Construction was suspended on Watts Bar Nuclear Plant Unit 2 in the late 1980s, and the plant sat idle for more than 20 years. Now, through equipment refurbishment and replacement, Unit 2 is on track to become the first new commercial nuclear reactor to come online in the U.S. in the 21st century.
Electricity consumption during the first 70 years of the 20th century grew at a steady rate of 7% per year, doubling every 10 years. To meet that demand, during the 1960s and early 1970s, commercial nuclear power plants were steadily increasing in numbers and size. New reactor orders were being placed with the expectation that this trend would continue.
The Tennessee Valley Authority (TVA) started construction at the Browns Ferry site in 1966, and the Sequoyah plant followed in 1969. Construction permits (CPs) for the TVA’s third nuclear site, located in southeastern Tennessee—Watts Bar (Figure 1)—were issued in 1973. The plant was slated to include two Westinghouse four-loop pressurized water reactors (PWRs) within ice-condenser containments.
|1. Better late than never. Construction on Watts Bar Unit 2 originally began in the 1970s. After a long interruption, the unit is currently forecast to begin commercial operation in 2015. Courtesy: TVA|
All of the TVA’s nuclear plant CPs were issued under the two-step Title 10 Code of Federal Regulations (10 CFR) Part 50—Domestic Licensing of Production and Utilization Facilities licensing process. In the first step, an approved CP application authorizes construction, while focusing on the plant’s preliminary design and site suitability. The second stage evaluates the operating license (OL) application, final plant design, safety evaluation, operational limits, and ability to respond to postulated accidents. The Nuclear Regulatory Commission (NRC) established a one-step licensing process under 10 CFR Part 52—Licenses, Certifications, and Approvals for Nuclear Power Plants in 1989.
Hiccups Along the Way
By 1976, many nuclear plant proposals were no longer viable due to a decrease in electricity demand, rising construction costs as a result of inflation—exacerbated by schedule delays, public opposition to projects, and changing regulatory requirements. By 1983, completed nuclear plants, on average, were costing 10 times their initial projections and taking 12 years to complete.
Eventually, more than 90 reactor orders in the U.S. were canceled. The TVA reevaluated its own nuclear plans. Ultimately, it canceled construction at Phipps Bend, Yellow Creek, and Hartsville, while delaying construction at the Bellefonte nuclear plant.
In 1985, the TVA took Browns Ferry and Sequoyah out of service and halted construction at the Watts Bar site. Unit 1 was thought to be nearly complete and ready to receive an OL. An NRC review had identified weaknesses in the TVA’s nuclear program, such as the lack of a sufficient number of experienced managers to provide leadership and proper direction, coupled with the absence of an effective organizational structure to ensure the safe design, construction, and operation of the TVA’s nuclear plants.
The TVA initiated a vigorous recovery program in 1986. Its Nuclear Performance Plan (NPP) was approved by the NRC and implemented to identify root causes and implement corrective actions of the aforementioned issues at the corporate and site-specific levels. Elements of the NPP were implemented at the Watts Bar site, including an employee concerns program to address issues at the plant level. Browns Ferry and Sequoyah were returned to service once necessary improvements were made.
The NRC issued a policy statement on deferred plants, which was published in the Federal Register on Oct. 14, 1987. A “deferred nuclear plant” is defined as a plant at which the licensee has ceased construction or reduced activity to a maintenance level, maintains the CP in effect, and has not announced termination of the plant. The TVA chose to defer Watts Bar Unit 2, while resuming construction on Unit 1 in 1990, which received its full-power operating license in 1996.
The policy statement on deferred plants was important because it called out requirements for how a plant was to package, ship, receive, store, and handle equipment. It also offered guidance on collecting, storing, and maintaining quality control documentation during an extended layup, even though this was not specifically addressed as a license condition.
The NRC had previously alerted the industry to degradation problems at various facilities due to improper storage during construction or extended plant outages when it provided Information Notice No. 85-56: Inadequate Environment Control for Components and Systems in Extended Storage or Layup to licensees in the summer of 1985. Some of the items identified in the notice included the following:
■ A cooling water heat exchanger for a high-pressure core spray diesel generator had accumulated water in the tube side of the unit. The heat exchanger had been delivered to the site and was “stored in place,” but it was not yet in service. It was hypothesized that the water was a result of inadequate draining after a manufacturer’s hydrostatic test.
