outages, and more than a decade of safe, environmentally clean, and economical electricity production from nuclear power. This renaissance is also being supported by a positive political climate that includes increased acknowledgement of the environmental, economic, and national security benefits of nuclear.
The optimistic note on which PLIM + PLEX 2003 began was continued throughout, as subsequent presenters reinforced that feeling with several specific examples.
LIFE MANAGEMENT PROGRAMMES
The session on life management programmes included details on licence renewal of US nuclear plant operating licences, the restart of currently idle nuclear units including Browns Ferry 1 and the Bruce A nuclear units, and programmes in Romania and Switzerland. The licence renewal presentations covered the status of the US licence renewal efforts that have now resulted in issuance of renewed licences for 19 of the 104 operating licences by the US Nuclear Regulatory Commission (NRC). The original operation licence for US plants has a 40-year term. Licence renewal provides the option to extend this term in additional 20-year increments.
The industry and the regulatory perspectives on this relatively new process indicate that it is an efficient, effective, and stable regulatory process. The NRC currently allocates approximately 20,000 staff-hours per licence renewal application over a 22-month review period. A number of initiatives were described that have been successful in reducing the cost of obtaining a renewed licence and that are planned to further improve the efficiency of the licence renewal review process.
Due in large part to the success of this process, over 50% of the US nuclear fleet has already committed to seek licence renewal over the next three years. Rather than expecting a significant decline in the US nuclear capacity beginning in 2010, which would have occurred without licence renewal, the current trend of licence renewal will avoid this decline until at least 2030. By that time, new nuclear plant construction should be underway if the renaissance projections are correct.
The restart of currently idle nuclear units is also enjoying renewed interest. TVA is planning to spend $1.8 billion to restart Browns Ferry 1 by May 2007. Unit 1 has been idle since 1985 when all three units at Browns Ferry were voluntarily shutdown to address regulatory, safety, and management issues. Units 2 and 3 were restarted in 1991 and 1995 respectively, and since restart have been top performers based on performance measures such as load factor, refuelling outage duration, cost of electricity generated and overall plant safety. The unit 1 restart is being coordinated with other improvement and enhancement activities including power uprate and licence renewal for all three units. The restart and other activities are the result of favorable environmental assessments and attractive financial analysis results.
The Bruce A units 3 and 4 in Canada, leased to Bruce Power by Ontario Power Generation, have been idle for approximately five years. Bruce Power took over control of the operating units of Bruce B and the idle units of Bruce A in 2001. The newly formed company has gained a reputation as a strong industry player in the Ontario power industry and is nearing the final phase of the restart of units 3 and 4, two 750MWe units. Unit 4 went critical in late August of this year and is currently proceeding to full power operation. Unit 3 is on schedule for returning to operation approximately one month after unit 4 returns to service.
Plant life management programmes in Romania and in Switzerland have been on-going for a number of years. In Romania, Cernavoda 1 has been the subject of a pilot plant life management programme to help ensure plant life attainment and to prepare for plant life extension. The Cernavoda project is based on the Candu life management programme that is already in use by a number of other utilities with Candu reactors. The project includes both passive and active components. For active components, methods are being developed to select critical systems to optimise maintenance as well as health monitoring programmes. These methods are based upon streamlined reliability centered maintenance techniques that have been enhanced for efficiency and value. Once the pilot work is complete, the programme will be conducted in three phases: life management assessment, plant life attainment, and plant extended operation.
Since the early 1990s, the plant life management programme for Swiss nuclear plants has been coordinated through the Swiss Utility Working Group (GSKL) for ageing management. This group is responsible for coordinating systematic reviews of safety-related components and structures regarding effects of ageing and addressing the need for ageing management programmes. This group addresses both technology ageing and material ageing issues. The GSKL has developed documents to support ageing management including a programme for reviewing and optimising ageing management measures; a catalogue of ageing mechanisms for various material, environment, and loading combinations; and guidelines for preparing ageing management review files (Steckbrief files). The Swiss life management programme is based on an expected 60 years of economic life and even longer for technology ageing issues.
