The Construction of Watts Bar Nuclear Plant Essay Example for Free

The Construction of Watts Bar Nuclear Plant Essay The Watts Bar Nuclear Plant (WBN) is operated by the Tennessee Valley Authority (TVA), a government owned authority. The site is approximately ten miles south of Spring City, TN, approximately 1. 25 miles south of the Watts Bar Dam that it is named for, and on the west bank of the Tennessee River. There are two units, Unit 1 which is operational and Unit 2 which is unfinished. The Groundbreaking for Unit 1 took place in 1972, with major construction beginning in 1973 (TVA website). However Unit 1 did not begin commercial operation until 1996 – twenty-three years after major construction started and according to Munson (2002) at a cost of $7 billion – and Unit 2 has yet to be completed. Construction licenses for both units were awarded by the nuclear regulator of the time the Atomic Energy Commission (AEC) in 1973, and construction of both units was supended in 1985. Unit 1 construction was restarted in 1990 and the full power operating license was issued in 1996. Unit 2 remained only partially constructed until 2007 when TVA announced it would resume construction. Detailed information about the original tender, construction process, numbers of workers, time scales and original budgets is not available for Unit 1 as the project began in the early 1970s and the information is archived and not easily retrievable (Johnson, personal communication). However Unit 1 is typical of the reactors of its time so some general information is available. For example, in terms of the plant overall, figures from 1974 (Peterson, 2003) indicate that the construction of a typical nuclear plant required 40 metric tons (MT) of steel and 190 cubic meters (m3) of concrete per average megawatt of electricity (MW(e)) generating capacity. With a capacity of over 1000 MWe, figures for the construction of Unit 1 can be estimated as over 40,000 MT of steel, and 190,000 m3 of concrete. Due to the geologic features of the site (see below), it is reasonable to assume that the real figures were even higher. There is some information with regards the restart of construction for Unit 2. Reactors Both units are Westinghouse Four-loop Pressurized-Water Reactor (PWR), as shown in the figure below (TVA website) capable of electrical output of 1125 MWe. A four-loop Westinghouse plant has four steam generators, four reactor coolant pumps, and a Pressurizer. There are 193 fuel assemblies arranged in a 17 x 17 array inside a reactor vessel that has an internal diameter of 173 inches. The reactor vessel is constructed of a manganese molybdenum steel, and all surfaces that come into contact with reactor coolant are clad with stainless steel to increase corrosion resistance. The reactor coolant flows to the steam generator (USNRC, 2003). Typically, PWR containments typically consist of heavily steel-reinforced concrete cylinders ranging in thickness from 3. 5 feet to 4. 5 feet, capped by a hemispherical dome of steel-reinforced concrete. The cylinder is typically 140 feet high, with a 140-foot diameter. Reinforcement bars that form a cage within the concrete are typically Grade 60 #18 steel bars on 12-inch to 15-inch centers. A #18 rebar is two and one-quarter inches in diameter (ABS Consulting, 2002). Additional reinforcement may be called for depending on the results of the seismic survey undertaken for the site. This was the case for the Watts Bar reactors. The Final Safety Analysis Report for WBN (TVA 1991), reported that the plant is located in the Valley and Ridge Province of the Appalachian Highlands, and the major geologic feature at the site is the Kingston thrust fault, which developed 250 million years ago. The fault has been inactive for many millions of years, and recurrence of movement is not expected. The fault lies to the northwest of the site area and is not involved in the foundation for any of the major plant structures. The SAR for the WBN states that it was designed based on the largest historic earthquake to occur in the Southern Appalachian Tectonic Province the 1897 Giles County, Virginia earthquake. This earthquake is estimated to have had a body wave magnitude of 5. 8. The Safe Shutdown Earthquake for the plant has been established as having a maximum horizontal acceleration of 0. 18 g and a simultaneous maximum vertical acceleration of 0. 12 g WBN Unit 2 Restart of Construction As Unit 2 is essentially identical to Unit 1, the scope of work for Unit 2 duplicates that of Unit 1 as much as possible with some additional scope for Unit 2 not included in the Unit 1 startup such as another cooling tower, transmission system, various upgrades and work completed since Unit 1 startup such as a process computer upgrade (Moll, 2007). Estimated cost of the project to complete startup is 2. 