40OP-9ZZ07 Mode 1 To 3

Question 1

What are the two methods that satisfy the requirements of the Safety Analysis that apply whenever CEAs are capable of being withdrawn?

Answer 1

Two of the considerations that help protect the plant in the event of “Uncontrolled CEA Withdrawal from Subcritical Conditions” are:

• Having Reactor Protection System logic, Reactor Trip Circuit Breakers (RTCBs), and manual trips operable. Refer to Tech Spec 3.3.1, 3.3.2, 3.3.5, and 3.3.6.
• Maintaining boron concentration greater than the Shutdown Margin Technical Specification requirements for RTCBs closed.

Question 2

What is the required response if Main Turbine vibration increases during Turbine shutdown?

Answer 2

If filtered turbine bearing vibration rapidly increases above the setpoints listed below, break condenser vacuum. Breaking vacuum above 1200 rpm may damage the low pressure turbine last stage buckets, so it should be done only when a rapid increase in vibration is indicated.

Less than 800 rpm - 8 mils

800-1400 rpm - 14 mils

1400-1800 rpm - 12 mils

Question 3

What are the Main Turbine bearing limits during plant shutdown?

Answer 3

Main Turbine bearing oil temperature parameters can be monitored at MTN-TR-303, located on RMN-B07. They can also be monitored on the PC, monitored and trended on ERFDADS, as well as monitored locally. The following limits apply to the Main Turbine/Generator system with respect to bearings:

• The maximum lube oil temperature when the shaft comes to rest for turning gear operations is 102°F.
• The MTLO Conditioner has a minimum temperature limit of 100°F, as indicated on OSNTIC-0001, for “high flow rate” (30 gpm) operation.
• With a Main Turbine Lube Oil cooler outlet temperature of 110-120°F, the oil temperature rise across a journal bearing must not exceed 50°F.
• The maximum journal bearing metal temperature is not to exceed 250°F. Consider any sudden increase in oil drain temperature (10°F or greater) abnormal even though the temperature or temperature rise is within the limit.
• The normal temperature rise of the oil across the thrust bearing shall not exceed 45°F. Consider any sudden increase in the average temperature rise (5°F or greater) abnormal, even though the total rise is within 45°F.
• The maximum thrust bearing metal temperature is not to exceed 190°F. Any sudden increase in metal temperature (10°F or greater) above initial reference temperature or any temperature above 180°F shall be reported to GE.

Question 4

What are the Condenser vacuum limits for Main Turbine operation and describe the effects of varying condenser vacuum (backpressure) on the Main Turbine?

Answer 4

• Do not operate the Main Turbine when load is less than 410 MWs with vacuum greater than four inches HgA but less than five inches HgA for more than one hour.
• Do not operate the Main Turbine when load is less than 410 MWs and vacuum is greater than or equal to five inches HgA.

Turbine vibrations during power reductions are more prevalent the deeper the condenser vacuum. Optimum operation is with condenser backpressure greater than two inches HgA and less than four inches HgA, but as close to four inches HgA as possible. Condenser backpressure should be closely monitored during NORMAL power reductions (power reductions that are scheduled or in preparation for a scheduled outage). The rate of change of condenser backpressure is directly related to power reduction rate. Something to be considered also here is the securing of CW fans and/or CW pumps.