The session on economics included the topics of power uprates or capacity improvements, proactive and risk-informed asset management, nuclear insurance strategies, and considerations of PLIM in new plant design. In the USA, there have been 98 power uprates licensed by the NRC that have yielded approximately 4000MWe of additional capacity from the existing fleet of operating nuclear plants. These power uprates are attractive economically since they add capacity with a modest additional investment. In one example, Entergy spent approximately $300 million to obtain over 460MWe due to uprates. This amounts to a very economical $650 per kWe average capital cost. Since there is no significant additional O&M cost associated with power uprate of nuclear plants, the low capital cost is even more attractive to nuclear utilities. Operating history for uprated nuclear units has demonstrated that these power increases have not resulted in lower reliability or lower capacity factors, which was once a concern. In general, the uprated units have operated as well or better than before the uprate.
In Germany when the electricity market deregulated, the cost of nuclear generated electricity had to become competitive. Power uprate was one way to accomplish this goal. Some of the German uprates involve ‘green megawatts’ that are associated with secondary system improvements that do not require regulatory approval. When secondary system improvements are combined with reactor core power uprates, synergy of the two uprates can result in more megawatts than the sum of each individual uprate. For example, one 1300MWe PWR got an extra 155MWe from a 75MWe increase due to a core power increase and a 60MWe increase due to a secondary system improvement, based on measuring the uprate performance of the two changes independent of each other.
Insurance risks associated with ageing power plants have been assumed to increase when using conventional risk assessment processes. The result is higher insurance premiums or economic penalties due to the ‘bathtub curve effect’ of ageing that predicts higher loss rates for older plants. However, the nuclear industry has implemented effective inspection and regulatory strategies that mitigate the predicted increase in risk with age. As a result, the nuclear insurance industry has adopted a qualitative risk-informed process to refine the conventional risk assessment and inspection to a more contemporary approach. This approach enhances identification of significant insurance risk and takes greater advantage of the results of regulatory and jurisdictional oversight. The result is a better tool for discussion of insurance risk between the insured and insurer, which minimises the economic impact on the nuclear utilities depending on the facility insurance.
With the maturing of the PLIM programmes, information is now available for application to new plant designs. One example is the Candu PLIM programme that has captured important ageing management data that is being used in the design process for the advanced Candu reactor. With application of the PLIM assessment concepts, there is opportunity to enhance on-line refuelling processes, optimise on-line maintenance, and reduce outage frequency and duration. The result of these efforts to employ existing PLIM considerations in the design of new nuclear plants will include lower O&M costs for the next generation of nuclear plants as well as enhance plant life management.
INSTRUMENTATION AND CONTROL
The session on instrumentation and control (I&C) included topics on control room modernisation, environmental qualification of a new generation of Class 1E cables, and managing I&C obsolescence. Due to the ageing and obsolescence of control room instrumentation, many utilities are planning for upgrades to digital technology. Usually this must be done in stages due to the magnitude and expense of such upgrades for operating nuclear plants. The Electric Power Research Institute is working with a group of utilities to develop guidelines for human factoring and implementing these staged upgrades (see page 28). The vision for this work is the ‘100 person plant’ concept. Although getting to an operating plant staffing level of 100 persons is not likely to be successful, the goal helps ensure the guidelines will make the upgraded digital control rooms more efficient to operate.
Habia Cable AB in Sweden has been working with Korean nuclear utilities to develop Class 1E (safety grade) electrical cables that have a qualified life of 60 years. Using semi-crystalline linear aromatic polymer polyetheretherketone (PEEK) insulation and an irradiation cross-linked
EVA-copolymer jacket, thin wall cables have passed stringent requirements for a qualified life of 60 years for the Korean new generation nuclear plants. The qualification requirements for these cables included LOCA and post-LOCA conditions, fire testing, and chemical spray testing.
