David G. Pettinari
Detroit Edison
James Radomicki
Frank W. Hake, Inc.
ABSTRACT
The Detroit Edison Company recently completed a turbine retrofit project at their Fermi 2 Nuclear Power Station. The goal of the retrofit project was to replace components damaged during a past turbine failure. A critical element to an on schedule completion of the project was the handling and packaging of the replaced components. Detroit Edison, Frank W. Hake, Inc. and Hake Associates developed a joint plan for containerization of all replaced contaminated components associated with the project. The plan was designed to serve the needs of the outage management group (absolute minimal in plant handling), the radioactive waste group (complete enclosure of all components in strong tight containers) and the railroad carrier (an effective tie down scheme designed to safely secure a 180 ton, completely enclosed turbine rotor for rail shipment). Based in part on the successful execution of the handling and packaging of the replaced components, the retrofit project was completed without impact to refuel the outage critical path duration.
TEXT
Detroit Edison's Fermi 2 Nuclear Power Station is an 1136 MW General Electric Boiling Water Reactor (BWR) located in Newport, Michigan. On December 25, 1993, the plant experienced a massive turbine/generator failure which resulted in the plant being shut down for an extended maintenance outage of approximately one year. During that outage, the seventh and eighth stage blades on each of the three low pressure turbine rotors were removed and pressure plates were installed in their place. The unit was placed in service derated to approximately 876 MWe for the next cycle and plans were made to install a new low pressure steam path during the next scheduled refuel outage.
Following the December, 1993 failure, all three low pressure rotors were shipped offsite for repair. At that time, two issues needed to be resolved prior to shipment of the rotors. The first issue, what type of package would be used to ship the components, was resolved by sandblasting the rotors on the turbine deck and then shipping the components one rotor per rail car as limited quantity packages covered only by a tarpaulin. The second issue, reduction of the physical dimension of the rotors to comply with rail shipment restrictions, was resolved by removing the seventh and eighth stage blades prior to shipment. As previously mentioned, the seventh and eighth stage blades had been targeted for removal as part of the root cause repair to the rotors.
Refuel Outage 5 (RF05) was scheduled for 45 days with the low pressure steam path replacement being critical path. The scope of the project included replacement of three low pressure rotors and 96 turbine diaphragms and removal of the previously installed six pressure plates as well as the six flow guides. In keeping with the corporate philosophy that only a minimum amount of radioactive waste be stored on site, Detroit Edison decided to contract with a waste processor for decontamination and disposal of the components. During the initial outage planning, it became evident that, due to space limitations on the turbine deck and time constraints on use of the turbine building cranes, the ability to complete the low pressure steam path replacement on schedule was in large part dependent upon the duration needed for removal and preparation for shipment of these components.
To ensure that component removal would not interfere with the low pressure steam path replacement critical path, Detroit Edison developed the following criteria for the project: 1) to minimize the use of the turbine building cranes, the rotors would be handled only once; 2) to maximize the amount of available space on the turbine deck and to avoid construction of any additional facilities, none of the components would be decontaminated on site; and 3) to ensure a continued flow of traffic through the turbine building railroad/truck bay, a method had to be available to contain the contaminated rotors so that all three could be removed from the casings and transported out of the turbine building within a 24 hour period.
Fermi's radioactive materials release limit is no detectable activity. As a result, the complete containerization, including the end bells, of the LP rotors precluded any concerns of possible migrant contamination on the rotor end bells posing a delay in the critical path removal of the rotors. Together with Frank W. Hake, Inc. and Hake Associates, a method for complete rotor and component containerization was devised. Hake, Inc. designed a box container which enclosed an entire rotor and mounted on a rail car. All the other turbine components (diaphragms, pressure plates, and flow guides) were also completely containerized due, again to the lack of decontamination opportunity. Hake Associates provided modified C vans for the diaphragms, modified Fuel Rack boxes for the flow guides and designed individual "flat rack" boxes for the pressure plates. In all Hake removed over 2 million tons of contaminated metal from the Fermi site during this past refueling outage.
Turbine Rotors
The container design for the low pressure rotors featured a two piece box with the lower component (base) being attached to the rail car itself. The container design incorporated the structural steel skids (rotor stands) used during the original delivery of the rotors. The skids were welded to the base of the container. Rolled seats were installed into the cradle of each rotor stand, allowing for quick and precise positioning of each rotor onto the skid. Two sets of U-bolts were used to secure each rotor journal end to its respective stand. The U-bolts were designed so that the rotors could be easily secured prior to removal of the rail car from the truck bay. The rotor and skid were covered with a 1.98 centimeter (14 gauge) thick galvanized sheet steel container which was secured to the base with 28 bolts. A neoprene gasket was used to ensure an adequate sealing surface between the base and the top portion of the container. Both the sheet metal skin and the floor deck were constructed to be weathertight with special attention given to prevention from wind driven rain entering the container. Since the skids were modified to become integral parts of the container, all tie-downs were outside of the box, and all tie-down activities were able to be performed outside of the turbine truck bay and off of the critical path.
