Decommissioning of Dairyland Power s Lacrosse Boiling Water Reactor

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Alexis Natalie Gardner
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1 Decommissioning of Dairyland Power s Lacrosse Boiling Water Reactor

Dairyland Power Cooperative The plant achieved initial criticality in July, 1967. Full power was reached in August, 1969 and was declared for commercial use in February of 1971.

2 Dairyland Power Cooperative The plant achieved initial criticality in July, Full power was reached in August, 1969 and was declared for commercial use in February of The plant was permanently shut down in April of 1987 and placed in SAFSTOR for decommissioning at a later date. Due to the pending closure of the disposal site for the reactor vessel, decommissioning was started in 2005.

3 The Decommissioning Challenge An experienced decommissioning team was selected to provide design engineering and on-site decommissioning services to remove the reactor vessel and ship to the disposal site. Bluegrass Concrete Cutting, Inc was responsible for providing access for the vessel removal. Four major activities were required to provide the required access including: 1.Cutting an opening in the reactor containment building. 2.Segmentation and removal of the reactor shield plugs. 3.Cutting for removal a section of the biological shield wall surrounding the vessel. 4.Cutting free from the vessel the reactor nozzles, control rod drive tubes and all other vessel attachments. Of significant concern for the project was the spent reactor fuel that was still contained in the spent fuel pool located approximately 2 meters from where some of the work would take place.

4 Cut An Opening in the Reactor Containment Building The initial activity was to cut an opening in the containment building of sufficient size for the reactor vessel to pass through. The containment wall consisted of 9 (230 mm) of concrete, a small air gap and a 1 (25 mm) steel plate. The opening to be cut was 60 feet (18 meters) high and 16 feet (4,870 mm) wide.

Diamond wire saw set up for cutting of containment opening.

5 Cutting An Opening in the Reactor Containment Building Diamond core drilling for diamond wire access. Diamond wire saw set up for cutting of containment opening. The use of diamond tools was critical to maintaining required tolerances and to smoothly cut through the steel plate liner and refractory bars.

6 Cutting An Opening in the Reactor Containment Building The access opening for removal of the reactor vessel was cut through the reactor containment building wall in eight separate sections.

7 Removal of Reactor Containment Building Wall Access Opening would eventually be 60 feet high by 16 feet wide.

Cutting and Removal of Reactor Shield Plugs The reactor shield plug consisted of three separate plugs approximately 1 3 (380 mm) thick and 15 (4,570 mm) in diameter made from high density

8 Cutting and Removal of Reactor Shield Plugs The reactor shield plug consisted of three separate plugs approximately 1 3 (380 mm) thick and 15 (4,570 mm) in diameter made from high density concrete and lined with steel plate. Each of the three plugs was cut into six sections each with a diamond wire saw for sufficient size reduction to fit through the very small containment hatch opening.

high density concrete and lined with steel plate.

9 Segmentation and Removal of Reactor Plugs The reactor shield plug consisted of three separate plugs made from high density concrete and lined with steel plate. The plugs were housed for cutting and sectioned into six sections each.

10 Removal of a Portion of the Bio Shield Wall Access to the reactor vessel meant removing a significant portion of the bio shield wall.

11 Removal of a Portion of Bio Shield Wall Access to the Bio Shield required removal of sections of the operating floor and support beams.

12 Removal of a Portion of Bio Shield Wall The biological shield wall had significant challenges due to very tight tolerances. Precise wire access and rigging holes had to be diamond core drilled at compound angles through up to 10 feet (3,650 mm) of concrete and steel plate in order to penetrate the circular edge of the shield wall without touching the vessel. With precision layout and specially designed angle brackets all holes were drilled in the proper orientation. Cutting then proceeded from the top down, cutting the shield wall into 20 ton sections. In all, 23 separate sections of biological shield wall were cut and removed to provide access for the vessel removal.

13 Removal of a Portion of Bio Shield Wall Drawing of the (23) sections of bio shield wall to be removed.

14 Removal of a Portion of Bio Shield Wall Access through Bio shield wall would require 23 individual sections to be cut and removed.

