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<br />OOlG83 <br /> <br />I, <br />past without significant damage. However, if the situation of a failed seal in hollow-jet valve No. 'I' <br />1, and the locked wheels on the 6- by 13-foot fixed-wheel gate are coupled, the outlet works flow <br />and resulting damage may not be controlled. Continued cavitation damage anhe 6- by 13-foot <br />gate could proceed through the concrete and steel into the open tunnel around the 110-inch pipe. <br />This failure mode is similar to the recent incident at Flaming Gorge Dam. The possibility of this <br />scenario must be considered due to the present condition of hollow-jet valve No.1 and the 6- by <br />13-foot fixed-wheel gate. The only possibility for control would be at the 72-inch ring-follower <br />gates. The original design of the main Qutlet works intended three possible points of control for <br />the outlet works. With the current equipment conditions, the reliable control points are reduced <br />to one. The risk of developing this situation is substantially increased at high flows. <br /> <br />Thorough physical inspections of the gates, valves, and 110-inch pipe should be performed before <br />and after flows exceeding 3,200 f\3ls from the main outlet works. Prior to operational testing (: <br />above 3,200 fPls, the following conditions should be met: <br /> <br />1) Both ring-follower gates are determined to be fully operational, based on the results of the " <br />verification (rod end amplification) testing procedure included in Appendix D, and any <br />necessary repairs are completed. <br /> <br />2) Hangers ~e provided for both ring-follower gates. If an incident occurs that fails either <br />gate hanger in the future, that outlet shall be removed from service until repair of the hanger, <br />to ensure the gates cannot drift into the flow. <br /> <br />3) If any ring-follower gate is used to shut down flows above 500 fWs, an internal mechanical <br />inspection shall be performed following gate closure. <br /> <br />4) A complete overhaul of the 6- by 13-foot fixed-wheel gate is performed and tested, to <br />restore emergency closure capability. The repair work should include replacement of the <br />frozen wheels, welding of deep corrosion, bonnet cover stud replacement, gate hanger repair, <br />addition of grounding rods, and a check of the cathodic protection system. Stnlcture' <br />modifications will be required for access to the maintenance chamber [20]. <br /> <br />5) Any operational failure of the gates or valves, especially involving hollow-jet valve No.1, <br />requires an immediate inspection. A determination of the ability to proceed with high flows <br />will be determined from the inspection. Drifting of greater than 1 percent per day, locking of <br />the valve under flow, unusual hydraulic operating pressures, or evidence of oil in the stilling <br />basin will be considered a failure, as well as any incident considered a failure by the Dam <br />Maintenance Supervisor. <br /> <br />6) If there is any incident involving the 110-inch pipe, including suspected cavitation noises, <br />leakage, vibration or evidence thereof (cracking paint or grout, etc.), changes in structural <br />mounts, failure of the ultrasonic flow measurement equipment, inability to hold the 6- by 13- <br />foot gate fully open, or any evidence considered by the Dam Maintenance Supervisor to <br />constitute an incident, a normal shutdown offlow at the 72-inch outlet works and closure of <br /> <br />26 <br />