Entergy and BNFL presented operating experience in dealing with I&C obsolescence. The approaches included repair, refurbishment or upgrade, cloning, reverse engineering, and new design. Examples of each approach were discussed and the estimated cost savings were presented. By creative repair, redesign, and upgrading of obsolete I&C components, cost and future maintenance savings can be significant. Examples included plant personnel designing and building replacements for obsolete controller units at a cost of $150,000 and savings of at least $100,000; designing and building a digital operators module for $250,000 and savings of over $1,750,000. The skills developed during reverse engineering, cloning, and redesign have also proved to be valuable in diagnosing and solving other I&C problems encountered during forced outages. The opportunity for cost avoidance and better use of plant engineers by predicting and managing design risks associated with obsolescence are significant.
VESSEL HEAD REPLACEMENT
The session on vessel head replacement included experiences at North Anna, Surry, and Davis-Besse nuclear plants, and reactor vessel head vendor perspectives on this new and significant challenge for the nuclear industry. Recent events that relate to the primary water stress corrosion cracking (PWSCC) degradation of the Alloy 600 components in reactor vessel closure heads are requiring utilities to consider various options for continuing plant operation. Failure of Alloy 600 penetrations is no longer a question of “will they fail?” The question is now “when will they fail?”
Framatome ANP and Babcock & Wilcox Canada presented their experiences with reactor vessel closure head replacements. The decision to repair or replace the vessel head is primarily an economic decision. The factors to consider include plant susceptibility to cracking, risk assumptions, replacement power expense, and the estimated selling price of electricity in the future. Once the decision is made to replace the reactor vessel closure head, the new head should incorporate some improved ageing management, inspection, and maintenance features. Replacing the Alloy 600 components with Alloy 690 reduces the susceptibility to PWSCC. Other improvements discussed included provisions for better leak detection, control rod drive mechanism nozzle anti-ejection restraints, lower cold work and welding stresses during manufacturing, and improved service structure handling features to simplify refuelling activities.
Dominion’s experience with finding vessel head cracking at North Anna 2 during a refuelling outage in 2002 was presented. The utility found more than 60 crack indications that required repair. Although the utility had already planned to replace the reactor vessel head in 18 months, the cost of repairing more than 60 indications forced a new plan. The result was an aggressive and complex plan to obtain a French designed and manufactured vessel head, qualify it to US regulatory standards, ship it to the USA on a Russian Antonov heavy-lift aircraft, and install it in about the same time as it would have taken to repair the crack indications. This plan was successful and the lessons learned were applied to the vessel head replacement projects for North Anna 1 and for the Surry units.
The Davis-Besse experience showed how a top performing nuclear plant could become isolated and complacent, resulting in a shutdown of more than one year. The reactor vessel head degradation at Davis-Besse was discovered in March 2002, after over four years of indications that a problem might exist. The subsequent replacement of the reactor vessel head has addressed the material ageing problem, however the regulatory and management problems have been much more difficult to address. Davis-Besse remains in an extended shutdown and is not expected to restart until later this year. Some of the primary lessons learned at Davis-Besse were a need to focus on safety and a safety conscious work environment, and to implement a robust corrective action programme to ensure conditions adverse to quality and safety were promptly identified and resolved in a timely manner.
THE NEXT STEP
PLIM + PLEX 2003 meeting started and adjourned on a positive note regarding the renaissance of the nuclear power industry around the world. Many examples of successful plant life management and plant life extension programmes were presented. It is clear from these presentations that the future of nuclear power is bright, nuclear plant safety is continuing to improve as it has for the past several years, the cost of electricity from nuclear power is becoming more competitive with other sources, and the environmental benefits of nuclear power are becoming more widely recognised. The next step for the nuclear power industry is to maintain the current momentum of the nuclear renaissance and to help ensure it gains additional momentum by creating more successes associated with PLIM and PLEX around the world. These new successes will be reported at the next PLIM + PLEX conference in 2005!
Garry Young, Entergy Nuclear, Arkansas Nuclear One, 1448 S.R. 333, Russellville, AR 72802, USA; Tim Abney, Tennessee Valley Authority, Browns Ferry Nuclear Plant, PAB-1G, PO Box 2000, Decatur, AL 35609, USAExternal weblinksNuclear Engineering International is not responsible for the content of external internet sites.View the final programme of PLIM + PLEX '03 and download conference papers