■ A site construction organization did not have a program for inspection or surveillance of equipment in storage, resulting in significant corrosion damage to heat exchanger tubes, tube sheets, and water boxes.
■ Corrosion attack had been found on internal surfaces of two auxiliary feedwater pumps, even though the pumps had not been operated. The source of the corrosion was determined to be contaminated water inadvertently left in the pumps after pre-startup flushing.
To Be, or Not to Be?
On Aug. 1, 2007, the TVA board of directors authorized completion of Watts Bar Unit 2. At the time, a Detailed Scoping, Estimating and Planning study found Unit 2 to be effectively 60% complete with $1.7 billion invested. Because the containment and turbine buildings were in place, and the reactor pressure vessel, reactor coolant system piping, and steam generators were installed, the plant was expected to be finished in 60 months for a cost of $2.5 billion.
However, certain challenges complicated the mission. Input for the PWR construction project relied on lessons learned from a five-year, $1.8 billion, maintenance-type restart of Browns Ferry Unit 1, which is a boiling water reactor, so not all of the experience translated. Also, various pieces of equipment, such as pumps, motors, and valves, had been salvaged for use in Watts Bar Unit 1 and the Sequoyah plant.
To address the unique history of Watts Bar Unit 2, a customized construction inspection program was created. It provided the policies and requirements needed to resume construction and recorded inspection activities, applicant actions, and technical issues resolved to support issuance of an OL. The TVA still planned to complete Unit 2 under the two-part 10 CFR 50 licensing process.
Notwithstanding the evolution in new NRC design requirements and lessons learned to bring Watts Bar Unit 2 online, a revised estimate in 2011 recalculated construction progress. The plant was estimated at the time to actually be 35% to 40% complete.
The economic analysis and decision to proceed on Watts Bar Unit 2 was based on the need for additional power. The second unit at the site was considered a valuable asset not only for the TVA but also for ratepayers. As the cost of fuel fluctuates, the TVA would be capable of maintaining a balanced generation portfolio with Unit 2 in the fleet, allowing an appropriate mix of nuclear, fossil/coal, hydro, and renewables.
Furthermore, the TVA’s peak demand is projected to grow 1.5% annually through 2023. After accounting for retirement of coal plants and reduced power demand achieved through the TVA’s demand-side programs, the TVA will need more than 5,000 MW of new electricity generation by 2023 just to maintain its current level of reliability.
The Turnaround Begins
Typically, layups are for short periods of time—weeks to months. Units are placed in hot or cold standby during outages to preserve equipment and mitigate component corrosion damage. Given that most of the safety-related and quality-related equipment at Watts Bar Unit 2 was installed during original construction, the TVA’s layup lasted about two decades.
Taking the perspective of a license renewal project, the TVA utilized the NRC’s Generic Aging Lessons Learned (GALL) Report (NUREG-1801 ) and the Electric Power Research Institute’s (EPRI’s) report, Plant Support Engineering: Aging Effects for Structures and Structural Components (Structural Tools) (1015078), for evaluating structures, systems, and components (SSCs) subject to aging mechanisms (Table 1).
|Table 1. Aging mechanisms and terms. The Generic Aging Lessons Learned (GALL) Report identified several plant-aging mechanisms, some of which are listed here. Source: NUREG-1801|
In August 2011, the TVA named Michael Skaggs—former site vice president at the Browns Ferry, Sequoyah, and Watts Bar nuclear plants—senior vice president for Nuclear Generation Development and Construction. Also, the TVA and its main contractor, Bechtel Power Corp., amended their contract giving the TVA greater responsibility for the overall management of completing Watts Bar Unit 2 and establishing completion milestones.
I recently interviewed Skaggs regarding the layup, preservation, and reactivation activities at Watts Bar Unit 2. He said that site engineering had the lead and decision-making responsibility for the extended layup and preservation program. Turning to industry resources for additional information, such as the Institute of Nuclear Power Operations (INPO) and EPRI, and utilizing lessons learned from Watts Bar Unit 1, the primary goal was to meet core NRC SSC requirements. The layup and preservation program was intended to maintain an acceptable environment in and around the equipment.
