ML100710414

Licensee Response to Request for Additional Information Emergency TS Change for TS 3.8.1, AC Sources-Operating

ML100710414
Person / Time
Site:	Diablo Canyon
Issue date:	03/12/2010
From:	Parker L Pacific Gas & Electric Co
To:	Baldwin T, Wang A Plant Licensing Branch IV, Pacific Gas & Electric Co
Wang, A B, NRR/DORL/LPLIV, 415-1445
Shared Package
ML100710385	List: ML100710405 ML100710414 ML100710423
References
TAC ME3505, TAC ME3506
Download: ML100710414 (3)

Text

Draft Response to general justification for "EMERGENCY":

DCPP entered LCO 3.8.1 as a result of compensatory measures taken in response to discovery of a nonconservative TS SR 3.3.5.3. The nonconservative TS was concluded based on inspectors insisting our design should consider worst case degraded voltage and timing even if it is non-mechanistic. When these worst case scenarios were postulated, permanently connected class 1E loads such as auxiliary saltwater pumps and component cooling water pumps were determined to trip on overcurrent prior to the second level undervoltage relay time delay transferring them to EDGs.

Detailed timeline is pending.

Other stations have been challenged on similar scenarios but have treated these as URI's.

1. Provide a detailed list and descriptions of all compensatory measures being used during this extended Allowed Outage Time (AOT) for the Offsite Circuit. This list shall include demonstrated operability of remaining offsite circuit(s), demonstrated operability of all site Emergency Diesel Generators (EDGs), demonstrated operability of all safety busses and the necessary circuits which provide them power from the offsite sources and the EDGs, demonstrated operability of all supporting vital DC systems, demonstrated functionality of both switchyards (230 kV and 500 kV) to support output of both main generators and provide stable offsite power to the plant safety systems, controls in place to prevent maintenance, testing of and protect the aforementioned systems and components during the extended AOT as well as avoid possible plant transients or abnormal plant evolutions, details of plans made with the Transmission Operator for oversight of transmission system operation during this AOT to ensure continued availability and reliability.

Draft Response:

Compensatory Measures:

The compensatory measure taken for the non-conservative Technical Specification was to cut out the auto transfer to the standby offiste circuit (Startup power) for one vital 4 kv bus. The bus was selected based on which Auxiliary Saltwater (ASW) pump and which Component Cooling Water (CCW) pumps are running. If the transfer to Startup is disabled for a bus, then the running ASW and CCW pumps would not be exposed to the postulated degraded Startup voltage and would not trip on overcurrent.

Cutting out the auto transfer to Startup places the affected unit in Technical Specification 3.8.1, "AC Source - Operating". In this configuration, there is no need for any procedure revisions, as a bus transfer to emergency diesel generator (EDG) is already covered by the Emergency Operating Procedure (EOP) set. If the EDG fails to start or load, operators would re-energize the bus from offsite power in accordance with EOP ECA-0.3 "Restore 4kV Buses". Operators are already trained on ECA-0.3. If an overcurrent does occur, operators would respond in accordance with Operations policy B-2, "Electrical Alarm Relay Response". B-2 allows the operators to attempt one reset of an inverse time overcurrent trip if the equipment is needed to stabilize the plant. Resetting the relay is accomplished by turning the pump control

switch to the left on the main control boards. This is a simple manipulation and the operators are currently trained on this topic.

Operability of Remaining Offsite Circuits:

The remaining offsite circuit - 500 kV is in operation with all three lines connecting the 500 kV switchyard to the Pacific Intertie in normal service. Both units are at 100 percent power and connected to the 500 kV switchyard. Should the units go offline and both 230 and onsite power was unavailable, this 500 kV source would provide power to ESF loads as a delayed source of power, following operators opening of the motor operated disconnect and initiating backfeed. Procedure AD7.DC6 implements protective measures for all these systems.

Operability of all onsite EDGs:

All onsite EDGs remain operable. During the FLUR setpoint modification the risk status is elevated resulting in additional protective measures such as postings Operability of all safety buses and necessary circuits:

Operability of all supporting vital DC systems:

Functionality of both switchyards:

2. Provide detailed information concerning ability of the offsite circuits to also provide the necessary power and voltage for starting of all required 1E loads as a result of the scenarios which caused the problems with the running 1E loads.

Draft Response:

Relays prevent loading the offsite circuit when voltage is below 85%.

3. Provide a description of and describe whether training has been completed for any procedures required for the configuration of the plant during the extended AOT. For example, a procedure for restarting a 1E pump that would happen to trip on overload.

Draft Response:

The compensatory measure taken for the non-conservative Technical Specification was to cut out the auto transfer to the standby offiste circuit (Startup power) for one vital 4 kv bus. The bus was selected based on which Auxiliary Saltwater (ASW) pump and which Component Cooling Water (CCW) pumps are running. If the transfer to Startup is disabled for a bus, then the running ASW and CCW pumps would not be exposed to the postulated degraded Startup voltage and would not trip on overcurrent.

Cutting out the auto transfer to Startup places the affected unit in Technical Specification 3.8.1, "AC Source - Operating". In this configuration, there is no need for any procedure revisions, as a bus transfer to emergency diesel generator (EDG) is already covered by the Emergency Operating Procedure (EOP) set. If the EDG fails to start or load, operators would re-energize the

bus from offsite power in accordance with EOP ECA-0.3 "Restore 4kV Buses". Operators are already trained on ECA-0.3. If an overcurrent does occur, operators would respond in accordance with Operations policy B-2, "Electrical Alarm Relay Response". B-2 allows the operators to attempt one reset of an inverse time overcurrent trip if the equipment is needed to stabilize the plant. Resetting the relay is accomplished by turning the pump control switch to the left on the main control boards. This is a simple manipulation and the operators are currently trained on this topic.

4. Provide a detailed description of the maintenance plan and the post maintenance operability testing required to implement compensatory measures for the purpose of justifying the 24-hour AOT extension.

See schedule attached to e-mail. Post Mod Test is accomplished by STP M-75, "4KV Vital Bus Undervoltage Relay Calibration "

5. Provide a detailed discussion about the affects on plant operations under the current configuration with the automatic transfers being disabled.

Draft Response: See Response to #3.

6. Confirm that a dual unit trip is part of the Diablo Canyon Power Plant (DCPP) licensing basis in addition to being required by the Transmission Provider.

Draft Response:

The dual unit trip is also a licensing basis in accordance with the NRC's 12/14/2009 letter. DCPP's design is capable of handling the worst case of dual unit trip or accident in one with a spurious SI in the other unit.