Driving down outage times30 April 2001
Waterford 3 trimmed eight days off of its previous outage duration record after a 34-day refuelling outage.
Entergy’s Waterford 3 was reconnected to the electrical grid after a 34 day refuelling outage, the shortest yet in the plant’s 15-year operating history. In addition to the refuelling, outage work was also carried out at this time, which included high temperature chemical cleaning of the steam generators, which was the first time that the practice had been carried out in the USA.
A cost-benefit analysis was carried out to determine whether chemical cleaning or preventative maintenance was the best option.
During the course of the outage, a number of maintenance tasks were carried out. These included the replacement of the internals of a reactor coolant plant. This involved splitting the pump casing, refurbishing or replacing the internals, replacement of the pump motor, and reconstruction of the pump.
In addition, there were signs of leakage from an instrument nozzle, which had to be checked and replaced.
Other major work activities during this outage included:
•Replacing internals and restoring a gasket on one of four reactor coolant pumps.
•Performing preventative maintenance on the main turbine to ensure reliable generation.
•Repairing instrument nozzles on the reactor coolant loops.
•High temperature chemical cleaning of the steam generator tubes.
High temp. chemical cleaning
Waterford 3 was the first USA plant to make use of the Siemens High Temperature chemical cleaning process for steam generators. Entergy believes that this chemical cleaning will provide another 10 years of operation without significant tube problems or reduction in power. This could potentially result in achievement of the original plant design life of 40 years.
Evaluations performed in Spring 1998 clearly indicated that chemical cleaning of the steam generators was needed to maintain steam generator integrity and design performance. Chemical cleaning is not new to the US industry. The US industry standard is the EPRI Steam Generator Owners Group (SGOG) method. This is done during refuelling and takes about ten days. One option that was considered was the method used at Palo Verde and Byron using the Framatome high temperature chemical cleaning process at 290°F. However, this did not meet Waterford’s cleaning objectives or outage duration goals. Therefore, a high temperature Siemens process at 325°F was proposed for Refuelling Outage 10 in October 2000.
On completion of a rigourous cost benefit analysis and feasibility study, a contract was placed with Siemens (as it then was). The work scope included several months of waste processing and disposal, which has since been successfully completed.
Waterford 3 initiated a Framatome/ Siemens feasibility study. This was used as a rough input for the process description, goals and objectives. A highly detailed Technical Specification was issued to solicit a Framatome proposal. Maximum use was made of SONGS and Palo Verde plant experience as an outline for cost effectiveness. This was used to supplement the Entergy General Services Agreement. Specific contractual performance measures were added to protect Waterford’s commercial and technical interests. It was issued on schedule on 25 October 1999, and a purchase order was placed on 15 December 1999 to start work. Significant savings were realised by the decision to have Waterford staff assume chemical procurement and waste disposal responsibilities. In addition, potential royalties exist for the future based on contract initiatives.
Mock-up qualification testing was accomplished by Siemens laboratory tests in Erlangen, Germany and by Dominion Engineering tests at Catholic University. Waterford 3 chemistry input was vital for the process ultimately chosen for Waterford 3. Framatome operating and chemical process procedures were integrated into a site specific Waterford 3 special test procedure. This first time process was then tried in advance on the plant simulator, and feedback was integrated into classroom training of operations and team members. The project found that this significantly enhanced the knowledge of the two shifts dedicated to perform the required steps. Experience gained during several simulator runs and training classes proved to be very valuable in duplicating plant response and promoting operator confidence in the process.
Support from Entergy Division allowed the extensive economic installation of 13.8kV cable and transformer. The new electrical system worked perfectly, and permitted the transition to waste reduction without any lost time. Its design took advantage of the opportunity to enhance the reliability of the present site system.
A tank farm with about 300,000 gallons of storage was located outside the protected area. This involved design and procurement of significant cribbing and subsequent placement of ten 40K and 25K gallon tanks, boiler, evaporator, and cooling tower using a 150 ton crane. Location of over 20 SeaLand containers and trailers and installation of fencing and co-ordination of six chemical tank trucks was also accomplished.
Most tie-ins to the plant systems were made as temporary alterations using existing equipment. In addition, a ‘field run’ method was used whenever applicable. Implementation of this concept, alone, saved many man-hours of unnecessary engineering and procurement. It enabled rapid construction of the many interfaces and associated cost saving. Modifications did not require network due to the scrutiny applied through the engineering Design Review Committee (DRC) and Plant Operational Review Committee (PORC) review processes.
On 13 October, 2000, Waterford 3 began refuelling outage 10 (RF10). During plant shutdown, chemical cleaning was successfully implemented in under five days. Chemicals were injected using a two-step process at 325°F and 150°F temperature holds to remove iron, and then copper and lead deposits. Several ‘first-time’ manipulations of the plant were necessary: hard venting for boiling via the steam bypass control system; application of significant amounts of nitrogen to assist draindown time; the use of the condenser to vacuum dry residual solvent in the steam generator using coondenser vacuum and sparging the steam generator through the blowdown nozzle from a bank of air compressors. A local industrial hygienist contractor was coupled with the Safety Department. They were strategically placed around the site and equipped with monitors to ensure that ammonia fumes were within Occupational Safety and Health Standards (OSA) limits as predicted by analysis. Emergent flush and sludge lancing evolutions were rapidly dispositioned by a temporary chemistry procedure based on organising a group of senior chemists from Framatome, Siemens, Westinghouse and Dominion Engineering to obtain expert recommendations.
Monitors were strategically placed and recorded data for later retrieval.
Mission objectives were to remove steam generator corrosion products, improve heat transfer, minimise cost, accomplish work within an aggressive refuelling outage, and do no harm to equipment, site personnel, or the environment. Soon after the team was formed, Entergy Team Alignment Performance Improving Training (TAPIT) was provided to those individuals and others who were scheduled to participate later in the project as key members.
Radiation safety records
During the course of the outage, 11 records for low levels of worker radiation exposure for the plant were set.
Planning an outage
As described, there was considerable planning involved in ensuring that the outage proceeded smoothly on a tight schedule. Two shifts were trained for a month prior to the outage to ensure that they were familiar with the requirements of the job. Training two shifts ensured that it would be possible for work during the maintenance and refuelling outage on a round-the-clock basis.
This training included practice at moving equipment and plant items around in a simulated environment. This helped to ensure that the operators would be familiar with the layout, enhancing safety. Everything was tested in advance.
Another objective of the outage was to ensure that the level of radioactive waste produced to a minimum.
To carry out the high temperature chemical cleaning, heat from the reactor coolant system was used, and one steam generator was always maintained for use as a potential heat sink if required. In addition, one steam generator was always kept available for use as a heat sink.
The high temperature chemical cleaning prevented future loss of thermal performance from the steam generators. The reduction in eggcrate thickness resulting from the cleaning is such that one more cleaning process would be possible. It is not expected that another such process would be required, however, given the expected remaining life of the plant, and the marked reduction in transport of iron to the steam generators.
Entergy learned that it was capable of effectively carrying out a maintenance outage in a short period of time. The outage re-inforced the lessons that had been learnt during the planning and training stages.
One important lesson that Entergy drew from the outage was that it was important to clean steam generator tubes sooner rather than later. Doing this soooner means that their are fewer deposits to remove. In the case of Waterford, approximately 7000lbs of deposit per steam generator were removed.
It was also accepted that emerging issues will challenge any training. As a result, training alone is insufficient to prepare the outage workers for the demands of the outage. To deal with the unexpected problems that can arise during the course of an outage, the maintenance staff need to be able to understand the implications of the possible consequences of any actions they might take.
TablesPercentage reduction from previous record