Relative humidity is a critical factor in controlling corrosion. Dry layup consists of placing desiccant inside components and sealing all openings throughout the vessel-turbine-generator system to prevent the inward migration of moisture. Flexible ducting, commonly referred to as an “elephant trunk,” is frequently connected to air-handling equipment to force a continuous flow of air through equipment, while dehumidifiers remove the residual moisture and reduce the relative humidity below the corrosion threshold (less than 35% to 40% relative humidity).
For systems backfilled with water for preoperational testing (such as for wet layup), adjusting pH, filtering particulates, and applying protective film inhibitors on metal surfaces are methods used to reduce corrosion buildup. Instrumentation can be affected by the same degradation mechanisms as mechanical equipment (that is, corrosion and erosion). However, it can also be subject to surface abrasion, overheating/burn damage, metal “whiskers” or dry joints, and drift. Software also can quickly become obsolete or difficult to support.
Independent of the plant type, basic layup/preservation lessons learned can be applied to remove moisture and prevent corrosion degradation. Examples include feeding a constant airflow in at a higher elevation, using a lockout/tagout system to align check valves or removing valve internals to establish airflow paths, and having an open flow path at lower elevations.
Drains and traps can continue to collect water, even after initially being verified dry, and they must routinely be drained and revalidated. All rotating equipment should be “exercised,” that is, the shafts should be rotated several revolutions every week to coat the bearings with lubricant and prevent brinelling, and rust preventive coatings should be applied to exposed surfaces.
Refurbishment and Restoration
Skaggs said that when the Watts Bar Unit 2 plant design was reissued to restart construction, the natural evolution of a nuclear plant since the 1970s required the TVA to make modifications. Much of the equipment was replaced. For example, changes in piping prompted replacing pipe supports. Some conduit was added and cable re-pulled. Also, new digital instrumentation allowed remote monitoring with hand-held computers.
“From an equipment scope, we broke down the components into active components or passive components. Active components provide a function, for example. pumps, valves, motors, switchgears, relays. Passive components include piping, cables, and pipe supports. We put together a program to verify they meet the original specifications from the vendor or industry requirements,” said Skaggs.
The process resulted in the creation of the TVA’s refurbishment/restoration program. The program was intended to restore Unit 2 equipment and components to their original specifications to meet the 40-year licensing basis requirement. If items couldn’t be restored, they were replaced. Skaggs noted that the TVA did not rely on the layup and preservation options for the active and passive components.
The advantage of installing new components, or equipment refurbished to like-new condition, is that it is just like building a new power plant. Program steps included:
■ Refurbishing or replacing active components and instruments based on programmatic requirements, vendor input, operational experience, or sound technical judgment to achieve like-new status.
■ Determining potential degradation mechanisms and contributing environmental factors for each component category.
■ Developing acceptance criteria from the licensing basis, design specifications, and vendor specifications.
■ Establishing inspections and testing to identify degradation in accordance with applicable vendor and design specifications or requirements.
■ Verifying final confirmation of restoration through preoperational testing.
Skaggs and his team engaged with vendors that provided equipment and replacement parts for the components being used at Watts Bar to confirm that current specifications were met. A sampling of the equipment and systems covered, and actions taken as part of the refurbishment/restoration program, follows.
Pumps. All pumps were refurbished to original equipment manufacturer’s acceptable conditions. Parts that were found unacceptable, such as age-related degradation of rubber or soft material gaskets in seals, were replaced. Missing parts were replaced with an approved equivalent component. For example, rebuilt high-pressure and low-pressure inlet valves were installed on the main feedwater pump. If refurbishment was not an option, pumps were entirely replaced. For example, eight new raw water cooling pumps were installed at the river intake water station.
Valves. In the auxiliary and reactor building, more than 470 motor-operated valves were disassembled, cleaned, lubricated, and refitted with replacement parts.
Piping/Tubing. Borescope surveys and ultrasonic testing were used to inspect piping and internals at different locations. The carbon-steel piping in the feedwater system was replaced with chrome-moly piping, which has increased high-temperature strength and better corrosion resistance due to the chromium and molybdenum content in the steel. Copper-alloy condenser tubes were replaced with an alloy that is highly resistant to raw water. More than 27,000 tubes that carry the cooling water were replaced to ensure no leaks and a long condenser life.
