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|Reporting criterion:||10 CFR 50.73(a)(2)(iv)(B), System Actuation|
10 CFR 50.73(a)(2)(iv)(A), System Actuation
|ENS 41257||10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation|
|2502004006R00 - NRC Website|
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Turkey Point Unit 3 05000250
DESCRIPTION OF THE EVENT
On December 14, 2004, at 11:40 with Units 3 and 4 operating in Mode 1 at 100 percent power, a Class B fire was reported at the North end of the Unit 3 High Pressure Turbine [TRB], in the area of the number 2 bearing, beneath the turbine deck. At 11:45 Unit 3 was manually tripped due to the fire in the High Pressure Turbine area. The fire brigade responded to the fire and the fire was extinguished at 11:49. No offsite support was requested or required. This event did not meet the Turkey Point Plant Radiological Emergency Plan Emergency Action Level criteria for declaration of an Unusual Event due to an uncontrolled fire within the power block lasting longer than 10 minutes.
In accordance with 10CFR 50.72(b)(2)(iv)(B), a four-hour Emergency Notification System report was made to the NRC Operations Center on December 14, 2004, at 12:45 (Event Number 41257) for the manual reactor trip.
ANALYSIS OF THE EVENT
The Reactor Coolant System (RCS) ) [AB] pressure remained above the safety injection actuation setpoint and the RCS pressure remained below the setpoint for pressurizer PORV or Code safety valve actuation.
CAUSE OF THE EVENT
High Pressure Turbine, beneath the turbine deck. The cause of the Unit 3 High Pressure Turbine fire was an oil leak from the number 2 bearing seal assembly, which caused the insulation on the High Pressure Turbine lower housing to become saturated with oil. The high temperature of the High Pressure Turbine casing in the vicinity of the saturated insulation caused the oil to begin evaporating. These oil vapors began mixing with the air in the area, causing the flash point of the oil to drop substantially, from about 425 degrees F to about 270 degrees F. At this lower flash point, the surfaces of the nearby equipment, including the High Pressure Turbine casing and the gland steam piping, were sufficiently hot to cause the mixture to ignite.
The cause of the seal oil leak was a result of poor workmanship performed during the spring 2003 refueling outage turbine seal overhaul.
Background Information The oil seal rings are fabricated in halves and are secured to the bearing support housing by socket head cap screws or bolts. The upper and lower seal ring halves are joined at the horizontal joint by socket head screws. The rings contain seal strips inserted into grooves in the seal halves. Oil that is adhering to the shaft and which is not thrown from the turbine rotor by centrifugal force is captured by the seal rings. The captured oil flows downward through a series of clearances between the ring and the shaft. The seal ring is installed with a 0.005 inch clearance at the bottom, which results in a 0.035 inch top clearance while the DOCKETFACILITY NAME (1) LER NUMBER (6) PAGE (3)NUMBER 2 shaft is at rest. This clearance provides an allowance for the expected upward movement of the shaft (up to 0.020 inch).
Inspection upon disassembly revealed several oil leakage paths through the seal. Deficiencies that contributed to the oil leakage path were:
1. Top Half of Oil Seal Ring Vertical Face Failure to install a gasket in the sealing surface between the vertical face of the top half of the seal ring and the bearing cover. The top half of the seal ring was removed during the spring 2003 refueling outage to facilitate the Low Pressure turbine overhaul.
Use of inappropriate gasket sealing compound caused the sealant to run down into the bottom half of the seal, clogging the drain holes.
2. Horizontal Joint Between the Top and Bottom Halves of the Seal Two shims were installed on the horizontal joints of the seal during the spring 2003 refueling outage.
The shims were installed to establish the proper clearance at the top of the seal. The shims were fabricated to cover part of the seal face instead of the full seal face. This created a leak path along the face of the seal not covered by the shim.
A gasket was installed in the bottom half of the seal, creating a 1/16 inch gap between the edges of the two horizontal faces.
3. Oil Seal Ring Excessive Clearance The oil seal ring had excessive clearances (0.049 inch) at the sides of the ring halves, creating a flowpath for oil along the turbine shaft.
4. Missing and Loose Bolting The lower half of the seal assembly was improperly installed. Three bolts on the lower half of the seal were found loose and one bolt was missing.
Extent of Condition Visual inspections were performed on the Unit 3 and Unit 4 turbine to determine the extent of condition. An oil leak on the Unit 3 number 1 bearing was identified. No issues were identified in the Unit 4 turbine.
DOCKETFACILITY NAME (1) LER NUMBER (6) PAGE (3)NUMBER (2)
A review of the reporting requirements of 10 CFR 50.72 and 10 CFR 50.73 and NRC guidance provided in NUREG-1022, Revision 2, Event Reporting Guidelines 10 CFR 50.72 and 10 CFR 50.73, was performed for the subject condition. As a result of this review, the condition is reportable as described below.
10CFR50.73(a)(2)(iv)(A) states that the licensee shall report any event or condition that resulted in a manual or automatic actuation of any of the systems listed in 10CFR50.73(a)(2)(iv)(B). This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(B)(1), actuation of the Reactor Protection System (RPS), since Unit 3 was manually tripped in response to the turbine fire.
In addition, in accordance with 10CFR 50.72(b)(2)(iv)(B), a four-hour Emergency Notification System report was made to the NRC Operations Center on December 14, 2004, at 12:45 (Event Number 41257) for the manual reactor trip.
ANALYSIS OF SAFETY SIGNIFICANCE
This event had no significant effect on the health and safety of the public. The turbine fire did not impact any safety related systems. A manual reactor trip was initiated in response to the turbine fire. As discussed in the Analysis of Event Section, all safety systems operated as designed; therefore, there were no actual safety consequences for the event.
Short Term 1. The Unit 3 turbine number 1 and 2 seals were rebuilt.
2. Other identified leak points on the main turbine were corrected.
3. The oil soaked insulation was removed and replaced.
4. Metal lagging was added to areas that could be affected by leaking oil.
5. An oil leak inspection of the turbine oil system was performed prior to restart of Unit 3.
6. The Unit 4 turbine was inspected for possible oil leaks.
Long Term 1. Turkey Point will investigate the use of insulation that does not absorb oil.
2. Turkey Point will inspect other equipment in Units 3 and 4 that could have oil soaked insulation and high surface temperatures.
3. Turkey Point will revise Turbine Overhaul procedures and work instructions to provide more detailed requirements for a) gasket installation, b) bolting installation and torquing requirements, c) shim installation and clearance acceptance criteria, and d) to identify critical steps and require additional oversight for these critical steps.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Turkey Point Unit 3 05000250 2004 -�006 00
second component function identifier (if appropriate)].
FAILED COMPONENTS IDENTIFIED:�NONE
A review of previous Licensee Event Reports in the past three years did not indicate any similar reportable events at Turkey Point.