15 Removal of a Portion of Bio Shield Wall View of concrete core, with liner plate attached, illustrating the compound angles required to penetrate the circular shield wall, while not touching the reactor vessel.

16 Removal of a Portion of Bio Shield Wall Typical diamond wire saw setups required to reach cuts with limited access.

17 Removal of a Portion of Bio Shield Wall Diamond wire saw set-ups for sectioning bio shield wall into pieces small enough to fit through the small containment hatch opening.

18 Removal of a Portion of Bio Shield Wall Core drilling of biological shield wall. View of a section of biological shield wall after cutting with rigging attachments installed for lifting and removal.

19 Sectioning and Removal of the Bio Shield Wall The biological shield wall that had to be cut in unusual shapes in order to provide clearance for the reactor vessel.

20 Sectioning and Removal of the Bio Shield Wall

21 Sectioning and Removal of the Bio Shield Wall The tight tolerances and the curved inside edge of the biological shield wall required precision cuts.

22 Sectioning and Removal of the Bio Shield Wall Section of biological shield wall wrapped and ready to be removed from containment.

In all, there were 10 steam and recirculation inlet and outlet nozzles, 29 stainless steel control rod drive tubes, 2 large support trunions and 25 other smaller nozzles of various size and materials.

23 Cutting Reactor Nozzles, Control Rod Drive Tubes and All Other Vessel Attachments. The last item was to cut all nozzles pipes and other welded attachments from the vessel at precise tolerances so the vessel would fit in the transport package. In all, there were 10 steam and recirculation inlet and outlet nozzles, 29 stainless steel control rod drive tubes, 2 large support trunions and 25 other smaller nozzles of various size and materials. The recirculation inlet and outlet nozzles along with the control rod drive tubes were especially difficult due to very limited access and high radiation and contamination levels. Special brackets were fabricated to guide the diamond wire through the maze of pipes. Controls were located remotely to keep exposures to a minimum. The diamond wire successfully cut every nozzle and metal attachment eliminating any need for thermal cutting.

Cutting Reactor Nozzles, Control Rod Drive Tubes and All Other Vessel Attachments. Note the limited space available to access cutting of the control rod drive tubes.

24 Cutting Reactor Nozzles, Control Rod Drive Tubes and All Other Vessel Attachments. Note the limited space available to access cutting of the control rod drive tubes. Additional challenges included the requirement to cut the control rod drive tubes flush to the bowl shaped bottom of the vessel so the vessel would fit into its specially designed transport package.

25 Cutting Reactor Nozzles, Control Rod Drive Tubes and All Other Vessel Attachments. Very limited access was available for installation of equipment and guide pulleys and to make cutting operations as remote as possible.

26 Cutting Reactor Nozzles, Control Rod Drive Tubes and All Other Vessel Attachments. Pulley set-ups used to access nozzle cuts with very limited access.

vessel. In each case, the metal and/or concrete structures were cut at a precise location.

27 Cutting Reactor Nozzles, Control Rod Drive Tubes and All Other Vessel Attachments. Cutting the reactor nozzles, control rod drive tubes, and all other vessel attachments free from the vessel. In each case, the metal and/or concrete structures were cut at a precise location. Radiation dose was reduced significantly by operating the equipment from a remote location. The cuts were very smooth and completed on schedule.

28 Reactor Vessel Removal Reactor vessel being removed and placed in encapsulation and transport canister.

29 Reactor Vessel Removal Cut reactor nozzles after removal of vessel. Complete package being loaded onto trailer for transport to barge slip.

30 Reactor Vessel Removal Package loaded and ready for transport to burial site.

31 Reactor Vessel Removal Package at burial site. All phases of the project were successfully performed with no injuries or accidents. For all of the work, cooling water for the diamond wire was controlled, captured and in some instances recycled to reduce overall volume.

FIG. 1. Fort St. Vrain Nuclear Generation Station.

FIG. 1. Fort St. Vrain Nuclear Generation Station. Invited Paper XA9848067 FORT ST. VRAIN DECOMMISSIONING PROJECT M. FISHER Public Service Company of Colorado, Denver, Colorado, USA Abstract Public Service Company of Colorado (PSCo), owner of the Fort