49 billion, over 54 months with commercial operation of the unit scheduled for early 2012 (Westinghouse, 2008). Moll reports that peak staffing is estimated at 2,300 craft and technical personnel. The project phases will include the Engineering and Analysis phase, which will include plant walk downs to establish the current condition of the plant, the engineering evaluations of program work and identification of design discrepancies. The second phase as outlined by Moll is the Design Production phase to correct identified deficiencies and design changes required to maintain consistency between units. The third phase is the implementation phase which will include the construction, the modifications required in supporting two units, the maintenance activities, testing, non-design repairs and clean up. Finally the Startup Test phase that will ensure the systems are capable of safe shutdown before the operations phase. Major Issues Affecting the Contruction of WBN Unit 1 Nuclear power reactors are regulated by federal and state laws to protect human health and the environment. These regulatory requirements are of paramount consideration in the construction of any nuclear facilities. Regulatory costs for the nuclear industry are a significant percentage of construction and on-going operating costs and as such regulatory considerations play a large role in dictating all aspects of the project from the chosen site to the reactor design to the management of on-going operations. The construction period of the Watts Bar reactors coincided with significant changes in the regulatory environment. The most significant nuclear regulatory authority in the US is United States Nuclear Regulatory Commission (US NRC). The Watts Bar reactors were in the construction phase when the accidents occurred at Three Mile Island in 1979, and later, Chernobyl in 1986. Reaction to these events resulted in further and more stringent regulatory requirements. Environmental obligations have also become ever more important, and operators must also satisfy requirements for environmental impact statements. Construction of both units was suspended in 1985, primarily because numerous TVA staff made complaints that the construction process was inadequate and that there may be resulting safety risks (NRC, Safety Evaluation Report, 1995). On September 17, 1985 the NRC required TVA to address various deficiencies in its activities and TVA withdrew its certification that Unit 1 was ready to load fuel. The NRC Safety Evaluation Report notes the findings that there were significant problems in construction quality and quality assurance. Deficiencies in construction involved a number of systems and issues including the quality of welding and cabling. There were many staff concerns and complaints that also needed to be addressed. In the report the NRC itself recognises its own role in not providing sufficient regulatory oversight. The report notes the extensive corrective actions performed by TVA, which included a Nuclear Performance Plan to address material, design and programmatic deficiencies and included inspection and testing of the construction issues and programs to respond to staff concerns. Unit 1 construction was resumed in 1990. In terms of estimating and producing time lines for such a project, The Watts Bar example demonstrates that as well as being aware of industry codes and building standards it is crucial to understand the regulatory requirements for the relevant industry. Unforseen delays also need to be considered, as does whether risks of such are allocated to the contractor. If risks are allocated to the contractor, the risk of a long delay should be considered in the estimate. Some of this risk may be offset when components in a project can be worked on independently or concurrently with each other, rather than build components that need to be constructed sequentially. The Watts Bar Unit 1 reactor is a good example of unforseen events affecting the construction process (for example, discovery of the fault, the changes in the regulatory environment after the Three Mile Island accident in 1979). Although Unit 1 was on-line by September 11, 2001, security requirements for installations such as nuclear power stations were increased, and on-going construction projects for security sensitive projects were affected at that time. Changes to regulatory requirements, standards and codes need to be tracked for any project. Quality Assurance systems must be in place, and accounted for in the initial estimating process. References 1. TVA Website Watts Bar Nuclear Plant Retrieved April 3, 2008 from : http://www. tva. gov/power/nuclear/wattsbar. htm 2. Munson, Richard.The Electricity Journal, Vol:15, Issue:10, December 2002 pp76-80. 3. NRC, Partial Chronology WB Unit 2 (Table) (2007 August 23) Retrieved April 3, 2008 from: http://www. nrc. gov/reactors/plant-specific-items/watts-bar/watts-bar-partial-chronology. html 4. (Terry W Johnson, Communications, Tennessee Valley Authority, personal communication, April 5, 2008). 5. Peterson, F. â€Å"Will the United States Need a Second Geologic Repository? † The Bridge National Academy of Engineering Vol:33, No. 3, Fall 2003. 6. TVA Website (Figure of Reactor). Retrieved April 3 2008 from: http://www. tva. gov/sites/wattsbarnuc. htm# 7. USNRC Technical Training Center, Pressurized Water Reactor (PWR) Systems 2003. Retrieved April 7, 2008 from: http://www. nrc. gov/reading-rm/basic-ref/teachers/04. pdf 8. ABS Consulting and ANATECH, Aircraft Crash Impact Analyses Demonstrate Nuclear Power Plant’s Structural Strength, December 2002. Retrieved April 7, 2008 from: http://www. stpnoc. com/EPRI%20study. doc 9. The Final Safety Analysis Report for WBN (TVA 1991), excerpt retrieved from: http://www. hanford. gov/rl/uploadfiles/ea/ea1210/section4. htm