To allow for tie-down to occur outside of the turbine building in the unlikely event that the coupling ends of the rotor were contaminated, clean adapter end stubs were designed to be bolted onto the rotor coupling ends prior to lowering the rotors from the turbine deck. The use of these adapters allowed the contaminated rotor to be completely enclosed within the box while providing a point to secure exterior stanchions to prevent lateral movement of the package during shipment. Access panels were installed in the lower portion of the container to allow entrance into the closed container should any unforeseen reason to access the rotor after enclosure was complete occurred. The container design thus required that only the bolting on of the adapters, setting of the rotors on the skids and attaching and securing the U-bolts were required to be done on critical path.
Diaphragms
The task of designing containers for the 72 diaphragms was complicated by the various dimensions and weights of the components. Since the diaphragms were to be initially stored on the moisture/separator roof and removed from the turbine deck during non-critical path crane time, the main objective in container design was ease of loading and shipment. The containers needed to be mobile so that they could be transported close to the diaphragm storage area, thus reducing the distance over which the contaminated components needed to be transported. For economic purposes, the containers also needed to be sized so that transport offsite could be accomplished using a minimum number of truck shipments. It was decided to modify sea/land and fuel rack containers to transport the diaphragms. Shoring modifications using heavy I-beams and angle irons provided the containers with vertical and lateral movement restriction for loads up to 24,948 kilograms.
Pressure Plates
Containerization of the seventh and eighth stage pressure plates was problematic due to the size and weight of the components. The pressure plates were semicircular high carbon steel discs weighing from approximately 17,237 kilograms to 20,412 kilograms and with dimensions ranging from 1.52 meters in diameter for the seventh stage to 1.83 meters in diameter for the eighth stage. The plates were originally shipped to the site upright individually on flatbed trucks. Since the components were now contaminated, this method of shipment was no longer viable because it would require a large container capable of handling the weight of all the pressure plates. The design chosen for the pressure plate containers had to be both strong enough to support the weight of the component and sized so that it could be shipped by truck. It was finally decided to use what was referred to as a "flat rack" container. The "flat rack" containers actually began as standard sea/land containers. Since the vertical walls of the containers played no role in the support of the pressure plates, they were cut down from 2.44 meters to 1 meter. This allowed the boxes to be stacked. It increased handling capability and allowed the container to be placed horizontally and shipped one to a flat bed truck. For support, the floors of the wooden boxes were covered with 16 gauge steel. A gasketed closure was incorporated into the box to form an air tight enclosure. Vertical and lateral steel shoring were also installed.
Flow Guides
Disposal of the turbine flow guides, conical, wedge-shaped steel components weighing from approximately 1361 kilograms to 2722 kilograms apiece, was added to project shortly before the start of the outage. Hake Associates used modified fuel rack transport boxes to contain the flow guides. The boxes were structurally supported with steel angle irons and had tie down mechanisms installed prior to shipment.
SUMMARY
The intent of this paper was to describe how Detroit Edison, Frank W. Hake Inc. and Frank W. Hake Associates utilized containerization to package and ship large, contaminated metal components within the unique time constraints of a low pressure steam path replacement outage. Certainly, two circumstances surrounding the Fermi outage made containerization a viable option. First, since the seventh and eighth stage low pressure turbine rotor blades were already removed, the rotors were small enough to be transported by rail without modification. If the seventh and eighth stage rotor blades had been required to be removed prior to transport, decontamination of the rotors may have been required for ALARA considerations. Second, the clearances along the rail route between Detroit and Memphis allowed for transport of the low pressure rotor containers. The same containers could not have been shipped from the East Coast to Memphis due to tighter clearances.
The concept of containerization did provide numerous benefits which are applicable to all disposal projects integral to the on-time completion of a critical path schedule. Foremost amongst the benefits was that the decision to package the contaminated components removed any risk associated with meeting the schedule. Packaging the components reduced the potential impact which may have been caused by unanticipated contamination levels on the components. We were thus able to enter the project with the confidence that whatever radiological conditions were present (for example, surface contamination on the journal ends of the turbine rotors) the project would not be delayed. Since all containers used (including the turbine rotor boxes) were designed to meet Industrial Packaging I Criteria, there was no concern whether the component shipments qualified as Limited Quantity Material (UN2910) or as Surface Contaminated Objects (UN2913).
Containerization also allowed the Radwaste Department flexibility in utilizing its resources. Because the packages were weathertight, they could be stored outside immediately following loading of the components. By not using plant space for storage, shipment of the packages was made off of the critical path and did not impact the flow of outage waste through the plant's Onsite Storage Facility.
Finally, containerization was significantly less expensive than on site decontamination in preparation for shipment. The cost of container construction and handling was roughly 10-15% of the total cost of the low pressure steam path disposal project and roughly 50% less than the projected cost for off critical path decontamination in preparation for shipment.
Containerization is not a viable option for all contaminated component disposal projects. However, due to the experience of the Fermi low pressure steam path replacement outage, both Detroit Edison and the Hake Group of companies feel that containerization should be evaluated when planning projects which require strict schedule adherence and have a low tolerance for adverse contingencies.