Snubbers. Dynamic restraints, known as snubbers, are designed to protect components from excessive shock or sway as a result of seismic disturbances, water hammer, or other transient forces. At Watts Bar Unit 2, all snubbers were disassembled, cleaned, and inspected; lubricants and elastomers were replaced.
Reactor Vessel/Nuclear Steam Supply System (NSSS). Portions of the NSSS were modified to meet regulatory requirements concerning potential operational embrittlement. Early performance of this activity supported the reduction of personnel radiological dose. Traceability of the reactor vessel (Figures 2 and 3) and NSSS were certified and verified in accordance with American Society of Mechanical Engineers (ASME) codes.
|2. Delicate business. Assembly of the core barrel requires care during lifting. Courtesy: TVA|
|3. Let ‘er down slowly. Like a jigsaw puzzle, everything must fit into place. Courtesy: TVA|
Turbine/Generator. A significant amount of work was done, totaling more than 40,000 individual replacement parts, including one new high-pressure (HP) turbine; three new low-pressure (LP) turbines; complete modernization of the generator (Figure 4), including a RIGI-FLEX rewind of the stator and new retaining rings; exciter rotor refurbishment; and six new moisture separator reheaters.
|4. A patriotic touch. Many components on the turbine floor were modernized. Courtesy: TVA|
Main Control Room. The Unit 2 portion of the control room (Figure 5) was ergonomically redesigned. The annunciation system was replaced, and panel indicators, recorders, and controllers were upgraded.
|5. They didn’t have those in the 1970s! Justin Gallagher, senior reactor operator, completes a training scenario in the Watts Bar Unit 2 control room. Courtesy: TVA|
Cleanliness. Particulate contaminants, such as sand, sawdust, metal chips, rust, weld splatter, and tape, were removed from accessible interior surfaces by vacuuming, rinsing, or flushing until particulate requirements were met.
Warehouse Storage. For equipment kept in warehouses, all openings were sealed with manufacturer-approved shields to minimize the introduction of foreign material, and then the equipment was stored in its appropriate orientation—horizontally or vertically. Fluids were analyzed for water content and particulates, and internal heaters were energized to prevent condensation. Motors were covered with a tarpaulin for dust protection, and vents were kept open for ventilation.
Overcoming Bumps in the Road
The TVA was fined $70,000 by the NRC in 2013 related to its commercial-grade dedication (CGD) program, a process used to ensure that components purchased from a commercial supplier are equivalent to nuclear-grade items. The intent of the program is to confirm that critical characteristics of an item, for example material strength or input/output voltage, are acceptable. The purchaser or an independent third party verifies acceptability through inspections, tests, or analyses.
The NRC found that the TVA had not properly verified critical characteristics for an unknown number of safety-related items. It was determined that cancelation of a Bechtel CGD procedure early in the project and lack of training on CGD package preparation for the procurement engineering group contributed to the problem.
Of the 12 packages with potential deficiencies, eight were found to be acceptable. The remaining four packages required additional testing and inspection prior to use. The TVA decided to conduct an independent review of the CGD packages. The NRC noted that tests confirmed that installed commercially dedicated equipment and/or components would have been able to perform their intended safety functions. In total, tests and inspections were conducted on 1,342 commercial-grade items. The TVA continues to test items that have already been purchased or installed.
Although detractors have emphasized that the plant has been cobbled together with retrofits and that completion costs are high—estimated at $4.5 billion—Unit 2 has already accomplished several significant milestones, including these:
■ Completed hydrostatic pressure testing of the reactor coolant system, steam generators, and steam supply system.
■ Assembled the nuclear reactor vessel.
■ Conducted open vessel testing verifying that safety-related systems inject water into the reactor vessel as designed.
■ Finished all environmental impacts from construction.
■ Constructed and outfitted its FLEX storage building in response to the Fukushima requirements.
In February 2015, the Advisory Committee on Reactor Safeguards, an independent review body within the NRC, sent a letter to the NRC chairman recommending approval of the Watts Bar Unit 2 OL once remaining work and NRC inspections are complete.
Skaggs concluded, “Even though the construction was started a long time ago, what we have here is essentially a newly designed plant, an existing footprint with new equipment or refurbished equipment that meets original design specifications.” ■
— James M. Hylko ([email protected]), MPH, CQA specializes in safety, quality, and emergency management issues and is a frequent contributor to POWER.